Improvement of the mechanical properties of Al–Mg–Si alloys with nano-scale precipitates after repetitive continuous extrusion forming and T8 tempering

Abstract

Repetitive continuous extrusion forming (R-Conform) followed by T8 tempering treatment was found to be a viable approach for obtaining superior strength with high ductility in an Al–Mg–Si alloy. The evolution of mechanical properties and microstructure of the Al–Mg–Si alloy, and its mutual relationship during this novel approach were investigated. The results showed that a homogeneous and refined microstructure was formed during the R-Conform process, which improved the mechanical properties of the alloy. Concurrently, the R-Conform process caused effective dynamic strain redissolution of β″ precipitates, and the precipitation kinetics were affected by the subsequent T8 tempering process. The refined (sub)grains and induced high densities of the dislocations accelerated the formation of numerous dispersive nano-scale β″ precipitates during an additional T8 tempering treatment at a low artificial aging temperature (120°C) and a short aging time (3h). Therefore, remarkable improvements in both the tensile strength and ductility were achieved by 7 R-Conform passes and T8 tempering.