Effect of Laser Surface Texturing and Al2O3 Particles on Microstructure and Properties of Tungsten Inert Gas-Welded Steel–Aluminum Lap Joints

Interfacial evolution of steel–aluminum (Fe-Al) joint prepared by weld-brazing technique closely correlates with its mechanical properties. Enhancing the quality of Fe-Al joint is always pursued and is trying to be realized. In this work, laser surface texturing and coating Al2O3 powder were synchronously applied to change the surface morphology of steel plate for altering the interfacial reaction behavior. Lots of lap joints of AA6061 Al and DP590 steel with surface texturing or not were performed by using the tungsten inert gas welding (TIG) combined with ER4043 filler metal. Given grooves were prefabricated by laser surface texturing process, and Al2O3 powder with different sizes was pre-sprayed on the steel sheet. The wetting and spreading behavior of liquid Al on the processed steel sheet and the joint microstructure were analyzed, respectively. The tensile–shear stress of the joint was also tested. Investigations showed that the laser surface texturing technique can change the interface roughness of the Fe/Al lap joint and alter the wetting–spreading behavior of the liquid Al on the steel sheet. When the same size Al2O3 powder was coated on the steel plate, the wetting angle changes smaller with increasing the textured line space. The interfacial microstructure indicated that the thickness of IMCs is obviously reduced by using this proposed new process. The average tensile–shear strength of the joint with 30 nm Al2O3 particles achieves the maximum value of 75.6 MPa when the textured line space is 100 μm. However, the average tensile–shear strength decreases with the increase in line space (>100 μm), and its maximum value with 1 μm Al2O3 particles addition achieves 79.7 MPa when the line space is 130 μm. Analysis infers that the hump shape of the groove opening on the steel side is preserved after the addition of Al2O3 particles, which further enhances the mechanical locking of the bending interface on the joint and intercepts the crack expansion in the groove.