State Key Laboratory of Advanced Brazing Filler Metals & Technology, Zhengzhou Research Institute of Mechanical Engineering Co., Ltd., Zhengzhou 450001, China
Abstract: Ag-based brazing filler metal has been used widely due to its suitable melting temperature range, good fluidity, wettability and excellent mechanical properties. Ribbon-shaped silver solder has been popular in recent years because of its ability to pre-set the workpiece to fill the gap, facilitate automation, improve welding efficiency, and save energy and materials. However, the rolling process is the key to make ribbon-shaped brazing filler metal with clean surface and less oxidized inclusions. At present, the impurities introduced by the cumbersome rolling pass affect the appearance of the product, but more importantly, the wettability and fluidity of the solder will fluctuate greatly, which will eventually lead to the decrease of the brazing joint quality. In order to obtain good surface quality of brazing metal and reduce the probability of impurity introduction, appropriate annealing process should be selected before rolling to optimize the structure of brazing metal, so as to reduce rolling times, improve quality and improve production efficiency. In this work,the changes of microstructure and hardness of BAg30CuZnSn solder under different annealing temperatures and times were stu-died by many analytical methods, such as metallographic microscope, scanning electron microscope (SEM), energy spectrum analysis (EDS), microhardness tester and so on.The results showed that the microstructure and hardness of BAg30CuZnSn varied greatly under different annealing temperatures and holding times. With the increment of the annealing temperature, the Ag in the silver-rich phase matrix continuously diffused into the network phase,with Ag content decreasing gradually and the overall uniformity increasing. When the temperature exceeded 500 ℃, the crystal grains became coarse and a large number of dendrites appeared. Sn and Ag continuously enriched at the ends of the dendrites and expanded along the crystal axis. When annealing at 500 ℃ for 90 minutes, a uniform and fine grain structure could be obtained, and the hardness of the solder reduced greatly. The maximum reduction of 9 mm in a single rolling pass could be achieved without rolling cracks, which was diffe-rent from the traditional annealing at 550℃ for 120 min.
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2023, Vol. 37 
