Joining structure

A joining structure having a welded part for connecting joined members made of a metal that forms a passive film when the metal is welded, wherein

• an outermost surface portion of the welded part has a pitting potential;
• the welded part comprises:
• a welded part main body formed inside, and
• a surface-modified layer formed in contact with the welded part main body;
• the surface-modified layer includes the outermost surface portion having the pitting potential and a portion formed by remelting and solidifying a melt-semi-solidified metal;
• the welded part is formed by remelting and solidifying only the portion of the surface-modified layer without remelting the welded part main body, which is deeper than the surface-modified layer, such that formation of a keyhole in the welded part is prevented;
• the portion of the surface-modified layer formed by remelting and solidifying the melt-semi-solidified metal has a depth range of 0.5 μm or greater and 100 μm or smaller from the outermost surface portion of the welded part in a welding depth direction such that thermal deformation is suppressed;
• and
• after remelting and solidifying the portion of the surface-modified layer, spinel oxide is not detectable by an X-ray absorption fine structure analysis of the outermost surface portion of the surface-modifier layer due to the portion of the surface-modified layer of the welded part being remelted and solidified to prevent formation of the keyhole.