Reliability studies of Cu/Al joints brazed with Zn-Al-Ce filler metals

This paper examines the effect of different Ce content on the properties and microstructures of Zn-22Al filler metals and Cu/Al brazing joints. The results indicate that, the spreading area on Cu substrates of Zn-22Al filler metal could be improved by 29.7% with the addition of 0.03 wt% Ce, whereas the oxidation resistance of the alloy increased significantly. The thermal behaviors of Zn-22Al filler metals were minimally influenced by the addition of Ce. The Zn-22Al-xCe filler metals show finer and more uniform microstructures when the added Ce content is in the range 0.03-0.05 wt%. Particularly, the addition of trace Ce into the Zn-22Al filler metal can refine the microstructures and decrease the thickness of the layer of intermetallic compounds produced in the Cu/Al brazing joints. Some bright (Zn,Al)-Ce intermetallic compounds particles were observed in the alloy when the Ce content exceeds 0.08 wt%. The results also indicate that the shear strength of Cu/Al joint brazed with Zn-22Al-0.05Ce is 30.3% higher than that of the Zn-22Al filler metal. Some hard and brittle Ce-bearing intermetallic compounds particles appear in the fracture surface when the Ce content is 0.25 wt%, which resulted in the weakening of the mechanical properties of Cu/Al brazing joints. (c) Ltd 2012 Elsevier Ltd. All rights reserved.