Fatigue strength of spot welded joints on Al-Mg alloy sheets for auto body

With an increase in the automotive applications of Al-Mg alloy sheets, the fatigue strength of spot welded joints has become an important subject. In this paper, the influence of nugget diameter, successive spot welding and oxide film on the base metal surface on the fatigue property of spot welded joints were examined for the Al-4.500Mg-Cu alloy sheets. The tensile shear fatigue strength of the spot welded joints increased in proportion to the nugget diameter. An acid cleaning of the base metal was fairly useful to prevent degradation of the mechanical property of the joints successively spotwelded. The cleaning significantly lowered the electric contact resistance of an Al-4.5Mg-Cu alloy and resulted in the improvement of the nugget quality.