A welding method in which a metal material with a lower melting point than the base material is used as the solder, and the liquid solder is used to wet the base material and fill the gap between the workpiece interface and make it diffuse with the base material. The brazing deformation is small, and the joints are smooth and beautiful. It is suitable for welding precise, complex components and components composed of different materials, such as honeycomb structure plates, turbine blades, cemented carbide tools and printed circuit boards. Before brazing, the workpiece must be carefully processed and strictly cleaned to remove oil stains and excessively thick oxide film to ensure the interface assembly gap. The gap is generally required to be between 0.01 and 0.1 mm.
Types According to the different welding temperature, brazing can be divided into two categories. Welding heating temperature lower than 450 ℃ is called soft soldering, higher than 450 ℃ called brazing.
Soft soldering is mostly used for welding conductive, airtight and watertight devices in the electronics and food industries. Tin-lead alloy is the most commonly used solder. The solder generally needs to use a flux to remove the oxide film and improve the wetting performance of the solder. There are many types of flux, and rosin alcohol solution is used for soft soldering in the electronics industry. The residue after soldering of this kind of flux has no corrosive effect on the workpiece and is called non-corrosive flux. The flux used when welding copper, iron and other materials is composed of zinc chloride, ammonium chloride and petroleum jelly. When welding aluminum, it is necessary to use fluoride and fluoroborate as the flux, and also use hydrochloric acid and zinc chloride as the flux. The residue after welding of these fluxes has a corrosive effect, which is called corrosive flux, which must be cleaned after welding.
The brazing joints have high strength, and some can work at high temperatures. There are many types of brazing filler metals, with aluminum, silver, copper, manganese and nickel based filler metals being the most widely used. Aluminum-based brazing filler metals are often used for brazing aluminum products. Silver-based and copper-based solders are often used for brazing copper and iron parts. Manganese-based and nickel-based solders are mostly used to weld parts such as stainless steel, heat-resistant steel, and high-temperature alloys that work at high temperatures. For welding refractory metals such as beryllium, titanium and zirconium, as well as materials such as graphite and ceramics, brazing materials such as palladium-based, zirconium-based and titanium-based are commonly used. The characteristics of the base material and the requirements for joint performance should be considered when selecting the brazing filler metal. Brazing flux is usually composed of alkali metal and heavy metal chlorides and fluorides, or borax, boric acid, fluoroborate, etc., and can be made into powder, paste and liquid. In some solders, lithium, boron, and phosphorus are also added to enhance their ability to remove oxide films and wetting. After welding, the flux residue should be cleaned with warm water, citric acid or oxalic acid.