Enhancement of the laser welded AA6061-carbon steel joints by using Al5Si intermediate layer

The microstructures and mechanical properties of laser welding joints with/without Al5Si foil interlay in an overlap steel-on-aluminum configuration have been investigated. The joints with Al5Si foil interlayer are superior to that without the interlayer at the same welding condition. The Al-Fe intermetallic compound (IMC) layers at the fusion interface are FeAl layer adjacent to the steel matrix, FeAl3 layer close to the aluminum, and the intermediate Fe2Al5 between the FeAl and FeAl3. Si addition can restrict growth of the IMC layer, and change the proportion of the Al-Fe IMCs. The overall thickness of the IMCs can be reduced to 2.0 μm under the welding conditions: laser power: 2.8 kW, defocus distance: 10 mm, and welding speed: 1.5 m/min. The tensile strength of the joints can be improved significantly by the Al5Si foil interlayer. The fracture of the joint with Al5Si interface occurs in the heat-affected zone of the carbon steel at the maximum tensile strength.

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