Growth behaviors of intermetallic compound layers in Cu/Al joints brazed with Zn-22Al and Zn-22Al-0.05Ce filler metals

The structure development and growth rate of intermetallic compounds in Cu/Al brazed joint formed under aging treatment were investigated in this paper. Trace amount of rare earth Ce (0.05 wt.%) was added into Zn-22Al filler metal in order to reform the properties of the Cu/Al joint. The interfacial morphology and constituent phases at the interface were examined by the scanning electron microscopes (SEM) and X-ray energy dispersion spectrometry (EDS), respectively. The growth kinetics of intermetallic compounds formed in both systems (Zn-22Al and Zn-22Al-0.05Ce) was also investigated under different aging conditions. The results indicated that interface structure of Cu/Al brazed joints changed from CuAl2/CuZn3 to CuAl2/CuAl/CuZn3 and finally to epsilon/CuAl2/CuAl/CuZn3 during aging. The growth rate of intermetallic compounds observed in the Zn-22Al system was higher than that in Zn-22Al-0.05Ce. Meanwhile, the activation energy of CuAl2 phase increased from 76.9 kJ/mol to 87.6 kJ/mol with the 0.05 wt.% Ce addition. The results also revealed that the joint brazed with Zn-22Al-0.05Ce constantly possessed higher shear strength than that of Zn-22Al throughout the aging treatment. The addition of Ce into the Zn-22Al filler metal decreased the thickness of the intermetallic compound layer produced in the aging, resulting in higher fracture toughness. (c) 2013 Elsevier Ltd. All rights reserved.