Steel to aluminium key-hole laser welding

The laser joining of a low carbon steel to a 6000 series aluminium alloy was realised in key-hole welding mode in a steel-on-aluminium overlap configuration and was investigated in a three-fold approach: (1) process optimisation, (2) material characterisation and (3) mechanical testing. No-defect welds, composed of a solid solution of aluminium in iron and richer aluminium “white solute bands” of FeAl phases were obtained when limiting steel penetration in aluminium to below 500 μm. Embrittlement of the joining zone was observed, mainly located on the weld–aluminium interfaces composed of Fe2Al5 and/or FeAl3 phases with thicknesses between 5 μm and 20 μm. Limiting penetration to below 500 μm allowed to restrict steel to aluminium dilution in order to confine the hardness of the welds. With such penetration depths, up to 250 N/mm in linear strength could be achieved, with failures located in the weld–aluminium interfaces. Increasing penetration depth led to a change in the assembly weak points (in the weld and on the steel–weld interfaces) and induced a severe decrease in strength.