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Rare Met. DOI 10.1007/s12598-014-0306-3

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Microstructures and mechanical properties of WE43 magnesium alloy prepared by friction stir processing Jin Li, Da-Tong Zhang*, Fang Chai, Wen Zhang

Received: 30 July 2013 / Revised: 17 October 2013 / Accepted: 5 May 2014 Ó The Nonferrous Metals Society of China and Springer-Verlag Berlin Heidelberg 2014

Abstract Mg-3.99Y-3.81Nd-0.53Zr (WE43) casting alloy was subjected to single-pass friction stir processing (FSP) at a constant processing speed of 60 mm
min-1 and various rotation speeds of 400, 800, 1200, and 1500 r
min-1, and microstructures and mechanical properties of the experimental materials were investigated. FSP results in the generation of fine-grained microstructure, and fundamental breakage and dissolution of the coarse second phases. With the rotation speeds increasing, the average grain size of the FSP specimen in the stir zone first decreases and then increases, and the finest microstructure (*2 lm) was prepared at the rotation speed of 800 r
min-1. Owing to the finer and more uniform microstructure, the mechanical properties of WE43 alloy after FSP are significantly improved. The variation tendency of the tensile properties is consistent with the change of the grain size. The maximum tensile strength, elongation, and average microhardness of the FSP WE43 alloy obtained at 800 r
min-1 are 290 MPa, 17.2 %, and HV 92.9, respectively. The fracture morphology shows that small dimples can be observed on the FSP specimens, while the as-cast alloy fails through cleavage fracture. Keywords WE43 magnesium alloy; Friction stir processing; Microstructure, mechanical property; Rare earth elements

J. Li, D.-T. Zhang*, F. Chai, W. Zhang National Engineering Research Center of Near-Net-Shape Forming for Metallic Materials, South China University of Technology, Guangzhou 510640, China e-mail: [email protected]

1 Introduction Magnesium alloys containing rare earth (RE) elements have good creep resistance due to their excellent thermal stability [1]. The recent thrust for weight reduction in aircraft, automobiles, and other transportation vehicles makes magnesium-RE alloys very attractive as structural materials. Considerable attention was paid to explore high strength Mg-RE alloys. Xu and Mohri et al. [2, 3] developed high-performance magnesium alloys (Mg-6.26Zn0.78Zr-0.66Y and Mg-4Y-3RE), the specific strength and creep resistance of which were significantly higher than those of the existing commercial magnesium alloys. However, the ductility of these alloys is very low due to the presence of high RE content and dispersed stable particles. Panigrahi et al. [4] reported that the forged WE43 samples combined with peak aging treatment (60 h at 453 K) exhibited an excellent combination of high strength and high ductility with an average grain size of 21 lm. Ryspaev et al. [5] carried out thermo-mechanical treatments on the QE22 (Mg-2Ag-2RE-Zr) and EZ33 (Mg-2.5Zn-3REZr) magnesium alloys, and found that the fine-grained MgRE alloys with an averag