Effect of joining parameters on microstructure of dissimilar metal joints between aluminum and galvanized steel

• Weld joints obtained with different welding parameters were investigated.
• The phases of the intermetallic compound layer at the interface were studied.
• Effect of heat input in base metal on the intermetallic phases was discussed.
• Thermodynamic calculation was carried out for the Fe2Al5 and FeAl3 phases.
• The formation process of the intermetallic compound layer was analyzed.

The interfacial microstructures of aluminum and galvanized steel dissimilar joint formed by pulsed double electrode gas metal arc (Pulsed DE-GMA) welding–brazing were characterized. Electron probe microanalyzer (EPMA) analysis revealed that the intermetallic compound layer of the welding–brazing joint consisted of Fe2Al5 and FeAl3. Comprehensive analysis of the effect of the heat input parameters showed that, at a constant total welding current (Itotal), the thickness of intermetallic compound at the interface of aluminum and steel decreased with the increase of bypass current. Thermodynamic calculations were carried out to derive the Gibbs free energy diagram for Fe2Al5 and FeAl3. These calculations presented that Fe2Al5 firstly formed, subsequently FeAl3 precipitated during welding process. Further model of the Fe2Al5 and FeAl3 intermetallic compounds formation process was proposed.