Study Of High Zinc Magnesium Alloy

Yao san jiu of Wuhan University of Technology have studied on effect of Zn,Al content on the density,microstructure and mechanical properties of high-zinc magnesium alloy.Ignition point of the magnesium alloy is 740℃, and its the density is about 2.2 g/cm²,it can be melt under conventional conditions.But this alloy is very brittle,the effect of RE and spherical quasicrystal,heat treatment on microstructure and mechanical properties of the magnesium alloy was studied,we hope to improve its tensile strength and impact toughness.The research contents mainly include three parts:The first part,a kind of high zinc magnesium alloy with15%-25%Zn was fabricated by a conventional casting technique.The alloys are identified by optical microstructure(OM),x-ray diffraction(XRD),scan electric microscopy (SEM)/energy dispersive spectrometer(EDS),and macro-hardness,impact toughness and tensile properties test。The results show that:the microstructure of high zinc magnesium alloy with different amounts of Zn consisted of matrixα-Mg,φ(Al₂Mg₅Zn₂)phases,Ï„(Mg₃₂(Al,Zn)₄₉)phases.The dendritic of ZA155 high zinc magnesium alloy is thicker than that of ZA205 and ZA255,eutectic quantity of ZA155 high zinc magnesium alloy is fewer than that of ZA205 and ZA255,the morphology of this kind of eutectic on the grain boundaries presents continuous net-like and thick.The tensile strength of ZA155,ZA255 high zinc magnesium alloy reaches 168 MPa,160 Mpa,impact toughness of ZA155,ZA255 high zinc magnesium alloy reaches 3.3J/cm²,2.2J/cm².The macro-hardness values of alloy increase with the increasing of Zn addition.The macro-hardness values of ZA155,ZA255 high zinc magnesium alloy reaches 71.7HB,90HB.The second part,the effect of RE on microstructure and mechanical properties of ZA155,ZA255 high zinc magnesium alloy was studied.The researchs show that:the microstructure of ZA155,ZA255 high zinc magnesium alloy with RE consisted of matrixα-Mg,φ(Al₂Mg₅Zn₂) phases,Ï„(Mg₃₂(Al,Zn)₄₉)phases,Mg₃Al₄Zn₂RE compound。The matrix can be refined obviously,most of RE reacts with magnesium,zinc,aluminum to form needle-like compounds of Mg₃Al₄Zn₂RE compound with high melting point and elevated temperature stability,which improves distribution state of the phases at grain boundaries.The macro-hardness values of as-casting alloys increases with the increasing of RE addition.When adding 1.5wt.%RE into ZA155 high zinc magnesium alloy,its room-temperature tensile strength reaches 203MPa and improves by 21%;impact toughness reaches 4.50J/cm². impact toughness of ZA255 high zinc magnesium alloy reaches 2.63J/cm²,room-temperature tensile strength reaches 185.9MPa.The third part,the effect of spherical quasicrystal on microstructure and mechanical properties of ZA155,ZA255 high zinc magnesium alloy was studied,the elevated temperature mec hanical properties and heat treatment mechanical properties,friction and wear properties were investigated of high zinc magnesium alloy after different modification.The results show that:the microstructure of ZA155,ZA255 high zinc magnesium alloy with quasicrystal master alloy addition consisted of matrixα-Mg supersaturating solid solution,φ(Al₂Mg₅Zn₂) phases,Ï„(Mg₃₂(Al,Zn)₄₉)phases and quasicrystal phases with elevated temperature stability.The matrix microstructure of ZA155,ZA255 high zinc magnesium alloy can be refined obviously by the addition of quasicrystal master alloy,and the morphology ofÏ„(Mg₃₂(Al,Zn)₄₉)phases on the grain boundaries changes from continuous net-like to discontinuous shape,even to particles. when adding 5wt.%spherical MZYM quasicrystal master alloy, room-temperature tensile strength of ZA155 high zinc magnesium alloy reaches 207MPa and improves by 23%;impact toughness reaches 5.5J/cm²,The macro-hardness values of as-casting ZA155,ZA255 high zinc magnesium alloy increase with the increasing of MZYM quasicrystal master alloy addition.room and elevated temperature tensile strength of the high zinc magnesium alloy have no significant.The elevated temperature tensile strength of ZA155 high zinc magnesium alloy declines about 5%,ZA155+RE declines about 3%,ZA155+MZYM declines about 2%,The range of reduction is very little,The range of reduction of ZA155+RE and ZA155+MZYM is lower than ZA 155.after solution treatment theφ(Al₂Mg₅Zn₂)phases were dissolved to the matrix completely,some ofÏ„(Mg₃₂(Al,Zn)₄₉)phases were dissolved to the matrix,needle-like compounds of Mg₃Al₄Zn₂RE and MZYM quasicrystal were not dissolved to the matrix,after aging treatment room,elevated temperature mechanical properties,impact toughness,macro-hardness of high zinc magnesium alloy after different modification are increased.