Growth Manner of Intermetallic Compounds at the Weld Interface of Steel/Aluminum Alloy Lap Joint Fabricated by a Defocused Laser Beam

抄録

An interrupted welding method was performed in order to investigate the formation and growth manner of IMC at the weld interface of steel/aluminum alloy lap joint during defocused laser beam welding. Microstructural transition at the weld interface was precisely investigated by both TEM diffraction pattern analysis and TEM-EDX chemical composition analysis. It was revealed that Al₁₃Fe₄ and Al₂Fe formed at the early stage of welding process, and the formation of Al₅Fe₂ subsequently occurred between Al₁₃Fe₄ and Al₂Fe. Preferential and abrupt growth of Al₅Fe₂ resulted in the IMC layer which was composed of coarse Al₅Fe₂ and Al₁₃Fe₄. The dominant factor controlling the interfacial microstructure is considered to be the post-welding thermal history. Increase of energy density gave rise to an increment of the IMC layer thickness, and brought about reduced bonding strength. Therefore, lower energy input (higher welding speed when other welding conditions are fixed) is considered to be useful in order to suppress the abrupt grain growth of the IMCs in the layer which possibly occurred during the post-welding thermal history.