Abstract
The primary disadvantage of friction stir spot welding is the keyhole reminds after the welding process which removing of this keyhole is considered in this study. In addition, alumina nanopowder is incorporated into the weld stir zone as a technique to increase the joint strength. Flat friction stir spot welds with and without alumina nanopowder are examined, and the influences of the main process parameters on the joint strength and weld microstructure were investigated. It was found that the most effective parameters on the joint strength were the normal plunge depth, dwell time, and tool rotational speed, respectively. Tool rotational speed of 1120 rpm, 5 s dwell time, and normal plunge depth of 2.75 were found as the optimum process parameters. In this case, the strength of the friction stir spot weld increased 23% due to adding alumina nanopowder. The hardness of the stir zone was also increased, somewhat.
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