The Effect of Casting Speed on Microstructure, Microsegregation, and Mechanical Properties of High-Strength Mg-Nd-Zn-Zr
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The Effect of Casting Speed on Microstructure, Microsegregation, and Mechanical Properties of High-Strength Mg-Nd-Zn-Zr Alloy Xingwei Zheng, Peng Luo, Jie Dong, and Shiming Wang (Submitted December 23, 2017; in revised form December 16, 2018) High-quality Mg-Nd-Zn-Zr magnesium alloy billets were successfully prepared by direct chill casting. The effect of casting speed on microstructure, microsegregation, and mechanical properties of the Mg-Nd-Zn-Zr alloy was systematically investigated. The results show that the as-cast microstructure is composed of equiaxed a-Mg and Mg12Nd. Optimum values of mechanical properties were obtained corresponding to the casting speed of 90 mm/min. An age hardening at 200 °C took a remarkable effect on the mechanical properties of billets. The maximum ultimate tensile strength 323.4 MPa was obtained in the billet undergoing T6 heat treatment. The shapes of concentration curves of various alloying elements (e.g., Nd and Zn) in Mg-Nd-Zn-Zr, as predicted by the Gulliver–Scheil model, resemble reasonably with the shapes measured by electron probe microanalysis. Keywords
casting speed, mechanical properties, Mg-Nd-Zn-Zr alloy, microstructure
1. Introduction Having the pronounced advantages such as low density, high specific strength, excellent machinability, and satisfactory magnetic shielding capacities, magnesium alloys are endowed with considerable promise for the forthcoming applications in fields of automotive industries where weight saving becomes the primary concern (Ref 1). It is likely that the research and development of magnesium alloys has become one of the most attractive topics over the last two decades. To date, a series of commercial magnesium alloys, such as AZ31, AZ61, and ZK60 alloys, have been developed, however, which suffer from poor corrosion resistance and an inferior level of high-temperature mechanical properties. Particularly, it has been found that the addition of rare earth (RE) is beneficial to enhance both the corrosion resistance and high-temperature mechanical properties of magnesium alloys (Ref 2, 3). Nowadays, some novel magnesium alloys have been designed by introducing RE, a typical representative of which is the AE series such as AE42 Xingwei Zheng, College of Engineering Science and Technology, Shanghai Ocean University, Shanghai 201306, PeopleÕs Republic of China; and National Engineering Research Center of Light Alloy Net Forming, Shanghai Jiaotong University, Shanghai 200240, People’s Republic of China; Peng Luo, Shanghai Collaborative Innovation Center for Heavy Casting/Forging Manufacturing Technology, School of Materials, Shanghai Dianji University, Shanghai 201306, PeopleÕs Republic of China; Jie Dong, National Engineering Research Center of Light Alloy Net Forming, Shanghai Jiaotong University, Shanghai 200240, PeopleÕs Republic of China; and Shiming Wang, College of Engineering Science and Technology, Shanghai Ocean University, Shanghai 201306, People’s Republic of China. Contact e-mail: [email protected]
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