Two step friction stir spot welding between aluminium and carbon steel sheets

A two step friction stir spot welding has been developed to join a 2 mm thick low carbon steel sheet and a 3 mm thick aluminium sheet. In the first step, a consumable aluminium tool is used to develop frictional heat and plasticise the aluminium layer from the tool which fills the cavity in the aluminium sheet, progressively. In the subsequent step, the plasticised layer is squeezed by a non-consumable forming tool made of high carbon steel with an inverted semi-hemispherical profile. To understand the efficacy of the contact area of the plasticised metal, five different tool rotational speeds were used. The integrity of the joint was evaluated by different mechanical and metallurgical examinations.