Influence of time on residual stresses in friction stir welds in agehardenable 7xxx aluminium alloys

Friction stir welding (FSW) can be used to weld 7xxx series wrought aluminium alloys. As these materials are age-hardenable, their properties can change with time. This work used the neutron diffraction technique to measure the residual stresses around a FSW in a 7xxx alloy and to determine how these residual stresses changed with time. It was found that the residual stresses associated with the weld nugget decreased, while those associated with the heat-affected zone increased with time. This is in contrast to strength and hardness values that increased in all regions of the weld with time.