Resistance spot welding of Aluminium alloy 5182 to zinc Coated DP600 Steel using process tape technique

With the demanding need for improvement in the strength to weight ratio in automotive and transportation industries, joining of dissimilar materials such as aluminium with steel has become a stimulating and challenging issue. Many investigations were done in order to achieve a successful joining of both materials using different welding processes but an efficient joining using a thermal welding process is still problematical. Not only that extreme difference in the physical and chemical properties of both materials has to be considered but on the other hand a brittle intermetallic phase (IMP) is formed between steel and aluminium leading to a poor weld or no weld at all. In all of the thermal welding processes, due to its high economical potentiality, resistance spot welding remains the leading joining process used in the automotive industry. Investigations have shown that due to the disturbance of heat balance, a conventional resistance spot welding process is not appropriate for joining aluminium with steel. Steel has higher electric resistance than aluminium while aluminium dissipates heat much faster than steel which leads to an unbalanced heat gradient, moving the heat center towards steel. In this work a technique that depends on correcting the heat balance and generating heat with higher density in the aluminium sheet using the process tape technique was found to be efficient. Welding experiments using varying process parameters were carried out to identify the best parameters in terms of the shear strength of the joints. Lap-shear tensile tests were performed and it is shown that an improvement of at least 70% in the shear strength of joined samples of zinc coated DP600 steel with aluminium alloy 5182 compared to aluminium/aluminium welded samples is achieved. Metallographic investigation and scanning electron microscopy (SEM) have shown the formation of the intermetallic phase (IMP) with thickness not exceeding 4μm in optimum samples.