Analysis and modeling of the growth of intermetallic compounds in aluminum-steel joints

In this work, we experimentally and numerically studied the microstructures and growth of intermetallic compounds (IMCs) formed in Al-Fe (aluminum-steel) joints welded by a pulsed double electrode gas metal arc welding (DE-GMAW)-brazing method. The IMCs consist of Fe₂Al₅ and FeAl₃, with Fe₂Al₅ being the main compound in the joints. The thickness of an IMC layer increases with an increase of the welding current (heat input) into the base metal. EBSD measurement suggests that the preferred crystal orientation of the Fe₂Al₅ IMC likely provides the necessary path for Al atoms to migrate through the IMC layer for further growth of the Fe₂Al₅ IMC layer toward the steel substrate. The Monte Carlo method was used to simulate growth of the IMCs in the joints. Numerical results are in good accord with the experimental results, suggesting that Fe₂Al₅ IMC is first formed in the initial brazing interface between liquid Al and steel substrate, and then the interface between the liquid Al and steel substrate evolves into two new interfaces: one is an interface between the Fe₂Al₅ IMC layer and the steel substrate, and the other is an interface between the Fe₂Al₅ IMC layer and liquid Al. During growth of the Fe₂Al₅ IMC, FeAl₃ IMC forms in the interface between the Fe₂Al₅ IMC layer and the Al and then grows into the Al. The thickness of the Fe₂Al₅ layer increases nonlinearly with an increase in the growth time.