连铸直接成形矩形断面铜包铝复合材料界面及其在轧制中的变化

摘要

Copper cladding aluminum (CCA) rods with the section dimensions of 50 mm×30 mm and the sheath thickness of 3 mm were fabricated by horizontal core­filling continuous casting (HCFC) technology, and the bonding strength, micro­morphology and composition distribution of the casting rod interface were characterized by tensile shear test, XRD, SEM, EDS and EPMA. The results show that the primary intermetallic compounds in the interface of the casting composite rod include CuAl2 and Cu9Al4 phase. The interface at the side of Cu is composed of the Cu9Al4 planar layer (zone Ⅰ) and CuAl2 cellular crystal (zone Ⅱ), and that at the Al side isα(Al)+CuAl2 eutectic texture (zone Ⅲ). At different positions of transverse section of the CCA rod, the interface has the same microstructure, but the total thickness of the interface is different. The interface at the top position has the largest thickness of 220μm, and coarse CuAl2 cellular crystal;that at the side position has the total thickness of 110μm, and that at the bottom position is 150μm. The total thickness of the interfacial layer, especially, the CuAl2 cellular crystal, has serious influence on the bonding strength. So, the bonding strength of interface at the top position is the lowest, which is 24.7 MPa, and the bonding strengths at the side and bottom position are approximate, which are 35.6 and 33.4 MPa, respectively. XRD and fractography analyses indicate that the interface is separated in zonesⅠandⅡafter the tensile shear test. In the subsequent rolling process, the interfacial layer is fractured and fragmented. The fragmentation degree increases with the deformation degree increasing. When the total reduction is greater than 67.7%, a great deal of Cu/Al direct bonding interface is generated which has no obvious diffusion, and the intermetallic compound which is formed in the casting process distributes discontinuously as micro­fragments along the interface.%　　采用水平连铸直接复合成形工艺，制备断面尺寸为50 mm×30 mm、铜包覆层厚度为3 mm的铜包铝复合棒材，并分别采用拉剪试验、XRD、SEM、EDS和EPMA等对铸棒界面的结合强度、形貌和组成进行表征。结果表明：铜包铝复合铸棒界面层的主要组成为CuAl2和Cu9Al4，在近铜侧由平面状Cu9Al4(Ⅰ区)和CuAl2胞晶(Ⅱ区)两区组成；在近铝侧为α(Al)+CuAl2共晶组织(Ⅲ区)。在铸棒横断面上不同位置的界面层结构相同，但界面总厚度不均匀，上部厚度最大，达到220μm，且CuAl2胞晶组织较发达；侧部厚度最小，约为110μm；下部厚度为150μm。界面层总厚度，特别是Ⅱ区CuAl2胞晶层厚度对界面剪切强度有显著影响，因而横断面上部的界面剪切强度较低，为24.7 MPa；侧部和下部的界面剪切强度接近，分别为35.6和33.4 MPa。XRD和断口分析表明，界面分离发生在界面层的Ⅰ区和Ⅱ区内。在后续轧制加工过程中，界面层发生断裂而破碎，其破碎程度随变形程度的增加而增加；当压下率达到67.7%以上时，形成大量纯铜和纯铝直接接触无明显扩散的结合界面，原界面化合物层破碎为尺寸较小的碎片沿界面不连续分布。