TWI

Friction stir lap welding of aluminium alloy to magnesium alloy was investigated, emphasising the tensile strength, fracture location in the joint and microstructure evolution in the weld under different welding heat inputs. Dissimilar joints between 3 mm sheet AC4C cast Al (Al, 0.3%Mn, 0.15%Fe, 0.2%Ca, 7.5%Si) and 2.5 mm AZ31 Mg (Mg, 3%Al,1%Zn) were made with Al on top in a lap configuration, varying the welding speed (20 or 80 mm/minute). Tensile failure loads and fracture locations for different welding speeds were determined. Joint cross sections were examined to determine macrostructure, distribution of elements (micro-XRD spectra), and composition of the interface region. The intermetallic compounds produced in the stir zone are discussed. The effect of welding speed on the dimensions of the reaction zone was identified including the role of liquation cracking. The effects of welding and cooling speed on cracking are outlined.

7th International Symposium, 20-22 May 2008, 9A: Dissimilar Materials, Paper 04