NEWS
After the brazing process is complete. At the appropriate temperature, the thermal insulation treatment will sometimes make the brazing joint microstructure uniformity and increase the strength of the joint; But sometimes improper handling will destroy the organization of the joint, so that the strength of the joint is greatly reduced, and even self-fracture.
When the main element of the filler metal is the same as the base material, and the other elements have little solid solubility in the base material, the brazing joint is most suitable for insulation. For example, when A1-SU2 is used to braze aluminum alloy 3A21, the melting temperature of the brazing filler metal is 577, and the brazing temperature is 600. After undergoing different holding time at the original temperature, the metallography of brazing joint is shown in FIG. -28 [w. FIG. 1-283 shows the gold phase of the brazing joints without thermal insulation treatment; FIG. 1-281), c and d show the brazing joints after thermal insulation for lmin, 3min and 7min, respectively. It can be seen that, with the extension of time, the penetration of the molten cosolder along the grain boundary deepens, the diffusion of the brazing joints widens, and the eutectic silicon tends to converge into larger grains. After holding for 7min, the eutectic silicon almost disappeared, only discontinuous silicon grains remained in the brazing microstructure, and the brazing joints actually no longer exist in the metallographic sense. This phenomenon is caused by the fact that the solid solubility of Si in WXTC in A1 is less than 1% (mass fraction), and it is impossible for all the Si in the solder to form solid solution in A1. At this time, the smaller grains were dissolved by large surface energy, while the larger grains were further deposited and grown larger by small surface energy. It is obvious that the joint with the structure of FIG. l-28d has better properties than that of FIG. l-28a.
Similar to the brazing of aluminum with Al-Si eutectic brazing filler metal, a similar phenomenon is observed with C.1-P brazing filler metal at 800 × 800, but the dispersed phase is Cu3P.
If there is an intermetallic compound generated between the base metal and the filler metal, the first principal component of this intermetallic compound is the same as the base metal, and other principal components and the base metal have a certain solid solubility, after thermal insulation treatment will reduce or even disappear this intermetallic compound.
The first main component of the filler metal and the base metal is the same, and the other components and the base metal have a great solid solubility, after heat preservation treatment, with the increase of temperature preservation time, the brazing joint will be filled with different degrees of solid solution. For example, after brazing copper with H62(Cu62Zn) brazing filler metal and holding heat in gSOT, it can be seen that the brazing joint is filled with the a phase of Cu-Zn rich copper solid solution; In addition, a similar phenomenon was observed after brazing lCrl8Ni9Tie stainless steel with Ni75CrSiB brazing material in 11201 insulated lOtnin, where the joint was filled with a terpolymer solid solution of Ni-Cr-Fe.
In the main component of brazing metal and base metal liquid and solid mutual solubility are very large, if the welding temperature and insulation temperature is high and the time is long, often make the brazing joint and base metal damaged. The phenomenon is particularly prominent when pure gold is used as filler metal and the base metal is thin. For example, with Zn brazing aluminum, in more than 500<€insulation; Brazing copper In greater than TOOT insulation; With Cu brazing nickel, more than 1300 never temperature; Ga brazed aluminum, more than 30"C insulation, etc. In this case, the temperature should be reduced as much as possible and the operation time should be shortened.
The above insulation effect, whether positive or negative, depends on the necessary solid solubility of the main component of the filler metal and the base metal. In the case that there is no solid solubility between the filler metal and the base metal, there will be no structural dispersion phenomenon even after a long time of thermal insulation treatment.以上翻译结果来自有道神经网络翻译（YNMT）· 通用场景
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