A Study on the Combined Treatment of Cryorolling, Short-Annealing, and Aging for the Development of Ultrafine-Grained Al 6063 Alloy with Enhanced Strength and Ductility

High-strength ultrafine-grained (UFG) metals and alloys often show a reduced tensile ductility when compared with their coarse-grained counterparts. The earlier attempts in trying to improve their ductility usually have led to sacrificing its strength. Optimized process conditions are proposed to achieve both high strength and high ductility in the Al 6063 alloy in the current work. It involves solution treatment of the Al 6063 alloy to dissolve the second-phase particles, cryorolling (CR) to produce a high density of dislocations, short annealing (SA) treatment to recrystallize partially the microstructure without affecting the age-hardening effect, and finally aging treatment to generate highly dispersed nano precipitates. The solution treatment prior to CR combined with post-CR SA at 428 K (155 °C) for 5 minutes followed by aging treatment at 398 K (125 °C) for 12 hours are the optimum processing conditions to obtain the UFG microstructure with improved tensile strength (286 MPa) and good tensile ductility (14 pct) in the Al 6063 alloy. It is observed that the accumulation of dislocations and the formation of nanosized precipitates are responsible for improving the strength, whereas both a low dislocation density and a high density of nanosized precipitates contribute to the improvement in ductility of the CR Al 6063 alloy subjected to an optimized treatment of short annealing and aging.