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Selection of Filler Metals

  • The choice of solder is as follows:
  1. Try to select the brazing material with the same main component and the main component of the parent metal.
  2. The liquidus of the brazing filler metal should be at least 20 ~ 301 lower than the solidus of the parent metal.
  3. The melting interval of the solder, that is, the temperature difference between the solidus line and the liquidus composed of the solder is as small as possible, otherwise it will cause technical difficulties. If the temperature difference is too large, it may cause dissolution or erosion.
  4. An important component of the solder should be able to interact with the parent material in a liquid miscible, solid solution or solid-liquid hetero-compound, thus enabling a strong bond. In general, it is not necessary to select a solder that forms a solid-liquid aliquot compound from an important component of the solder.
  5. The main component of the brazing filler metal and the main component of the parent metal in the elemental period should be at the top of the cliff: close to this, the etched corrosion caused by such brazing filler metal is small, that is, the joint has good corrosion resistance.
  6. At the brazing temperature, the main component of the solder should have high chemical and thermal stability, ie, low vapor pressure and low oxidizability to avoid changes in solder composition during brazing.
  7. The brazing material preferably has good forming processability so as to be able to form profiles such as wires, rods, sheets, foils, and powders.
  • Only a few of the above can be fully represented on a solder. For example, when Al-Si eutectic solder is used to braze the aluminum base material, almost all of the above principles are available. In most cases, this cannot be done comprehensively. This is because the melting point, performance, position on the periodic table, and phase relation with other elements are fixed and cannot be changed. Only the possible combinations are selected. In recent years, many literatures have studied the modification of solder properties by micro-enhanced elements, which is also an important measure to improve the properties of solder.
  • A brazing material containing a certain metal as a main component is referred to as a “some” base brazing filler metal. The pure metal has the highest melting point, so the upper limit of the melting temperature of the “certain” brazing filler metal is the melting point of the pure metal, and the lower limit is the temperature of the binary or multi-alloy eutectic. Any one of the base solders has only a small range of melting temperatures available. Different bases of brazing filler metal were produced to accommodate the needs of different parent metal brazing and different melting temperature zones.
  • There are not too many brazing materials that can be used as commodities. The number of Brazing furnace materials varies from country to country. The method of brazing grades in China, such as BAg25CuZn, the first U-B, the other materials. That is, its composition is actually the indium number and specification of 25As41Cu-34Zn„ commercial solder.
  • In some cases, there are special requirements for the melting temperature and composition of the solder, and existing products or common solders do not meet the requirements. Appendix D of this book: “The composition and melting point or solidus line of the practical solder. -liquidus” can provide reference

Matching of Filler Metal with Flux

  • In the brazing, the brazing material is preferably melted at 2 to 3» after the flux is melted, and it is most likely to catch up with the active orgasm of the flux. This time interval of course depends mainly on the melting temperature of the flux and the solder itself, and can also be adjusted by heating the enthalpy. Rapid heating will shorten the time interval between the flux and the melting temperature of the solder, and slow heating will delay the time interval between the two.
  • For workpieces with a slow heating rate, the melting temperature of the flux should be chosen to be close to the temperature of the liquidus of the solder. The slower the temperature rise, the temperature at which the flux melting temperature is close to the liquidus of the solder should be selected. Sometimes even slightly beyond the liquidus of the solder. Premature melting of the flux will cause the solder to melt without catching the active orgasm of the flux. For the brazing material with a large melting temperature interval, that is, the temperature of the smell phase and the liquidus of the brazing material are far apart, the brazing needs to be heated rapidly, otherwise the low-melting portion which starts to melt flows away with the brazing seam to cause dissolution. Leave a non-melting solder tumor. At this point, the melting temperature at which the flux begins should be chosen to be higher, staying close to or slightly above the phase of the solder to delay the arrival of the flux activity ore, thereby avoiding premature melting of the low melting portion of the solder. flow away.
  • At the brazing temperature, the mutual solubility of the solder and the base material is large, and it is most difficult to stop the solder after it has been melted for a long time. This will cause severe corrosion. The time during which the flux melts should be controlled. The active orgasm of the flux should just arrive when the solder melts, allowing the solder to flow away as soon as it melts.
  • For the control of the melting temperature range of the flux and the ruthenium, the heating process needs to be modulated according to the specific conditions during the brazing in the furnace. Sometimes, when the temperature is to be raised quickly, the furnace is burned to a high temperature; even if the melting point of the base material is much higher than that of the base material, the workpiece is sent to the extreme method of immediately releasing the Ff in the brazing process. Sometimes the mass or volume of the workpiece is large, heat transfer takes time, and extreme methods cannot be used. The flow of the furnace atmosphere is often accelerated to accelerate the temperature rise of the workpiece. As for flame brazing, it only depends on the skill of the operator. However, the basic principle is that the T. piece can only be heated by the flame, and the heat is transferred to the brazing material and the flux to melt it. The flame cannot be directly aligned with the brazing material and the flux to heat it.