The effect of ultraviolet(UV)radiation and biocide benzalkonium chloride(BKC)on fungal-induced corrosion of AA7075 induced by Aspergillus terreus(A.terreus)was deeply studied using analysis of biological activity,surf...The effect of ultraviolet(UV)radiation and biocide benzalkonium chloride(BKC)on fungal-induced corrosion of AA7075 induced by Aspergillus terreus(A.terreus)was deeply studied using analysis of biological activity,surface analysis,and electrochemical measurements.Results demonstrated that the planktonic and sessile spore concentrations decline by more than two orders of magnitude when UV radiation and BKC are combinedly used compared with the control.UV radiation can inhibit the biological activity of A.terreus and influence the stability of passive film of AA7075.Except for direct disinfection,the physical adsorption of BKC on the specimen can effectively inhibit the attachment of A.terreus.The combination of UV radiation and BKC can much more effectively inhibit the corrosion of AA,especially pitting corrosion,due to their synergistic effect.The combined application of UV radiation and BKC can be a good method to effectively inhibit fungal-induced corrosion.展开更多
The evolution of microstructure during hot deformation is key to achieving good mechanical properties in aluminum alloys.We have developed a cellular automaton(CA) based model to simulate the microstructural evolution...The evolution of microstructure during hot deformation is key to achieving good mechanical properties in aluminum alloys.We have developed a cellular automaton(CA) based model to simulate the microstructural evolution in 7075 aluminum alloy during hot deformation.Isothermal compression tests were conducted to obtain material parameters for 7075 aluminum alloy,leading to the establishment of models for dislocation density,nucleation of recrystallized grains,and grain growth.Integrating these aspects with grain topological deformation,our CA model effectively predicts flow stress,dynamic recrystallization(DRX) volume fraction,and average grain size under diverse deformation conditions.A systematic comparison was made between electron back scattered diffraction(EBSD) maps and CA model simulated under different deformation temperatures(573 to 723 K),strain rates(0.001 to 1 s^(-1)),and strain amounts(30% to 70%).These analyses indicate that large strain,high temperature,and low strain rate facilitate dynamic recrystallization and grain refinement.The results from the CA model show good accuracy and predictive capability,with experimental error within 10%.展开更多
A self-developed forced convection rheoforming （FCR） machine for the preparation of light alloy semisolid slurry was introduced. The microstructure characteristics of 7075 aluminium alloy semisolid slurry at differe...A self-developed forced convection rheoforming （FCR） machine for the preparation of light alloy semisolid slurry was introduced. The microstructure characteristics of 7075 aluminium alloy semisolid slurry at different stirring speeds prepared by the FCR process were analyzed. The experimental results suggest that with the increase of the stirring speed, the mean grain size of the semisolid decreases and the shape factor as well as the number of primary grains increase. Meanwhile, the preparation process of semisolid slurry was numerically simulated. The flow characteristics of the melt in the device and the effect of the stirring speed on temperature field and solid fraction of the melt were investigated. The simulated results show that during the preparation process of semisolid slurry, there is a complex convection within the FCR device that obviously changes the temperature field distribution and solid fraction of the melt. When the convection intensity increases, the scope of the undercooling gradient of the melt is reduced and temperature distribution is improved.展开更多
The semi-solid slurry of 7075 aluminum alloy was prepared by a serpentine pouring channel （SCP）. Influences of pouring temperature and the number of turns on the microstructure of semi-solid 7075 alloy slurry were i...The semi-solid slurry of 7075 aluminum alloy was prepared by a serpentine pouring channel （SCP）. Influences of pouring temperature and the number of turns on the microstructure of semi-solid 7075 alloy slurry were investigated. The results demonstrated that the semi-solid 7075 aluminum alloy slurry with satisfied quality could be generated by a serpentine pouring channel when the pouring temperature was in the range of 680-700 ℃. At a given pouring temperature, the equivalent size of the primaryα（Al） grains decreased and the shape factor increased with the increase of the number of turns. During the slurry preparation of semi-solid 7075 aluminum alloy, the flow direction of alloy melt changed many times when it flowed in a curved and closed serpentine channel. With the effect of“stirring”in it , the primary nuclei gradually evolved into spherical and near-spherical grains.展开更多
7075 aluminum alloy was used to obtain elbow parts by complex thixoextrusion and the microstructure evolution and mechanical properties during this process were studied by SEM,TEM and other analytical methods.The resu...7075 aluminum alloy was used to obtain elbow parts by complex thixoextrusion and the microstructure evolution and mechanical properties during this process were studied by SEM,TEM and other analytical methods.The results show that different parts in 7075 aluminum alloy show quite different microstructures.The microstructure of the thin walls formed by back-extrusion is stratified,and the bottom of the parts formed by angular extrusion is obviously deformed.Shear forces contribute to the crushing of grains and the coarse second phase.The main strengthening phases in the material areηphase and E phase,whose amounts greatly decrease during heating to semi-solid and thixoextrusion.After heat treatment,they can precipitate evenly to improve the mechanical properties of the material.The average tensile strength of whole part after thixoextrusion and heat treatment is 485.49 MPa,while the average elongation is 5.49%.展开更多
The static recrystallization behavior of 7075 aluminum alloy containing Al_(3)(Sc,Zr)phase prepared by casting and the relationship between recrystallization behavior and mechanical properties were studied.The additio...The static recrystallization behavior of 7075 aluminum alloy containing Al_(3)(Sc,Zr)phase prepared by casting and the relationship between recrystallization behavior and mechanical properties were studied.The addition of Sc and Zr made the Sc−Zr−7075 aluminum alloy remain the most of fibrous structure and high-density dislocations formed in the extrusion process,resulting in the recrystallization fraction of the alloy decreasing from 35%to 22%,and the corresponding fraction of substructure increasing from 59%to 67%.The Sc and Zr effectively inhibited the recrystallization behavior of 7075 aluminum alloy mainly,which was attributed to the fact that the existence of fine and coherent Al_(3)(Sc,Zr)phase(r=35 nm,f=1.8×10^(−3))strongly pined the dislocations and grain boundaries,preventing the dislocations from rearranging into sub-grain boundaries and from developing into high angle grain boundaries,and further hindering the formation and growth of recrystallized core of the alloy.展开更多
The effect of solution treatment time on the post-formed plasticity and ductile fracture of 7075 aluminum alloy in the hot stamping process was studied.Tensile tests were conducted on the specimens subjected to the ho...The effect of solution treatment time on the post-formed plasticity and ductile fracture of 7075 aluminum alloy in the hot stamping process was studied.Tensile tests were conducted on the specimens subjected to the hot stamping process with different solution treatment time.The digital image correlation(DIC)analysis was used to obtain the strain of the specimen.Based on the experiments and modeling,the Yld2000-3d yield criterion and the DF2014 ductile fracture criterion were calibrated and used to characterize the anisotropy and fracture behavior of the metal,respectively.Furthermore,the microstructure of specimens was studied.The experimental and simulation results indicate that the 7075 aluminum alloy retains distinct anisotropy after the hot stamping process,and there is no obvious effect of extending the solution treatment time on the material anisotropy.However,it is found that a longer solution treatment time can increase the fracture strain of the aluminum alloy during the hot stamping process,which may be related to the decrease of the second-phase particles size.展开更多
The torsional fretting wear tests of 7075 aluminum alloy flat against 52100 steel ball in dry condition were carried out on a new high-precision torsional fretting-wear tester.The kinetics behaviors and damage mechani...The torsional fretting wear tests of 7075 aluminum alloy flat against 52100 steel ball in dry condition were carried out on a new high-precision torsional fretting-wear tester.The kinetics behaviors and damage mechanism of 7075 aluminum alloy under different angular displacement amplitudes were investigated in detail.The results show that the torsional fretting running behaviors of 7075 aluminum alloy can be defined by three fretting regimes(i.e.partial slip regime(PSR),mixed fretting regime(MFR) and slip regime(SR)) with the increase of angular displacement amplitudes.In PSR,the damage occurs at the lateral portion of the contact zone with a slight annular shape.However,in MFR and SR,more severe damages are observed and the debris layer covers the wear scars.Friction torque and dissipation energy which are strongly dependent upon the imposed angular displacement amplitudes and presented in three stages were discussed in detail.The mechanisms of torsional fretting wear of aluminum alloy are mainly oxidative wear,abrasive wear and delamination in the three fretting regimes.In addition,the oxidative debris plays an important role during the torsional fretting wear processes.展开更多
The combined effects of equal channel angular pressing (ECAP) and subsequent heating to a semi-solid temperature on the microstructural characteristics of the 7075 aluminum alloy were investigated. The microstructure ...The combined effects of equal channel angular pressing (ECAP) and subsequent heating to a semi-solid temperature on the microstructural characteristics of the 7075 aluminum alloy were investigated. The microstructure is influenced by several parameters including the number of ECAP passes, ECAP route, consequent heating temperature, and holding time. The effects of these parameters on the microstructural characteristics including grain size and shape factor of the 7075 aluminum alloy were studied using experimental tests and Taguchi method. The results indicate that five-pass ECAP in route BA and subsequent isothermal holding at 630 °C for 15 min are more appropriate for achieving a semi-solid microstructure. The processing route and holding time have the highest impact on the grain size while the number of ECAP passes and heating temperature have the least impact on the grain size. Meanwhile, the shape factor is significantly influenced by the processing route, holding time and heating temperature while it is less influenced by the number of ECAP passes.展开更多
A 0.3wt%graphene nanoplatelets(GNPs)reinforced 7075 aluminum alloy matrix(7075 Al)composite was fabricated by spark plasma sintering and its strength and wear resistance were investigated.The microstructures of the in...A 0.3wt%graphene nanoplatelets(GNPs)reinforced 7075 aluminum alloy matrix(7075 Al)composite was fabricated by spark plasma sintering and its strength and wear resistance were investigated.The microstructures of the internal structure,the friction surface,and the wear debris were characterized by scanning electron microscopy,X-ray diffraction,and Raman spectroscopy.Compared with the original 7075 aluminum alloy,the hardness and elastic modulus of the 7075 Al/GNPs composite were found to have increased by 29%and 36%,respectively.The results of tribological experiments indicated that the composite also exhibited a lower wear rate than the original 7075 aluminum alloy.展开更多
The anodizing parameters of voltage, current density, temperature, and electrolyte choice were assessed to find an appropriate combination for the superheated slurry cast 7075 Al alloy substrate.The alloy was anodized...The anodizing parameters of voltage, current density, temperature, and electrolyte choice were assessed to find an appropriate combination for the superheated slurry cast 7075 Al alloy substrate.The alloy was anodized in sulfuric acid electrolyte or alternatively in sulfuric acid mixed with boric acid or citric acid. The voltages applied were in the range of 15-30 V. Anodizing current densities tested were 2 and 3 A/dm^2,while temperatures tested were 5 and 15 ℃. Thickness, surface morphology, hardness,and corrosion resistance of the oxide film were then evaluated.It was found that 25 V,2 A/dm^2 and 5 ℃ were suitable for this alloy when anodized in sulfuric acid. The oxide film was smooth with uniform thickness, low porosity, high hardness,and had the highest corrosion resistance at these parameters. However, discontinuous oxide films were observed from samples anodized at higher temperature of 15 ℃.Alternative electrolytes considered were sulfuric acid mixed with boric acid or citric acid. The results showed that electrolytes with boric acid or citric acid increased thickness, hardness, corrosion resistance and quality of the oxide films.However, these oxide films were inferior to those obtained with sulfuric acid electrolyte at lower temperature(25 V, 2 A/dm^2 and5 ℃).展开更多
The further application of semi-solid processing lies in the in-depth fundamental study like rheological behavior. In this research, the apparent viscosity of the semi-solid slurry of 7075 alloy was measured using a C...The further application of semi-solid processing lies in the in-depth fundamental study like rheological behavior. In this research, the apparent viscosity of the semi-solid slurry of 7075 alloy was measured using a Couette type viscometer. The effects of solid fraction and shearing rate on the apparent viscosity of this alloy were investigated under different processing conditions. It can be seen that the apparent viscosity increases with an increase in the solid fraction from 10% to 50% （temperature 620 ℃ to 630 ℃） at steady state. When the solid fraction was fixed, the apparent viscosity can be decreased by altering the shearing rate from 61.235 s-1 to 489.88 s-1 at steady state. An empirical equation that shows the effects of solid fraction and shearing rate on the apparent viscosity is fitted： ηα = [0.871 - 0.00849. γ0.74924]. exp（3.7311, fs） . The microstructure of quenched samples was examined to understand the alloy＇s rheological behavior.展开更多
The heat treatment process has great effects on microstructure and conductivity of ingots. In this study, the ingots of high strength 7075 aluminum alloy were prepared by low frequency electromagnetic casting(LFEC), a...The heat treatment process has great effects on microstructure and conductivity of ingots. In this study, the ingots of high strength 7075 aluminum alloy were prepared by low frequency electromagnetic casting(LFEC), and the effect of different homogenization processes(single-step homogenization at 465 ℃ for different holding times and three-step homogenization) on the microstructure and conductivity of 7075 aluminum alloy were studied by means of metallographic microscopy, electrical conductivity test, differential thermal analysis and X-ray diffraction phase analysis. For comparison, the ingot by conventional direct casting(DC) under the same conditions was also prepared. Results show that the non-equilibrium eutectic phases with low melting point in the ingot dissolve continuously into the matrix as the holding time of single-step homogenization increases. The endothermic peak of non-equilibrium phases can not be completely eliminated through a 24 h single-step homogenization, but can be eliminated after a three-step homogenization(200 ℃/2 h + 460 ℃/6 h + 480 ℃/12 h). Meanwhile, the homogenization has a better effect on the LFEC ingot than the conventional DC ingot. Under the same homogenizing conditions, the grains of LFEC ingot are characterized by a lower content of low melting point phases and the ingot shows higher electrical conductivity than DC ingot.展开更多
The precipitated phases in the WNZ,TMAZ,HAZ and BM of the friction stir welding(FSW)joint were observed using the transmission electron microscopy(TEM)and the lattice fringe spacing of the precipitated phases was meas...The precipitated phases in the WNZ,TMAZ,HAZ and BM of the friction stir welding(FSW)joint were observed using the transmission electron microscopy(TEM)and the lattice fringe spacing of the precipitated phases was measured.Combined with X-ray diffraction(XRD),the types of precipitated phases among the joint were confirmed and then the strength mismatch mechanism was revealed.The results show the precipitated phases of 7075 aluminum alloy FSW joint mainly consist of MgZn_(2),AlCuMg and Al_(2)CuMg.The microzone of the joint experienced different thermal cycles,the types and sizes of precipitated phases are different and the strengthening effect is different.The strengthening effect of the AlCuMg and Al_(2)CuMg are better than that of MgZn_(2).The precipitated phase in the WNZ mainly includes AlCuMg and Al_(2)CuMg,as well as the grain size is fine,the microhardness in this zone is pretty high.The number of precipitated phase AlCuMg and Al_(2)CuMg is smaller in the TMAZ and the MgZn_(2)is relatively more,which lead the microhardness decrease.The number of precipitated phase MgZn_(2)is relative larger in the HAZ,as well as the grain coarsening,the microhardness in this zone is lowest of the joint.At the same time,there are the precipitate free zones(PFZ)among the 7075 aluminum alloy FSW joint,which decreases the microhardness of the whole joint to some extent.展开更多
The hardness, the tensile and the high-cycle fatigue（HCF） performances of 7075 aluminum alloy were investigated under temper T651, solution treated at 380 ℃ for 0.5 h and aged at different temperatures（150, 170, 1...The hardness, the tensile and the high-cycle fatigue（HCF） performances of 7075 aluminum alloy were investigated under temper T651, solution treated at 380 ℃ for 0.5 h and aged at different temperatures（150, 170, 190 ℃） for 10 hours. The optimal microstructures and the fatigue fracture surfaces were observed. The results show that the hardness and the tensile performances are at their optimum at T651, but the fatigue life is the shortest. The hardness and the elongation are the lowest after solution treatment. With the aging temperature increasing（150-190 ℃）, the HCF is improved. The crack is initiated from the impurity particles on the subsurface. Treated at 170 ℃,the area of the quasi-cleavage plane and the width of parallel serrated sections of the crack propagation are the largest. With increasing aging temperature, the dimple size of finally fracture surfaces becomes larger and the depth deeper.展开更多
The microstructures after casting and extruding, the mechanical properties and electrical conductivity after RRA treatment of conventional DC casting and low frequency electromagnetic casting （LFEC） 7075 aluminum al...The microstructures after casting and extruding, the mechanical properties and electrical conductivity after RRA treatment of conventional DC casting and low frequency electromagnetic casting （LFEC） 7075 aluminum alloy were investigated. The results showed that finer grains which distributed more homogeneously was obtained in LFEC ingots compared with those conventional DC ingots. The extruded bars of LFEC alloy kept its fine grain features of original as-cast structure. In the RRA treatment, with the extension of second aging time, the tensile strength and hardness of alloy decreased, but the electrical conductivity increased. Meanwhile, as the second aging temperature raised, the phase change rate in precipitation also increased. Under the same conditions, extruded bars of LFEC alloy had better performance than that of conventional DC cast alloy. The optimum RRA heat treatment process was 120 ℃/24 h＋180 ℃/30 min＋120 ℃/24 h. The LFEC extruded bars acquired tensile strength 676.64 MPa, hardness 198.18, and electrical conductivity 35.7% IACS respectively, which were higher than that in the T6 temper, indicating that a notable RRA response takes place in LFEC extruded bars, whose second-step retrogression time was 30 min, and it was suitable for mass production.展开更多
The dynamic softening behaviors during hot deformation of 7075 aluminum alloy were studied by isothermal hot compression tested at temperatures of 250, 300, 350, 400 and 450 ℃ and strain rates of 0.01, 0.1, 1 and 10 ...The dynamic softening behaviors during hot deformation of 7075 aluminum alloy were studied by isothermal hot compression tested at temperatures of 250, 300, 350, 400 and 450 ℃ and strain rates of 0.01, 0.1, 1 and 10 s-1 on Gleeble1500. The results show that the temperature changes have a significant effect on the dynamic softening rate. It is indicated that the considerable dynamic softening rate associated with dynamic recrystallization leads flow stress value decreasing gradually. A group of coefficients needed by the phenomenological constitutive model containing a softening ratio item were calculated by the multiple linear regression method. The optical microstructures show that the grains of billets compressed become more and more refined with strain rate increasing as well as the degree of dynamic softening and work-hardening higher. The phenomenological constitutive description of 7075 aluminum alloy can accurately describe the relationships among flow stress, temperature, strain rate, strain and dynamic softening, and offer the basic model for plastic forming process simulation.展开更多
7075 aluminum alloy thick plates were produced by three processing routines: commercial hot rolling followed by heat treatment of quenching and ageing (HR+QA), combination of large deformation processing of multi dire...7075 aluminum alloy thick plates were produced by three processing routines: commercial hot rolling followed by heat treatment of quenching and ageing (HR+QA), combination of large deformation processing of multi directional warm forging and subsequent warm rolling followed by heat treatment of quenching and ageing (LD+QA), and that followed by annealing at moderate temperature (LD+AN). Tensile strength, yield strength and elongation were measured by tension test, and the metallographic structures were examined by optical microscopy (OM) and transmission electron microscopy (TEM), also the fracture morphologies were observed by scanning electron microscopy (SEM). It is shown that higher tensile strength and yield strength are obtained from (LD+QA) processing in comparison with those from (HR+QA) and (LD+AN) processings. Tensile strength and yield strength obtained from (LD+QA) processing are 9.9% and 8.6% higher respectively than those from (HR+QA) processing, and 48.6% and 57.7% higher respectively than those from (LD+AN) processing; while the elongations of all the samples show no significant difference and keep 10%12%. Analyses of OM and TEM reveal that the mechanical behaviors are deeply associated with the formation of refined structures with fine grains and very fine precipitates, leading to fine grained hardening and excellent age hardening.展开更多
The influence of quenching water temperature, pre stretching amount and aging temperature and times on residual stress in 7075 aluminum thick plate was studied by the measurement of residual stress using drilling hole...The influence of quenching water temperature, pre stretching amount and aging temperature and times on residual stress in 7075 aluminum thick plate was studied by the measurement of residual stress using drilling hole method. The results indicate that residual stress decreases by 30% with increasing quenching water temperature from 40 ℃ to 80 ℃, 20% with increasing aging temperature from 100 ℃ to 180 ℃,and 20% with increasing aging times from 5 h to 25 h. Also, residual stress decreases to zero with increasing pre stretching amount to approximately 2%. Hence, residual stress in 7075 aluminum thick plate is reduced by the control of quenching water temperature at 80 ℃ and with pre stretching amount of about 2%. An optimal aging temperature and time should be systemically investigated to obtain combination of high mechanical performances and lower residual stress for manufacturing of 7075 aluminum alloy thick plates.展开更多
In order to investigate the influence of hydrostatic pressure on compression limit of the ring, numerical simulation and experimental research were carried out. The effect of hydrostatic pressure on the deformation of...In order to investigate the influence of hydrostatic pressure on compression limit of the ring, numerical simulation and experimental research were carried out. The effect of hydrostatic pressure on the deformation of aluminum alloy 7075 ring was obtained by numerical simulation. The die set for compressing ring under high hydrostatic pressure was designed and manufactured. Experimental results show that the compression limit increases linearly as the hydrostatic pressure increases in a certain range. At 100 MPa the maximum compressive strain is increased by 32.42%. At strain limit, the cracks initiate from the corner of the outer wall to the middle of the inner wall along the direction of the maximum shear stress.展开更多
基金supported by the Guangdong Basic and Applied Basic Research Foundation,China(No.2023A1515012146)the National Natural Science Foundation of China(No.52271083)+1 种基金the Fundamental Research Funds for the Central Universities,China(No.22qntd0801)the Shanghai Engineering Technology Research Centre of Deep Offshore Material,China(No.19DZ2253100)。
文摘The effect of ultraviolet(UV)radiation and biocide benzalkonium chloride(BKC)on fungal-induced corrosion of AA7075 induced by Aspergillus terreus(A.terreus)was deeply studied using analysis of biological activity,surface analysis,and electrochemical measurements.Results demonstrated that the planktonic and sessile spore concentrations decline by more than two orders of magnitude when UV radiation and BKC are combinedly used compared with the control.UV radiation can inhibit the biological activity of A.terreus and influence the stability of passive film of AA7075.Except for direct disinfection,the physical adsorption of BKC on the specimen can effectively inhibit the attachment of A.terreus.The combination of UV radiation and BKC can much more effectively inhibit the corrosion of AA,especially pitting corrosion,due to their synergistic effect.The combined application of UV radiation and BKC can be a good method to effectively inhibit fungal-induced corrosion.
基金Funded by the Central Government Guides Local Funds for Science and Technology Development(No.YDZJSX20231A045)the Fundamental Research Program of Shanxi Province(Nos.202103021223288 and 202103021224282)。
文摘The evolution of microstructure during hot deformation is key to achieving good mechanical properties in aluminum alloys.We have developed a cellular automaton(CA) based model to simulate the microstructural evolution in 7075 aluminum alloy during hot deformation.Isothermal compression tests were conducted to obtain material parameters for 7075 aluminum alloy,leading to the establishment of models for dislocation density,nucleation of recrystallized grains,and grain growth.Integrating these aspects with grain topological deformation,our CA model effectively predicts flow stress,dynamic recrystallization(DRX) volume fraction,and average grain size under diverse deformation conditions.A systematic comparison was made between electron back scattered diffraction(EBSD) maps and CA model simulated under different deformation temperatures(573 to 723 K),strain rates(0.001 to 1 s^(-1)),and strain amounts(30% to 70%).These analyses indicate that large strain,high temperature,and low strain rate facilitate dynamic recrystallization and grain refinement.The results from the CA model show good accuracy and predictive capability,with experimental error within 10%.
基金Project (2011CB606302-1) supported by the National Basic Research Program of ChinaProject (2013AA031001) supported by Hi-Tech Research and Development Program of China
文摘A self-developed forced convection rheoforming （FCR） machine for the preparation of light alloy semisolid slurry was introduced. The microstructure characteristics of 7075 aluminium alloy semisolid slurry at different stirring speeds prepared by the FCR process were analyzed. The experimental results suggest that with the increase of the stirring speed, the mean grain size of the semisolid decreases and the shape factor as well as the number of primary grains increase. Meanwhile, the preparation process of semisolid slurry was numerically simulated. The flow characteristics of the melt in the device and the effect of the stirring speed on temperature field and solid fraction of the melt were investigated. The simulated results show that during the preparation process of semisolid slurry, there is a complex convection within the FCR device that obviously changes the temperature field distribution and solid fraction of the melt. When the convection intensity increases, the scope of the undercooling gradient of the melt is reduced and temperature distribution is improved.
基金Project (2011CB606302-1) supported by the National Basic Research Program of China
文摘The semi-solid slurry of 7075 aluminum alloy was prepared by a serpentine pouring channel （SCP）. Influences of pouring temperature and the number of turns on the microstructure of semi-solid 7075 alloy slurry were investigated. The results demonstrated that the semi-solid 7075 aluminum alloy slurry with satisfied quality could be generated by a serpentine pouring channel when the pouring temperature was in the range of 680-700 ℃. At a given pouring temperature, the equivalent size of the primaryα（Al） grains decreased and the shape factor increased with the increase of the number of turns. During the slurry preparation of semi-solid 7075 aluminum alloy, the flow direction of alloy melt changed many times when it flowed in a curved and closed serpentine channel. With the effect of“stirring”in it , the primary nuclei gradually evolved into spherical and near-spherical grains.
文摘7075 aluminum alloy was used to obtain elbow parts by complex thixoextrusion and the microstructure evolution and mechanical properties during this process were studied by SEM,TEM and other analytical methods.The results show that different parts in 7075 aluminum alloy show quite different microstructures.The microstructure of the thin walls formed by back-extrusion is stratified,and the bottom of the parts formed by angular extrusion is obviously deformed.Shear forces contribute to the crushing of grains and the coarse second phase.The main strengthening phases in the material areηphase and E phase,whose amounts greatly decrease during heating to semi-solid and thixoextrusion.After heat treatment,they can precipitate evenly to improve the mechanical properties of the material.The average tensile strength of whole part after thixoextrusion and heat treatment is 485.49 MPa,while the average elongation is 5.49%.
基金The authors are grateful for the financial supports from the National Natural Science Foundation of China(No.51871111)the Natural Science Foundation of Shandong Province,China(No.ZR2018LE001)+1 种基金the Science and Technology Program of University of Ji’nan,China(Nos.XKY2036,XKY1713)the Key Research and Development Program of Shandong Province,China(No.2019GGX102008).
文摘The static recrystallization behavior of 7075 aluminum alloy containing Al_(3)(Sc,Zr)phase prepared by casting and the relationship between recrystallization behavior and mechanical properties were studied.The addition of Sc and Zr made the Sc−Zr−7075 aluminum alloy remain the most of fibrous structure and high-density dislocations formed in the extrusion process,resulting in the recrystallization fraction of the alloy decreasing from 35%to 22%,and the corresponding fraction of substructure increasing from 59%to 67%.The Sc and Zr effectively inhibited the recrystallization behavior of 7075 aluminum alloy mainly,which was attributed to the fact that the existence of fine and coherent Al_(3)(Sc,Zr)phase(r=35 nm,f=1.8×10^(−3))strongly pined the dislocations and grain boundaries,preventing the dislocations from rearranging into sub-grain boundaries and from developing into high angle grain boundaries,and further hindering the formation and growth of recrystallized core of the alloy.
基金the National Natural Science Foundation of China(No.U1760205).
文摘The effect of solution treatment time on the post-formed plasticity and ductile fracture of 7075 aluminum alloy in the hot stamping process was studied.Tensile tests were conducted on the specimens subjected to the hot stamping process with different solution treatment time.The digital image correlation(DIC)analysis was used to obtain the strain of the specimen.Based on the experiments and modeling,the Yld2000-3d yield criterion and the DF2014 ductile fracture criterion were calibrated and used to characterize the anisotropy and fracture behavior of the metal,respectively.Furthermore,the microstructure of specimens was studied.The experimental and simulation results indicate that the 7075 aluminum alloy retains distinct anisotropy after the hot stamping process,and there is no obvious effect of extending the solution treatment time on the material anisotropy.However,it is found that a longer solution treatment time can increase the fracture strain of the aluminum alloy during the hot stamping process,which may be related to the decrease of the second-phase particles size.
基金Project(2007CB714704) supported by the National Basic Research Program of ChinaProjects(50775192,50821063) supported by the National Natural Science Foundation of China
文摘The torsional fretting wear tests of 7075 aluminum alloy flat against 52100 steel ball in dry condition were carried out on a new high-precision torsional fretting-wear tester.The kinetics behaviors and damage mechanism of 7075 aluminum alloy under different angular displacement amplitudes were investigated in detail.The results show that the torsional fretting running behaviors of 7075 aluminum alloy can be defined by three fretting regimes(i.e.partial slip regime(PSR),mixed fretting regime(MFR) and slip regime(SR)) with the increase of angular displacement amplitudes.In PSR,the damage occurs at the lateral portion of the contact zone with a slight annular shape.However,in MFR and SR,more severe damages are observed and the debris layer covers the wear scars.Friction torque and dissipation energy which are strongly dependent upon the imposed angular displacement amplitudes and presented in three stages were discussed in detail.The mechanisms of torsional fretting wear of aluminum alloy are mainly oxidative wear,abrasive wear and delamination in the three fretting regimes.In addition,the oxidative debris plays an important role during the torsional fretting wear processes.
文摘The combined effects of equal channel angular pressing (ECAP) and subsequent heating to a semi-solid temperature on the microstructural characteristics of the 7075 aluminum alloy were investigated. The microstructure is influenced by several parameters including the number of ECAP passes, ECAP route, consequent heating temperature, and holding time. The effects of these parameters on the microstructural characteristics including grain size and shape factor of the 7075 aluminum alloy were studied using experimental tests and Taguchi method. The results indicate that five-pass ECAP in route BA and subsequent isothermal holding at 630 °C for 15 min are more appropriate for achieving a semi-solid microstructure. The processing route and holding time have the highest impact on the grain size while the number of ECAP passes and heating temperature have the least impact on the grain size. Meanwhile, the shape factor is significantly influenced by the processing route, holding time and heating temperature while it is less influenced by the number of ECAP passes.
基金This work was financially supported by the Program for New Century Excellent Talents in University(No.NCET-11-0951).
文摘A 0.3wt%graphene nanoplatelets(GNPs)reinforced 7075 aluminum alloy matrix(7075 Al)composite was fabricated by spark plasma sintering and its strength and wear resistance were investigated.The microstructures of the internal structure,the friction surface,and the wear debris were characterized by scanning electron microscopy,X-ray diffraction,and Raman spectroscopy.Compared with the original 7075 aluminum alloy,the hardness and elastic modulus of the 7075 Al/GNPs composite were found to have increased by 29%and 36%,respectively.The results of tribological experiments indicated that the composite also exhibited a lower wear rate than the original 7075 aluminum alloy.
基金financially supported by the Higher Education Research Promotionthe National Research University Project of Thailand, Office of the Higher Education (Contract No. ENG580529S)+2 种基金Center of Excellence in Materials Engineering (CEME)the Graduate Engineer Scholarship and the Graduate School ScholarshipPrince of Songkla University, including Surat Thani Campus (2016)
文摘The anodizing parameters of voltage, current density, temperature, and electrolyte choice were assessed to find an appropriate combination for the superheated slurry cast 7075 Al alloy substrate.The alloy was anodized in sulfuric acid electrolyte or alternatively in sulfuric acid mixed with boric acid or citric acid. The voltages applied were in the range of 15-30 V. Anodizing current densities tested were 2 and 3 A/dm^2,while temperatures tested were 5 and 15 ℃. Thickness, surface morphology, hardness,and corrosion resistance of the oxide film were then evaluated.It was found that 25 V,2 A/dm^2 and 5 ℃ were suitable for this alloy when anodized in sulfuric acid. The oxide film was smooth with uniform thickness, low porosity, high hardness,and had the highest corrosion resistance at these parameters. However, discontinuous oxide films were observed from samples anodized at higher temperature of 15 ℃.Alternative electrolytes considered were sulfuric acid mixed with boric acid or citric acid. The results showed that electrolytes with boric acid or citric acid increased thickness, hardness, corrosion resistance and quality of the oxide films.However, these oxide films were inferior to those obtained with sulfuric acid electrolyte at lower temperature(25 V, 2 A/dm^2 and5 ℃).
基金supported by the National Basic Research Program of China(No.2011CB606302-1)the National Natural Science Foundation of China(No.51074024)
文摘The further application of semi-solid processing lies in the in-depth fundamental study like rheological behavior. In this research, the apparent viscosity of the semi-solid slurry of 7075 alloy was measured using a Couette type viscometer. The effects of solid fraction and shearing rate on the apparent viscosity of this alloy were investigated under different processing conditions. It can be seen that the apparent viscosity increases with an increase in the solid fraction from 10% to 50% （temperature 620 ℃ to 630 ℃） at steady state. When the solid fraction was fixed, the apparent viscosity can be decreased by altering the shearing rate from 61.235 s-1 to 489.88 s-1 at steady state. An empirical equation that shows the effects of solid fraction and shearing rate on the apparent viscosity is fitted： ηα = [0.871 - 0.00849. γ0.74924]. exp（3.7311, fs） . The microstructure of quenched samples was examined to understand the alloy＇s rheological behavior.
基金financially supported by the National Natural Science Foundation of China(youth)(No.51004036)the Fundamental Research Funds(N120309002)
文摘The heat treatment process has great effects on microstructure and conductivity of ingots. In this study, the ingots of high strength 7075 aluminum alloy were prepared by low frequency electromagnetic casting(LFEC), and the effect of different homogenization processes(single-step homogenization at 465 ℃ for different holding times and three-step homogenization) on the microstructure and conductivity of 7075 aluminum alloy were studied by means of metallographic microscopy, electrical conductivity test, differential thermal analysis and X-ray diffraction phase analysis. For comparison, the ingot by conventional direct casting(DC) under the same conditions was also prepared. Results show that the non-equilibrium eutectic phases with low melting point in the ingot dissolve continuously into the matrix as the holding time of single-step homogenization increases. The endothermic peak of non-equilibrium phases can not be completely eliminated through a 24 h single-step homogenization, but can be eliminated after a three-step homogenization(200 ℃/2 h + 460 ℃/6 h + 480 ℃/12 h). Meanwhile, the homogenization has a better effect on the LFEC ingot than the conventional DC ingot. Under the same homogenizing conditions, the grains of LFEC ingot are characterized by a lower content of low melting point phases and the ingot shows higher electrical conductivity than DC ingot.
基金supported by the Natural Science Foundation of Hebei(Grant No.E2012210001)Natural Science Foundation of Jiangsu(Grant No.BK20141181)。
文摘The precipitated phases in the WNZ,TMAZ,HAZ and BM of the friction stir welding(FSW)joint were observed using the transmission electron microscopy(TEM)and the lattice fringe spacing of the precipitated phases was measured.Combined with X-ray diffraction(XRD),the types of precipitated phases among the joint were confirmed and then the strength mismatch mechanism was revealed.The results show the precipitated phases of 7075 aluminum alloy FSW joint mainly consist of MgZn_(2),AlCuMg and Al_(2)CuMg.The microzone of the joint experienced different thermal cycles,the types and sizes of precipitated phases are different and the strengthening effect is different.The strengthening effect of the AlCuMg and Al_(2)CuMg are better than that of MgZn_(2).The precipitated phase in the WNZ mainly includes AlCuMg and Al_(2)CuMg,as well as the grain size is fine,the microhardness in this zone is pretty high.The number of precipitated phase AlCuMg and Al_(2)CuMg is smaller in the TMAZ and the MgZn_(2)is relatively more,which lead the microhardness decrease.The number of precipitated phase MgZn_(2)is relative larger in the HAZ,as well as the grain coarsening,the microhardness in this zone is lowest of the joint.At the same time,there are the precipitate free zones(PFZ)among the 7075 aluminum alloy FSW joint,which decreases the microhardness of the whole joint to some extent.
基金Funded by the National Natural Science Foundation of China(Nos.51375500,and 51375162)Scientific Research Project of Hunan Province Department of Education(No.17C0886)Open Funded Projects of Hunan Provincial Key Laboratory of Health Maintenance for Mechanical Equipment(No.201605)
文摘The hardness, the tensile and the high-cycle fatigue（HCF） performances of 7075 aluminum alloy were investigated under temper T651, solution treated at 380 ℃ for 0.5 h and aged at different temperatures（150, 170, 190 ℃） for 10 hours. The optimal microstructures and the fatigue fracture surfaces were observed. The results show that the hardness and the tensile performances are at their optimum at T651, but the fatigue life is the shortest. The hardness and the elongation are the lowest after solution treatment. With the aging temperature increasing（150-190 ℃）, the HCF is improved. The crack is initiated from the impurity particles on the subsurface. Treated at 170 ℃,the area of the quasi-cleavage plane and the width of parallel serrated sections of the crack propagation are the largest. With increasing aging temperature, the dimple size of finally fracture surfaces becomes larger and the depth deeper.
基金Funded by the National Natural Science Foundation of China(Nos. 51004036 and N110408005)
文摘The microstructures after casting and extruding, the mechanical properties and electrical conductivity after RRA treatment of conventional DC casting and low frequency electromagnetic casting （LFEC） 7075 aluminum alloy were investigated. The results showed that finer grains which distributed more homogeneously was obtained in LFEC ingots compared with those conventional DC ingots. The extruded bars of LFEC alloy kept its fine grain features of original as-cast structure. In the RRA treatment, with the extension of second aging time, the tensile strength and hardness of alloy decreased, but the electrical conductivity increased. Meanwhile, as the second aging temperature raised, the phase change rate in precipitation also increased. Under the same conditions, extruded bars of LFEC alloy had better performance than that of conventional DC cast alloy. The optimum RRA heat treatment process was 120 ℃/24 h＋180 ℃/30 min＋120 ℃/24 h. The LFEC extruded bars acquired tensile strength 676.64 MPa, hardness 198.18, and electrical conductivity 35.7% IACS respectively, which were higher than that in the T6 temper, indicating that a notable RRA response takes place in LFEC extruded bars, whose second-step retrogression time was 30 min, and it was suitable for mass production.
基金Projects(10872221,10272120) supported by National Natural Science Foundation of China
文摘The dynamic softening behaviors during hot deformation of 7075 aluminum alloy were studied by isothermal hot compression tested at temperatures of 250, 300, 350, 400 and 450 ℃ and strain rates of 0.01, 0.1, 1 and 10 s-1 on Gleeble1500. The results show that the temperature changes have a significant effect on the dynamic softening rate. It is indicated that the considerable dynamic softening rate associated with dynamic recrystallization leads flow stress value decreasing gradually. A group of coefficients needed by the phenomenological constitutive model containing a softening ratio item were calculated by the multiple linear regression method. The optical microstructures show that the grains of billets compressed become more and more refined with strain rate increasing as well as the degree of dynamic softening and work-hardening higher. The phenomenological constitutive description of 7075 aluminum alloy can accurately describe the relationships among flow stress, temperature, strain rate, strain and dynamic softening, and offer the basic model for plastic forming process simulation.
文摘7075 aluminum alloy thick plates were produced by three processing routines: commercial hot rolling followed by heat treatment of quenching and ageing (HR+QA), combination of large deformation processing of multi directional warm forging and subsequent warm rolling followed by heat treatment of quenching and ageing (LD+QA), and that followed by annealing at moderate temperature (LD+AN). Tensile strength, yield strength and elongation were measured by tension test, and the metallographic structures were examined by optical microscopy (OM) and transmission electron microscopy (TEM), also the fracture morphologies were observed by scanning electron microscopy (SEM). It is shown that higher tensile strength and yield strength are obtained from (LD+QA) processing in comparison with those from (HR+QA) and (LD+AN) processings. Tensile strength and yield strength obtained from (LD+QA) processing are 9.9% and 8.6% higher respectively than those from (HR+QA) processing, and 48.6% and 57.7% higher respectively than those from (LD+AN) processing; while the elongations of all the samples show no significant difference and keep 10%12%. Analyses of OM and TEM reveal that the mechanical behaviors are deeply associated with the formation of refined structures with fine grains and very fine precipitates, leading to fine grained hardening and excellent age hardening.
文摘The influence of quenching water temperature, pre stretching amount and aging temperature and times on residual stress in 7075 aluminum thick plate was studied by the measurement of residual stress using drilling hole method. The results indicate that residual stress decreases by 30% with increasing quenching water temperature from 40 ℃ to 80 ℃, 20% with increasing aging temperature from 100 ℃ to 180 ℃,and 20% with increasing aging times from 5 h to 25 h. Also, residual stress decreases to zero with increasing pre stretching amount to approximately 2%. Hence, residual stress in 7075 aluminum thick plate is reduced by the control of quenching water temperature at 80 ℃ and with pre stretching amount of about 2%. An optimal aging temperature and time should be systemically investigated to obtain combination of high mechanical performances and lower residual stress for manufacturing of 7075 aluminum alloy thick plates.
基金Project(HIT.2002.33) supported by the Scientific Research Foundation of Harbin Institute of Technology
文摘In order to investigate the influence of hydrostatic pressure on compression limit of the ring, numerical simulation and experimental research were carried out. The effect of hydrostatic pressure on the deformation of aluminum alloy 7075 ring was obtained by numerical simulation. The die set for compressing ring under high hydrostatic pressure was designed and manufactured. Experimental results show that the compression limit increases linearly as the hydrostatic pressure increases in a certain range. At 100 MPa the maximum compressive strain is increased by 32.42%. At strain limit, the cracks initiate from the corner of the outer wall to the middle of the inner wall along the direction of the maximum shear stress.
