Effect Of Alloying Elements (Y+Gd), Ca And Sb On Microstructure And Mechanical Properties Of ZA63 Magnesium Alloys

Mg-Zn-Al(ZA) alloys are new developed magnesium alloys which controlled by increasing the Zn content and Zn/Al ratio, the alloys are characterized by the use of low cost alloying elements as far as possible to improve the overall performance of the alloys. ZA alloys are considered to be promising high temperature creep resistant magnesium alloys, however, the current research in it are very limited. This paper studied the effect of some alloying elements on microstructure and mechanical properties of ZA63(Mg-6%Zn-3%Al-0.25Mn) magnesium alloy by using alloying method, so can determine the best dosage of the alloying elements, in order to provide alloy design ideas and theoretical basis for further broaden the application areas of ZA magnesium alloys.Through the alloy preparation, heat treatment, microstructure analysis and mechanical properties test, the effect of rare earth elements(RE) Y and Gd, alkaline earth element Ca and the fifth main group element Sb on microstructure and mechanical properties of ZA63 magnesium alloys have been investigated.By adding 0～2.0wt%RE elements(Y+Gd) in ZA63 alloys can obtain the following results. When with appropriate RE addition, the compositions in the alloys do not change, but the microstructure of the alloys fine obviously, and semi-continuous networkτ-phase at grain boundary change into rod-like and distribution more uniform, island-likeεphase change into small granular. When the total content of RE element is 1.5wt%, the mechanical properties of ZA63+RE alloys at room temperature and high temperature both reach their best, the tensile strength of the aged alloys at room temperature,150℃and 175℃all up to their maximums, are 248.7MPa, 188.4Mpa, 184.6Mpa, respectively, and its tensile strength at room temperature increases by 34.7% compared with ZA63 without RE elements. The specific elongation increases as the tensile temperature increases, at the same temperature, the alloy with 1.5wt%RE has the best plasticity and highest specific elongation.By adding 0～1.5wt%Ca element in ZA63 alloys can obtain the following results. When with appropriate Ca addition, the microstructure of the alloys fine obviously, granular high melting point Al2Ca phase forms at grain boundary and intracrystalline, and semi-continuous networkτphase at grain boundary change into rod-like, island-likeεphase change into small granular. When ZA63+Ca alloys after solid solution and aging treatment,its mechanical performance are greatly improved. When the content of Ca element is 1.0wt%, the tensile strength of the alloys at room temperature,150℃and 175℃all up to their maximums, are 219.9MPa, 196.8MPa, 173.3Mpa, respectively. And its tensile strength at 150℃can compare with ZA63+1.5wt%RE alloy. When with 1.0wt%Ca addition, the plasticity of the aged alloys are greatly improved, its tensile fracture type at room temperature changes from brittle fracture to ductile fracture based.By adding 0～1.0wt%Sb element in ZA63 alloys can obtain the following results. When with appropriate Sb addition, the microstructure of the aged alloys is significantly improved, and granular high melting point Mg3Sb4 phase forms. As-casting ZA63+Sb alloys after solid solution and aging treatment, its tensile strength at room temperature all increase about 20MPa. When the content of Sb element is 0.75wt%, the tensile strength of the aged alloys at room temperature,150℃and 175℃all up to their maximums, are 221.3MPa, 180.7MPa, 164.8Mpa, respectively, also this component the elongation at every temperature are best. As the tensile temperature increases, the tensile fracture of ZA63+0.75wt%Sb alloy increase toughness characteristics, and reduce brittle characteristics.