Patent ID: 7521129

Claim:
A steel sheet for dissimilar materials weldbonding to an aluminum material, said steel sheet containing, in mass, C: 0.02 to 0.3%, Si: 0.2 to 5.0%, Mn: 0.2 to 2.0%, and Al: 0.002 to 0.1%, further one or more of Ti: 0.005 to 0.10%, Nb: 0.005 to 0.10%, Cr: 0.05 to 1.0%, and Mo: 0.01 to 1.0%, and the balance consisting of Fe and unavoidable impurities, wherein the proportion of the oxide containing Mn and Si by 1 at . % or more in total in the external oxide layer which is newly formed after an original oxide layer having already existed on the surface of said steel sheet is once removed and now exists on the surface of the base steel material of said steel sheet is 50 to 80% in terms of the average proportion of the total length of said oxide to 1 μm length of the interface between said base steel material and said external oxide layer nearly in the horizontal direction.