TWI

The influence of welding tool design on the microstructure of the interface and friction stir spot welded joint between aluminium alloy and low carbon steel was investigated. Two types of welding tool were evaluated: a tool comprising a probe and shoulder and a probe-free columnar tool. Lap welds were made in 1050 aluminium (1 mm thickness), 6022 AlMgSi alloy (1.2 mm thickness) and SPCC low-carbon steel (1 mm thickness). Tool rotation speed was 3000 rpm and the holding time was 3-60 s. Microstructures and interfacial grain size were examined using scanning electron and transmission electron microscopy. The formation of an interfacial metallic compound layer along the interface and the decreasing thickness of the layer with increasing distance from the centre of the welded area and increasing holding time was studied. The characteristic growth behaviour of the interfacial metallic compound layer is discussed in terms of the heat input induced by stirring of Al and friction heat generated between the Al and the welding tool.

8th International Symposium, 18-20 May 2010, Session 10B: Automotive Spot 2, Paper 03