Strength recovery in friction stir welding of AA6061-AA2024 during various post weld heat treatments

This study addressed the friction stir welding of AA2024-T351 and AA6061-T6 aluminum alloys with added reinforcing particles at 800 rpm, and a traverse speed of 31.5 mm/min. The specimens were heat-treated for different time durations to study the impact of SiC particles on aging kinetics during welding in different metallurgical regions. The Vickers micro-hardness and optical microscopy showed that the reinforcing particles enhanced aging kinetics and decreased the grain size in the stir zone. Moreover, compared to micro-sized SiC particles, the addition of SiC nanoparticles led to a higher hardness at the stir zone following the post-weld heat treatment. Although the joint containing SiC nanoparticles was associated with a higher strength after heat treatment, the trends of changes in strength with time were similar for all specimens with the maximum strength obtained after 20 hours of artificial aging at 160℃. The fracture was controlled by the weakest point of the joint which was located near the thermo-mechanically affected zone on the AA6061 side in all specimens. The mechanical behavior of the joint after heat treatment was identical to the stress-strain behavior of the AA6061 base metal.