Brazing is industrially defined as the use of a solder having a lower melting temperature than the base material, and the operating temperature is a soldering technique that is lower than the solid phase of the base material and higher than the liquidus of the solder. Brazing is (the longest history, the base metal is not melted, the temperature is low, the deformation is small, and the dissimilar materials are combined and detachable.) Brazing is a solid phase connection. Unlike the fusion welding method, the base metal is not brazed. For melting, a solder having a lower melting temperature than the base material is used, and the heating temperature is a connection method lower than the solid phase line of the base material and higher than the liquidus of the solder. When the connected parts and solder are heated to melt the solder, the liquid solder is wetted on the surface of the base material, spread and spread with the base metal, and wetted in the gap between the base materials, capillary flow, caulking and base metal. Inter-dissolution and diffusion to achieve the connection between parts. The difference between the two is mostly based on temperature as a criterion for differentiation. Brazing for which the liquidus temperature of the solder is higher than 450 °C is brazed, and brazing for soldering below 450 °C is soldering. Due to its high strength, brazing can be used to braze stressed components for a wide range of applications. It includes aluminum-based materials, silver-based materials, copper-based materials, manganese-based brazing filler metals, nickel-based brazing filler metals, gold-based brazing filler metals, and palladium-based brazing filler metals. The joint strength is high, and some can work at high temperatures. The aluminum-based solder is based on an aluminum-silicon alloy, and elements such as copper, zinc, and antimony may be added to meet the requirements of process performance for brazing aluminum and aluminum alloys. Silver-based solders are mainly based on silver-copper and silver-copper-zinc alloys. They can also be added with cadmium, tin, manganese, nickel, lithium and other elements to meet different brazing requirements. It is the most widely used brazing filler metal. Copper-based solders have found wide application in the brazing of steel, alloy steel, copper and copper alloys. Manganese-based solders meet the needs of different processes. Manganese-based brazing filler metal has good ductility, good wetting ability to stainless steel and heat-resistant steel, high temperature and high temperature strength of brazing joint, moderate oxidation resistance and corrosion resistance, no obvious corrosion to base metal effect. Nickel-based brazing filler metal is often added with elements such as chromium, silicon, boron, iron, phosphorus and carbon. It has excellent corrosion resistance and heat resistance and is commonly used for brazing austenitic stainless steel, duplex stainless steel and martensitic stainless steel. Elements such as copper and nickel are often added to the gold-based solder. The gold-based brazing filler metal has a small degree of action with the base metal, and is often used for brazing of thin parts. Palladium-based solder has the characteristics of strong wetting ability, low vapor pressure, good ductility, high strength, and low tendency to dissolve metal base metal. It is suitable for brazing of stainless steel, nickel-based alloys, etc., mainly used in aviation and aerospace, electronics. Industry and other departments. The brazing flux is usually composed of a chloride and a fluoride of an alkali metal and a heavy metal, or a borax, a boric acid, a fluoroborate or the like, and can be formed into a powder, a paste or a liquid. Lithium, boron and phosphorus are also added to some solders to enhance their ability to remove oxide film and wet. After soldering, the flux residue is cleaned with warm water, citric acid or oxalic acid. Commonly used are tin-based solders, lead-based solders, cadmium-based, zinc-based and gold-based solders, and low-melting solders such as gallium-based, germanium-based and germanium-based solders. The most widely used is tin-lead solder. When the tin-lead alloy WSn is 61.9%, a eutectic having a melting point of 183 ° C is formed, which has the highest strength and hardness. Used in the welding of conductive, airtight and watertight devices in the electronics and food industries. Soldering with tin-lead alloy as the brazing material is most commonly used. Solder generally requires a flux to remove the oxide film and improve the wetting properties of the solder. There are many kinds of fluxes, and the electronics industry mostly uses rosin alcohol solution for soldering. The flux after soldering has no corrosive effect on the workpiece and is called a non-corrosive flux. The flux used for welding copper, iron and other materials is composed of zinc chloride, ammonium chloride and petrolatum. Fluoride and fluoroborate are used as fluxes for the welding of aluminum, and hydrochloric acid plus zinc chloride is used as the flux. The residue after soldering of these fluxes has a corrosive effect, called a corrosive flux, which must be cleaned after soldering. The contact surface of the base metal should be very clean, so use a flux. The function of the flux is to remove oxides and oil impurities on the surface of the base metal and the solder, to protect the contact surface of the solder and the base material from oxidation, and to increase the wettability and capillary fluidity of the solder. The melting point of the flux should be lower than that of the solder, and the flux residue should be less corrosive to the base metal and the joint. The flux commonly used for soldering is a rosin or zinc chloride solution, and the usual flux for brazing is a mixture of borax, boric acid and basic fluoride. Most of the flux residue corrodes the brazed joint and also hinders the inspection of the braze joint, which often needs to be cleaned. The rosin-containing active flux residue can be removed with an organic solvent such as isopropyl alcohol, alcohol or trichloroethylene. A flux composed of an organic acid and a salt is generally soluble in water and can be washed with hot water. A solder composed of a mineral acid is dissolved in water and thus can be washed with hot water. A flux containing an alkali metal and an alkaline earth metal chloride (for example, zinc chloride) may be washed with a 2% hydrochloric acid solution. The borax and boric acid flux residues for brazing are substantially insoluble in water and difficult to remove, and are generally removed by sand blasting. A better method is to put the brazed workpiece into the water in a hot state, so that the flux residue is cracked and easily removed. The residue of the borofluoride potassium or potassium fluoride hardener (e.g., agent 102) can be boiled or removed in 10% citric acid hot water. The aluminum residue can be removed with an organic solvent such as methanol. The aluminum hard residue is highly corrosive to aluminum and must be removed after brazing. The cleaning methods listed below can give better results. (1) Soak in hot water at 60-80 °C for 10 min, carefully clean the residue on the brazing joint with a brush, rinse with HNO3 15% aqueous solution in cold water for about 30 minutes, then rinse with cold water. (2) 60-80 ° C flowing hot water rinse 5 -10min placed in 65 ~ 75 ° C, CrO32%, H3RO45% aqueous solution soaked for 15min, and then rinsed with cold water.
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What is the difference between brazing and soldering?
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