The influence of Tip aspect ratio on the microstructure, mechanical properties, and work hardening behavior of the Tip/Mg-Gd-Y-Zn composites

Abstract

In this work, the spherical Tip was introduced into Mg-7Gd-2Y–3Zn (GWZ723) alloy by semi-solid stir casting process, then the Tip/GWZ723 composites were prepared and subjected to extrusion at 380–450 °C. After that, the aspect ratio of the Tip was adjusted according to the extrusion temperature. The effects of the Tip aspect ratio on microstructure, mechanical properties, and work-hardening behavior of Tip/GWZ723 composites were investigated. The results revealed that after hot extrusion, the Tip elongated along the extrusion direction (ED), and its aspect ratio increased as the decrease of extrusion temperature. When the extrusion temperature decreased to 380 °C, the aspect ratio of the Tip reached to 12:1. With the increasing Tip aspect ratio, the hardness of the Tip decreased while the Mg matrix increased. Moreover, both the recrystallized grains and LPSO phase were also refined simultaneously. The yield strength (YS), ultimate tensile strength (UTS), work hardening rate and dynamic recovery rate of the Tip/GWZ723 composites increased with the increasing of Tip aspect ratio. During the tensile process, strain concentration tended to occur at the sharp corner of the elongated Tip, nevertheless, the strain distribution in the matrix became more uniform accompanied with the increasing Tip aspect ratio, which was conducive to suppress crack initiation and delay fracture. It was the laminar-like configuration formed by the elongated Tip and the Mg matrix along the ED contributed to the excellent comprehensive mechanical properties of the Tip/GWZ723 composites. When the Tip aspect ratio was 12:1, the YS and UTS reached as high as 454.3 MPa and 492.2 MPa, respectively.