Laser spot welding of laser textured steel to aluminium

Goncalo Pardal,Sonia Meco,Andrew Dunn,Stewart Williams,Supriyo Ganguly,Duncan P Hand,Krystian L Wlodarczyk

doi:10.1016/j.jmatprotec.2016.10.025

Goncalo Pardal, Sonia Meco + Show 5 more

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https://doi.org/10.1016/j.jmatprotec.2016.10.025

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Abstract

Laser welding of dissimilar metals (steel and aluminium) was investigated with the aim to increase the maximum tensile shear load of the Fe-Al joints. The increase was achieved by texturing the surface of steel prior to the laser spot welding process which was performed in a lap-joint configuration with the steel positioned on top of the aluminium and with a texture faced down to the aluminium surface. This configuration enabled an increase of the bonding area of the joints, because the molten aluminium filled in the gaps of the texture, without the need of increasing the process energy which typically leads to the growth of the intermetallic compounds. Different textures (containing hexagonally arranged craters, parallel lines, grid and spiral patterns) were tested with different laser welding parameters. The Fe-Al joints obtained with the textured steel were found to have up to 25% higher maximum tensile-shear load than the joints obtained with the untextured steel.

Highlights

One of the challenges in the automotive industry is to reduce the carbon emission of manufactured vehicles (Church, 2015; Havrilla, 2014; Lesemann et al, 2008)
A preliminary study was carried out to determine the best texture for laser spot welding in terms of crater depth, diameter and spacing for different welding parameters
The results suggested that the fracture propagated through the aluminium located on the peripheral region and through the intermetallic compounds (IMC) located in the central area of the weld

Summary

Introduction

One of the challenges in the automotive industry is to reduce the carbon emission of manufactured vehicles (Church, 2015; Havrilla, 2014; Lesemann et al, 2008). A thin sheet of steel (DC04 grade) can be successfully welded to an aluminium alloy (6111-T4) using a conduction mode laser spot welding process (Pardal et al, 2014) This novel welding technique relies on the incidence of a defocused laser beam on the top surface of steel and the generation of heat resultant from the laser-material interaction that is conducted to the aluminium through the steel. The backing bar underneath the Al alloy is used to facilitate the heat extraction and minimise the IMC growth (Borrisutthekul et al, 2007) This technique differs from regular laser welding because here only aluminium is melted whilst steel remains in solid state. This trend is not observed in dissimilar metal joining because the IMC layer becomes thicker simultaneously with the growth of the bonding area

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