How to deal with the surface before brazing
Care must be taken to remove oxides, grease, dirt, paint, etc. from the surface of the workpiece prior to brazing, as the molten solder does not wet the surface of the uncleaned part and does not fill the joint gap. Sometimes, in order to improve the brazing property of the base metal and improve the corrosion resistance of the brazed joint, the part must be pre-plated with a certain metal layer before brazing.
(1) Removal of oily oil can be removed with organic solvent
Commonly used organic solvents are alcohol, carbon tetrachloride, gasoline, trichlorin, dichloroethane and trichloroethane. In small batches, the zero is immersed in an organic solvent and cleaned. The most widely used in mass production is degreasing in the vapor of organic solvents. In addition, satisfactory results can be obtained by washing in a hot alkaline solution. For example, steel parts can be immersed in a 10% caustic soda solution at 70-80 ° C for degreasing. Copper and copper alloy parts can be cleaned in 50 g of trisodium phosphate, 50 g of sodium bicarbonate plus 1 L of water, and the solution temperature is 60-80 °. C. The degreasing of the parts can also be carefully washed with water after degreasing in the detergent. When the surface of the part is completely wetted by water, it indicates that the surface grease has been removed. For small parts with complex shapes and large numbers, ultrasonic cleaning can also be used in special grooves. Ultrasonic degreasing efficiency is high.
(2) Scavenging oxides
Prior to brazing, the oxides on the surface of the part can be processed by mechanical methods, chemical etching methods, and electrochemical etching methods. When the mechanical method is cleaned, the knives, metal brushes, sandpaper, grinding wheels, sand blasting, etc. can be used to remove the zero: oxide film on the surface. Among them, boring and sandpaper cleaning is used for single-piece production, and the grooves formed during cleaning are also beneficial for the wetting and spreading of the solder. Grinding wheels, metal brushes, sandblasting, etc. are used in mass production. The surface of aluminum and aluminum alloys and titanium alloys should not be mechanically cleaned.
(3) Metal plating on the surface of the base metal
The main purpose of plating metal on the surface of the base metal is to improve the brazing property of some materials, increase the wetting ability of the brazing filler metal to the base metal, and prevent the interaction between the base metal and the brazing filler metal on the joint quality, such as preventing the occurrence of defects. Cracks, reducing the interface to produce brittle intermetallic compounds; as a solder layer to simplify the assembly process and increase productivity.