Effects of alloying composition on the microstructures and mechanical properties of Mg-Al-Zn-Ca-RE magnesium alloy

Abstract

With the purpose of increasing our understanding of the microstructural evolution and mechanical properties of Mg-Al-Zn-Ca-RE system alloy, Mg-xAl-(8-x)Zn-4Ca and Mg-xAl-(8-x)Zn-3Ca-1RE (wt. %) casting alloys were studied in this paper. The α-Mg dendrite was refined, and the intermetallic compounds became finer and less divorced by increasing the Al content. During solidification RE addition consumed Al and Zn to form RE-containing phase in the initial solidification stage, and then the residual liquid solidified to form Ca-containing phase without RE participation. The majority phases, Al11RE3 and C36, were transformed into Al2REZn2 and Ca2Mg6Zn3 as the Al content was decreasing. The Ca-containing phases tended to form a highly interconnected network which would deteriorate the ductility, while the substitution of RE for a part of Ca would make the structure less continuous. A range of eutectic morphologies were found in Ca-containing phases. C36 phase could shape a lamellar eutectic structure, and Ca2Mg6Zn3 phase was prone to exhibit as a divorced morphology. Besides, Ca2Mg6Zn3 formed at a relatively low temperature which will bring about microshrinkage. Mg-6Al-2Zn-3Ca-1RE alloy containing refined and more evenly distributed C36 with less continuous morphology showed the best mechanical performance.