Exploration and Research Based on the Brazing Problem of Automobile Radiator
In the mid-1960s, the brazing process has been successfully applied to the production of automobile copper radiators, and the research on its process stability has been carried out. Brazing of copper and its alloys is easy to achieve, but from a metallurgical point of view, it is a rather complex process. A stable brazing process depends on several factors, namely the material to be brazed, the composition of the brazing filler metal, the brazing temperature, the duration of the brazing temperature, the degree of agitation of the brazing filler metal, the composition of the flux, and the brazing shielding gas. These factors affect and interact with each other, thus determining the effect of the brazing process.
1. Vehicle radiator solder composition
Effect of brazing filler metal composition on racing radiator on brazing strength. Although 85-15 lead-tin solder has high brazing strength for alloy 260, it is not the best solder for brazing this alloy. For each brazing material, the brazing strength varies due to the brazing temperature. That is, each combination between the brazing filler metal and the workpiece material has an optimal brazing temperature to achieve the highest brazing strength. The effects of brazing time 5s, temperature and brazing filler metal composition on 260 alloy brazing crack initiation strength at 0-168℃. It can be seen that the brazing strength of silver-containing solder under high temperature conditions is higher than that of lead-tin solder. This discovery prompted further experiments on lead-tin-silver alloys to find alloy compositions with higher brazing strengths. The following three brazing materials selected by the analysis are now identified. The test results show that: under the same conditions, comparing the brazing strength obtained from the test with that of the brazing filler metal containing silver, it can be seen that when the temperature is 168°C, the brazing strength of the improved brazing filler metal is twice that of the original brazing filler metal.
2. Brazing temperature of automobile radiator
The effect of brazing temperature on fracture initiation strength shows that each material and each solder alloy has its own optimal brazing temperature, and changes in flux composition will also result in changes in optimal brazing temperature. According to the liquidus temperature of the solder used, brazing is generally divided into three types:
(1) Soldering: The liquidus temperature of the solder is lower than 450 ℃, and flux is usually used. Due to the low melting point of the solder, the brazed parts only need to be heated to a lower temperature. The strength of soldered joints is lower, especially at higher temperatures.
(2) Brazing: the liquidus temperature of the solder is higher than 450 ℃, and the flux is generally used. Brazed joints have high strength, sometimes reaching the strength of the base metal, so they can be used for stressed components.
(3) High-temperature brazing: brazing methods in which the liquidus temperature of the solder exceeds 900 °C without the use of flux, such as vacuum brazing, gas shielded brazing and vacuum high-frequency induction brazing.
3. Duration of brazing temperature of automobile radiator
From the effect of brazing temperature duration on fracture initiation strength, it can be seen that the fracture initiation strength does not change when the brazing temperature duration of the racing radiator does not exceed 5 s. Therefore, the duration of 5 s was used in all experimental studies. When the time is prolonged, the reaction zone between the brazing filler metal and the workpiece material will thicken. The results of metallographic research and microprobe analysis show that the reaction zone contains a kind of easily cracked metal compound, and the crack of the brazing joint is first in this area. produced within.
4. Stirring of vehicle radiator solder
Comparing the brazing of the agitated solder and the brazing of the unstirred solder, it can be seen that when the solder is vigorously stirred, the reaction speed between the solder and the workpiece is 3-4 times that of the unstirred solder. It is important to reduce the thickness of the reaction zone due to the frangible metal compounds contained in the reaction zone. Therefore, agitation of the solder must be avoided to obtain the highest brazing strength.
5. Components of vehicle radiator flux
A general requirement for fluxes is to form a rust-free surface that can be removed during the brazing process. Due to the difference of the flux, the brazing strength is obviously different at different brazing temperatures. Further test results show that the brazing temperature must be adjusted accordingly no matter how the flux composition is changed. affect the situation.
6. Car radiator protective gas
During the brazing process, no flux can completely prevent the oxidation of the workpiece surface, because atmospheric oxygen can dissolve into the flux and re-oxidize the metal surface. Therefore, the use of argon to shield the solder and limit the effect of oxygen on the workpiece is part of the overall experimental study. The results show that the use of shielding gas reduces the brazing slag on the surface and the oxidized surface of the workpiece, so that the formed brazing fillet and brazing strength are more uniform. In addition to argon gas, as long as the flammable gas is carefully controlled, nitrogen, etc. also have obvious effects.