To investigate the effect of separate Al_(2)Ca and Mg_(2)Ca phases on the corrosion properties of Mg−Al−Ca−Mn alloys,OM,SEM,immersion and electrochemical tests were conducted on the as-cast and ECAP Al_(2)Ca-containin...To investigate the effect of separate Al_(2)Ca and Mg_(2)Ca phases on the corrosion properties of Mg−Al−Ca−Mn alloys,OM,SEM,immersion and electrochemical tests were conducted on the as-cast and ECAP Al_(2)Ca-containing(2Ca)and Mg_(2)Ca-containing(4Ca)alloys.At the beginning of corrosion,the two as-cast alloys are corroded slowly compared with ECAP alloys.With prolonging the corrosion time,the corrosion of ECAP alloys becomes slighter than that of as-cast alloys,which is mainly ascribed to the dispersion and refinement of the second phase in ECAP alloys.Moreover,the corrosion degree of 2Ca alloys is always slighter than that of 4Ca alloys,suggesting that Al_(2)Ca phase is more beneficial to the enhancement of corrosion resistance of Mg−Al−Ca−Mn based alloys than Mg_(2)Ca phase.Finally,based on the examinations of corrosion surface and electrochemical testing results,different corrosion mechanisms caused by the distributions and morphology of Al_(2)Ca and Mg_(2)Ca phases are discussed.展开更多
Crystal structures,growth characteristics,and transformation of the precipitates in a Mg-7Gd-5Y-1Nd-2Zn-0.5Zr(wt.%)alloy aged at 200℃for various durations were investigated using transmission electron microscopy(TEM)...Crystal structures,growth characteristics,and transformation of the precipitates in a Mg-7Gd-5Y-1Nd-2Zn-0.5Zr(wt.%)alloy aged at 200℃for various durations were investigated using transmission electron microscopy(TEM)and high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM).A detailed Mg-Gd type precipitation sequence for Mg-Gd-Y-Nd-Zn alloys was proposed as follows:supersaturated solid solution→solute clusters→zigzag GP zones+β''(I)→β'→β'+protrusions/joints→pre-β_(1)→β_(1)→β.Solute clusters formed in the early stage of aging consisted of one or more rare-earth(RE)/Zn-rich atomic columns with different configura-tions.RE/Zn-rich solute clusters grew into zigzag GP zones andβ''(I)as aging time extending.The paired-zigzag GP zones might grow up to beβ'precipitates directly.In the peak-and plat-aging stages,the number of solute clusters in the matrix decreased until they disappeared,and most existed as zigzag arrays and super hexagons.Protrusions formed at the end ofβ'at an angle of 120°,then grew into joints when two differentβ'variants encountered together.Protrusions/joints comprise zigzag arrays,super-hexagons,β'F,β''(II),β_(T),and hybrid structures rich in solute atoms,and act as catalysts for the growth of theβ'variants.Largerβ'grow by joints consumption while smallerβ'precipitates dissolve to form joints.β_(1)precipitates essentially evolve from pre-β_(1)precipitates,with four-point diamond structures formed by RE/Zn atomic substitution and atomic migration based on the originalα-Mg structure.展开更多
In this study,a composite deformation strategy of pre-kinking(equal channel angular pressing(ECAP))followed by large-ratio hot extrusion(HE)was designed to refine the 18R long period stacking ordered(LPSO)phase into s...In this study,a composite deformation strategy of pre-kinking(equal channel angular pressing(ECAP))followed by large-ratio hot extrusion(HE)was designed to refine the 18R long period stacking ordered(LPSO)phase into sub-micron range in a Mg_(97)Y_(2)Zn_(1)(at.%)alloy.After the composite processing,the mechanical properties of the alloy are significantly enhanced,superior to the majority of reported Mg_(97)Y_(2)Zn_(1) and other LPSO-containing Mg alloys.Among the composite deformed alloys,the 16P-HE alloy exhibits the best mechanical properties with tensile yield strength(TYS)of 475 MPa,ultimate tensile strength(UTS)of 526 MPa,and fracture elongation(FE)of 14.5%.Quantitative analysis of 18R phase indicates that increasing ECAP pass from 1 to 16 gradually decreases the average size of 18R phase from 5.1μm to 2.3μm.After HE,the 18R phase is further refined with a corresponding decrease in the average size in the descending order of 1P-HE(4.3μm),4P-HE(3.2μm),and 16P-HE(1.4μm)alloys.Calculation of the strengthening contributions confirms that the superior mechanical properties of 16P-HE alloy are mainly due to its strongest interface strengthening(145 MPa)and grain boundary strengthening(189 MPa)from the sub-micron 18R phase andα-Mg grains.Moreover,the strengthening effect of 18R phase decreases gradually with their morphology changing from particles to fibers,and to blocks.The obtained results further deepen and broaden the strengthening-toughening theory of 18R phase.展开更多
This study systematically investigated the influence of the microstructure evolution,mechanical properties and corrosion behaviors on Zn–1.5Mg(wt%)alloy processed by room-temperature rolling.The as-cast Zn–1.5Mg all...This study systematically investigated the influence of the microstructure evolution,mechanical properties and corrosion behaviors on Zn–1.5Mg(wt%)alloy processed by room-temperature rolling.The as-cast Zn–1.5Mg alloy consists ofη-Zn matrix andη-Zn+Mg_(2)Zn_(11)eutectic structure.As rolling reduction increases,the average grain size of the alloy reduces from 42.9 to 1.7μm,and the eutectic structure undergoes fragmentation and refinement,changing from a network distribution surrounding the matrix to a lamellar alternating distribution with the matrix.The ultimate tensile strength of the as-rolled alloy(80%reduction)is increased to 366±3.7 MPa,along with a good elongation of 18.4%±2.0%.Immersion tests in Hanks’solution indicate that the initial corrosion rate of the 80%-rolled alloy is 0.030 mm/year and finally stabilizes at 0.034 mm/year when the immersion duration is extended to 21 days.According to X-ray diffractometer and X-ray photoelectron spectroscopy analyses,Ca_(3)(PO_(4))_(2),CaCO_(3),Ca(OH)_(2),Zn_(3)(PO_(4))_(2),Zn(OH)_(2),ZnO and a small amount of MgO and MgCO_(3)are the main corrosion products on the surface.Due to the microstructure refinement,the developed alloy exhibits uniform corrosion,and the corrosion morphology is dominated by pitting pits.展开更多
基金financial supports from the National Natural Science Foundation of China (Nos.51901068,51979099)the Key Research and Development Project of Jiangsu Province,China (No.BE2021027)+1 种基金the Opening Project of Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology,China (No.ASMA202102)the Research Fund from Key Laboratory for Light-weight Materials of Jiangsu Province,China。
文摘To investigate the effect of separate Al_(2)Ca and Mg_(2)Ca phases on the corrosion properties of Mg−Al−Ca−Mn alloys,OM,SEM,immersion and electrochemical tests were conducted on the as-cast and ECAP Al_(2)Ca-containing(2Ca)and Mg_(2)Ca-containing(4Ca)alloys.At the beginning of corrosion,the two as-cast alloys are corroded slowly compared with ECAP alloys.With prolonging the corrosion time,the corrosion of ECAP alloys becomes slighter than that of as-cast alloys,which is mainly ascribed to the dispersion and refinement of the second phase in ECAP alloys.Moreover,the corrosion degree of 2Ca alloys is always slighter than that of 4Ca alloys,suggesting that Al_(2)Ca phase is more beneficial to the enhancement of corrosion resistance of Mg−Al−Ca−Mn based alloys than Mg_(2)Ca phase.Finally,based on the examinations of corrosion surface and electrochemical testing results,different corrosion mechanisms caused by the distributions and morphology of Al_(2)Ca and Mg_(2)Ca phases are discussed.
基金supported by the National Natural Science Foundation of China(51871195)Youth Fund Project of GRINM(G12620213129038)Henan Provincial Department of Science and Technology Research Project(No.222102230113).
文摘Crystal structures,growth characteristics,and transformation of the precipitates in a Mg-7Gd-5Y-1Nd-2Zn-0.5Zr(wt.%)alloy aged at 200℃for various durations were investigated using transmission electron microscopy(TEM)and high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM).A detailed Mg-Gd type precipitation sequence for Mg-Gd-Y-Nd-Zn alloys was proposed as follows:supersaturated solid solution→solute clusters→zigzag GP zones+β''(I)→β'→β'+protrusions/joints→pre-β_(1)→β_(1)→β.Solute clusters formed in the early stage of aging consisted of one or more rare-earth(RE)/Zn-rich atomic columns with different configura-tions.RE/Zn-rich solute clusters grew into zigzag GP zones andβ''(I)as aging time extending.The paired-zigzag GP zones might grow up to beβ'precipitates directly.In the peak-and plat-aging stages,the number of solute clusters in the matrix decreased until they disappeared,and most existed as zigzag arrays and super hexagons.Protrusions formed at the end ofβ'at an angle of 120°,then grew into joints when two differentβ'variants encountered together.Protrusions/joints comprise zigzag arrays,super-hexagons,β'F,β''(II),β_(T),and hybrid structures rich in solute atoms,and act as catalysts for the growth of theβ'variants.Largerβ'grow by joints consumption while smallerβ'precipitates dissolve to form joints.β_(1)precipitates essentially evolve from pre-β_(1)precipitates,with four-point diamond structures formed by RE/Zn atomic substitution and atomic migration based on the originalα-Mg structure.
基金financially supported by the National Natural Science Foundation of China(Nos.51901068 and 52271101)the Key Research and Development Program of Jiangsu Province(No.BE2021027)+2 种基金the Opening Project of Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology(No.ASMA202102)the Jiangsu Key Laboratory for Light Metal Alloys(No.LMA202101)the Research Fund from Key Laboratory for Light-weight Materials of Jiangsu Province.
文摘In this study,a composite deformation strategy of pre-kinking(equal channel angular pressing(ECAP))followed by large-ratio hot extrusion(HE)was designed to refine the 18R long period stacking ordered(LPSO)phase into sub-micron range in a Mg_(97)Y_(2)Zn_(1)(at.%)alloy.After the composite processing,the mechanical properties of the alloy are significantly enhanced,superior to the majority of reported Mg_(97)Y_(2)Zn_(1) and other LPSO-containing Mg alloys.Among the composite deformed alloys,the 16P-HE alloy exhibits the best mechanical properties with tensile yield strength(TYS)of 475 MPa,ultimate tensile strength(UTS)of 526 MPa,and fracture elongation(FE)of 14.5%.Quantitative analysis of 18R phase indicates that increasing ECAP pass from 1 to 16 gradually decreases the average size of 18R phase from 5.1μm to 2.3μm.After HE,the 18R phase is further refined with a corresponding decrease in the average size in the descending order of 1P-HE(4.3μm),4P-HE(3.2μm),and 16P-HE(1.4μm)alloys.Calculation of the strengthening contributions confirms that the superior mechanical properties of 16P-HE alloy are mainly due to its strongest interface strengthening(145 MPa)and grain boundary strengthening(189 MPa)from the sub-micron 18R phase andα-Mg grains.Moreover,the strengthening effect of 18R phase decreases gradually with their morphology changing from particles to fibers,and to blocks.The obtained results further deepen and broaden the strengthening-toughening theory of 18R phase.
基金the Key Research and Development Program of Jiangsu Province(BE2021027)the Project on Excellent Postgraduate Dissertation of Hohai University(422003518)+2 种基金the Postgraduate Research&Practice Innovation Program of Jiangsu Province(SJCX23_0175)the Opening Project of Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology(ASMA202102)the Jiangsu Key Laboratory for Light Metal Alloys(LMA202101).
文摘This study systematically investigated the influence of the microstructure evolution,mechanical properties and corrosion behaviors on Zn–1.5Mg(wt%)alloy processed by room-temperature rolling.The as-cast Zn–1.5Mg alloy consists ofη-Zn matrix andη-Zn+Mg_(2)Zn_(11)eutectic structure.As rolling reduction increases,the average grain size of the alloy reduces from 42.9 to 1.7μm,and the eutectic structure undergoes fragmentation and refinement,changing from a network distribution surrounding the matrix to a lamellar alternating distribution with the matrix.The ultimate tensile strength of the as-rolled alloy(80%reduction)is increased to 366±3.7 MPa,along with a good elongation of 18.4%±2.0%.Immersion tests in Hanks’solution indicate that the initial corrosion rate of the 80%-rolled alloy is 0.030 mm/year and finally stabilizes at 0.034 mm/year when the immersion duration is extended to 21 days.According to X-ray diffractometer and X-ray photoelectron spectroscopy analyses,Ca_(3)(PO_(4))_(2),CaCO_(3),Ca(OH)_(2),Zn_(3)(PO_(4))_(2),Zn(OH)_(2),ZnO and a small amount of MgO and MgCO_(3)are the main corrosion products on the surface.Due to the microstructure refinement,the developed alloy exhibits uniform corrosion,and the corrosion morphology is dominated by pitting pits.
