Effects of Zn content on microstructures and mechanical properties of Mg–Zn–RE–Sn–Zr–Ca alloys

Abstract

The effects of Zn content on microstructures and mechanical properties of Mg–Zn–RE alloys have been investigated. The results indicate that RE-rich phases will change from the MgY and Mg12Nd binary phases in turn to Z (Mg12ZnRE), Z+W (Mg3Zn3RE2), W and W+I (Mg3Zn6RE) ternary phases as the Zn content increases from 0% to 4%. The grain size decreases when the Zn content increases from 0% to 2% and then increases, which is attributed to the variation of growth restriction factor resulted from the phase changes. The hardness continuously increases due to the formation of the ternary phases and their amount increase. The UTS and elongation first increase as the Zn content increases within the range of 0–2% and then decrease. The W phase is an ideal strengthening phase because the grain bonding strength of the unique W phase-containing alloy is higher than that of the Z or Z+W phase-containing alloy. Shrinkage porosities are easy to generate and the ternary phases distribute more and more continuously due to their amount increase when the Zn content exceeds 2%. The fracture regime changes from intergranular mode to transgranular mode as the Zn content increases from 0% to 2%, and then turns into transgranular mode again.