Effects of processing time on strengths and failure modes of dissimilar spot friction welds between aluminum 5754-O and 7075-T6 sheets

The effects of the processing time on the strengths and failure modes of two types of dissimilar spot friction welds between aluminum 5754-O and 7075-T6 sheets are investigated by experiments. Dissimilar 5754/7075 and 7075/5754 spot friction welds made at different processing conditions were tested under lap-shear loading conditions. The experimental results indicate that the failure loads of both types of welds in lap-shear specimens increase when the processing time increases for the given ranges of the processing time. The optimal processing times to maximize the failure loads of the 5754/7075 and 7075/5754 welds under lap-shear loading conditions are identified. The maximum failure load of the 7075/5754 welds is about 40% larger than that of the 5754/7075 welds. Selected optical and scanning electron micrographs of both types of welds made at different processing times before and after failure are examined. The micrographs show different weld geometries and different failure modes of the welds made at different processing times. The failure modes of the dissimilar 5754/7075 and 7075/5754 spot friction welds are quite complex and appear to strongly depend on the geometry and strength of the interfacial surface between the two deformed sheet materials.