<p>A welding method in which workpieces that are an aluminum casting member (1) and an aluminum expanded member (3) are welded together by AC arc welding with the use of a wire (7) while the polarity of voltage applied between the wire (7) and the workpieces is alternated. The AC arc welding is performed with the relationship of |B|/(A + |B|) = not less than 0.128 maintained, where A is the time integration value of an electric current when the wire (7) has a positive polarity and B is the time integration value of an electric current when the wire (7) has a negative polarity. This sets the amount of input heat in welding the aluminum casting member (1) to be not more than 67.8 J/mm<SUP>2</SUP>.</p>
