Microstructure, texture evolution and mechanical properties of multi-directional forged Mg-13Gd-4Y–2Zn-0.5Zr alloy under decreasing temperature

Abstract

In this study, homogenized Mg-13Gd-4Y–2Zn-0.5Zr alloys were applied to multi-directional forging (MDF) process at decreasing temperatures from 480 °C to 420 °C by 4 passes. The microstructure, texture evolution and mechanical properties of the alloys during the MDF process were investigated. The result showed that the average grain size was refined remarkably to 4.0 μm and the microstructure distribution became homogeneous after 3 passes with cumulative strain of 9. After 4 passes with cumulative strain of 12, the average grain size increases to 5.4 μm. It is observed that large number of dynamic recrystallized (DRXed) grains and spherical precipitated phases of Mg5(Gd,Y,Zn) occurred during the MDF processing. The area fraction of DRXed grains was increased to 97.3% that can be regarded as achieving complete dynamic recrystallization (DRX) after 3 passes. The grain refinement was mainly caused by DRX, and the DRX was induced via particle stimulation nucleation (PSN) mechanism. Moreover, part of lamellar long-period stacking ordered (LPSO) phases were kinked and brought about numerous kink bands during multi-directional forging (MDF) process, which had an important impact on the grain refinement. As the MDF passes and cumulative strain increase, the basal texture transformed from strong basal texture to a random distribution gradually. The maximum ultimate tensile strength (UTS) and tensile yield strength (TYS) were 399 MPa and 308 MPa after 3 passes. The maximum failure elongation (FE) was 18.1% after 4 passes.