Synergistic effect of broken Mg2Si and sub-micron Mg17Al12 induced by EX- ECAP on the strength and ductility of deformed Mg-4Al-1Si-1Gd alloy

In order to obtain higher synthetically mechanical properties, Mg-4Al-1Si-1Gd alloy was deformed by the combination of hot extrusion and equal channel angular pressing (ECAP). The results show that combined deformation process can further promote grain refinement of Mg-4Al-1Si-1Gd alloy, so that Mg2Si phase distributes more uniformly and induce the precipitation of Mg17Al12 particles. With the addition of subsequent ECAP, the grain size of the alloy was reduced from 10.68 ± 0.2 μm to 2.48 ± 0.1 μm. After the hot extrusion at 300 ℃ and two passes ECAP at 200 ℃, the short rod-like Mg2Si phase was broken and evenly distributed in the matrix. Remarkably, a large number of sub-microns Mg17Al12 precipitation particles along the grain boundaries were observed, and the average particle size was 0.43 ± 0.05 μm, which can inhibit grain growth to promote grain refinement. And Mg17Al12 precipitation particles can be able to prevent the dislocation from moving in view of the Orowan mechanism. At the same time, the broken Mg2Si particles with uniform distribution can enhance the elongation of alloy by reducing the crack source. Therefore, the optimum mechanical properties can be obtained. Specifically, the tensile strength is 293.8 MPa, the yield strength is 241.5 MPa and the elongation reaches 30.1%.