Al/Mg异质合金固相焊接中产生的金属间化合物(IMCs)的形貌对焊缝性能有重要影响。然而，目前焊缝中等轴状β-Al3Mg2晶粒的产生机理尚不清晰。本研究结合实验和多相场模拟，揭示了焊接过程力场与热场的作用。通过Gleeble热-力模拟制备不同变形量接头，焊接后β-Al3Mg2和γ-Al12Mg17均为单层柱状晶。 400 °C退火1 h后，β-Al3Mg2形貌为多层等轴晶。实验结果表明，该转变源于热场驱动的原子扩散，非沉淀相或Kirkendall效应所致；力场仅促使工件焊合形成焊缝。多层Al3Mg2等轴晶是在热场诱导的原子扩散过程中产生的，而力场仅仅起到了使工件紧密结合形成焊缝的作用。针对退火时间段内的IMCs生长过程建立了多相场模型，以解决实验无法动态再现等轴状β相晶粒在热扩散过程中的形成过程与机理的问题。结果表明，较高的驱动力有利于β-Al3Mg2在Al/Al3Mg2界面成核，而γ-Al12Mg17在Mg/Al12Mg17界面成核的驱动力较低。此外，β-Al3Mg2层的扩散系数明显大于Al基体的扩散系数，且Al3Mg2的溶解度范围较窄，导致生长速率低于溶质原子的扩散速率。因此，溶质原子在Al3Mg2前沿聚集，形成Al基过饱和固溶体，为β-Al3Mg2提供较高的成核驱动力。在焊合后的Al基体中，细小的晶粒提供了更多的形核位置。这些因素共同促进了多层等轴β-Al3Mg2晶粒的形核和生长，而γ-Al12Mg17层保持了原有的柱状形貌。
The experimental characterization and multiphase-field simulation methods were combined to explain the reasons why the different morphologies of two intermetallic compounds (IMCs) were generated in dissimilar Al/Mg alloys solid-state welding process. The Gleeble thermo-mechanical device was used to obtain solid-state welded joints of dissimilar Al/Mg alloys with varying degrees of deformation. The results shown that, regardless of the degree of deformation, the morphology of the two IMCs (β-Al3Mg2, γ-Al12Mg17) after welding is a single layer of columnar crystals. After annealing the joints at 400°C for 1 hour, it was found that, regardless of the degree of deformation, the morphology of β-Al3Mg2 was a multi-layer equiaxed crystal structure. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) analysis showed that the formation of multi-layer Al3Mg2 equiaxed crystals is not caused by precipitation phases or the Kirkendall effect. A multiphase-field model was established to analyze the growth process of IMCs during the annealing period, and the reasons for the formation of multi-layer Al3Mg2 equiaxed crystals were investigated. By analyzing the driving force for IMCs growth, it was found that a supersaturated Al-based solid solution exists at the Al/Al3Mg2 interface, providing a nucleation driving force for the formation of Al3Mg2 nuclei. In contrast, at the Mg/Al12Mg17 interface, the nucleation driving force for Al12Mg17 is very small. Comparing the diffusion coefficients of the phases, it was observed that the diffusion coefficient of the Al3Mg2 is much larger than that of Al12Mg17. When solute atoms diffuse to the Al3Mg2 layer, it cannot accommodate a large number of solute atoms, causing them to be expelled to the adjacent Al matrix, forming a supersaturated Al-based solid solution that provides a nucleation driving force for Al3Mg2. The finer grains of the deformed Al matrix provide more nucleation sites for Al3Mg2. Therefore, the growth of Al3Mg2 manifests as the nucleation and growth of multi-layer equiaxed crystals, while the growth mechanism of Al12Mg17 grains remains the growth of the original single-layer columnar crystals.
