TWI

To meet the needs of lightweight automobile design to join thin steel structures to thicker aluminium sheets, two joint geometries for high-strength friction stir welding (FSW) of dissimilar and unequal thickness sheets were developed: one involving local folding of a steel sheet edge to be friction stir butt welded to thicker aluminium (increased cross-section by folding, or ICBF) and the other employing a tool with a stepped pin to generate a combined lap and butt joint (CLB) within one welding run. The automotive materials selected were HC 340LA high strength steel and AW 6016-T4 aluminium alloy. The folds required for the ICBF joints were manufactured on an hydraulic press using free bending and subsequent flattening. All weldments were produced force controlled on a "Legio" 3ST FSW machine at rotational speeds of 1000-2000 rpm and travel speeds of 750-1500 mm/min. Joints were characterised by microstructure observations as well as tensile and fatigue testing.

11th International Symposium, 17-19 May 2016, Session 5A: Techniques I, Paper 03