Thermo-mechanical simulation using microstructure-based modeling of friction stir spot welded AA 6061-T6

Abstract

An innovative analysis methodology integrated microstructure-based modeling and thermo-mechanical coupling simulation was developed to analyze processing thermal history and then attain simulated mechanical properties of FSSW joint with a higher accuracy. Such numerical evaluation model with measured geometry, hook defect as precast cracks and modified material properties as well as attached thermal residual stress was validated to mainly cover mechanical results produced by processing course. A series of thermal simulation settings which approached actual manufacturing conditions were applied, considering a moving heat source model coupled with Gauss surface and double ellipsoidal body, axial welding force, TCC varied with pressure at the steel-Al contact interface and preheating temperature field of the tool. So then the variations of heat generation, interfacial pressure, temperature field and residual stress distribution were numerically calculated. Finally, tensile fracture simulation of the established joint model was performed to test the simulated accuracy in mechanical performance using this method. The mechanical evolution mechanism to failure was also unveiled. Moreover, the cut-off temperature to achieve improved material properties in SZ and TMAZ was found to be about 375 degrees. The regulation mechanism of such solid phase welding was inferred to be the negative feedback of temperature by means of the decreasing yield stress with increasing temperature. The predicted thermal cycle, geometries of several metallurgical zones, fracture mode and load bearing characteristics were all in good agreement with the experimentally measured ones, validating the reliability of this proposed approach.