Investigation On Processing,Microstructure And Mechanical Properties Of Squeeze Cast Mg-Al And Mg-Zn Alloys

The current research has applied squeeze casting technology to the production of 8-inch wheels with Mg-7Al-2Sn?AT72?and Mg-6Zn-0.1Ca-0.5Mn?ZX60?alloys.The microstructure and mechanical properties of alloys were investigated via sampling from the spoke and the rim.Previous study has shown that AT72 magnesium alloys exhibited the most balanced combination of strength and ductility compared with commercial AZ91,AM50 alloys or the other Mg-Al-Sn alloys.The effect of applied pressure,pouring temperature and plunger speed on microstructure and mechanical properties of as-cast AT72 alloy were investigated.As the most important feature of squeeze casting,the pressure could raise nucleation rate of?-Mg and promote the formation of Mg₁₇Al₁₂,suggesting how the solidification behavior was influenced.Mechanical properties were improved with increased pressure as well.Though the effect of pouring temperature and plunger speed on as-cast microstructure seemed to be insignificant,the mechanical properties can be optimized by tuning those parameters.The ZX60 alloy was designed by adding trace amount of Ca into Mg-6Zn alloy in order to enhance age-hardening response.The effect of pouring temperature and heat treatment on microstructure and mechanical properties of ZX60 alloy was presented.It has been found that lower pouring temperature was beneficial for the reduction of dendritic arm spacing,dispersed distribution of second phase and improvement of tensile yielding strength,but somehow lowered the ultimate tensile strength and elongation.After solution treatment at 380?for 16h,the second phase in ZX60 alloy has completely dissolved,and only fine?-Mn particles remained.The solution-treated ZX60 alloy was aged at 150?,175?and200?,and the age-hardening response of 0³00h was plotted.The heat treatment parameters were then optimized according to the mechanical properties at peak-aged condition of various aging temperature.After heat treatment of 380?/16h+175?/8h,the yielding strength,ultimate tensile strength and elongation of ZX60 alloy have increased by 122%,62%and 32%in comparison with the as-cast state,showing outstanding age-hardening response.The main strengthening phase of ZX60 alloy in T6 state is the rod-like MgZn₂ precipitate.