Wettability of Zn-Al-Li and Zn-Al system brazes on aluminum matrix composite of SiC _p/ZL101

In order to characterize the diffusion behavior of Zn as melting point depressant (MPD) and its potential ability on removing oxide film during the brazing of aluminum matrix composite and improve the wettability of Zn based filler metals by adding active element of Li, the wettability of pure Zn, Zn-5Al eutectic, the developed Zn-6Al-1Li ternary eutectic and Zn-21Al-3Li ternary quasi-eutectic on the aluminum metal matrix composite of SiC _p/ZL101 were tested with sessile drop method at 520°C for 10-30 min within flowing argon (5 L/min) atmosphere. The results and that, for the Zn-base filler metal without lithium, with increasing the soaking time, the Zn atoms only penetrated into the matrix in local area only along the grain boundary, resulting in the dissolution of the grain boundary and even local erosion, but the grain dissolution can not occur, and the gap between the matrix and residual filler metal is obvious. For the active filler metal with lithium at a moderate level of about 3% (mass fraction), Zn can uniformly diffuse into the matrix along grain boundary on the whole surface of the matrix covered by the filler, eliminating the local erosion and the interface gap, and hence improving the wettability on the composite. The diffusion of Zn into the matrix of ZL101 causes the precipitation of lots of silicon particles of about 10 μm along the interface.