Our main products are car radiator copper radiator system, the production requires a lot of tin-lead solder, tin-lead solder many different types, the amount is also large, the amount of the annual production of about 100 tons of tin-lead is rare and precious raw materials, welding In the process, after the tin-lead solder is heated and melted in the furnace, it is easily oxidized for a long time at a high temperature, and a thick tin ash is formed on the surface. Therefore, it is important to improve the oxidation resistance of tin-lead solder and reduce the burning loss of liquid tin-lead solder. In order to improve the oxidation resistance of tin-lead solder, it is necessary to be able to form a uniform oxide film on the surface of the liquid solder. When the surface oxide film is mechanically destroyed, a new film of the same structure can be formed immediately, and the protection is continued. Antimony is to improve the oxidation resistance of liquid tin-lead solder most common and economical alloying elements. First, tin-lead solder oxidation When the tin-lead solder alloy is in a liquid state, its oxidation is very rapid, and when the oxide layer on the surface of the solder tank is removed by the slag-removing method, a new oxidized slag is formed rapidly, and the surface of the solder tank is oxidized. The main body of the layer is an oxide of tin. The analysis shows that the surface SnO 2 has a thickness of 2 mm, and the underlying metal lead particles are dispersed by SnO, followed by SnO and tin and lead. It can be seen that the oxidation problem of the solder is mainly the oxidation of tin. For the anti-oxidation problem of tin, it can be roughly divided into physical methods and chemical methods. (1) Physical methods The physical method is to achieve oxidation resistance by isolating the liquid solder from direct contact with the atmosphere. A common method is to add an organic liquid substance to cover the surface of the solder. The oxidation pressure of the tin liquid surface is greatly reduced, so that not only the contact of the tin liquid with the atmosphere but also the oxygen content dissolved in the tin is lowered. The organic substances currently used as antioxidants are generally of two types, one is a tin alloy antioxidant composed of a low molecular weight polymer and an acid thereof, and most typically a mixture of low molecular weight polyphenylene ether and polyphenylene ether carboxylic acid, the mixture As the content of polyphenylene carboxylic acid increases, the effect of antioxidants is significantly enhanced. However, its disadvantage is that it is difficult to prepare and expensive. Another type of antioxidant is made up of oils and reducing agents. These antioxidants are rich in raw materials, cheap, and highly reductive, but have poor heat resistance and service life. (2) Chemical methods The chemical method is to add a trace amount of surface active element in the liquid solder alloy, which is more oxophilic than Sn and Pb, and forms a stable and dense surface film with the oxides of Sn and Pb to keep the Sn and Pb alloys from further oxidation.锑 is one of the protection elements. Second, the experiment Experimental samples: pure tin, pure lead, 15% tin, 50% tin solder oxidation test (all without 锑) Each time, 300 g of the test sample solder was weighed and placed in a heating furnace of SKC-2H-1 solderability tester. The temperature was controlled at a constant temperature of 360 ° C. At the beginning of the complete melting of the solder, the surface of the liquid surface was removed. Exclude the influence of unmelted impurities in the solder on the test results. After the slag was removed every 2 hours, and then stirred for 1 minute, 4 hours was a cycle, and weighing was used as a measure of the oxidation rate. The experiment lasted for 8 hours, and two groups were made in parallel to obtain an average value. The oxidized slag was weighed using a T328A optical reading analytical balance. The experimental data is shown in Table 1. Table 1 Weight unit g of several kinds of solder after oxidation Solder First stage (4h) Second stage (8h) Total weight Pure tin 1.543 1.424 2.967 S-Sn50 1.756 1.605 3.361 S-Sn15 2.256 2.106 4.362 Pure lead 2.478 2.265 4.743 The experimental data of the six different oxidation contents of six different contents of antimony tin are shown in Table 2. Table 2 Weight of slag after oxidation of several different bismuth contents of solder S-Sn50PbSbA First stage (4h) Second stage (8h) Total weight 锑0% 1.756 1.605 3.361 锑 0.2% 1.645 1.538 3.183 锑0.5% 1.536 1.437 2.973 Containing 0.7% 1.426 1.398 2.824 锑0.8% 1.394 1.345 2.739 Containing 锑1.0% 1.338 1.327 2.665 Containing 1.2% 1.332 1.315 2.647 The experimental data of six different kinds of tin-containing tin containing 15% brazing oxidation are shown in Table 3. Table 3 Weight of slag after oxidation of several different bismuth contents of solder S-Sn15PbSbA First stage (4h) Second stage (8h) Total weight 锑0% 2.256 2.106 4.362 锑 0.2% 2.125 2.023 4.148 锑0.5% 2.045 1.945 3.99 Containing 0.7% 1.896 1.794 3.69 锑0.8% 1.723 1.634 3.357 Containing 锑1.0% 1.714 1.608 3.322 Containing 1.2% 1.717 1.612 3.329 Third, the experimental results and discussion Several anti-oxidation properties of antimony-free solder: The oxidation rate of the solder can be qualitatively judged by the speed of the color change. The surface of the liquid tin-lead solder initially exhibits metallic luster. After a period of heating and oxidation, the surface oxide film on the surface of the liquid solder increases, the color changes from silvery white to slightly golden yellow, and then becomes grayish black, and the surface appears as powdery particles. The higher the brazing, the darker the surface of the solder, and the resulting black powdery particles increase. The higher the lead content, the darker the surface of the solder and the increased black powdery particles produced. By comparison, it was found that pure tin and 50% tin-containing solder first produced a metallic luster oxide film on the surface for a longer period of time than pure lead and tin-containing 15% solder. Therefore, the oxide film formed in advance may function to block the air and keep the solder from being further oxidized. Table 1 is the weighing of the slag after the solder is oxidized. From the results of Table 1, it is seen that the lead oxide of the pure lead is more than that of the pure tin, and the solder slag having a high lead content is much lower than the lead content. Tin oxides are available in SnO and SnO 2 . The film of SnO is loose and not dense enough. The structure of SnO 2 is dense and complete, which can effectively prevent oxygen from diffusing into the liquid solder, and thus has good antioxidant capacity. When the tin content is low, the tin oxide is mostly in the form of SnO, and its oxidation resistance is not good; when the tin content is increased, a sufficient SnO 2 dense protective film can be formed to prevent the intrusion of oxygen. The oxide formed by lead is PbO, which is wet with liquid lead and can be dissolved in it. It cannot form a dense oxide film on the surface and becomes powdery. Therefore, oxygen can continue to penetrate into the liquid solder through the oxide film of PbO, resulting in oxidation. The increasing number of substances has reduced their antioxidant properties. In summary, both the low tin solder and the high tin solder have different degrees of oxidation in a high temperature liquid state, and cover the surface of the solder in the form of slag. The effect of niobium on the oxidation resistance of solder: It can be seen from Table 2 and Table 3 that as the content of niobium increases, the weight of the oxidized slag removed from the brazing filler metal decreases, indicating that the anti-oxidation performance of the brazing filler metal is improved. As the niobium content continues to increase, the weight of the removed oxidized slag tends to be saturated. Macroscopic observation of the formed oxide film, when the amount of germanium in the solder is small, the oxide film is golden yellow, and then dark brown; when the germanium is contained, the oxide film is formed faster, and the color is silver white, and the color has a longer duration. . When the slag is removed, it is found that when the ruthenium or ruthenium is not reduced, the oxide film is thick, and the wet solder is often wrapped with the solder; and when the ruthenium is contained, the oxide film is thin and uniformly floats on the surface of the solder. Therefore, the bismuth improves the oxidation resistance of the solder, and changes the structure of the loose oxide film on the surface of the original solder to form a dense oxide film. Fourth, the conclusion (1) The oxidation resistance of tin is better than that of lead, and the oxidation resistance of high tin solder is better than that of low tin solder. (2) Antimony is an element that improves the oxidation resistance of tin braze. As the antimony increases, the oxidation resistance increases. When it increases to a certain amount, the oxidation resistance tends to be saturated. (3) While improving the oxidation resistance of the brazing filler metal, the wettability of the brazing filler metal is reduced. Therefore, the content of niobium in the brazing filler metal should be moderate, and the optimum niobium content is 0.5% to 0.8%. 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