Influence of tool pin length and dissimilar material configuration on friction stir lap welding of Al and Mg alloys

Friction stir lap welding of Al-to-Mg sheets has great application potentials in manufacturing industry. The pin length and base material configuration are the key factors affecting the quality of dissimilar joints. In this work, three levels of pin lengths (short, middle, and long) and two lap configurations (Al on top or Mg on top) were used to carry out friction stir lap welding experiments of dissimilar Al and Mg alloy sheets of thickness 3.0 mm under three sets of process parameters. Local liquefaction behavior was observed in Al/Mg configuration with 5.2 mm pin length. Except for Al/Mg configuration with 5.2 mm pin length, when the pin length increased, the interface temperature and the thickness of intermetallic compounds (IMCs) increased, vertical materials flow extent got stronger, and the tensile shear strength of weld joints became lower in both Al/Mg and Mg/Al configurations. All values of the interface temperature, material flow degree, and the IMC thickness in Al/Mg configuration were larger than those in Mg/Al configuration, while the tensile shear strength in Al/Mg configuration was lower than that in Mg/Al configuration. The optimized process conditions were determined to obtain the highest tensile shear strength of Mg/Al lap joints with 3.8 mm pin length.