%0 journal article %@ 0261-3069 %A Reimann, M., Goebel, J., dos Santos, J.F. %D 2017 %J Materials and Design %P 283-294 %R doi:10.1016/j.matdes.2017.07.013 %T Microstructure and mechanical properties of keyhole repair welds in AA 7075-T651 using refill friction stir spot welding %U https://doi.org/10.1016/j.matdes.2017.07.013 %X Thermal cycle measurements revealed high heating rates and peak temperatures of up to 540 °C in the weld center. Leftover grains from the base metal that did not recrystallize were determined in the stirred zone of the weld center. The welds showed a W-shaped hardness distribution with a lowest hardness of 70% of base metal values in the heat affected zone. Under quasi-static loading, two failure modes were determined, with mode 1 failure occurring in the heat affected zone and mode 2 failure occurring in the outer regions of the stirred zone with crack initiation in the lower portions of the weld. Post-weld natural aging was proven to be highly significant for the mechanical properties of the welds and is effective for up to 4 weeks after welding.