Arc welding method for dissimilar material bonding

An arc welding method for dissimilar material joining for joining a first plate made of an aluminum alloy or a magnesium alloy and a second plate made of steel, the method comprising:

• placing a steel-made joining assist member that has a stepped external shape including a large-diameter portion and a small-diameter portion that is smaller in maximum outer diameter than the large-diameter portion, has a hollow portion formed to penetrate the large-diameter portion and the small-diameter portion, and has a total height of the large-diameter portion and the small-diameter portion being equal to or larger than a thickness of the first plate, in a manner that the small-diameter portion faces the first plate, and applying a pressure to the joining assist member to punch the first plate;
• overlapping the first plate with the second plate;
• and
• filling the hollow portion of the joining assist member with a weld metal, and melting the weld metal until a penetration bead is formed on the second plate, to weld the second plate and the joining assist member together by any method of the following (a) to (e):
• (a) a gas-shielded arc welding method using, as a consumable electrode, a welding wire to provide the weld metal made of an iron alloy or a Ni alloy;
• (b) a non-gas arc welding method using the welding wire as a consumable electrode;
• (c) a gas tungsten arc welding method using the welding wire as a non-consumable electrode filler;
• (d) a plasma arc welding method using the welding wire as a non-consumable electrode filler;
• and
• (e) a coated arc welding method using, as a consumable electrode, a coated arc welding rod to provide the weld metal made of an iron alloy or a Ni alloy.