Bonding method of dissimilar materials made from metals and bonding structure thereof

A bonded structure of dissimilar materials made from metals, comprising:

• at least two plate layers of a steel material;
• a plate layer of a second metallic material having a melting point lower than the steel material;
• a dissimilar material interface between a plate layer of the steel material and the plate layer of the second metallic material;
• a steel material interface between adjacent plate layers of the steel material, wherein a contact resistance in the dissimilar material interface is lower than a contact resistance in the steel material interface;
• a first nugget formed in the dissimilar material interface to bond the plate layer of the steel material and the plate layer of the second metallic material, the first nugget having a first diameter Dd;
• and
• a second nugget formed in the steel material interface to bond the adjacent plate layers of the steel material, the second nugget having a second diameter Ds, wherein the first diameter Dd is larger than the second diameter Ds.