The influence of pouring temperature and mold temperature on the fluidity and hot tearing behavior of Al-2Li-2Cu-0.5Mg-0.15Sc-0.1Zr-0.1Ti alloys was investigated by experimental investigation and simulation assessment...The influence of pouring temperature and mold temperature on the fluidity and hot tearing behavior of Al-2Li-2Cu-0.5Mg-0.15Sc-0.1Zr-0.1Ti alloys was investigated by experimental investigation and simulation assessment.The results showed that the length of the spiral fluidity sample increases from 302 to 756 mm as the pouring temperature increases from 680 to 740℃,and from 293 to 736 mm as the mold temperature increases from 200 to 400℃.The hot tearing susceptibility(HTS)firstly decreases and then increases with increasing pouring and mold temperatures,which is mainly caused by the oxide inclusion originating from the high activity of Li at excessive pouring temperature.Excessive pouring and mold temperatures easily produce oxide inclusions and holes,leading to a reduction in fluidity and an increase in HTS of the alloy.Combining the experimental and simulation results,the optimized pouring and mold temperatures are~720℃ and~300℃ for the cast Al-Li alloy,respectively.展开更多
Magnesium and its alloys offer lightweight advantage and have extensive development prospects,particularly in aerospace.However,their flammability poses a significant barrier on the development of Mg alloys.The igniti...Magnesium and its alloys offer lightweight advantage and have extensive development prospects,particularly in aerospace.However,their flammability poses a significant barrier on the development of Mg alloys.The ignition resistance of these alloys often depends on the protectiveness of the oxide film formed on the surface.This paper elucidates the formation mechanism of oxide film from thermodynamics and kinetics,classifying oxide films based on their layered structure to assess their protective properties.Furthermore,it comprehensively reviews the impact of characteristics on the protective effectiveness such as compactness,continuity,thickness,and mechanical properties.The paper also introduces various characterization methods for the microstructure and properties of oxide film.The primary objective of this paper is to enhance the comprehension of oxide film concerning the ignition resistance of Mg alloys and to furnish references for future advancements and research in Mg alloys with heightened ignition resistance.展开更多
A comprehensive analysis of the microstructure and defects of a thixomolded AZ91D alloy was conducted to elucidate their influences on mechanical properties.Samples were made at injection temperatures ranging from 580...A comprehensive analysis of the microstructure and defects of a thixomolded AZ91D alloy was conducted to elucidate their influences on mechanical properties.Samples were made at injection temperatures ranging from 580 to 640℃.X-ray computed tomography was used to visualize pores,and crystal plasticity finite element simulation was adopted for deformation analysis.The microstructure characterizations reveal a hierarchical cell feature composed of α-Mg and eutectic phases.With the increase of injection temperature,large cell content in the material decreases,while the strength of the alloy increases.The underlying mechanism about strength change is that coarse-grained solids experience smaller stress even in hard orientations.The sample fabricated at a moderate temperature of 620℃ exhibits the highest elongation,least quantity and lower local concentration of pores.The detachment and tearing cracks formed at lower injection temperature and defect bands formed at higher injection temperature add additional crack sources and deteriorate the ductility of the materials.展开更多
Additive manufactured Mg-RE alloys usually show exceptional mechanical properties,which is mainly attributed to their refined grains in previous studies.Since Mg-RE series are typical age-hardenable alloys,this study ...Additive manufactured Mg-RE alloys usually show exceptional mechanical properties,which is mainly attributed to their refined grains in previous studies.Since Mg-RE series are typical age-hardenable alloys,this study focuses on the aging behavior of wire arc additive manufactured Mg-9Gd-3Y-0.5Zr(GW93K)alloy and compares it with the as-cast counterpart,providing a new insight into the strengthening mechanism of additive manufactured alloys.It was revealed that both the refined equiaxedα-Mg grains and small-sized(only 5~10 nm)β′precipitates with an extremely high number density(~2.53×10^(4)µm^(-2))should be considered for the strengthening mechanisms of the deposited alloy.The promoted precipitation behavior is facilitated by the dislocation pile-ups formed under multiple thermal cycles and a high cooling rate during deposition.As a result,the deposited alloy at peak-aged state exhibits better comprehensive properties of UTS=392 MPa and EL=3.3%,which is 19%and 18%higher than that of the cast sample,individually.展开更多
High temperature performance of magnesium alloys can be tailored by either grain size or precipitates in the grain interior.In this study,exceptional creep resistance was successfully acquired in a RE-free cast Mg-Al-...High temperature performance of magnesium alloys can be tailored by either grain size or precipitates in the grain interior.In this study,exceptional creep resistance was successfully acquired in a RE-free cast Mg-Al-Ca-Ti(AC51Ti)alloy.Microalloying of Ti(0.01 wt.%)has been found to be beneficial to the improvement of the tensile creep resistance in a RE-free cast Mg-5Al-0.35Mn-(1Ca)(AC51)alloy,showing a low state creep rate(SCR)of 2.70×10^(−9)s^(−1)at 200℃/50 MPa,which is even better than that of many reported RE-containing Mg alloys.The presence of trace Ti contributes to the substantial refinement and more uniform distribution of Al_(2)Ca precipitates in the matrix.At the same time,the microalloying of Ti improves the solubility of Al and Ca in the matrix.It is reasonable to believe that the microalloying of Ti induced re-organization of Al_(2)Ca precipitates,dissolved a larger amount of Al and Ca atoms into magnesium lattice,and increased the possibility of interaction between GB/dislocations and precipitates,which strongly correlates with the high temperature properties.The creep strengthening mechanisms primarily attributed to both second phase strengthening and solid solution strengthening were separately proposed based on the experimental investigations.展开更多
Mg–3Nd–0.2Zn–0.4Zr(NZ30K,wt.%)alloy is a new kind of high-performance metallic biomaterial.The combination of the NZ30K Magnesium(Mg)alloy and selective laser melting(SLM)process seems to be an ideal solution to pr...Mg–3Nd–0.2Zn–0.4Zr(NZ30K,wt.%)alloy is a new kind of high-performance metallic biomaterial.The combination of the NZ30K Magnesium(Mg)alloy and selective laser melting(SLM)process seems to be an ideal solution to produce porous Mg degradable implants.However,the microstructure evolution and mechanical properties of the SLMed NZ30K Mg alloy were not yet studied systematically.Therefore,the fabrication defects,microstructure,and mechanical properties of the SLMed NZ30K alloy under different processing parameters were investigated.The results show that there are two types of fabrication defects in the SLMed NZ30K alloy,gas pores and unfused defects.With the increase of the laser energy density,the porosity sharply decreases to the minimum first and then slightly increases.The minimum porosity is 0.49±0.18%.While the microstructure varies from the large grains with lamellar structure inside under low laser energy density,to the large grains with lamellar structure inside&the equiaxed grains&the columnar grains under middle laser energy density,and further to the fine equiaxed grains&the columnar grains under high laser energy density.The lamellar structure in the large grain is a newly observed microstructure for the NZ30K Mg alloy.Higher laser energy density leads to finer grains,which enhance all the yield strength(YS),ultimate tensile strength(UTS)and elongation,and the best comprehensive mechanical properties obtained are YS of 266±2.1 MPa,UTS of 296±5.2 MPa,with an elongation of 4.9±0.68%.The SLMed NZ30K Mg alloy with a bimodal-grained structure consisting of fine equiaxed grains and coarser columnar grains has better elongation and a yield drop phenomenon.展开更多
Currently,the hierarchical structure is one of the most effective means to enhance the strength and plasticity of metal materials,since the strain localization can be effectively delayed by the coordination of the uni...Currently,the hierarchical structure is one of the most effective means to enhance the strength and plasticity of metal materials,since the strain localization can be effectively delayed by the coordination of the unique microstructure.In this study,a hierarchical structure of Mg-15Gd-1Zn-0.4Zr(GZ151K)alloys containing grain,twin,and precipitation structural units was prepared by ultrasonic surface rolling process(USRP)and recrystallization annealing(RU).The results showed that the stress gradient generated by USRP formed a twin gradient structure,which will activate the twin-assisted precipitation(TAP)effect and twin-induced recrystallization(TIR)effect during RU.Then,the twin gradient structure transformed into a twin-precipitation gradient structure,and finally into a hierarchical structure with grain-twinprecipitation as the increasement of recrystallization degree.Besides,the dual gradient structure with twin and precipitation structural units had the highest strength and microhardness owing to the precipitation strengthening.However,the hierarchical structure with grain,twin,and precipitation structural units exhibited the most excellent combination of strength and plasticity under grain refinement and precipitation strengthening.展开更多
This work investigated the microstructure and impact behavior of Mg-4Al-5RE-xGd(RE represents La-Ce mischmetal;x=0,0.2,0.7 wt.%)alloys cast by high-pressure die casting(HPDC),permanent mold casting(PMC),and sand casti...This work investigated the microstructure and impact behavior of Mg-4Al-5RE-xGd(RE represents La-Ce mischmetal;x=0,0.2,0.7 wt.%)alloys cast by high-pressure die casting(HPDC),permanent mold casting(PMC),and sand casting(SC)techniques.The results indicated that with increasing Gd content,the grain sizes of the HPDC alloy had a slight change,but the grains of the PMC and SC alloys were significantly refined.Besides,the acicular Al_(11)RE_(3)phase was modified into the short-rod shape under the three casting conditions.The impact toughness of the studied alloy was mainly dominated by the absorbed energy during the crack initiation.With increasing Gd content,the impact toughness of the studied alloy monotonically increased due to the lower tendency of the modified second phase toward crack initiation.The impact stress was higher than the tensile stress,exhibiting a strain rate sensitivity for the mechanical response;however,the HPDC alloy had an inconsistent strain rate sensitivity during the impact event due to the transformation of the deformation mechanism from twinning to slip with increasing strain.Abundant dimples covered the fracture surface of the fine-grained HPDC alloys,indicating a typical ductile fracture.Nevertheless,due to the deficient{1012}twinning activity and the suppressed grain boundary sliding during the impact event,the HPDC alloys showed insufficient plastic deformation capacity.展开更多
In this study,we investigated the oxidation of the Mg-11Y-1Al alloy at 500℃in an Ar-20%O2environment.Multiscale analysis showed the network-like long-period stacking ordered(LPSO)phase transformed into needle-like LP...In this study,we investigated the oxidation of the Mg-11Y-1Al alloy at 500℃in an Ar-20%O2environment.Multiscale analysis showed the network-like long-period stacking ordered(LPSO)phase transformed into needle-like LPSO and polygonal Mg24Y5 phases,leading to the formation of a high-dense network of needle-like oxides at the oxidation front.These oxides grew laterally along the oxide/matrix interfaces,forming a thicker,continuous scale that effectively blocked elemental diffusion.Hence,the preferential oxidation along the needle-like LPSO is believed to accelerate the formation of a thicker and continuous oxide scale,further improving the oxidation resistance of the Mg-11Y-1Al alloy.展开更多
Mg-Nd-Zn-Zr(JDBM)alloy was studied as a candidate for biodegradable implant material because of its moderate mechanical properties,good biocompatibility,and favorable uniform degradation behavior.To verify whether JDB...Mg-Nd-Zn-Zr(JDBM)alloy was studied as a candidate for biodegradable implant material because of its moderate mechanical properties,good biocompatibility,and favorable uniform degradation behavior.To verify whether JDBM alloy exhibits electroplasticity effect and then study the mechanism of electropulsing treatment on JDBM alloy,in this study,homogenized and pre-tensile deformed samples were treated by electropulsing.After the electropulsing treatment,the average grain size was refined due to recrystallization,micron-scale Mg12Nd secondary phases precipitated slightly,while the morphology of nanoscale Zr particles changed from rodlike to ellipsoidal shape.The elongation to failure(EL)increased obviously for the homogenized and pre-tensile deformed JDBM alloy samples after electropulsing treatment,accompanying with no obvious sacrifice of the yield strength(YS)for the former and an evident decrease of YS for the latter,mainly due to the reduction of the dislocation density.The YS decrement and EL increment(77.57%)for the latter are more apparent attributed to the higher density of dislocations introduced by pre-tensile deformation.Therefore,the electropulsing treatment can obviously improve the mechanical properties of JDBM alloy,especially for the plasticity.The present work opens a new window for the fabrication of JDBM alloy profiles with high mechanical properties,especially for the plasticity,such as the cold drawing wires and tubes for biomedical applications.It also could provide theoretical references for other magnesium alloy processing.展开更多
Heterogeneous composites have strong anisotropy and are prone to dynamic recrystallization during hot compression,making the me-chanical response highly nonlinear.Therefore,it is a very challenging task to intellectua...Heterogeneous composites have strong anisotropy and are prone to dynamic recrystallization during hot compression,making the me-chanical response highly nonlinear.Therefore,it is a very challenging task to intellectually judge the thermal deformation characteristics of magnesium matrix composites(MgMCs).In view of this,this paper introduces a method to accurately solve the thermoplastic deformation of composites.Firstly,a hot compression constitutive model of magnesium matrix composites based on stress softening correction was established.Secondly,the complex quasi-realistic micromechanics modeling of heterogeneous magnesium matrix composites was conducted.By introducing the recrystallization softening factor and strain parameter into the constitutive equation,the accurate prediction of the global rheological response of the composites was realized,and the accuracy of the new constitutive model was proved.Finally,the thermal pro-cessing map of magnesium matrix composites was established,and the suitable processing range was chosen.This paper has certain guiding values for the prediction of the thermodynamic response and thermal processing of magnesium matrix composites.展开更多
The Mg-Gd-Y-Zn-Zr alloys are representational and potential age-hardening systems as reported in the past ten years,but their mechanical properties are still dependent on the grain size and its distribution.The effect...The Mg-Gd-Y-Zn-Zr alloys are representational and potential age-hardening systems as reported in the past ten years,but their mechanical properties are still dependent on the grain size and its distribution.The effect of bimodal structure on mechanical properties of Mg-8Gd-3Y-0.5Zr alloy with bimodal grain size distributions was investigated.The results suggested that the volume fraction of fine grain(FG)and coarse grain(CG)could be controlled by combined processes of hot forging,extrusion and annealing.And for the present alloys with bimodal grain size distribution,the improvement of strength is still attributed to the grain refinement.The morphology of bimodal grain size distribution has a marked impact on the ductility of the alloy,i.e.with the increase of coarse grain volume fraction,the elongation to failure increases at the beginning and then decreases.The mechanism of the toughening effect of bimodal grain size distribution on the Mg-Gd-Y-Zn-Zr alloys with bimodal grain size structure has been discussed.展开更多
In the application of WE43,it is found that Y_(2)O_(3)inclusion formed in the process of casting seriously reduced the mechanical properties of the products.The reduction of the mechanical properties is even more dist...In the application of WE43,it is found that Y_(2)O_(3)inclusion formed in the process of casting seriously reduced the mechanical properties of the products.The reduction of the mechanical properties is even more distinct when it comes to the application in the thin walled complex-precision castings.In order to decrease the Y_(2)O_(3)inclusions,Gd element was used to replace part of the Y element in Mg-Y-RE series alloys.The effect of Y content(Mg-x Y-1Gd-2Nd-0.5Zn-0.5Zr)and Y/Gd ratio(Mg-x Y-(5-x)Gd-2Nd-0.5Zn-0.5Zr)on the microstructure and mechanical properties of Mg-Y-RE alloys were investigated in this paper.With decreasing Y content,the grain size of the alloys increased,both ultimate tensile strength(UTS)and yield strength(YS)of alloys decreased monotonically.Replacing part of Y content with Gd and keeping the total rare earth content unchanged,the low Y content Mg-2Y-3Gd-2Nd-0.5Zn-0.5Zr alloy showed the same mechanical properties as the high Y content Mg-4Y-1Gd-2Nd-0.5Zn-0.5Zr alloy at both room and elevated temperatures.After solution treatment at 525°C for 8 h and aging treatment at 225°C for 10 h,the UTS,YS and elongation(ε)of Mg-2Y-3Gd-2Nd-0.5Zn-0.5Zr alloy reached 281.7 MPa,198 MPa and 11.1%at room temperature,and 216.7 MPa,171.6 MPa and 16.1%at 250°C.The new low Y content Mg-2Y-2Nd-3Gd-0.5Zn-0.5Zr alloy is expected to replace the high Y content WE43 alloys,which can be used in the complex thin-walled parts of aviation products.展开更多
Microstructure and mechanical properties of Mg-15wt.%Gd-5 wt.%Y-0.5wt.% Zr alloy were investigated in a series of conditions. The eutectic was dissolved into the matrix and there was no evident grain growth after soln...Microstructure and mechanical properties of Mg-15wt.%Gd-5 wt.%Y-0.5wt.% Zr alloy were investigated in a series of conditions. The eutectic was dissolved into the matrix and there was no evident grain growth after solntionized at 525 ℃ for 12 h. The evolution of the phase constituents from as-cast to cast-T4 was as follows： α-Mg solid solution＋Mg5（Gd,Y） entectic compound→α-Mg solid solution＋ spheroidized Mg5（Gd, Y） phase→α-Mg supersaturated solid solution＋cuboid-shaped compound （Mg2Y3Gd2）. And the precipitation sequences of Mg-15Gd-5Y-0.5Zr alloy were observed, according to the hardness response to isothermal ageing at 225-300 ℃ for 0-128 h.展开更多
Laser surface cladding was applied on a TC4 Ti alloy to improve its surface properties. Mixed TiC and Ti powders with a TiC-to-Ti mass ratio of 1：3 were put onto the TC4 Ti alloy and subsequently treated by laser bea...Laser surface cladding was applied on a TC4 Ti alloy to improve its surface properties. Mixed TiC and Ti powders with a TiC-to-Ti mass ratio of 1：3 were put onto the TC4 Ti alloy and subsequently treated by laser beam. The microstructure and composition modifications in the surfaee layer were carefully investigated by using SEM, EDX and XRD. Due to melting, liquid state mixing followed by rapid solidification and cooling, a layer with graded microstructures and compositions formed. The TiC powders were completely dissolved into the melted layer during melting and segregated as fine dendrites when solidified. The inter-dendritic areas were filled with fine a＇ phase lamellae enrich in A1. Mainly due to the reduced TiC volume fraction with increasing depth, the hardness decreases with increasing depth in the laser clad layer with a maximum value of HV1400, about 4.5 times of the initial one.展开更多
In order to verify the feasibility of producing Mg−rare earth(RE)alloy by selective laser melting(SLM)process,the microstructure and mechanical properties of Mg−15Gd−1Zn−0.4Zr(wt.%)(GZ151K)alloy were investigated.The ...In order to verify the feasibility of producing Mg−rare earth(RE)alloy by selective laser melting(SLM)process,the microstructure and mechanical properties of Mg−15Gd−1Zn−0.4Zr(wt.%)(GZ151K)alloy were investigated.The results show that fine grains(~2μm),fine secondary phases and weak texture,were observed in the as-fabricated(SLMed)GZ151K Mg alloy.At room temperature,the SLMed GZ151K alloy has a yield strength(YS)of 345 MPa,ultimate tensile strength(UTS)of 368 MPa and elongation of 3.0%.After subsequent aging(200℃,64 h,T5 treatment),the YS,UTS and elongation of the SLMed-T5 alloy are 410 MPa,428 MPa and 3.4%,respectively,which are higher than those of the conventional cast-T6 alloy,especially with the YS increased by 122 MPa.The main strengthening mechanisms of the SLMed GZ151K alloy are fine grains,fine secondary phases and residual stress,while after T5 treatment,the YS of the alloy is further enhanced by precipitates.展开更多
As most Mg alloy products are now produced by a casting process,the development of high strength cast Mg alloys can promote their further applications and has already become one of the hot research areas of Mg alloys....As most Mg alloy products are now produced by a casting process,the development of high strength cast Mg alloys can promote their further applications and has already become one of the hot research areas of Mg alloys.The present paper reviews the strengthening mechanisms,tensile properties and modification results of commercial high strength cast Mg alloys;as well as the development of Mg-Gd,Mg-Nd and Mg-Sn based alloys.It concludes that precipitation strengthening is the most important strengthening mechanism in high strength cast Mg alloys,which contributes more than 60%of yield strength in solution&peak-aged(T6)cast Mg alloys.For the yield strength,the alloys follow the sequence of Mg-Gd(Y)-Ag>Mg-Gd(Y)-Zn>Mg-Gd-Y/Sm/Nd>Mg-Y-Nd(WE series)>ZK61>Mg-Nd>AZ91>Mg-Sn.Mg-Gd(Y)-Ag based alloys are the strongest cast Mg alloys at present,followed by Mg-Gd(Y)-Zn based alloys.The high yield strengths of Mg-Gd(Y)-Ag and Mg-Gd(Y)-Zn cast alloys are due to the co-precipitation of basal and prismatic meta-stable phases.展开更多
The microstructure and mechanical properties of Mg-Zn-Ho-Zr alloys have been investigated in detail. The grain size of the as-cast Mg-Zn-Ho-Zr alloy was greatly decreased by the addition of Ho, and the grain growth du...The microstructure and mechanical properties of Mg-Zn-Ho-Zr alloys have been investigated in detail. The grain size of the as-cast Mg-Zn-Ho-Zr alloy was greatly decreased by the addition of Ho, and the grain growth during solution treatment was suppressed by Mg-Zn-Ho phases formed at grain boundaries. These thermally stable Mg-Zn-Ho phases could not completely dissolve into the matrix dur- ing solution treatment, and the strengthening effect of solution-plus-ageing treatment weakened. The addition of Ho can greatly enhance the high-temperature elongation of the Mg-Zn-Ho-Zr alloy, but the increase of high-temperature tensile strength was just a little.展开更多
The microstructure and corrosion behavior of the as-homogenized and as-extruded Mg-xLi-3Al-2Zn-0.5Y alloys(x=4,8,12,wt.%)were studied.The results show that as the Li content increases from 4%to 12%,the matrix transfer...The microstructure and corrosion behavior of the as-homogenized and as-extruded Mg-xLi-3Al-2Zn-0.5Y alloys(x=4,8,12,wt.%)were studied.The results show that as the Li content increases from 4%to 12%,the matrix transfers from singleα-Mg phase,(α-Mg+β-Li)dual phase to singleβ-Li phase.A mixed corrosion feature of intergranular corrosion and pitting corrosion occurs in the Mg-4Li-3Al-2Zn-0.5Y and Mg-12Li-3Al-2Zn-0.5Y alloys.The former is related to the precipitated AlLi phase along the grain boundaries,and the latter is related to the high potential difference between the second phase and the matrix.The corrosion resistance of the as-extruded alloys is better than that of the as-homogenized alloys.The superior corrosion resistance of the as-extruded Mg-8Li-3Al-2Zn-0.5Y alloy with the lowest corrosion rate(P_(W)=(0.63±0.26)mm/a)is attributed to the more uniform distribution of second phases,the protectiveα-Mg phase via sacrificing theβ-Li phase and the relatively integrated oxide film.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.51871148,51821001)。
文摘The influence of pouring temperature and mold temperature on the fluidity and hot tearing behavior of Al-2Li-2Cu-0.5Mg-0.15Sc-0.1Zr-0.1Ti alloys was investigated by experimental investigation and simulation assessment.The results showed that the length of the spiral fluidity sample increases from 302 to 756 mm as the pouring temperature increases from 680 to 740℃,and from 293 to 736 mm as the mold temperature increases from 200 to 400℃.The hot tearing susceptibility(HTS)firstly decreases and then increases with increasing pouring and mold temperatures,which is mainly caused by the oxide inclusion originating from the high activity of Li at excessive pouring temperature.Excessive pouring and mold temperatures easily produce oxide inclusions and holes,leading to a reduction in fluidity and an increase in HTS of the alloy.Combining the experimental and simulation results,the optimized pouring and mold temperatures are~720℃ and~300℃ for the cast Al-Li alloy,respectively.
基金supported by the National Key Research and Development Program of China(Grant No.2021YFB3501002)the National Natural Science Foundation of China(Grant No.52301059,No.52271009)the Shanghai Post-doctoral Excellence Program(Grant No.2023372).
文摘Magnesium and its alloys offer lightweight advantage and have extensive development prospects,particularly in aerospace.However,their flammability poses a significant barrier on the development of Mg alloys.The ignition resistance of these alloys often depends on the protectiveness of the oxide film formed on the surface.This paper elucidates the formation mechanism of oxide film from thermodynamics and kinetics,classifying oxide films based on their layered structure to assess their protective properties.Furthermore,it comprehensively reviews the impact of characteristics on the protective effectiveness such as compactness,continuity,thickness,and mechanical properties.The paper also introduces various characterization methods for the microstructure and properties of oxide film.The primary objective of this paper is to enhance the comprehension of oxide film concerning the ignition resistance of Mg alloys and to furnish references for future advancements and research in Mg alloys with heightened ignition resistance.
基金supported by the National Natural Science Foundation of China(Nos.51825101,52001202)the National Key Research and Development Program of China(No.2021YFA1600900)。
文摘A comprehensive analysis of the microstructure and defects of a thixomolded AZ91D alloy was conducted to elucidate their influences on mechanical properties.Samples were made at injection temperatures ranging from 580 to 640℃.X-ray computed tomography was used to visualize pores,and crystal plasticity finite element simulation was adopted for deformation analysis.The microstructure characterizations reveal a hierarchical cell feature composed of α-Mg and eutectic phases.With the increase of injection temperature,large cell content in the material decreases,while the strength of the alloy increases.The underlying mechanism about strength change is that coarse-grained solids experience smaller stress even in hard orientations.The sample fabricated at a moderate temperature of 620℃ exhibits the highest elongation,least quantity and lower local concentration of pores.The detachment and tearing cracks formed at lower injection temperature and defect bands formed at higher injection temperature add additional crack sources and deteriorate the ductility of the materials.
基金supported by the National Natural Science Foundation of China(Nos.U2037601,U2241231,and 51821001).
文摘Additive manufactured Mg-RE alloys usually show exceptional mechanical properties,which is mainly attributed to their refined grains in previous studies.Since Mg-RE series are typical age-hardenable alloys,this study focuses on the aging behavior of wire arc additive manufactured Mg-9Gd-3Y-0.5Zr(GW93K)alloy and compares it with the as-cast counterpart,providing a new insight into the strengthening mechanism of additive manufactured alloys.It was revealed that both the refined equiaxedα-Mg grains and small-sized(only 5~10 nm)β′precipitates with an extremely high number density(~2.53×10^(4)µm^(-2))should be considered for the strengthening mechanisms of the deposited alloy.The promoted precipitation behavior is facilitated by the dislocation pile-ups formed under multiple thermal cycles and a high cooling rate during deposition.As a result,the deposited alloy at peak-aged state exhibits better comprehensive properties of UTS=392 MPa and EL=3.3%,which is 19%and 18%higher than that of the cast sample,individually.
基金supported by National Natural Science Foundation of China(Nos.12102280,12172238,12332012)Postdoctoral Fellowship Program of CPSF(No.GZB20230473)Support of Ultramicroscopy Research Center(URC,Kyushu University)are highly acknowledged.Yao Chen acknowledges the support of JSPS Fellowship(No.JP22F22720)and JSPS KAKENHI(No JP22K03828).
基金funded by the National Natural Science Foundation of China(Grant numbers U22A20187,52374405,52371177).
文摘High temperature performance of magnesium alloys can be tailored by either grain size or precipitates in the grain interior.In this study,exceptional creep resistance was successfully acquired in a RE-free cast Mg-Al-Ca-Ti(AC51Ti)alloy.Microalloying of Ti(0.01 wt.%)has been found to be beneficial to the improvement of the tensile creep resistance in a RE-free cast Mg-5Al-0.35Mn-(1Ca)(AC51)alloy,showing a low state creep rate(SCR)of 2.70×10^(−9)s^(−1)at 200℃/50 MPa,which is even better than that of many reported RE-containing Mg alloys.The presence of trace Ti contributes to the substantial refinement and more uniform distribution of Al_(2)Ca precipitates in the matrix.At the same time,the microalloying of Ti improves the solubility of Al and Ca in the matrix.It is reasonable to believe that the microalloying of Ti induced re-organization of Al_(2)Ca precipitates,dissolved a larger amount of Al and Ca atoms into magnesium lattice,and increased the possibility of interaction between GB/dislocations and precipitates,which strongly correlates with the high temperature properties.The creep strengthening mechanisms primarily attributed to both second phase strengthening and solid solution strengthening were separately proposed based on the experimental investigations.
基金financial supports from the National Natural Science Foundation of China(52130104,51821001)High Technology and Key Development Project of Ningbo,China(2019B10102)。
文摘Mg–3Nd–0.2Zn–0.4Zr(NZ30K,wt.%)alloy is a new kind of high-performance metallic biomaterial.The combination of the NZ30K Magnesium(Mg)alloy and selective laser melting(SLM)process seems to be an ideal solution to produce porous Mg degradable implants.However,the microstructure evolution and mechanical properties of the SLMed NZ30K Mg alloy were not yet studied systematically.Therefore,the fabrication defects,microstructure,and mechanical properties of the SLMed NZ30K alloy under different processing parameters were investigated.The results show that there are two types of fabrication defects in the SLMed NZ30K alloy,gas pores and unfused defects.With the increase of the laser energy density,the porosity sharply decreases to the minimum first and then slightly increases.The minimum porosity is 0.49±0.18%.While the microstructure varies from the large grains with lamellar structure inside under low laser energy density,to the large grains with lamellar structure inside&the equiaxed grains&the columnar grains under middle laser energy density,and further to the fine equiaxed grains&the columnar grains under high laser energy density.The lamellar structure in the large grain is a newly observed microstructure for the NZ30K Mg alloy.Higher laser energy density leads to finer grains,which enhance all the yield strength(YS),ultimate tensile strength(UTS)and elongation,and the best comprehensive mechanical properties obtained are YS of 266±2.1 MPa,UTS of 296±5.2 MPa,with an elongation of 4.9±0.68%.The SLMed NZ30K Mg alloy with a bimodal-grained structure consisting of fine equiaxed grains and coarser columnar grains has better elongation and a yield drop phenomenon.
基金supported by the National Key Research and Development Program of China(No.2021YFB3501001)the National Natural Science Foundation of China(Nos.52061028,and 52061039)+1 种基金the Natural Science Foundation of Jiangxi Province(No.20212BAB204049)the Interdisciplinary Innovation Fund of Nanchang University(IIFNCU),China(No.9166–27060003-ZD05).
文摘Currently,the hierarchical structure is one of the most effective means to enhance the strength and plasticity of metal materials,since the strain localization can be effectively delayed by the coordination of the unique microstructure.In this study,a hierarchical structure of Mg-15Gd-1Zn-0.4Zr(GZ151K)alloys containing grain,twin,and precipitation structural units was prepared by ultrasonic surface rolling process(USRP)and recrystallization annealing(RU).The results showed that the stress gradient generated by USRP formed a twin gradient structure,which will activate the twin-assisted precipitation(TAP)effect and twin-induced recrystallization(TIR)effect during RU.Then,the twin gradient structure transformed into a twin-precipitation gradient structure,and finally into a hierarchical structure with grain-twinprecipitation as the increasement of recrystallization degree.Besides,the dual gradient structure with twin and precipitation structural units had the highest strength and microhardness owing to the precipitation strengthening.However,the hierarchical structure with grain,twin,and precipitation structural units exhibited the most excellent combination of strength and plasticity under grain refinement and precipitation strengthening.
基金supported by the National Natural Science Foundation of China(NSFC,Grant Nos.U1902220,51674166,51074106 and 50674067)the National Key Research and Development Program of China(Grant No.2016YFB0301001)。
文摘This work investigated the microstructure and impact behavior of Mg-4Al-5RE-xGd(RE represents La-Ce mischmetal;x=0,0.2,0.7 wt.%)alloys cast by high-pressure die casting(HPDC),permanent mold casting(PMC),and sand casting(SC)techniques.The results indicated that with increasing Gd content,the grain sizes of the HPDC alloy had a slight change,but the grains of the PMC and SC alloys were significantly refined.Besides,the acicular Al_(11)RE_(3)phase was modified into the short-rod shape under the three casting conditions.The impact toughness of the studied alloy was mainly dominated by the absorbed energy during the crack initiation.With increasing Gd content,the impact toughness of the studied alloy monotonically increased due to the lower tendency of the modified second phase toward crack initiation.The impact stress was higher than the tensile stress,exhibiting a strain rate sensitivity for the mechanical response;however,the HPDC alloy had an inconsistent strain rate sensitivity during the impact event due to the transformation of the deformation mechanism from twinning to slip with increasing strain.Abundant dimples covered the fracture surface of the fine-grained HPDC alloys,indicating a typical ductile fracture.Nevertheless,due to the deficient{1012}twinning activity and the suppressed grain boundary sliding during the impact event,the HPDC alloys showed insufficient plastic deformation capacity.
基金the financial support from the National Key Research and Development Program of China(No.2022YFB3708400)the National Science and Technology Major Project(J2019-VIII-0003-0165)the Space Utilization System of China Manned Space Engineering(No.KJZ-YY-WCL04).
文摘In this study,we investigated the oxidation of the Mg-11Y-1Al alloy at 500℃in an Ar-20%O2environment.Multiscale analysis showed the network-like long-period stacking ordered(LPSO)phase transformed into needle-like LPSO and polygonal Mg24Y5 phases,leading to the formation of a high-dense network of needle-like oxides at the oxidation front.These oxides grew laterally along the oxide/matrix interfaces,forming a thicker,continuous scale that effectively blocked elemental diffusion.Hence,the preferential oxidation along the needle-like LPSO is believed to accelerate the formation of a thicker and continuous oxide scale,further improving the oxidation resistance of the Mg-11Y-1Al alloy.
基金National Natural Science Foundation of China(No.U1804251)National Key R&D Program of China(2021YFC2400701)。
文摘Mg-Nd-Zn-Zr(JDBM)alloy was studied as a candidate for biodegradable implant material because of its moderate mechanical properties,good biocompatibility,and favorable uniform degradation behavior.To verify whether JDBM alloy exhibits electroplasticity effect and then study the mechanism of electropulsing treatment on JDBM alloy,in this study,homogenized and pre-tensile deformed samples were treated by electropulsing.After the electropulsing treatment,the average grain size was refined due to recrystallization,micron-scale Mg12Nd secondary phases precipitated slightly,while the morphology of nanoscale Zr particles changed from rodlike to ellipsoidal shape.The elongation to failure(EL)increased obviously for the homogenized and pre-tensile deformed JDBM alloy samples after electropulsing treatment,accompanying with no obvious sacrifice of the yield strength(YS)for the former and an evident decrease of YS for the latter,mainly due to the reduction of the dislocation density.The YS decrement and EL increment(77.57%)for the latter are more apparent attributed to the higher density of dislocations introduced by pre-tensile deformation.Therefore,the electropulsing treatment can obviously improve the mechanical properties of JDBM alloy,especially for the plasticity.The present work opens a new window for the fabrication of JDBM alloy profiles with high mechanical properties,especially for the plasticity,such as the cold drawing wires and tubes for biomedical applications.It also could provide theoretical references for other magnesium alloy processing.
基金supported by the National Natural Science Foundation of China with the project of No.52305158Youth Innovation Team of Shaanxi Universities(2024),Shaanxi Province Qin Chuangyuan“Scientist+Engineer”Team construction of No.2024QCY-KXJ-112,Funding from Aero Engine Cooperation of China(No.ZZCX-2022-020)the industry-university-research cooperation of Eighth Research Institute of China Aerospace Science and Technology Corporation with the project of No.USCAST2021-1.
文摘Heterogeneous composites have strong anisotropy and are prone to dynamic recrystallization during hot compression,making the me-chanical response highly nonlinear.Therefore,it is a very challenging task to intellectually judge the thermal deformation characteristics of magnesium matrix composites(MgMCs).In view of this,this paper introduces a method to accurately solve the thermoplastic deformation of composites.Firstly,a hot compression constitutive model of magnesium matrix composites based on stress softening correction was established.Secondly,the complex quasi-realistic micromechanics modeling of heterogeneous magnesium matrix composites was conducted.By introducing the recrystallization softening factor and strain parameter into the constitutive equation,the accurate prediction of the global rheological response of the composites was realized,and the accuracy of the new constitutive model was proved.Finally,the thermal pro-cessing map of magnesium matrix composites was established,and the suitable processing range was chosen.This paper has certain guiding values for the prediction of the thermodynamic response and thermal processing of magnesium matrix composites.
基金supports of the National Key Research and Development Plan(Grant Nos.2016YFB0701201 and 2016YFB0301103)the National Natural Science Foundation of China(Grant Nos.51771109 and 51631006).
文摘The Mg-Gd-Y-Zn-Zr alloys are representational and potential age-hardening systems as reported in the past ten years,but their mechanical properties are still dependent on the grain size and its distribution.The effect of bimodal structure on mechanical properties of Mg-8Gd-3Y-0.5Zr alloy with bimodal grain size distributions was investigated.The results suggested that the volume fraction of fine grain(FG)and coarse grain(CG)could be controlled by combined processes of hot forging,extrusion and annealing.And for the present alloys with bimodal grain size distribution,the improvement of strength is still attributed to the grain refinement.The morphology of bimodal grain size distribution has a marked impact on the ductility of the alloy,i.e.with the increase of coarse grain volume fraction,the elongation to failure increases at the beginning and then decreases.The mechanism of the toughening effect of bimodal grain size distribution on the Mg-Gd-Y-Zn-Zr alloys with bimodal grain size structure has been discussed.
基金This work is supported by National Natural Science Foundation of China(No.51775334,51771115)National Key Research and Development Program of China(No.2016YFB0301004)+1 种基金National Science and Technology Ma-jor Project(No.2017ZX04006001)Science Innovation Foundation of Shanghai Academy of Spaceflight Technology(No.SAST2016048).
文摘In the application of WE43,it is found that Y_(2)O_(3)inclusion formed in the process of casting seriously reduced the mechanical properties of the products.The reduction of the mechanical properties is even more distinct when it comes to the application in the thin walled complex-precision castings.In order to decrease the Y_(2)O_(3)inclusions,Gd element was used to replace part of the Y element in Mg-Y-RE series alloys.The effect of Y content(Mg-x Y-1Gd-2Nd-0.5Zn-0.5Zr)and Y/Gd ratio(Mg-x Y-(5-x)Gd-2Nd-0.5Zn-0.5Zr)on the microstructure and mechanical properties of Mg-Y-RE alloys were investigated in this paper.With decreasing Y content,the grain size of the alloys increased,both ultimate tensile strength(UTS)and yield strength(YS)of alloys decreased monotonically.Replacing part of Y content with Gd and keeping the total rare earth content unchanged,the low Y content Mg-2Y-3Gd-2Nd-0.5Zn-0.5Zr alloy showed the same mechanical properties as the high Y content Mg-4Y-1Gd-2Nd-0.5Zn-0.5Zr alloy at both room and elevated temperatures.After solution treatment at 525°C for 8 h and aging treatment at 225°C for 10 h,the UTS,YS and elongation(ε)of Mg-2Y-3Gd-2Nd-0.5Zn-0.5Zr alloy reached 281.7 MPa,198 MPa and 11.1%at room temperature,and 216.7 MPa,171.6 MPa and 16.1%at 250°C.The new low Y content Mg-2Y-2Nd-3Gd-0.5Zn-0.5Zr alloy is expected to replace the high Y content WE43 alloys,which can be used in the complex thin-walled parts of aviation products.
基金the Major State Basic Research Development Program of China (973 Program, 5133001E)
文摘Microstructure and mechanical properties of Mg-15wt.%Gd-5 wt.%Y-0.5wt.% Zr alloy were investigated in a series of conditions. The eutectic was dissolved into the matrix and there was no evident grain growth after solntionized at 525 ℃ for 12 h. The evolution of the phase constituents from as-cast to cast-T4 was as follows： α-Mg solid solution＋Mg5（Gd,Y） entectic compound→α-Mg solid solution＋ spheroidized Mg5（Gd, Y） phase→α-Mg supersaturated solid solution＋cuboid-shaped compound （Mg2Y3Gd2）. And the precipitation sequences of Mg-15Gd-5Y-0.5Zr alloy were observed, according to the hardness response to isothermal ageing at 225-300 ℃ for 0-128 h.
基金Project(J51402) supported by the Leading Academic Discipline Project of Shanghai Education Commission,ChinaProject(gjd08004) supported by the Foundation for Excellent Youth Scholar of China+2 种基金 Project(08QA14035) supported by the Shanghai Science and Technology Development Foundation, China Project(0852nm01400) supported by the Special Foundation of Shanghai Education Commission for Nano-Materials Research, China Project(08520513400) supported by Crucial Project of the Shanghai Science and Technology Commission,China
文摘Laser surface cladding was applied on a TC4 Ti alloy to improve its surface properties. Mixed TiC and Ti powders with a TiC-to-Ti mass ratio of 1：3 were put onto the TC4 Ti alloy and subsequently treated by laser beam. The microstructure and composition modifications in the surfaee layer were carefully investigated by using SEM, EDX and XRD. Due to melting, liquid state mixing followed by rapid solidification and cooling, a layer with graded microstructures and compositions formed. The TiC powders were completely dissolved into the melted layer during melting and segregated as fine dendrites when solidified. The inter-dendritic areas were filled with fine a＇ phase lamellae enrich in A1. Mainly due to the reduced TiC volume fraction with increasing depth, the hardness decreases with increasing depth in the laser clad layer with a maximum value of HV1400, about 4.5 times of the initial one.
基金financial supports from the National Key Research and Development Program of China(Nos.2016YFB0301000,2016YFB0701204)the National Natural Science Foundation of China(No.51821001).
文摘In order to verify the feasibility of producing Mg−rare earth(RE)alloy by selective laser melting(SLM)process,the microstructure and mechanical properties of Mg−15Gd−1Zn−0.4Zr(wt.%)(GZ151K)alloy were investigated.The results show that fine grains(~2μm),fine secondary phases and weak texture,were observed in the as-fabricated(SLMed)GZ151K Mg alloy.At room temperature,the SLMed GZ151K alloy has a yield strength(YS)of 345 MPa,ultimate tensile strength(UTS)of 368 MPa and elongation of 3.0%.After subsequent aging(200℃,64 h,T5 treatment),the YS,UTS and elongation of the SLMed-T5 alloy are 410 MPa,428 MPa and 3.4%,respectively,which are higher than those of the conventional cast-T6 alloy,especially with the YS increased by 122 MPa.The main strengthening mechanisms of the SLMed GZ151K alloy are fine grains,fine secondary phases and residual stress,while after T5 treatment,the YS of the alloy is further enhanced by precipitates.
基金supported by the National Natural Science Foundation of China(51201103&51304135)the Specialized Research Fund for the Doctoral Program of Higher Education(20110073120008)+2 种基金the New Century Excellent Talents in University of Ministry of Education of China(NCET-11-0329)the Program of Shanghai Subject Chief of Engineering(14XD1425000)the Assembly Pre-research Project(51312030706)
文摘As most Mg alloy products are now produced by a casting process,the development of high strength cast Mg alloys can promote their further applications and has already become one of the hot research areas of Mg alloys.The present paper reviews the strengthening mechanisms,tensile properties and modification results of commercial high strength cast Mg alloys;as well as the development of Mg-Gd,Mg-Nd and Mg-Sn based alloys.It concludes that precipitation strengthening is the most important strengthening mechanism in high strength cast Mg alloys,which contributes more than 60%of yield strength in solution&peak-aged(T6)cast Mg alloys.For the yield strength,the alloys follow the sequence of Mg-Gd(Y)-Ag>Mg-Gd(Y)-Zn>Mg-Gd-Y/Sm/Nd>Mg-Y-Nd(WE series)>ZK61>Mg-Nd>AZ91>Mg-Sn.Mg-Gd(Y)-Ag based alloys are the strongest cast Mg alloys at present,followed by Mg-Gd(Y)-Zn based alloys.The high yield strengths of Mg-Gd(Y)-Ag and Mg-Gd(Y)-Zn cast alloys are due to the co-precipitation of basal and prismatic meta-stable phases.
基金supported by the National Natural Science Foundation of China (No.51074106)the International Cooperation Fund of Shanghai Science and Technology Committee:Shanghai/Rhone-Alpes Science and Technology Cooperation Fund (No. 06SR07104)+1 种基金the National High-Tech Research and Development Program of China (No.2009AA033501)the National High-Tech Research and Development Program of China (No.2006BAE04B01-2)
文摘The microstructure and mechanical properties of Mg-Zn-Ho-Zr alloys have been investigated in detail. The grain size of the as-cast Mg-Zn-Ho-Zr alloy was greatly decreased by the addition of Ho, and the grain growth during solution treatment was suppressed by Mg-Zn-Ho phases formed at grain boundaries. These thermally stable Mg-Zn-Ho phases could not completely dissolve into the matrix dur- ing solution treatment, and the strengthening effect of solution-plus-ageing treatment weakened. The addition of Ho can greatly enhance the high-temperature elongation of the Mg-Zn-Ho-Zr alloy, but the increase of high-temperature tensile strength was just a little.
基金financially supported by the National Natural Science Foundation of China(Nos.51771115,51775334,51821001,U2037601)Open Fund of State Key Laboratory of Advanced Forming Technology and Equipment(No.SKL2020005)。
文摘The microstructure and corrosion behavior of the as-homogenized and as-extruded Mg-xLi-3Al-2Zn-0.5Y alloys(x=4,8,12,wt.%)were studied.The results show that as the Li content increases from 4%to 12%,the matrix transfers from singleα-Mg phase,(α-Mg+β-Li)dual phase to singleβ-Li phase.A mixed corrosion feature of intergranular corrosion and pitting corrosion occurs in the Mg-4Li-3Al-2Zn-0.5Y and Mg-12Li-3Al-2Zn-0.5Y alloys.The former is related to the precipitated AlLi phase along the grain boundaries,and the latter is related to the high potential difference between the second phase and the matrix.The corrosion resistance of the as-extruded alloys is better than that of the as-homogenized alloys.The superior corrosion resistance of the as-extruded Mg-8Li-3Al-2Zn-0.5Y alloy with the lowest corrosion rate(P_(W)=(0.63±0.26)mm/a)is attributed to the more uniform distribution of second phases,the protectiveα-Mg phase via sacrificing theβ-Li phase and the relatively integrated oxide film.
