| Summary: | 碩士 === 國立中正大學 === 機械工程學系暨研究所 === 99 === Aluminum Matrix Composites (AMCs) containing ceramic particles for particulate reinforcement have been developed for the applications demanding high specific stiffness, high strength and wear resistance. For the joining of particulate reinforced AMC, the FSW process provides a promising solution since the ceramic particles would remain uniformly distributed in the weld zone, while the effect of particulate reinforcement would be lost in the fusion zone if the AMCs were welded using conventional fusion welding processes. Friction stir tool is used to stir the surface material for work hardening or to stir the ceramic powder into substrate to form a localized composite material.
In this research, FSW process was developed for joining Al6061/SiCp AMCs containing various volume fraction and mesh size of SiC particles at different feed rates. The results show that increasing the tool feed rate would reduce the heat input, and the stir zone and HAZ become narrower, however, a smaller grain size shows elevated hardness in the stir zone at lower feed rate. Tensile fracture occurred generally in the HAZ and TMAZ where hardness was degraded. The welds obtained at lower feed rate were tensile fractured in HAZ, while those of higher feed rate were fractured in TMAZ and with higher strength. The tensile strengths after PWHT were restored and are generally higher than those of the as-welded conditions. The probe wear, in terms of diameter reduction, increases with decreasing feed rate.
To improve the coherence of ceramic particles to the aluminum matrix, we explored a novel concept by using electroless plating to coat a copper thin film on SiC particles, then by stirring copper coated SiC particles into a 6061 Aluminum alloy substrate by FSP to form a local particulate strengthened zone. Macro- and micrographs in the stir zone reveal aggregation of copper-coated SiC particles if the Cu thickness coated on the SiC particles increased. The EPMA analysis show diffusion between Cu film of coated SiC and Al substrate after PWHT. The stir zone containing copper-coated SiC particles reveals the effect of particulate-reinforment and interdiffusion between Cu and Al which results in higher hardness value. The tensile strength of the stir zone decreases with increasing copper film thickness coated on the SiC particles. This is mainly because of the aggregation the copper-coated SiC particles in the stir zone which may result is decrease in bonding strength.
Keyword: Friction stir welding, SiC particulate reinforced AMCs, electroless copper plating on SiC particles
|
|---|
