Effect of Al Content on Hot-Tearing Susceptibility of Mg-10Zn- x Al Alloys
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E has been increasing interest in developing light alloys for structural use based on magnesium. The prime reasons for this renewed interest among the scientific community to install Mg alloys as structural materials in place of aluminum or steel are their high-specific strength, stiffness, good damping capability, and functional properties, coupled with low density.[1] Pure magnesium cannot be used as a structural material due to its poor strength. Alloying can improve the mechanical properties of magnesium alloys. Popular alloying elements are Al, Zn, Ca, and Sr. Research of Mg-Al alloy system has offered us commercially popular die-cast alloys, such as AZ91D, AS41B, AE42, and G. VINODH, H.R. JAFARI NODOOSHAN, and DEJIANG LI are with the National Engineering Research Centre of Light Alloy Net Forming, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, P.R. China. Contact e-mail: [email protected] XIAOQIN ZENG is with the National Engineering Research Centre of Light Alloy Net Forming, School of Materials Science and Engineering, Shanghai Jiao Tong University and also with the State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, P.R. China. Contact e-mail: [email protected] BIN HU is with the General Motors China Science Laboratory, Shanghai 201206, P.R. China. JON T. CARTER and ANIL K.SACHDEV are with the General Motors Research & Development Centre, Warren, MI 48090. Manuscript submitted November 26, 2018. Article published online February 4, 2020 METALLURGICAL AND MATERIALS TRANSACTIONS A
AE44. Addition of rare-earth (RE) elements increases the alloy cost (such as AE series alloys). The presence of the thermally unstable Mg17A12 phase in Mg-Al alloys hinders their application where service temperature above 120 C is required.[2] Therefore, development of high strength/ductility and heat-resistant Mg alloy systems with low cost is an active focus of research. Zn is highly soluble in magnesium compared with other alloying elements, which means that Mg-Zn is a good candidate for solid solution and precipitation strengthening.[3] The development of a successful alternative to Mg-Al system alloys based on the Mg-Zn system is, however, plagued by major challenges, like hot tearing.[4] Zn in magnesium improves fluidity and room-temperature strength; conversely, Zn content increases the freezing range of the alloy, leading to hot-tearing defects in cast parts.[5,6] Mg alloys are usually prepared by a conventional casting process and the occurrence of hot tearing or hot shortness in these castings is a common problem. Defect-free castings are highly desirable for their widescale industrial application. Hot tearing is a solidification defect observed in different casting processes. It occurs above the solidus temperature due to obstruction of contraction in the solidifying alloy, often at a position where the casting solidifies last or at places that undergo large cross-sectional changes.[7] The mechanism of and criteria for the hot-tearin
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