Welding characterization evolutions for dual spot laser welded-brazed Al/steel joint with various spot configurations

In this research, satisfactory Al/steel butt joint was obtained by the dual spot laser welding-brazing technology with various spot configurations (+45° biased to steel side, in-line, -45° biased to Al side). The results showed that the interfacial IMC (Intermetallic compound) were composed of η–Fe 2 (Al,Si) 5 and θ–Fe(Al,Si) 3 for three joints. The interfacial IMC thickness reduced when the laser spot was biased from steel to Al side. In addition, IMC with larger thickness was produced at the top and middle regions than that of bottom region. The η–Fe 2 (Al,Si) 5 /steel interface would be changed from straight to finger-shaped with the reduction of η–Fe 2 (Al,Si) 5 layer thickness. Numerical simulation showed that interfacial IMC thickness variations were resulted from the difference of peak temperatures: higher peak temperatures, thicker interfacial IMC. Analysis of fractured behaviors presented that fractured locations would be changed with the reduction interfacial IMC thickness: from η–Fe 2 (Al,Si) 5 layer to η–Fe 2 (Al,Si) 5 layer and θ–Fe(Al,Si) 3 and finally to θ–Fe(Al,Si) 3 and partial weld seam when interfacial IMC thickness reduced from 6.1 μm to 5.1 μm and finally to 3.4 μm. Tensile strength values showed that fractured location of θ–Fe(Al,Si) 3 and partial weld seam in the interface joined with 2.9–3.5 μm Fe 2 (Al,Si) 5 layer and θ–Fe(Al,Si) 3 was most beneficial for interfacial strength and highest tensile strength of 142 MPa was obtained.