Dislocation strain energy based modeling for ultrasonic effect on friction stir lap welding process of dissimilar Mg/Al alloys

Abstract

Understanding of the ultrasonic effect on the process variables has important significance for the process optimization in ultrasonic vibration enhanced friction stir lap welding (UVeFSLW) of dissimilar Mg/Al alloys. In this study, the dislocation strain energy in both grain interior and grain boundary is considered to improve the formula for determing threshold thermal stress, and the constitutive equation is modified and used to develop the model for Mg/Al UVeFSLW process. The influences of ultrasonic vibration on heat generation, temperature profile, material flow and intermixing are quantitatively analyzed. It is found that the ultrasonic vibration induced the flow stress reduction gets larger, and the interfacial heat generation and viscous dissipation heat generation in the shear layer drop, which results in lower temperature at the tool/workpiece interface, intensifier material flow and larger material intermixed region in Mg/Al UVeFSLW. The interface temperature between the tool/workpiece and the profile of thermo-mechanically affected zone are experimentally measured, and compared with the predicted ones. The results show that the calculation accuracy of the modified model is improved.

Keywords

• Friction stir lap welding
• Ultrasonic vibration
• Dislocation strain energy
• Mg alloy
• Al alloy
• Numerical simulation