Thermal spray application on the dissimilar metals weld between aluminum and steel

Physical and mechanical properties differences between aluminum and steel, especially melting points, make them unable to be welded easily. Moreover, a hard and brittle intermetallic compound (IMC) is always formed at the interface of aluminum and steel. The thermal spray method was proposed to make interlayer for improving fusion and avoiding hard and brittle intermetallic compounds (IMC) at the interface of joined materials. Based on solubility into both steel and aluminum, nickel was chosen as interlayer material. The aim of this research was to investigate the effect of nickel layer thickness and welding variables on the properties of dissimilar metals diffusion welded between steel and aluminum. Nickel was layered into the steel surface using the thermal spray method before the joining process. The nickel interlayer thickness was in the range from 0.2 mm to 1.0 mm. Steel and aluminum were then welded by using the diffusion weld method. The constant pressure of 5 Mpa and constant holding time of 180 s were performed in diffusion welding, while the temperature was varied, i.e. 500^oC, 525^oC, and 550^oC. The thickness of the formed IMC layer increased along with the increase of the diffusion welding temperature. The highest tensile shear strength was obtained by the joint with the welding temperature of 525^oC. The nickel interlayer successfully avoided the formation of Fe-Al IMC and formed a stronger and more ductile diffusion area, and thus increased the strength of the steel and aluminum joint.