Effect of Zn and mechanical vibration agitation on the microstructure evolution in brazed joint of SiC particle-reinforced aluminum matrix composites

Abstract

In order to broaden SiC particle-reinforced aluminum matrix composites in the applications of high-temperature and high-power electronic devices for electronics packaging, three types of the zinc-containing fillers and a low-frequency/low-amplitude mechanical vibration agitation technology were introduced for brazing of 10 vol.% and 70 vol.% SiCp/Al-MMCs. The effect of Zn element and mechanical vibration agitation on the microstructure of the joints was investigated. The increasing aluminum concentration and the decreasing zinc concentration in the bond seam were confirmed by the microstructure images, weight loss measurements, and EDS results and were attributed to zinc penetration and volatilization. Vaporization of zinc in the liquid filler increased the voids and number of vacancies, which destroyed the arrangement structure of liquid filler, namely, short-range order and long-range disorder, and facilitated the mutual diffusion of other atoms. The joints of 70 vol.% SiCp/A356-MMCs with a shear strength of 16.6 MPa were produced at 480 °C and 0.5 MPa using Zn-25Al-10Ga-9Mg-1Ti interlayer. For 10 vol.% SiCp/A356-MMCs, sound joints with a shear strength of 119 MPa were obtained at 520 °C using the Zn-5Al-4Mg foil. Cracks are initiated from the particle/metal (P/M) interface and subsequently propagated to the matrix/metal (M/M) interface. Mg-Si-rich phases were observed in the bond seam and at the interface of 70 vol.% SiCp/Al-MMCs with different Mg content interlayers, which was also a weak interface for the joint. The results also indicated that the active element Mg in the filler should be controlled to an appropriate content for brazing of high volume fraction composites.