Introduction of several new and commonly used aluminum alloy brazing filler metals

【Summary Description】 In the brazing process, the welds are joined together by solidification of the molten solder. Therefore, the quality of the weld depends to a large extent on the solder. Aluminum brazing filler metal is mainly aluminum silicon alloy. Sometimes copper, zinc, germanium and other elements are added to meet the requirements of process performance. After years of practice and exploration, several series of aluminum brazing filler metals have been formed, many of which have achieved satisfactory brazing results under proper process conditions. The following mainly introduces several new, commonly used aluminum alloy brazing filler metal. 3.1 aluminum silicon solder Aluminum-silicon brazing filler metal is based on aluminum-silicon eutectic composition, and also includes sub-eutectic, over-eutectic and aluminum-silicon alloy with added elements not higher than 5%. This series of brazing filler metal has good brazing strength, base metal color, plating and corrosion resistance, and is an excellent brazing filler metal. Moreover, this series of solders can be modified, which can greatly increase the toughness and bending performance of solders and solder joints. At present, a new type of aluminum-silicon alloy solder has been developed by using rapid solidification technology. Compared with the ordinary crystalline solder, the liquid phase point of the solder is about 3-5 ℃ lower than that of the ordinary crystalline solder of the same composition, the wetting coefficient is increased by 18%, the strength is increased by 28.4, and the fluctuation is small, and it has certain processing flexibility. 3.2 copper solder The copper is welded by the contact reaction brazing principle. At present, aluminum contact reaction brazing is considered as an ideal method to solve the problem of aluminum brazing. The invention has the following advantages:(1) no flux is added, no pollution to the environment, the brazing product does not need to be cleaned, and the brazing seam has no chemical corrosion; ② selecting a suitable eutectic reaction alloy layer can reduce the brazing temperature, which not only reduces The energy consumption makes the brazing process easy to control, and the equipment requirements are low. The contact reaction of Cu on the aluminum substrate has obvious preferential spreading on the surface, which can destroy the oxide film and facilitate the formation of a uniform liquid filling layer between the joint interface during the contact reaction brazing process. On the other hand, the contact reaction preferentially penetrates the grain boundary in the depth direction of the aluminum matrix, and the bonding strength of the brazed joint can be ensured. According to the data, the suitable process parameters for aluminum contact reaction brazing with Cu as the intermediate layer material are: brazing temperature 570-580 ℃, holding time 15-20min. However, the electrochemical corrosion resistance of the copper welded joint is poor, and the eutectic reaction layer is brittle. In order to improve the performance of single copper as a solder, some other elements can be added to it. Solder metals for contact reaction brazing with aluminum alloys include silver, nickel, silicon, zinc, titanium, and the like. 3.3 a composite layer of copper and zinc as a reactive solder In order to make up for the deficiency of zinc and copper alone as solder, a composite layer of them may be used. Copper and zinc composite layers are used for contact eutectic brazing. Peritectic reaction occurs at the Cu/Zn interface, and eutectic reaction occurs at the Cu/Al interface, forming a eutectic liquid phase that destroys the oxide film on the aluminum surface. As a reactive brazing filler metal for aluminum, the copper-zinc composite layer must have a suitable copper and zinc content. Some data show that when δ(Zn)= 0.2mm and δ (Cu) < 0.1mm, the brazing effect is ideal. At this time, the reaction layer can not only destroy the oxide film, but also the joint has strong electrochemical corrosion resistance and high shear strength. 3.4 aluminum silicon copper zinc solder The liquidus temperature of the solder is in the range of 500-577°C. After adding copper to the aluminum-silicon solder, the fluidity of the solder is obviously enhanced. Due to the high content of CuAl2 intermetallic compounds, this ternary eutectic solder is very brittle and is only suitable for casting into strips, but it is difficult to process into wires or foils. The wettability and fluidity of the solder are enhanced when zinc is added to the aluminum-silicon solder. The solubility of silicon decreases rapidly with increasing zinc concentration. Since this solder does not contain compounds, its thermal workability is better than that of the aluminum-silicon-copper system. 3.5 aluminum-copper-silver-zinc solder The liquidus temperature range of the solder is 400-500 ° C., which is close to the liquidus temperature range of the aluminum alloy solder. Al-Cu-Ag ternary eutectic composition makes its color close to that of Al base metal, and it has good brazing fluidity but is fragile. Another ternary system is aluminum-copper-zinc. The color of this solder is also close to the base metal, and the workpiece can be better. The corrosion resistance of the solder can be improved by adding 0.05-0.08%(mass fraction, the same below) of Mg and 0.05% of Ni or Cr into the solder. There are many ideal aluminum solders. In general, the melting point of most existing solders for aluminum is close to that of aluminum alloys. Therefore, the search for lower melting point, better process performance of the solder is the task faced by the welding workers.

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