Method for joining aluminum material

A method for joining an aluminum material, comprising, in the following order:

• arranging a first wrought aluminum alloy material along a first jig in an internal space between the first jig and a second jig that is arranged to face the first jig and has an introduction port, and arranging a second wrought aluminum alloy material along the second jig in the internal space such that the second wrought aluminum alloy material is spaced apart from the first wrought aluminum alloy material;
• introducing molten aluminum toward the internal space through the introduction port under pressure to form a through-hole in the second wrought aluminum alloy material;
• introducing the molten aluminum into the internal space through the through-hole under pressure to cause the molten aluminum to collide with an inner surface of the first wrought aluminum alloy material, thereby removing a fraction of the first wrought aluminum alloy material at a collision position between the molten aluminum and the inner surface of the first wrought aluminum alloy material to form a reduced thickness portion on the inner surface of the first wrought aluminum alloy material around the collision portion;
• and
• flowing the molten aluminum together with a fraction of the first wrought aluminum alloy material removed around the collision position within the internal space along surfaces of the first and second wrought aluminum alloy materials.