Feasibility Study of Short Cycle Time Friction Stir Spot Welding Thin Sheet Al to Ungalvanised and Galvanized Steel

摘要

Dissimilar friction stir spot welds (FSSW) have been produced between 6111-T4 aluminium sheet and non-galvanised (DC04), hot dipped galvanized (DX54Z) or galv-annealed (DX53ZF) steel sheets, to investigate the feasibility of producing Al to steel welds with a industrially desired weld time of - 1 second and acceptable mechanical properties. Three approaches were explored, involving high and low friction FSSW tools, with and without a pin. The tensile strengths, fracture paths and microstructure of the joints were examined. Maximum failure loads, of 2.8 kN for AI-DC04, 3.2 kN for AI-DX54Z, and 2.4 kN for AI-DX53ZF, were obtained in lap shear tests and optimised joints were produced that failed by nugget pullout. The effects of plunge depth/rate, rotation speed and top-sheet material (Al or Steel) on the tensile strength, material flow, and fracture location of the FSSW joints, formed with a target time of 1 second, are discussed.