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 ε/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.