Microstructure and properties of Cu/Al joints brazed with Zn-Al filler metals

The mechanical properties and microstructural distribution of the Cu/Al brazing joints formed by torch-brazing with different Zn-Al filler metals were investigated. The microstructure of the Zn-Al alloys was studied by optical microscopy and scanning electron microscopy, and the phase constitution of the Cu/Al joints was analyzed by energy dispersion spectrometry. The results show that the spreading area of the Zn-Al filler metals on the Cu and Al substrates increases as the Al content increases. The mechanical results indicate that the shear strength reaches a peak value of 88 MPa when Al and Cu are brazed with Zn-15Al filler metal. Microhardness levels from HV122 to HV515 were produced in the three brazing seam regions corresponding to various microstructure features. The Zn- and Al-rich phases exist in the middle brazing seam regions. However, two interface layers, CuZn3 and Al2Cu are formed on the Cu side when the Al content in the filler metals is 2% and more than 15%, respectively. The relationship between intermetallic compounds on Cu side and Zn-xAl filler metals was investigated.