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Vacuum Heat Treatment Furnace

Vacuum Sintering Furnace

Vacuum Brazing Furnace

Vacuum Brazing Defects and Their Solutions

The main phenomena of vacuum brazing defects are:

1. Dissolution

Dissolution is a depression formed on the surface of the base metal by the melting of the molten solder.

(1) Causes of corrosion: The brazing filler metal does not match the brazing base metal, and a low melting point phase is formed between the brazing filler metal and a certain component in the base metal, which reduces the solidus temperature in some areas of the base metal. The heating rate of the parts is slow due to the large heat capacity of the tooling or the large amount of furnace loading, and the residence time in the solid-liquid phase temperature range of the solder is too long. At a certain temperature, the solder and a component in the parent phase are complexed to form a low melting point. The melting point of some regions of the parent phase alloy decreases and melts. The furnace temperature is not uniform, the local temperature of the brazing parts is too high, and the brazing temperature is too high, which leads to the melting of the low-melting components of the base metal through the diffusion area of the brazing filler metal. The temperature rises and falls slowly in the solid-liquidus range of the solder. Brazing holding time is too long.

(2) Elimination measures The solution is generally to replace the solder grade. Or quickly heat up when it is close to the melting point of the solder, reduce the amount of furnace loading, reduce the weight of the tooling, reduce the brazing temperature, and shorten the holding time of vacuum brazing.

2 The brazing strength of the product is low

(1) Reason The brazing holding time is short, and the diffusion time of a certain component to the base metal is short. In the solid-liquid phase range of the solder, the heating time is too long, and some components of the solder are more volatilized. The vacuum pressure is too high or the leakage rate of the vacuum furnace is large, and the brazing filler metal or base metal is partially oxidized during heating. The oxide film is not completely removed. The brazing filler metal or base metal is corroded during alkaline cleaning and changes the filler metal composition. The amount of flux is small, and the wettability of the solder is not good.

(2) Elimination measures Extend the holding time to make the diffusion fully completed. The temperature is increased in different intervals, and the temperature is rapidly increased in the solid-liquid phase of the solder to reduce the volatilization of the low melting point components of the solder. Reduce the vacuum pressure to prevent re-oxidation of the solder or base metal during heating. Check the pressure rise rate of the device. Increase the concentration or temperature of the lye solution, or prolong the time of alkaline etching to completely remove the oxide film. Reduce the concentration or temperature of the lye solution (generally controlled at 60°C), or shorten the alkaline etching time, and separate the solder or base metal for alkaline cleaning to prevent the composition of the solder from changing during alkaline cleaning. Increase the amount of flux to improve the wettability of the solder.

3 Missing welding

Leakage welding is an unwelded gap formed by the lack of solder or the melting and loss of solder at the brazing joint of the brazing parts.

(1) Reasons: The amount of solder is not enough or the connection gap is large. The brazing heating rate is too high, which leads to the deformation of the parts, and the joint gap increases, and the capillary phenomenon cannot be formed. The amount of flux used is large, and the wettability of the solder is too good, resulting in the loss of the solder or the brazing seam being too wide. In the solid-liquidus range of the solder, the heating rate is slow, and the volatilization of the low melting point components of the solder mostly changes the composition of the solder, increases the melting point of the remaining part of the solder, and reduces the mutual diffusion between the solder and the base metal. . The furnace capacity is large or the tooling design is unreasonable. The tooling is too heavy and absorbs too much heat, resulting in a slow heating rate. If the holding time is long or the cooling rate is slow, etc., the low melting point components of the solder will volatilize more. The solder is over-corroded, changing its composition and thus its melting point.

(2) Elimination measures Increase the amount of solder, increase the clamping force of the tooling, and reduce the gap at the joint. Before brazing, increase the stress relief annealing process of the brazed components, or increase the temperature in stages and set up an isothermal stage to rapidly increase the temperature above 500 °C. Reduce the amount of flux used.