Electrochemical corrosion of copper‐tin‐nickel‐phosphorus fillers for joining application: a case study on corrosion behavior of porous copper foam brazing using copper‐tin‐nickel‐phosphorus fillers

The brazing of porous copper foam (PCF) heat exchanger using copper‐based filler of copper‐tin‐nickel‐phosphorus (Cu‐Sn‐Ni‐P) could lead to a corrosion when exposed to an aggressive environment. The research on corrosion of copper‐based fillers and brazed joint interface between substrate and foam were carried out. The cyclic polarization of 10Sn6Ni7P, 9Sn7Ni6P and 4Sn10Ni8P fillers reveal that the corrosion potential ( E corr ) was shifted from less noble to more noble potentials. While corrosion density ( I corr ) shows 10Sn6Ni7P, 9Sn7Ni6P and 4Sn10Ni8P fillers shifted from more negative to more positive potentials. On the other hand, porous copper foam was brazed with copper using copper‐based filler and immersed in 3.5 % sodium chloride (NaCl) for 7 days. Optical microscope (OM) shows a thicker patina layer formation on joining interface of copper/porous copper foam (Cu/PCF) using 10Sn6Ni7P filler after the immersion test. Scanning electron microscope (SEM) and energy‐dispersive x‐ray spectroscopy (EDX) discover a formation of copper chloride (CuCl) on the unclean immersed specimens and a copper (II) oxide (Cu 2 O) compound on the clean immersed specimens. The chloride was found to selectively attack on the copper along the filler's area due to a more noble of copper phosphide (Cu 3 P) compared to copper.