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 degrees biased to steel side, in-line, -45 degrees biased to Al side). The results showed that the interfacial IMC (Intermetallic compound) were composed of eta-Fe-2(Al,Si)(5) and theta-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 eta-Fe-2(Al,Si)(5)/steel interface would be changed from straight to finger-shaped with the reduction of eta-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 eta-Fe-2(Al,Si)(5) layer to eta-Fe-2(Al,Si)(5) layer and theta-Fe(Al,Si)(3) and finally to theta-Fe(Al,Si)(3) and partial weld seam when interfacial IMC thickness reduced from 6.1 mu m to 5.1 mu m and finally to 3.4 mu m. Tensile strength values showed that fractured location of theta-Fe(Al,Si)(3) and partial weld seam in the interface joined with 2.9-3.5 mu m Fe-2(Al,Si)(5) layer and theta-Fe(Al,Si)(3) was most beneficial for interfacial strength and highest tensile strength of 142 MPa was obtained. (c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

In this research, satisfactory Al/steel butt joint was achieved using dual spot laser welding-brazing technology. The interfacial intermetallic compounds (IMCs) consisted of eta-Fe-2(Al,Si)(5) and theta-Fe(Al,Si)(3) for all three joints. The thickness of IMC at the interface decreased as the laser spot was biased from the steel side to the Al side. Additionally, the IMC had a greater thickness at the top and middle regions compared to the bottom region. Numerical simulation showed that the variation in IMC thickness was influenced by the peak temperatures. Fracture analysis demonstrated that the location of fracture changed with the reduction of IMC thickness, with the most beneficial location being the eta-Fe-2(Al,Si)(5) layer and theta-Fe(Al,Si)(3) at the interface. The highest tensile strength of 142 MPa was obtained when the interface joined with a 2.9-3.5 µm Fe-2(Al,Si)(5) layer and theta-Fe(Al,Si)(3).