Al–Steel Joining by CMT Weld Brazing: Effect of Filler Wire Composition and Pulsing on the Interface and Mechanical Properties

Cold metal transfer welding, a low-heat input process, was employed to weld-braze 6061-T6 aluminium alloy to galvanized interstitial free steel using Al–Si-based (4043 and 4047) filler wires in lap fillet configuration. The effects of current pulsing and filler composition on interface morphology and joint strength were investigated. Pulsing, as well as Si content in the filler, affected the interfacial intermetallic compound layer morphology and joint strength. The detailed micro-area X-ray diffraction studies of seam/steel interface revealed the presence of binary (Al–Fe type) and ternary (Al–Fe–Si type) intermetallic phases for joints made with 4043 and 4047 filler, respectively. Lap shear tests proved that joints made with 4047 filler having ternary intermetallic phases were stronger and fractured in the braze seam. However, joints made with 4043 filler having binary intermetallic phases recorded interfacial failure at lower loads than joints made with 4047 filler. Therefore, the type and morphology of the interfacial intermetallic compounds were found to influence the joint performance.