Corrosion behaviors of 316LN stainless steel joints brazed with Sn-plated silver filler metals

Abstract

AgCuZnSn filler metals were prepared from the BAg34CuZnSn filler metal by a combinative process of brush plating and thermal diffusion, and the prepared filler metals were applied to the induction brazing of the 316LN stainless steel. The corrosion behaviors of the brazed joints was evaluated based on local corrosion analyses, where the morphology of the joints was analyzed by scanning electron microscopy (SEM) after immersion in a 3.5 wt.% NaCl aqueous solution and electrolytic etching in a 10 vol.% oxalic acid solution. The microstructure of the brazed joints with the Sn-plated filler mainly consisted of the Ag phase, Cu phase, CuZn phase, Cu5Zn8 phase, Cu[Formula: see text]Sn[Formula: see text] phase and Ag3Sn phase. The local corrosion analysis results indicated that galvanic corrosion occurred near the interface between the stainless steel base metal and the brazing seam. With increasing local corrosion time, the corrosion rates of both the brazing seam and the base metal first exhibited an increasing trend, followed by a decreasing trend, and the corrosion rate of the brazing seam was slightly greater than that of the base metal. The corrosion behaviors analysis indicated that the corrosion resistance of the brazing seam was reduced, and concave defects emerged after electrolytic etching for 90 s.