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ASM International 1059-9495/$19.00

Influence of Effective Physical Contact Area on Microstructure and Mechanical Properties of Diffusion-Bonded TC4/1060Al Joints Guoqiang Luo, Jiayu He, Zhenfei Song, Jian Zhang, Mei Rao, Jianjun Mo, Yiyu Wang, Qiang Shen, and Lianmeng Zhang (Submitted May 12, 2018; in revised form September 14, 2018) In the present study, dissimilar TC4 alloy and 1060Al alloy were successfully diffusion-bonded at a very low temperature about 410 °C by improving the effective physical contact area. A sound joint with a crack-free interface and a high shear strength (128 MPa) is obtained with a combination of TC4 surface roughness of 109.90 lm (Sa) and 1060Al surface roughness of 101.43 lm (Sa), and customized parallel surface scratches. Under this condition, the two parent metals share the largest contact area during the physical contact stage of diffusion bonding process, which is consistent with the theoretical calculation. The results show that no Ti-Al binary intermetallic compounds are observed at the interface of the joints. The maximum shear strength of the joint reaches 128 MPa with optimized bonding parameters (410 °C for 120 min with a pressure of 20 MPa), which is higher than the shear strength of 1060Al (80 MPa) base metal. The fractography analysis indicates the joints failed with a ductile fracture at the 1060Al side. Keywords

1060Al alloy, diffusion bonding, microstructure, physical contact area, shear strength, TC4 alloy

1. Introduction Ti alloys are widely used in aerospace, chemical, and nuclear industries because of their high strength and thermal stability (Ref 1, 2). Al alloys are also extensively used in these industries because of their low density and excellent machining performance (Ref 3). Ti-Al welded joints combine the excellent characteristics of both materials while also reducing the weight and cost of the structure and integrating structure and function for modern industrial design (Ref 4, 5). However, the mismatch between the physical properties of Ti and Al alloys, such as their crystal structures and thermal expansion coefficients, poses some problems for their joining. For instance, in the friction welding of Ti and Al alloys, extensive plastic deformation and flow occur in the welded zone (Ref 6-9). In addition, use of the melting welding method causes the formation of brittle intermetallic compounds (IMCs), cracks, and other welding defects in the welding joint area (Ref 10-13). Diffusion bonding, a solid-state joining process, has been proven to be an effective method for joining dissimilar metals (Ref 14-19). Previous studies on the diffusion of Ti/Al have

Guoqiang Luo, Jiayu He, Jian Zhang, Mei Rao, Qiang Shen, and Lianmeng Zhang, State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, PeopleÕs Republic of China; Zhenfei Song and Jianjun Mo, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621000, PeopleÕs Republic of China; and Yiyu Wang, Department of Chemi