How to braze common precious metals

Precious metals mainly refer to gold, silver, palladium, platinum, rhodium, iridium and other materials. They have good conductivity, thermal conductivity, corrosion resistance and high temperature stability. In industry, they are mostly used as functional materials and precious metals as contact materials. Their common characteristics are small brazing area, good impact resistance, high strength, oxidation resistance and arc resistance, But it does not change the characteristics of contact materials and electrical properties of components. Due to the limitation of the brazed area of the contact and the non overflow of the solder, the welding parameters should be strictly controlled.

Most heating methods can be used to solder precious metal contacts. Flame brazing is often used for larger contact components, induction brazing is suitable for mass production, and resistance brazing can also be carried out with ordinary resistance welding machine. However, carbon block should be used as electrode to select smaller current and longer brazing time. When a large number of contact components need to be brazed at the same time or multiple contacts need to be brazed on one component, furnace brazing can be used, In order to obtain high quality brazed joints and ensure that the performance of the material itself will not be affected, it is best to use vacuum brazing.

Brazing gold and its alloy contacts mainly use silver base and copper base solder, which not only ensures the conductivity of the solder joint, but also is easy to wet. If the requirements of joint conductivity can be met, the brazing filler metal containing Ni, PD, Pt and other elements can also be used, and the brazing filler metal with good oxidation resistance can also be used. If Ag Cu Ti solder is selected, the brazing temperature shall not be higher than 1000 ℃.

The silver oxide formed on the surface of silver is not very stable, so it is easy to braze. Tin lead solder, zinc chloride solution or rosin can be used as brazing agent for silver soldering. In brazing, silver solder is often used, and borax, boric acid or their mixture are used as flux. When brazing silver and its alloy contacts in vacuum, the silver base solder bag61culn, bag59cusn and bag72cu are mainly used.

For brazing palladium contacts, gold-based and nickel-based solders, which are easy to form solid solution, or silver-based, copper-based or manganese based solders can be used.

For brazing platinum and its alloy contacts, silver base, copper base, gold base or palladium base solders are widely used. Using bau70pt needle material, not only does not change the color of platinum, but also can effectively improve the temperature of brazing seam remelting and increase the strength and hardness of brazing seam. If platinum contact is to be directly brazed on kovar alloy, B49 ticube solder can be selected. In noncorrosive medium, the copper solder with low cost and good process performance should be selected preferentially for platinum contact with working temperature not exceeding 400 ℃.

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