Thermal expansion behavior and performance of VLP diffusion-bonded joints of SiC_p/A356 composites

Effects of the bonding thermal cycle and heat treatment on thermal expansion behaviors and mechanical performance of SiC_p/A356 composites and their joints were investigated. Joints were made by using the vibration liquid phase (VLP) diffusion bonding process, and treated by the solution and aging. It has been found that the CTE of the base metal is not significantly influenced by the bonding thermal cycle and decreases slightly after the solution and aging treatment. The constituent phases of the base metal are composed of α-Al (Si), SiC and a compound of Al_3.21Si_0.47. The presence of the bond region shows no deleterious effect on the CTE of the bonded joint. After heat treatment, the CTEs of VLP bonded joints decreased with the bonding temperature and were lower than those of the as-bonded joints or the SiC_p/A356 composites. The tensile strength of VLP bonded joints increases with the bonding temperature due to an increase of the volume fraction of SiC particles and the Al content and a decrease of the Zn and CuZn₅ content in the bond. The disappearance of CuZn₅ and occurrence of Al_0.71Zn_0.29 in the bond region may account for the increased strength of the joint after heat treatment. The constituent phases of VLP bonded joints are composed of α-Al (Si), SiC and two compounds of Al_3.21 Si_0.47 and Al_0.71Zn_0.29.