The chemical activity of high aluminum, easy oxidation, pressure over 6 * 10-3 Pa, in the heating process, parent materials and the filler metal is oxidized to grey, filler metal can not be wet base material. Only when the pressure is less than 5 * 10 – 3 Pa, and slow heating at 500 DEG C, 30min stays at 450 degrees, to ensure that in the heating process to maintain the pressure in 5 * 10-3 Pa, in order to achieve brazing.
Ultimate pressure vacuum brazing furnace should be less than or equal to 10 – 4 Pa, the working pressure is less than 1 * 10 -3 to meet Pa, the rate of pressure rise “0.3Pa – H – 1. Adequate heating power, capable of quick heating, the heating rate of more than 12 DEG C – min -1. Vacuum brazing furnace should be equipped with air cooling system, which can be cooled quickly. The application of the fastest rate cooling in the premise of ensuring the shape and position tolerance of parts. The quality of Aluminum Alloy brazing temperature control precision, the brazing furnace temperature uniformity requirements higher, plus or minus 5 DEG C can satisfy the vacuum brazing of small parts on the market now, plus or minus 1 DEG C, + 3 DEG C temperature control accuracy of the furnace temperature uniformity of aluminum vacuum brazing furnace of soldering out high quality parts.
Vacuum brazing and heat preservation of aluminum alloy
Generally, the holding temperature is lower than the solidus temperature of the base metal, and higher than the liquidus temperature of the solder. When the temperature is too high, it is easy to produce the corrosion defects of the base metal. The temperature is too low, and the brazing strength is low and even the solder is not completely melted. Brazing time to solder the workpiece to reach the liquidus temperature after about 2min better, the holding time is too short, the soldering seam is not full rounded and not completely melted solder; the holding time is longer, there is overflow or leakage welding solder. The length of holding time is affected by the heat capacity of parts and tooling. The heat capacity is large and the holding time is longer. The vacuum brazing of different parts and furnace loading needs to test the brazing holding time.
Vacuum brazing cooling of aluminum alloy
The holding time of brazing should not be too long. After the end of heat preservation, it needs rapid cooling, and the forced gas is forced to uniformly cool. The deformation degree of parts meets the requirements, which is the best value of cooling rate. Slow cooling and holding time will produce overflow or leakage solder welding defects, for the larger size of the parts, rapid cooling is very important, parts and tooling and heat capacity is too large even if the gas forced cooling can eliminate such defects, the need to reduce the loading amount.
Performance index of vacuum aluminum brazing furnace:
The working pressure is less than 1 * 10 – 3 Pa, the pressure rise rate h < 0.3Pa -1, temperature control accuracy of plus or minus 1 DEG C, the temperature uniformity of – 3 DEG C, with gas cooling function.
Technological process of vacuum aluminum brazing furnace:
Solder cutting: the removal of oxide film on the base metal and the surface of brazing filler metal, brazing filler metal, assembly, vacuum brazing and testing.