Improving hook characterization of friction stir lap welded Al alloy joint using a two-section stepped friction pin

Abstract

Four millimeter-thick 7N01P Al alloy sheets were welded by friction stir lap welding (FSLW) with different tools at various welding heat inputs. Results showed that the highest load could be performed by the optimization of welding parameters using a traditional tool; but, the welding parameters had an obvious effect on the joint loads and fracture modes. The tools with the stepped sections, which could control stable material flow behavior at various welding parameters during FSLW, were introduced. The platform geometry of the stepped friction pin contained two types: one had a convex platform between two sections, and the other had a concave platform between two sections. The joints obtained by the tools with the stepped sections could have a stable load at different welding parameters. Especially, in comparison with the tool with a convex platform, the concave platform acted like a concave shoulder for second stepped pin, improving the material flow during the FSLW and realizing a sound joint with a relatively flat interface morphology, which insured the stability of the joint properties (from 5.2 kN to 5.9 kN) and fracture mode (shear mode) at various welding parameters.