The influence of silicon content on the structure of Cu55Ni6Mn4Zn brazing alloy and on the structure and properties of brazed joints

Cu55Ni6Mn4Zn (MNMts55-6-4) copper-zinc alloy is widely used for brazing hard-alloy tools and steels. However, the presence of silicon in the alloy (0.1–0.4 wt. %) can lead to the formation of brittle silicides of iron, nickel, and manganese, which negatively influences the strength of brazed joints. The purpose of the study was to determine the influence of the quantitative content of silicon in copper-zinc brazing alloy doped jointly with nickel and manganese on the structure of brazing alloy blanks before brazing and the structure and properties of brazed joints. In the work, to study the distribution of silicides in ingots, tapes, and brazed seams, the authors used microstructural analysis methods, including electron microscopy and X-ray spectral microanalysis. The results showed that with a silicon content of up to 0.2 wt. %, silicides form finely dispersed inclusions uniformly distributed throughout the seam. However, with an increase in the silicon content to 0.4 wt. %, the formation of continuous layers of iron silicides along the brazing alloy – steel boundary is observed, which leads to brittle failure of the joints under mechanical loads. The influence of small gaps turned out to be especially critical during brazing, where the formation of large crystals of iron silicides significantly reduces the strength of the joints. The scientific novelty of the work lies in identifying the optimal silicon content in the alloy (no more than 0.2 wt. %) to minimize the negative effect of silicides on the properties of brazed joints. The results obtained can be used to develop process recommendations for the production of brazing alloys and brazing of steels, which will allow improving the reliability and durability of brazed joints under production-line conditions.