Laser lap joining of high-strength steel to aluminum with cold sprayed steel coating

Owing to a multimaterial car body design that has been utilized in recent years in order to reduce vehicle weight, the joining of dissimilar materials is becoming a crucial issue. The authors have developed a new dissimilar laser lap joining method using a cold spray process. In this procedure, first of all, a steel coating was sprayed onto an aluminum surface, after which this together with a steel sheet were laser welded. When the aluminum remained in a solid state, porosity was observed in the weld metal, suggesting that the cold sprayed coating caused this, while the amount of the porosity decreased as the aluminum melted, indicating that this helped prevent this occurrence. The tensile shear strength of these joints was much greater than that of laser welds without the coating. The mechanical property was greatly influenced by the penetration depth and porosity, including the surface pores, in the weld metal. The study has shown that the melting of aluminum is critical in achieving a weld metal without porosity, though the laser welding should be carried out with as little heat input as possible in order to decrease the intermetallic compound layers and the cracks within them.