挤压温度及路径对Mg-Gd-Y-Zn-Zr合金 等通道角挤压组织及性能影响

The equal channel angular pressing (ECAP) experiments were conducted on Mg-13Gd-4Y-2Zn-0.6Zr magnesium alloy to investigate the effects of extrusion temperature and extrusion route on microstructure evolution and mechanical properties of Mg-Gd-Y-Zn-Zr alloy. The experimental results show that the grains are refined insignificantly at 350 ℃ and dynamic recrystallization (DRX) occurs at the deformed grains boundaries at 400 and 450 ℃ where the grains are refined. Furthermore, the grain boundaries are partially melted at 500 ℃, which weaken the grain boundaries. After 1p-ECAP of as-cast and homogenized samples at extrusion temperature of 450 ℃, the DRX occurs firstly in the coarse deformed grains boundaries, and the bimodal microstructure is formed for the coarse grains are surrounded with finer DRX grains. The tensile yield strength increases from 145.0 MPa to 175.6 MPa and the ultimate tensile strength increases from 254.3 MPa to 294.7 MPa respectively after 1p-ECAP for the homogenized sample, while the fracture elongation decreases for the existence of bimodal microstructure which causes the stress concentration at the interface of coarse deformed grains and finer DRX grains. The grain sizes of the samples are uneven after 4p-ECAP through A route, which brings the mechanical property differences in different parts of the extrusion samples. The grain sizes are evenly finer through Bc route due to the rotation of extruded sample and occurrence of dislocation cross slip after each pass, which results in higher tensile yield stress, ultimate tensile stress and fracture elongation.