Microstructure refinement, strengthening and ductilization mechanisms in Al–Mg–Mn–Er–Zr alloy with high Mn content by friction stir processing

Abstract

In the present work, the friction stir processing (FSP) has been conducted on the extruded Al–6.0Mg–1.1Mn–0.19Er–0.1Zr alloy and subsequently the microstructure evolution and mechanical property were systematically investigated after FSP. The results showed that FSP is an effective approach to achieve remarkable refinement and homogeneity of microstructure. The coarse band shape grains are gradually replaced by the fine equiaxial grains with a mean diameter of 2.54 μm after fully dynamic recrystallization, which can be ascribed to severe plastic deformation and considerable heat input from the stir effect. Additionally, both the primary intermetallic compounds and the short rod-like secondary dispersoids are refined and evenly distributed in the matrix during FSP. The tensile tests demonstrated that the elongation of the FSPed alloy can be improved by 105% without sacrificing any strength compared with that of the base material (BM), proving that FSP is a good method for improving alloy with a desirable combination of strength and ductility after FSP. Compared with the BM, the grain boundary strengthening and the dispersion strengthening mainly contribute to the compensation for the decrease of dislocation strengthening in the FSPed alloy. Based on the observation of the fracture surfaces and the side view near the fracture, the ductilization can be attributed to the refinement of the primary intermetallic compounds and the rod-like secondary dispersoids by suppressing the initiation and propagation of microcracks during the tensile deformation.