Pinless tools have been proposed to eliminate pinhole problems during friction stir welding; while strength of the joint could be decreased. Two probe tools with pin lengths of 2 and 3 mm and two pinless tools with the scroll groove and L-shaped grooves were used for lap welding of 2 mm thick 6061-T6 aluminum alloy sheets. The average tensile shear strength of the weld created by the long probe tool was about 3 times larger than that of the joint fabricated by the short probe tools. This difference was related to the larger stir zone and higher volume of the displaced metal resulted from the higher plunge depth, the higher heat input and more severe stirring induced by the long probe tool. The pinless welds were stronger due to the larger effective cross section area and absence of the keyhole. The application of the proposed pinless tool with L-shaped grooves produced welds with the average tensile shear strength of 2595 N in comparison to 2222 N of the welds created by the pinless tool with the scroll groove. This slight improvement was resulted from the larger stir zone and more severe stirring caused by the grooves with sharp corners.

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