Effects of antimony addition on the microstructures of ZA84 magnesium alloy

In this work, the effects of antimony on the microstructures of as-cast Mg-8Zn-4Al (ZA84) magnesium alloy were investigated by using optical microscopy, SEM, EDX, and XRD, etc. The results indicated that: (1) As antimony is a surface active agent, it may concentrates on the crystallizing front to prevent the ternary phase from growing during the solidification, so the micro-morphology of the ternary phases distributed on grain boundaries changes from semi-continuous-net shape to interrupted-net shape or particles in ZA84 magnesium alloy after the alloy is modified by Sb; meanwhile the grain size of the matrix is considerably refined. The grain size decreases from 120-130 μm to 50-60 μm with the addition of 0.3 wt% antimony modifier. (2) Due to the antimony distributed at the grain boundaries acts as an active agent, facilitating the atoms of Al and Zn to diffuse into the matrix, the microhardness of the as-cast ZA84 magnesium alloy obviously increases with the addition of antimony modifier, and it goes up by 11.5% when the addition reaches 0.5 wt%. (3) After adding Sb, an inter-metallic compound phase Mg3Sb2 with high melting point and a newly dual phase MgZn2 are formed in ZA84 magnesium alloy, and thus the high-temperature strength of ZA84 magnesium alloy is increased.