The Growth Behavior for Intermetallic Compounds at the Interface of Aluminum-Steel Weld Joint

In this work, the microstructure and growth behavior of Al-Fe intermetallic compounds (IMCs), which formed at interface of weld steel-aluminum joint, are successfully analyzed via the combination of experiment and physical model. A layer IMCs consists of Fe₂Al₅ and Fe₄Al₁₃, in which the Fe₂Al₅ is the main compound in the layer. The IMCs layer thickness increases with the increase of the heat input and the maximum thickness of IMCs layer is 22 ± 2 μm. The high vacancy concentration of Fe₂Al₅ IMCs provides the diffusion path for Al atoms to migrate through the IMCs layer for growing towards to steel substrate. By using the calculated temperature profiles as inputs, the combined 2D cellular automata (CA)-Monte Carlo (MC) model is applied to simulate the grain distribution and interfacial morphology evolution at the Al-steel interface. This 2D model simulates the IMCs nucleation, growth, and solute redistribution. The numerical results are in good agreement with the experimental results, suggesting that the growth process can be divided four stages, and the thickness of the Fe₂Al₅ layer increases nonlinearly with the increase of the growth time. The whole nucleation and growth process experienced 1.7~2 s, and the fastest growth rate is 8 μm/s. The addition of Si element will influence diffusion path of Al atom to form different interface morphology. The effects of peak temperature, cooling time, and the thermal gradient on the IMCs thickness are discussed. It shows that the peak temperature has the major influence on the IMCs thickness.