Laser keyhole welding of dissimilar metals with spiral contours: Metal mixing, microstructure, and mechanical strength

Abstract

Laser keyhole welding of dissimilar metals has broad applications in various industrial sectors, but, like many other fusion welding techniques, suffers from the formation of intermetallic compound (IMC) phases, which are brittle and can significantly compromise the mechanical performance of the joints. This is a critical challenge for the adoption of laser welding techniques by industry. This study focused on laser keyhole welding of lap joints of Aluminum (Al) on Copper (Cu) using spiral contours, which were expected to offer longer weld lengths in limited space and could potentially increase the maximum loading of the joints. Experiments were performed to produce spiral welds using different processing parameters and characterize the chemical composition, microstructure, and mechanical strength of the joints. Analysis revealed that by increasing the spiral distance and/or decreasing the laser power, the joint geometry is changed and the average Cu concentration in the joints is reduced, less brittle IMCs are formed in the joints, and the mechanical strength of the joints is improved. Furthermore, computational fluid dynamics simulations were leveraged to understand the dominating physics that drove the asymmetric fluid flow and metal mixing in melt pool with a curved contour, and the details of re-melting and Al-Cu re-mixing in the melt pools of adjacent spiral arcs were investigated.