As-cast microstructure of Mg-Al-Zn magnesium alloys
(1.重庆市重庆大学材料科学与工程学院
2.Chongqing Engineering Research Center for Magnesium Alloys, Chongqing University,Chongqing 400044, China
3.College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China)
2.Chongqing Engineering Research Center for Magnesium Alloys, Chongqing University,Chongqing 400044, China
3.College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China)
Abstract: The research achievements on as-cast microstructure in Mg-Al-Zn alloy were summarized. Under permanent mould cast condition, there are four kinds of primary compounds with distinct crystallographic morphology, Mg17Al12(γ)，Mg32(Al,Zn)49 (τ), MgZn (ε) and a ternary icosahedral quasi-crystalline compound (Q). Accordingly, Mg-Al-Zn alloy can be grouped into γ-, τ-, ε- and Q-type alloy by each characteristic compound. The volume fraction of γ-Mg17Al12 in commercial γ-type alloy increases with increasing Al content. MgZn and MgxAlyZnz ternary complex compounds emerge with the change of the element content Al and Zn and Zn/Al concentration ratio. A practical phase diagram showing microstructure constituent change with composition was proposed. The addition of micro-alloying elements Y and Sr results in not only obvious refinement of eutectic cluster but also eutectic morphological change from block to granule.
Key words: Mg alloys; Mg-Al-Zn alloys; microstructure; intermetallic compounds; solidification