Brazing is a method that uses a filler metal with a melting point lower than that of the workpieces, heating both the workpieces and the filler metal to a temperature above the melting point of the filler but below that of the workpieces, allowing the liquid filler to wet the base material, fill the joint gap, and diffuse into the base material to achieve a connection.Brazing technology. According to the melting point of the filler metal, it can be divided into: soft brazing, where the melting point is below 450°C; hard brazing, where the melting point is above 450°C. Based on brazing temperature, it can be categorized into: high-temperature brazing; medium-temperature brazing; low-temperature brazing. The classification temperatures vary for different materials in brazing. Based on heating methods, it includes: flame brazing; furnace brazing; induction brazing; resistance brazing; soldering iron brazing, etc. To achieve good welding results, the brazing technology must be proficient.

Brazing technology has a wide adaptability and can weld most metals and some non-metals; it has good accessibility for welding seams that are hard to reach; it offers high precision for high-precision, complex components with multiple seams, allowing for efficient one-time welding; the heating temperature for brazing is much lower than that of fusion welding, which has less impact on the microstructure and properties of the base material; deformation of the workpieces is minimal, especially when using uniform heating in brazing, which can reduce welding deformation to a minimum and ensure dimensional accuracy. However, brazing technology also has its drawbacks, mainly: lower strength; poorer heat resistance; due to most being overlapping joints, it increases material consumption and makes joints heavier.

Filler metal is the metal used to form the brazed joint during brazing. It is classified by melting point into soft filler (below 450°C), hard filler (above 450°C), and high-temperature filler (above 950°C); by chemical composition (metal elements) into nickel-based fillers, tin-based fillers, silver-based fillers, etc. Flux, also known as soldering aid, serves to remove oxides from the surfaces of the base material and liquid filler during heating to prevent further oxidation and improve wetting performance of the filler on the base material surface. Similarly, fluxes can be categorized into soft fluxes and hard fluxes based on their use; they can also be divided into: aluminum fluxes, powder fluxes, liquid fluxes, gas fluxes, paste fluxes, and no-clean fluxes.

　　Brazing technologyMost often, soldering is performed with a combination of filler metal and flux, but there are cases where soldering can be done directly without flux. The strength of the joint before soldering is lower than that of the base material. To increase strength, lap joints are commonly used; generally, the length of lap joints should be 3 to 4 times the thickness of the plate but not exceed 15mm. Pipes are mostly joined using socket connections for brazing. Before brazing, mechanical or chemical methods are used to clean oxidation films and dirt from the surface of workpieces. To prevent liquid filler from flowing freely, flow inhibitors are often applied to the surface of workpieces. If there is too much or too little assembly gap, it will affect capillary action and reduce joint strength; excessive joint size will waste filler.

The main process parameters for brazing technology are brazing temperature and holding time. The brazing temperature is generally set at 25-60°C above the melting point of the filler metal; temperatures that are too high or too low are not conducive to ensuring joint quality. The holding time should allow sufficient interaction between the workpiece metal and filler metal; shorter times for interactions between filler and base metal; longer times for larger gaps or larger workpiece sizes. After welding, most residues from flux have a corrosive effect on brazed joints and hinder observation of joints; therefore, they must be cleaned thoroughly.