thermal stability of serely deformed Almg3 sheets

Abstract

In this article a continuous severe plastic deformation (SPD) process entitled dual rolls equal channel extrusion (DRECE) for producing ultrafine-grained (UFG) microstructure of thin sheets is presented. The DRECE process combines conventional equal channel angular pressing (ECAP) process and continual CONFORM process, and it can be easily scaled for industrial use. Keeping constant both the cross section and the length of the severely deformed strip of sheet, the DRECE method promotes a refinement of the microstructure. The effect of post SPD annealing at different temperatures (150 °C, 180 °C, 200 °C, 250 °C, 300 °C and 350 °C) for 30 minutes on the stability of severely deformed microstructure of investigated AlMg3 aluminium alloy. The initial grain size was ~ 7.9 μm and was reduced to 6.8 μm with maximum density of dislocation after 6 passes at room temperature, which were accompanied by the formation that is typical for low strain structures. The annealing treatment at temperatures lower than 180°C did n ot affe cted the microstructure significantly. A continuous grain growth occurred at higher temperatures (180°C-300°C) due to the continuous recrystallization. A bimodal microstructure having a bimodal dislocation density distribution was obtained through the discontinuous recrystallization at 350°C. The annealing led to some sort of bimodal grain mixture with the larger grains embedded in the severely deformed structure that provide and excellent combination of strength and ductility. Therefore, the DRECE process could be a promising industrial SPD method to continuously produce advanced construction materials with the advantages of energy and cost saving and high process efficiency.