Influence of extrusion parameters on microstructure, texture, and second-phase particles in an Al-Mg-Si alloy

Abstract

The extrusion parameters greatly influence the microstructures of aluminum alloys, and further determine the mechanical properties of the final products. In this work, using a self-designed experimental device, a series of extrusion experiments was conducted to investigate the influence of the extrusion parameters on the microstructure, crystallographic texture, and second-phase particles in the Al-Mg-Si aluminum alloy (AA6N01), which is widely applied in the bodies of high-speed trains. Firstly, the billet discard in the press container was taken out for analyzing the material flow and microstructural evolution during the extrusion process. The results showed that continuous dynamic recrystallization occurred, and the initially coarse equiaxed grains in the as-homogenized billet evolved gradually into fine equiaxed grains at the die exit due to their dynamic recovery and dynamic recrystallization. More importantly, coarse grain layers were observed on the surface of the extruded profiles under specific extrusion conditions (460 °C/48 mm/min and 520 °C/48 mm/min). Then, the textures on the surface and at the center of the profiles were analyzed under different extrusion conditions by electron backscatter diffraction. The results showed that the textures of all the extruded profiles were mainly along <100> and <111 > , but the texture intensity was higher at the profile's center than that on the surface under the same extrusion condition. Finally, the second-phase particles in the as-homogenized billet and as-extruded profiles were compared and analyzed. The Fe-rich particles were broken under deformation conditions and their sizes decreased during the extrusion process. However, they were all still distributed on the grain boundaries after deformation, and the composition and content remained unchanged. The Mg2Si particles served as the main strengthening phase in AA6N01, and they were greatly aggregated as the extrusion temperature increased and the extrusion speed decreased.