Study On Diffusion Bonding Process Of Metal Matrix Composites

Aluminum matrix composites (MMCs) are widely used in the fields of aviation, spaceflight, motorcar manufacture and chemical industry due to their excellent properties such as high mechanical performance, high thermal conductivity and good design ability. With the development of science and technology, the advanced manufacturing techniques such as an appropriate bonding or joining technique play an important role in exploiting the new fields of MMCs' applications. But it is well known that the weldability of MMCs is very poor due to their special microstructures.This thesis selects aluminum matrix composites (SiCp/6061Al,SiC_w/6061Al,Al2O3/6061Al) as research object to study the process characteristics and mechanism of direct diffusion bonding, aluminum interlayer diffusion bonding and TLP diffusion bonding using mixed metal powders as interlayer. By investigation on the selection of bonding parameters and the analysis of microstructures, mechanical properties, distribution of elements and chemical constitution, the method of improving joints' performance was explored. At last, a new process of joining MMCs (mixed metal powders interlayer TLP diffusion bonding in low vacuum condition) was discovered.The result shows that tensile strength of Al2O3p/6061Al aluminum matrix composite joints bonded by aluminum interlayer diffusion bonding is higher than that of by direct diffusion bonding when bonding temperature is lower than 600℃ or higher than 640℃, while the tensile strength of joints bonded by direct diffusion bonding is higher when the bonding temperature is between 600℃ and 640℃.When above three kind aluminum matrix composites are joined by TLP diffusion bond process using mixed metal powders as interlayer, stronger joints are obtained. By analysis the microstructures and mechanical properties, an optimized region of joints' performance is found, which is a wide proportion scope of the compositions in interlayer. If bonded in this region, the microstructure and mechanical properties of joints will be improved greatly. By further research, it is found that the amount of liquid eutectic alloy can be controlled by adjusting the proportion of interlayer. Thus, the microstructures and mechanical properties can be designed, and there is no necessary to control the thickness of interlayer strictly.Based on the above experiments and analysis, the change of powdered interlayer, secondary distribution of reinforcements, the diffusion of elements and the break of oxidefilm are also discussed. The mechanism of mixed metal powder interlayer TLP diffusion bonding has been studied.