Thermal stability and microstructure evolution of ultra-fine grained Al-Mg alloy

The Al-Mg alloys are widely used in the automotive and marine industry due to their excellent properties such as corrosion resistance, good weldability and intermediate mechanical properties along with their low price. Magnesium has a high solubility in the aluminium ~17.35 wt. %. Its addition increases the work-hardening ability, thus an essential work hardening can be expected in those alloys. Refining the grain size of the aluminium-magnesium alloys to the ultra-fine (<1 μm) and even nanometric scale using severe plastic deformation processes become the most effective strategy to increase their mechanical strength, whereas the post plastic deformation treatments are strategies to increase ductility. Experiments were conducted to evaluate the mechanical behaviour of an AlMg5 alloy after ECAP processing and subjected to the post-ECAP annealing treatment. The initial grain size was ~270 μm and was reduced to ~20 μm by ECAP with post-ECAP annealing at 350 °C for 30 min. The annealing treatment led to some sort of bimodal grain mixture with the larger grains embedded in the original UFG structure that provide an excellent combination of strength and ductility.