Study On Alloying And Ageing Hardening Of Mg-Zn-Al-Ca Magnesium Alloy

This paper focuses on these questions, the effect of Ca on microstructure of ZA102 magnesium alloy were studied by optical microscope and Scanning electron microscopy. the structure of the phase of the test alloy were studied by XRD, the morphology and formation of aging precipitates researched by field emission transmission electron microscopy, the orientation relationships between ageing precipitates with the matrix analyzed by Crystal knowledge in the last.The results show that: effect is most significant with Ca content is up to 1%. The microstructure of ZA102 becomes fine obviously, semi-continuous networkτphase changes into small granular or rod-like, and granularεphase is smaller. In addition, granular high melting point Al2Ca phase is formed in alloy. The values of tensile strength, elongation and hardness of the alloy reach to their maximum 174 MPa,6% and 86 HV.Respectively, When the content of Ca more than 1%, alloy grain sizes become larger and alloying elements have a trend of segregation. With the solid solution at 360℃×10 h+180℃(T6)on ageing treatment, the microstructure of alloy and the mechanical properties can be improved and appeared aging precipitates MgZn2 and Ca₂Mg₆Zn₃. When added Ca to ZA102 alloy, the process of ageing strengthening is relatively slow, and hardness decreased slowly when it reaches the peak value with the time extended.Microstructure is most fine with Al content is up to 1% in Mg-4Zn-2Al-0.5Ca alloy. When the content of Ca more than 1%, alloy grain sizes become larger, but on the whole Al had no significant effect on the alloy microstructure. Hardness of Mg-4Zn-2Al-0.5Ca alloy reached it max value 120 HV and max hardness increments of 27 HV was produced by ageing treatment at 120℃after 70 hour. Natural ageing response was very slow, but ageing hardening also obvious, max hardness reached to 110 HV. In the process of aging, GP zone plays an important role in strengthening of magnesium alloys, ordered GP zone significantly increased strengthening of alloy. In ageing precipitates, the rod-ship precipitates areβ1 ' phase having the orientation relationship with the magnesium matrix such that '1< 2110 >β||(0001)Mg and 2[0001]β|| < 2110 >M g, plate precipitates areβ2' and Ca₂Mg₆Zn₃ having the orientation relationship with the magnesium matrix such that :'2[2110]β|| [0001]Mg and'2(0001)β|| (1210)Mg , 2 6 3[1210]Ca Mg Zn || [1010]Mg and 2 6 3(0001)Ca Mg Zn ||[1210]Mg。...