Applications of high-silicon aluminum alloys to dissimilar materials joining

• Main Author: Yang, Yongjing
• Other Authors: Zhou Wei
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2023
• Subjects: Engineering::Manufacturing
• Online Access: https://hdl.handle.net/10356/169042
• Institution: Nanyang Technological University

High-silicon aluminum (high-Si Al) alloys have been utilized in many engineering applications owing to the advantages of low density, good wear resistance and low coefficient of thermal expansion (CTE). Joining of high-Si Al alloys to other materials with dissimilar properties could combine their advantages to expand the applications of high-Si Al alloys. In this work, a simple and convenient approach for dissimilar material joining between ceramics and a wide range of Al alloys was developed through the use of high-Si Al alloys. First, the work focused on the dissimilar materials joining of high-Si Al alloys to ceramics including SiC and Al2O3. Because of the low CTE of high-Si Al alloys, strong high-Si Al/ceramic joints could be realized. Experimental results show that the bonding strength of Al/SiC joints increased significantly by using high-Si Al alloys with 30 wt.% and 50 wt.% Si. The shear strength achieved (28.8 MPa) is far higher than those joints reported previously. For joining with Al2O3, although the joint strength is not significantly affected by the addition of high amount of Si, the joint strength was at least over 37 MPa for all the brazing joints. Second, the investigation on contact reactive brazing of high strength 7xxx series Al alloy and high-Si Al alloys was carried out through the use of Cu foil. The effects of brazing temperature and holding time on the interfacial microstructures and mechanical properties of the joints were studied. It is important to control the diffusion of Cu into the base materials and the dissolution of base materials to realize higher joint strength. From the current results, low brazing temperature (slightly above the Al-Si-Cu eutectic temperature) and short soaking duration (about 2 min) were recommended for contact reactive brazing of high strength 7xxx Al alloy and high-Si Al alloys. Third, high-Si Al alloy (Al-50Si) was deposited over Al7075 substrate using later metal deposition at different laser powers. The generic microstructure of laser deposited Al-50Si alloy consisted of primary Si particles surrounded by a hypoeutectic microstructure comprising of supersaturated Al dendrites and Al-Si eutectic, regardless of the applied laser power in both single- and multi- tracks deposition. A finer microstructure was obtained at the laser power of 1900 W. Because of the fine uniformly distributed primary Si particles, the laser metal deposited Al-50Si alloy exhibited excellent wear resistance compared to its as-cast counterpart. This study provides an alternative strategy for dissimilar materials joining between high-Si Al and other Al alloys via additive manufacturing.