Remote Laser Welding of Zn Coated If Steel and 1050 Aluminium Alloy : Processing, Microstructure and Mechanical Properties

The integrity of steel-aluminium dissimilar alloy joints is dependent on the intermetallic phases (IMCs) and the extend of the bonding area. The excessive growth of brittle AlxFex IMCs within the weld pool and interfaces is disadvantageous due to the initiation and propagation of hot and cold cracking during the solidification. In order to study the formation of IMCs and impact of joint integrity, welding experiments with variable RLW parameters were performed. Results showed that while in conduction mode three IMCs were identified: η - Al5Fe2, κ - AlFe3 and θ - Al13Fe4; they formed in a non-continuous interfacial layer, the weld pool composition remained homogenous, and cracking was minimal. On the contrary, in keyhole mode welded samples produced a continuous and thick IMC layer, continuous and/or excessive cracking and an inhomogeneous weld pool composition due to the excessive mixing of steel and aluminium. The tensile lap shear tests for samples produced in conduction mode demonstrated a lap shear strength of 4 and 6 kN, for single and double seam welds, respectively. This work found a close link between the welding mode and weld pool chemistry which significantly determined the IMCs distribution and thickness