Intermetallic compounds (IMCs) formation during friction stir welding (FSW) of dissimilar metals such as aluminum (Al) and steel (St) is known to cause a reduction in the joint strength. IMCs are brittle and act as the preferential sites for fracture propagation. In the present study, a modified FSW was used to join a commercially pure Al to a mild carbon St. Several characterization techniques were performed to analyze the joint interface and the results revealed that a nanostructured IMC layer made of Fe₄Al₁₃ (θ) and a micrometer IMC layer made of Fe₂Al₅ (η) were formed adjacent to the Al side and St side, respectively. During the tensile test, the crack propagated through the interface of η-St and not through the IMCs layer. It was shown that the interface of η-St was prone to brittle debonding under normal load, but it showed a slight plastic deformation at the triple junctions with the η grain boundaries. At the triple junctions of boundaries, the loading state was shear and no debonding occurred during the tensile test. This promoted a pseudo-brittle fracture surface. The results of the present study showed that the grain refinement of the IMCs can improve the joint strength of the dissimilar materials through increasing the fracture toughness of the IMC and increasing the number of triple junctions at the interface of metal-IMC.

已知在铝 (Al) 和钢 (St) 等异种金属的搅拌摩擦焊 (FSW) 过程中形成金属间化合物 (IMC) 会导致接头强度降低。IMC 很脆，是裂缝扩展的首选位点。在本研究中，使用改进的 FSW 将商业纯铝连接到低碳碳 St。执行了几种表征技术来分析接头界面，结果显示由 Fe ₄ Al ₁₃ (θ)制成的纳米结构 IMC 层以及由 Fe ₂ Al ₅制成的微米级 IMC 层(η)分别与Al侧和St侧相邻形成。在拉伸试验期间，裂纹通过 η-St 的界面而不是通过 IMCs 层传播。结果表明，η-St 界面在正常载荷下容易发生脆性脱粘，但在与 η 晶界的三重连接处表现出轻微的塑性变形。在边界的三重连接处，加载状态为剪切，拉伸试验期间未发生脱粘。这促进了伪脆性断裂表面。本研究结果表明，IMCs的晶粒细化可以通过增加IMC的断裂韧性和增加金属-IMC界面处的三重结数量来提高异种材料的接头强度。