In dissimilar welding, interfacial metallurgical bonding typically involves the formation of brittle intermetallic compounds (IMCs). Effective bonding without interfacial IMCs was reported only in a few combinations with high mutual solubility, such as Ag/Au, or in limited specific cases involving Al/steel welding, where interfacial amorphous phases formed. This study reveals a new metallurgical bonding mechanism in friction stir lap welding between immiscible AZ31 Mg alloy and DC01 steel, using high-resolution transmission electron microscopy. Rather than IMCs, AZ31 and DC01 were bonded via a nanometer-thick interfacial layer of Fe(Al) solid solution formed by Al atoms diffusing across the interface from AZ31. This mechanism was found highly effective, as evidenced by the lap shear strength of AZ31/DC01 joint, reaching 101 MPa, which is 78 % of the shear strength of AZ31 base material and 89 % higher than that of pure Mg/DC01 joint. Fracture predominantly occurred in AZ31 stir zone rather than right along interface.

中文翻译：

---

通过异种焊接中的纳米厚界面固溶体实现卓越的冶金结合机制

在异种焊接中，界面冶金结合通常涉及脆性金属间化合物 （IMC） 的形成。仅在少数具有高互溶度的组合（例如 Ag/Au）或涉及 Al/钢焊接的有限特定情况下（形成界面非晶相）中报道了不含界面 IMC 的有效键合。本研究利用高分辨率透射电子显微镜揭示了不混溶的 AZ31 Mg 合金与 DC01 钢之间的搅拌摩擦焊中一种新的冶金结合机制。AZ31 和 DC01 不是 IMC，而是通过纳米厚的 Fe（Al） 固溶体界面层键合，该界面层由 Al 原子从 AZ31 扩散穿过界面形成。AZ31/DC01 接头的搭接剪切强度达到 101 MPa，是 AZ31 基材剪切强度的 78%，比纯 Mg/DC01 接头高 89%。断裂主要发生在 AZ31 搅拌区，而不是沿界面右侧。