Effect of rotating shear extrusion on the microstructure, texture evolution and mechanical properties of Mg-Gd-Y-Zn-Zr alloy

Abstract

In this paper, the Mg-9Gd-4Y–2Zn-0.5Zr (wt%) alloy after one pass of upsetting and extrusion was subjected to the rotating shear extrusion (RSE) method and backward extrusion (BE) method at 420 °C. Compared with the BE method, torsion deformation and shear deformation were synthetically introduced to the RSE process. The RSE technique had the advantages of a low forming load, large strain and more sufficient deformation. The results demonstrated that the RSE method had more advantages than the BE method in terms of grain refinement and mechanical performance improvement. The average grain size of the RSEed alloy was refined from ~22 µm of the original alloy to ~8.5 µm. In addition, the proportion of dynamic recrystallization (DRX) increased from ~56% of the original alloy to ~83% via the RSE process. The degree of fragmentation of the lamellar and block-shaped LPSO phases in the RSEed alloy was more intensive than that of the BEed alloy, and the particle phase distribution among the crystal grains was more uniform. The RSEed alloy presented a single texture and a strong [2−1−10] orientation component and effectively weakened the texture intensity. The ultimate tensile strength (UTS), tensile yield strength (TYS) and elongation (EL) of the RSEed sample were 350 MPa, 258 MPa and 17%, respectively. Compared with the BEed sample, the mechanical properties of 325 MPa (UTS), 240 MPa (TYS) and 12% (EL) had higher strength and toughness. After the same T5 (200 ℃/90 h) heat treatment, the mechanical properties of the RSEed sample could reach 420 MPa (UTS), 280 MPa (TYS) and 13% (EL), while BEed sample were 371 MPa (UTS), 273 MPa (TYS) and 10% (EL). Additionally, compared with the BEed alloy, the mechanical properties of the RSEed alloy are better due to finer grains, broken LPSO phases, dispersed particle phases and texture modification. • The RSE process could be effectively reduced the forming load and produce more strain than BE. • The LPSO phases are broken to a greater extent and granular phases are more distributed during the RSE process. • The RSE method could greatly change the texture and orientation of the initial alloy. • The RSE method could improve the strength and toughness of the alloy.