Residual stress, microstructure and microhardness measurements in AA7075-T6 FSW welded sheets

Friction stir welding (FSW) is a relatively new joining technique particularly for aluminium alloy which is difficult to weld by fusion. In this work, the experimental results on FSW AA7075-T6 sheets were studied. The residual stresses were measured across the weld by ultrasonic method. This technique has various advantages: nondestructive, reproducible, fast and not expensive. Thereafter, the microstructure phenomenon and microhardeness measurements were investigated both in parent metal and in the joint. The results show a higher residual stresses in the heat-affected zone. Small compressive residual stresses were detected in the parent metal adjacent to the heat-affected zone and the nugget zone. The microstructure reveals very fine grains in the weld zone compared to parent metal.