Microstructural analysis and mechanical property optimization for TP347HFG steel/6082 aluminum alloy electron beam welded joint

In view of the failure in direct joining between TP347HFG steel and 6082 aluminum alloy, electron beam welding with beam offset to 6082 is conducted to hinder the formation of Al–Fe intermetallic compounds. TP347HFG and 6082 are successfully joined, corresponding to the increased tensile strength and the maximum value up to 103.6 MPa (56% of 6082 base metal) when beam offset reaches 0.5 mm. θ-Al₃Fe with various morphologies like acicular, petaloid, and actinomorphic shape was the main precipitate inside the weld. In view of the increased Fe content inside the weld, the morphology of θ-Al₃Fe transforms from petaloid-like shape to coarse aciculiform and then to fine acicular clusters as the observed position moves from 6082 side to TP347HFG side. As the beam deviated to 6082 side, the volume of θ-Al₃Fe was decreased, indicating the decreased microhardness of the weld. The continuously distributed reaction layer consisting of brittle η-Al₂Fe₅ is detected at the fusion line of TP347HFG side, which is detrimental to the mechanical properties of the joint. The thickness of the reaction layer is decreased due to beam offset. O content inside the weld was not more than 90 ppm, demonstrating the superiority of electron beam welding.