Dynamic recrystallization behavior and mechanical properties response of rheo-extruded Al–Mg alloys with various Mg contents

Abstract

Processing of Al–Mg alloys with high Mg content is a challenge owing to the presence of brittle β-Al3Mg2 phases and coarse dendrites. In this work, the microstructural evolution and mechanical properties of rheo-extruded Al–Mg alloys with different Mg contents were investigated. The formation mechanism of equiaxed grains during continuous rheo-extrusion was revealed. The strengthening mechanisms of rheo-extruded Al–Mg alloys were discussed. The results showed that compared with the coarse grains with dendrites and secondary phases in the as-cast Al–Mg alloys, refined and equiaxed grains were formed in the rheo-extruded alloys, which were attributed to the high cooling rate and shear deformation. Furthermore, the continuous dynamic recrystallization resulting from the accumulative shear strain was responsible for the grain refinement during continuous rheo-extrusion. The Mg atoms with a high content that were dissolved in the matrix possessed a strong pinning effect on the dislocation motion and reduced the grain boundary mobility during deformation. With increasing Mg content from 5 to 7 wt%, the ultimate tensile strength and yield strength of rheo-extruded Al–Mg alloys were improved from 252.2 to 329.1 MPa and 97.2 to 139.9 MPa, respectively, accompanied by a slight decrease in elongation. Grain boundary strengthening, solid solution strengthening, and dislocation strengthening were the main strengthening mechanisms contributing to the yield strength enhancement for the rheo-extruded alloys.