Silver is a metal with excellent electrical, thermal and plastic properties.The chemical properties of silver and copper are very similar. At room temperature, when the oxygen pressure is lower than 13.33Pa, silver will not become black and lose luster in the air.When the temperature rises to 200℃, oxidation should begin.When the temperature rises to 507℃, silver alloys containing a small amount of Al, Cu, Si, Cd, Zn, Sn and other elements will undergo oxidation not only on the surface, but also deep inside the alloy.No matter in the liquid state or in the solid state nitrogen cannot be solid solution, its nitride is decomposed at room temperature.Hydrogen has a low solubility in the silver solid solution, and the hydrogen argylated produced by the reaction between silver and hydrogen is reddish-brown and decomposes at about 412℃
Silver can also form alloy with Au, Pt, Cu, Sn and other metals, which has certain applications in the electronics industry, electrical contact materials, test equipment, high vacuum technology, manufacturing silver base filler metals, etc.The welding property of silver and its alloy is good in extreme brazing property. Due to the high thermal conductivity of silver, the heat input velocity which is easy to form high porosity defect is needed in welding, so the welding heat source with concentrated energy should be chosen as far as possible.When welding, the welding parts can be preheated to 500 ~ 600℃ before welding if necessary. Due to the large coefficient of thermal expansion of silver and its alloy, it is easy to cause large welding stress and deformation in the welding process.
Silver has excellent plasticity and can be cold-pressed at room temperature.The area of annealed silver bar can be 150 ~ 200% of the original area by pressurized top forging. The silver plate can be connected by cold pressure welding after being cleaned on the surface. Good joint strength can be obtained when the deformation reaches 65 ~ 80%.If necessary, low temperature heating can also be used to strengthen the diffusion connection.
The brazing property of silver and its alloys is very good. Silver base filler metal is mainly used in brazing.FIG. 3 shows the solder used in vacuum brazing, which is commonly used in electronic products.Good brazing quality can also be obtained by using hydrogen or argon shielding
Contact reaction brazing USES ag-Cu eutectic reaction principle to realize the connection between silver and its alloy or between silver and its alloy and copper.For example, the surface of the welding piece of pure silver or silver alloy is coated with 2 ~ 8 m thick pure copper. Under the protection of vacuum or hydrogen or brazing agent, the welding piece is in pressurized contact. When the heating temperature reaches above 779℃ (that is, ag-Cu eutectic point), due to the migration and diffusion of silver and copper atoms, eutectic reaction occurs and eutectic liquid phase is generated to realize the connection.The silver and its alloys can also be connected with copper by contact reaction brazing. The silver side can be brazed without copper plating.
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