Effect of minor Ca and Mo addition on the microstructure and mechanical properties of semisolid die-casting Al–6Mg–2Si–0.6Mn alloy

Abstract

Micro-alloyed with Ca and Mo, the evolution of microstructure and mechanical properties of semisolid die-casting Al–6Mg–2Si–0.6Mn alloy was studied. Results show that the matrix mainly consists of primary α-Al, eutectic Mg2Si, and ɑ-Al(Fe, Mn) Si phase. Single addition of Ca promotes the formation of the Ca-rich phase, and refines the eutectic Mg2Si phase. Adding 0.2%Mo to the base alloy generates a coarse blocky-like Al18Mg3Mo2 phase, and the eutectic Mg2Si phase translates from lamellar and strip-like of the base alloy to petal-like and honeycomb. Synergistic addition Ca and Mo not only refines the eutectic Mg2Si phase, but also generates Al18Mg3Mo2 phase, and ɑ-Al(Fe, Mn, Mo)Si phase. Thus, the average ultimate tensile strength (UTS) and elongation (EL) both increase from 319.6 MPa and 7.61% of the base alloy to 335.1 MPa and 8.39% of the Ca+Mo modified alloy, respectively. Moreover, the ɑ-Al(Fe, Mn, Mo)Si phase, which segregated with Mg element, was also observed along the grain boundary. This is also beneficial in enhancing the ductility and strength of the alloys.