Characterization of Intermetallic Compound Layer Formed at the Weld Interface of the Defocused Laser Welded Low Carbon Steel/6111 Aluminum Alloy Lap Joint

Lap joining of the low carbon steel (SPCC: Steel Plate Cold-rolled C) and aluminum alloy 6111-T4 plates was carried out using a defocused YAG laser beam. Precise TEM and TEM-EDX analyses were performed for the intermetallic compound (IMC) layer formed at the welding interface of the lap joint, which was fabricated under the following conditions: (laser power: 3.0 kW, defocus distance: 20 mm, laser traveling speed: 2.17× 10^-2 ms^-1). The IMC layer consisted of very fine granular crystals. The fine IMC crystals with about 500 nm in diameter formed at the interface between IMC layer and solidified A6111 region. In contrast, IMC crystal grains at the central region of the layer were relatively large and the average size was 1 (mu)m. Both TEM-EDX and electron diffraction pattern analyses confirmed that the former is Al13Fe4 and the latter is Al5Fe2. The greater part of the IMC layer was occupied by Al5Fe2 in the present welding condition. Another ultra fine IMC grains were observed at the interface between the SPCC and IMC layer. The electron diffraction pattern analysis revealed that they were FeAl, Fe3Al and Al6Fe.