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The method to select the brazing material

Author:admin     Date :2012/9/26 1:50:59     Popularity:
Select the brazing material must be understood before evaluating solder three basic characteristics: the physical properties, the melting process and the form of which may be used.
Physical properties and the melting process
   Physical performance based solder metallurgy. (Brazing solder certain alloy is from two or more "pure" made of a metal.) Of these components to determine whether being connected to the metal compatibility - to wet the base material of this brazing material flowing through the connector area, and does not generate detrimental metallurgical component. In addition, due to the production needs may require special performance.
For example, if the vacuum brazing, it is required to solder without any volatile elements such as cadmium or zinc. Such as some of the electronic components, it requires a very high purity of the brazing material. Corrosion resistant joints need to solder both corrosion resistant and harmonious co-existence, but also is linked to the base metal.
    The melting process is based on the metallurgical composition. Since most of the brazing material is an alloy, they are generally unlike the pure metal to melting, with a temperature from solid to liquid. However, there is one very important exception. An alloy, referred to as co-crystal, they are also as pure metal as melting. Silver-copper alloy, 72% silver, 28% copper. This brazing in a single temperature of 780 C was completely melted. With metallurgical terms is that its melting point (solid phase point), and the flow state point (liquidus point) is the same.
     Note that at 72% silver, 28% copper component, the liquidus temperature and the solidus temperature is the same, and this left or right side of the eutectic composition of the alloy is not directly from solid to liquid, but after a "pasty" range - here alloy is a solid phase and a liquid phase coexist. This range is the difference between the temperature of the "solid phase point temperature and the liquidus point. "Solid Phase point" the temperature is the highest temperature of the alloy is completely cured, i.e. when the alloy is heated from that point begins to melt. "Liquidus temperature alloy is liquid temperature (i.e., when the alloy is cooled, and from that point on curing).
In brazing applications, brazing solder "Liquidus temperature" is a very important temperature. Brazing, you never want to - or do not need to melt the base metal, you should choose a solder liquidus point temperature than the solid-phase point temperature of the two base metal.
Some brazing, must particularly consider the factors of the liquid phase point. For example, when the sub-step brazing of a component, i.e., in the vicinity of the previously brazed joints brazing. The second brazing operation can not disturb the first connector. Preventing method is to use another solder. The low temperature of the liquid phase point temperature of the solder so that the second connector than the first joint use of the liquidus point of the brazing material. This approach ensures that the first connector when the second brazing is not melted.
Brazed assembly must also be subjected to a heat treatment, but also consider the temperature of the liquid phase point. At this time there are two options:
First, the first heat treatment, and then brazing. In this case, we should choose the liquid phase point temperature of the brazing material is lower than the heat treatment temperature. This method does not affect the hardness properties.
Second, the heat treatment and brazing at the same time. In this case, the liquid phase point temperature of the solder and heat treatment temperature should be considerable.