In this paper, TC4/AZ91D bimetallic composites has been prepared by liquid–solid compound casting process adapting various thickness of Cu coating. The effects of Cu coating thickness on the evolution of interface microstructures and joint mechanical properties are investigated. The results indicate that metallurgical bonded joints are obtained with Cu coating thickness ranging from 36.7 to 51.4 μm. With the increase of Cu coating thickness, the interface microstructure evolves from δ-Mg + Mg₂Cu eutectic structure to Mg–Cu intermetallic compound (IMC) Cu₂Mg + Mg₂Cu and Mg–Al–Cu ternary intermetallic compound. The calculation results of formation enthalpy and chemical potential of Mg–Al–Cu system suggest that Cu element prefers to react with Mg element and formed Mg–Cu IMC. In particular, when Cu coating thickness reaches 36.7 μm, the average shear strength of the bimetal reaches a maximum of 65.3 MPa. Further increasing Cu coating thickness leads to the generation of thick Mg₂Cu IMC layer and Mg₂Cu + Cu₂Mg mixed IMC layer which are proved to be harmful to the shear strength of TC4/AZ91D bimetals. All the fracture surfaces of the bimetallic composites exhibite to have a brittle fracture morphology. However, the fracture location is different with each other. For Cu coating thickness of 36.7 μm, the interface fractures at the δ-Mg + Mg₂Cu eutectic structure, while the interface fractures at the Cu₂Mg + Mg–Al–Cu ternary intermetallic layers when Cu coating thickness is 44.2 μm and 51.4 μm.

Graphic Abstract

中文翻译：

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Cu夹层对液固复合铸造Ti/Mg双金属接头形成的研究

在本文中，TC4/AZ91D 双金属复合材料采用液固复合铸造工艺制备，适合不同厚度的铜涂层。研究了Cu涂层厚度对界面微观结构和接头力学性能演变的影响。结果表明，铜镀层厚度范围为 36.7 至 51.4 μm，获得了冶金结合接头。随着Cu涂层厚度的增加，界面微观结构由δ-Mg + Mg ₂ Cu共晶结构演变为Mg-Cu金属间化合物（IMC）Cu ₂ Mg + Mg ₂Cu和Mg-Al-Cu三元金属间化合物。Mg-Al-Cu 体系生成焓和化学势的计算结果表明，Cu 元素优先与 Mg 元素反应形成 Mg-Cu IMC。特别是当Cu涂层厚度达到36.7 μm时，双金属的平均剪切强度最大达到65.3 MPa。进一步增加Cu涂层厚度导致产生较厚的Mg ₂ Cu IMC层和Mg ₂ Cu + Cu ₂已证明对 TC4/AZ91D 双金属的剪切强度有害的 Mg 混合 IMC 层。双金属复合材料的所有断裂面都表现出脆性断裂形态。然而，骨折位置彼此不同。对于 36.7 μm 的 Cu 涂层厚度，界面在 δ-Mg + Mg ₂ Cu 共晶结构处断裂，而当 Cu 涂层厚度为 44.2 μm 和 51.4时，界面在 Cu ₂ Mg + Mg-Al-Cu 三元金属间化合物层处断裂微米。

图形摘要