Dissimilar metal laser spot joining of steel to aluminium in conduction mode

Dissimilar joining of thin (similar to 1 mm) 6111-T4 aluminium alloy and DC04 uncoated low carbon steel used in automobile structures was carried out using laser spot joining in conduction mode. Two sets of experiments were carried out, using copper and aluminium backing bars, respectively. The welds were produced in overlap configuration with steel on the top. The steel surface was irradiated by the laser, and the heat was conducted through the steel into the aluminium. Temperature at the interface was controlled using the fundamental laser energy parameters so that aluminium melts and wets the steel surface. Reaction between the two metallic alloys resulted in the formation of intermetallic compounds (IMC). The formation pattern of IMC was dependent on the temperature profile and the distribution across the interface and was thicker in the centre of the weld and thinner near the edges. The stoichiometry of the IMC formed was varied across the layer and was principally composed of two different layers of Fe2Al5 and FeAl3. Micro hardness tests were carried out to characterise the IMC layer. Mechanical shear tensile tests showed a maximum joint shear strength of up to 68 % of the shear strength of the aluminium alloy.