Microstructure evolution and mechanical property improvement of aluminum alloys with high magnesium content during continuous rheo-extrusion

Abstract

Due to superior mechanical properties and corrosion resistance, aluminum alloys with high magnesium content varying from 3 to 10 wt% have been widely used as aircraft welding wire and automotive materials. However, it remains challenging to produce high magnesium containing aluminum alloys in wire form through conventional casting, extrusion and rolling. Therefore, the present work employs continuous rheo-extrusion to manufacture Al alloy wires with high magnesium contents, which can eliminate the formation of coarse dendrites and thus improve mechanical properties. Microstructures and properties of the alloy wires were investigated by metallurgical microscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Results show that coarse dendrites were completely converted into equiaxed grains. A solid solution with high solubility of Mg and nanosized Al3Mg2 phases were formed in the alloy due to the high cooling rate in continuous rheo-extrusion. Such microstructural features incurred serrated plastic deformation in tensile tests due to the interactions between the solid solution atoms and dislocations. With increasing magnesium content, ultimate tensile strength increased while the elongation decreased gradually. Ultimate tensile strength and elongation of Al-5Mg (wt%) alloy wires were improved by 73% and 8% than that of conventional casting respectively.