| The dissimilar metals joining between aluminum alloy LF2 and Q235 steel with electron beam welding (EBW) was investigated. Deflection electron beam welding was brought out to improve the heat input of both side dissimilar metals and the appearance of weld surface. Cu was added into the joint to prevent the intermetallic compound Fe-Al from generating. The structure of the joints and the appearance of fracture were studied with OM and SEM. The growing of joint was studied.The weld performance of aluminum alloy LF6 with 8 mm width was studied in experiment. The optimum processing parameters were determined as"U: 55kV, If: 2595mA, Ib: 31mA, v: 840mm/min". The tensile strength of the joint was 355 MPa, which was more than 95% of base metal. The microstructure of joint was analyzed. It's found that the structure of weld bead was very homogeneous. Neither hole nor flaw was found in joint.The gliding fracture was approved by analyzing the appearance of fracture.The result of EBW of LF2-Q235 showed that the molten pool was composed of two parts: main pool and assistant pool. The joint zone was composed of three parts: zone A, zone B and zone C. The reaction and product in each zone was determined by energy spectrum analysis. It's found that much intermetallic compound which was very brittle and layered distributed in zone C, which showed much weaker than other zones in joint. Fracture was found to happen in zone C through fracture appearance analysis. Intermetallic compound Fe3Al and Al2Cu were present on the fracture surface which were the main responsibility to brittle fracture. Based on the analysis of the structure of joint, the physical model on the formation of dissimilar metals joint between aluminum alloy LF2 and Q235 steel with EBW was built. The process of the formation of the joint was analyzed.
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