Aluminium-Steel Dissimilar Joints for Automotive Applications Produced by FSW and FSSW

The weight reduction is a very important aspect in transport industry due to fuel efficiency and environmental issues. The increasing use of lightweight alloys and advanced high strength steels for vehicle construction has generated the need to develop joining techniques able to produce aluminium-steel dissimilar joints of high quality. Friction Stir Welding (FSW) and Friction Stir Spot Welding (FSSW) have demonstrated their potential to produce such joints. Due to their solid state approach problems related to melting and solidification are avoided reducing the formation of brittle intermetallic compounds.

In this paper mechanical and microstructural properties of aluminium-steel dissimilar joints will be discussed. Joints have been produced by FSW and FSSW in overlap and butt configurations using a MTS ISTIR PDS machine. Different tool materials such as WC-Co, W₂₅Re or M42 have been employed as well as different tool geometries. Various material combinations have been studied using different high strength steels (22MnB5, DP600…) and aluminium alloys (6082, 5754…). The influence of process parameters on the joint properties will be discussed.

Mechanical properties of the joints have been evaluated by tensile tests and microhardness measurements in order to study the overall performance of the joints as well as the properties of different phases present at the joints. Microstructural examination of the joints have been performed by means of optical microscopy and scanning electron microscopy. Special attention has been paid to the intermetallic compound formation as that is an issue expected to have a large effect on joint properties.