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In the conventional friction stir welding (CFSW) process, a certain size spindle tilting angle and shoulder plunge depth were applied in order to obtain high-quality welds. However, what was the reason for the thinning phenomenon of weld and thus the weakening of weld bearing capacity? The reduction of spindle tilting angle and shoulder plunge depth was likely to cause the welding tool not being able to reach the weld root, and thus it was engendered for the kissing bond or the absence of complete penetration. In the present study, a novel welding tool with large-size shoulder and Archimedes spiral groove was designed in order to achieve non-thinning and lack of kissing bond welds. The microstructures and mechanical properties of the joints obtained by the Non-thinning and Penetrating Friction Stir Welding (NTPFSW) and the Penetrating Friction Stir Welding (PFSW) had been analyzed in detail. Compared with PFSW, NTPFSW had a narrow shoulder affected zone. The stir zones (SZ) obtained by the PFSW and NTPFSW were both composed of ne equiaxed grains. The grains in the upper part of NTPFSW joint were larger in size and the number of precipitates (θ' phase) was less. NTPFSW completely eliminated weld thinning phenomenon and the tensile properties were improved.

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