Effect of compound loading on microstructures and mechanical properties of 7075 aluminum alloy after severe thixoformation

Solid-liquid segregation often occurred during thixoforming of wrought aluminum alloys, which can result in uneven structures and mechanical properties. In this work, a novel compound loading method was introduced in thixoforming 7075 aluminum alloys. The results show that the solid-liquid segregation can be alleviated evidently by compound loading, and the microstructures of periphery area were improved significantly. As the secondary loading displacement increased from 0 mm to 5 mm, the ultimate tensile strength (UTS) of the periphery area increased little (∼510 MPa), and the yield strength (YS) even decreased slightly from 486 MPa to 470 MPa. However, the elongation to fracture of the periphery area increased from 1.94% to 4.3% with increment of 122%. On the contrary, the compound loading has limited effect on the tensile mechanical properties of the center area. The tensile fracture surfaces exhibited typical brittle rupture in the periphery area, while the fracture surfaces of the center were dominated by a large number of dimples and tear ridges showing typical ductile fracture features. Compound loading is an effective method to homogenize the microstructures and mechanical properties of thixoformed wrought aluminum alloys.