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The actual formulation of the flux

Table 2_7 lists the formulations and applications of aluminum brazes that have been published or become commercial.

Serial number Flux code Flux composition (mass fraction, %) Melting temperature / especially Special application
1 QJ201 UCl(32),KCl(50),NaF(10), ZnCl2 (8) ^=460
2 QJ202 UC1(42) ,KC1(28) ,NaF(6) ,ZnCl2(24) «440 —.
3 211 LiCl(14) ,KC1(47) ,NaCl(27),AlF3(5),CdCl2(4),ZnCl2(3) =550
4 YJ17 UC1(41),KC1(51),KF(3.7),A1F3(4.3) -370 s collapse brazing
5 H701 UC1( 12) ,KC1(46) ,NaCl(26) ,KF-A1F3 共晶(10) ,ZnCl2(l. 3) ,Cd(:l2(4.7) «500
6 0>3 NaCl (38),KCl(47)fNaF(10), SnCl2 (5)
7 4>5 LiCI(38) ,KC1(45) ,NaF(10) ,CdCl2(4) tSnCl2(3) *390
8 0124 LiCl(23),NaCl(22),KC1(41) ,NaF(6) ,ZnCl2 (8)
9 中B3X UC1(36),KC1(40) ,NaF(8) ,ZnCl2(16) «380
10 UC1(33-50) ,KC1(40-50) ,KF(9-13) ,ZnF2(3) ,CdCl2( 1-6) tPbCl2(l-2)
11 ZnCl2 (2040 ) , CuCl (60-80) «=300 Reaction flux
12 UC1(3040) ,NaCl(8-12) ,KF(4-6),AIF3(4*6),Si02(0. 5-5) #560 Epitaxy generates Al-Si layer
13 129A LiCl(11.8),IMaCl(33.0) ,KC1(49.5) ,LiF( 1.9) ,ZnQ2( 1.6) ,CdU2(2.2) 550
14 1291A UC1( 18.6) ,NaCl(24.8) ,KC1(45.1) ,UF(4.4) ,ZnQ2(3.0) ,CdCl2(4.1) 560
15 1291X UCl(11.2),NaCl(31.1),KCl(46.2)>LiF(4.4),ZnCI2(3.0),Cda2(4.I) **570
16 171B LiCl(24.2),NaCl(22.1) ,KC1(48.7) ,UF(2.0),110(3.0) 490 For 2A12 with Mg separation,
17 1712B UC](23.2),NaCl(21.3),KCl(46.9),yF(2.8),Tia(2-2).ZnrJ2(1.6),Cda2(2.0) 485 5A02
18 5522 M CaCI2(33.1),NaCl(16.0),KCl(39.4),UF(4.4),Zna2(3.0)tCdCl2(4.1) «570 Less moisture absorption
19 5572P SrCl2 (28.3),UC1 (60. 2),LiF(4.4) ,ZnCl2 (3.0) ,Cd02 (4.1) 524
20 1310P UC](41.0),KCl(50.0),ZnC]2(3.0),Cda2(1.5),IiF(l.4).\al”(0.4),KF(2.7) 350 Medium temperature aluminum flux
21 1320P LiCl(50) ,KC1(40) ,LiF(4) ,Si»C12(3) ,Zna2(3) 360 Suitable for Zn-Al solder
  • The practical effect of the flux %• The inclusion of M in the component (Fe, etc.) has a great relationship with the preparation of the art. If the components, especially uci, ZnCl2, Sn (l12, etc.) are dehydrated or hydrolyzed, the activity of the flux will be greatly reduced. The flux should be prepared by smelting method, then ball milled and crushed under closed conditions. It is not advisable to mix the salt directly at room temperature without melting.
  • In Tables 2-7, 17IB and 1712B agents numbered 17 and 18 have particular activity on aluminum alloys containing higher amounts of Mg, with the use of surfactant T1+ (铊). Its special mechanism of activity has not been studied intensively. It seems that it has a proper mutual solubility with magnesium in the solid phase, and there is a large difference in molten salt potential between it and magnesium, which is easy to be reduced and alloyed by magnesium. the reason. All other surfactant ions, except for Zn slightly stronger, have this condition. This may be the reason why it has a strong activity in removing magnesium oxide film. Unfortunately, metal T1, including all barium salts, is a regulated Class B poison, which limits its use, so special care should be taken when it is used under special conditions. In addition, Cd2* ions are also ruthenium, and its special advantage is that it is easy to dehydrate, not easy to absorb moisture and not easily hydrolyzed, and is much more stable than Zn2* and Sn2+. This is the main reason why it is difficult to be completely replaced.
  • In the aluminum base material, as the content increases, the brazing property of the vaporized solder becomes worse and worse. When the content of Mg exceeds 〖% (quality fraction, the same below), the brazing process becomes very difficult and is considered to be unbrazable. Interestingly, for magnesium alloys with a magnesium content of more than 95%, such as AZ31B, ordinary aluminum chloride fluxes are quite active, and the brazing process is not too difficult. The report of Wa- tanabe;, J6] is a lot of thinking. The composition of the composition is 59.7% Caa, -18.5% LiCl-21. 8% Nad (molar fraction) of flux and composition is 34. 5% Mg -64. 5% In-O. 8% Al-O. 2% Zn (mass fraction) solder, successfully brazed AZ31B magnesium alloy below 480. Although the report’s expression was tweaked and not to be blunt, it was still seen that he minimized or avoided the use of Zn2+ and metal Zn, whether in flux or in solder. However, Zn-Al and Zn_Mg have very different phase relationships. The former is easily miscible and has a large area of ​​solid solution, while the latter produces a high melting point compound MgZn2. This seriously affects the activity, wetting and panning of the Zn2*-containing flux or the Zn-containing solder in the high Mg base material t. In order to follow the relationship of Zn-A丨, 丨n-
  • Mg or Cd-Mg is the only choice, and a large-area solid solution rfo is also formed between them. This is probably why Watanabe chose In-Mg alloy as the base for the solder. The phase diagram of the molten salt of the LiCl-CaCl-NaCI matrix used is shown in Figure 2-9.
  • Why does the conventional vaporized aluminum flux have a relatively high activity on the A丨-Mb gold alloy containing more than Mgl% (mass fraction) but on the high-Mg alloy such as brazing A73II? It can be seen from the binary phase diagram of Ms-Zn that when the amount of Mg exceeds 50% (mass fraction), or the amount of Zn is very low, the phase region of the compound Mt5Zn2 has been left. That is to say, the vaporized flux of aluminum in the nail welding no longer has the interference of the MgZn2 compound formed on the AZ31B. In the salt bath flux used for dip Vacuum brazing furnace, A1F is often used, which doubles as a remover and an active agent (see
  • No. 4 in Table 2-7), without using a heavy sulfonium salt. It is understandable that A1F3 is soluble in LiCl-KCI eutectic molten salt to precipitate F- or form A1F, which acts as a membrane, but its activity is indirect. When the salt bath tip of the unbroken solder is made of refractory material, the refractory material 屮SiO 2 is the main component, and it has a certain solubility in the fluorine-containing molten salt, and forms a SiFf ion after entering the molten salt. When brazing, it is reduced on the AI ​​surface to precipitate element Si, [a] alloyed with A1, and this mass transfer process acts as a T activation. The rate of dissolution of Si in the refractory material is roughly the same as the rate at which it is deposited on the aluminum surface, while maintaining the balance of the SiF concentration in the salt bath, without the need to add additional active agents at all times. The commonly used heavy metal salt active agent, if used here, has many disadvantages, not only the above-mentioned advantages, but also the heavy metal bismuth deposition cannot be completely and aluminum alloyed, suspended in the molten salt and soiled the entire salt bath and welding. Parts make the weldment difficult to wash. Figure 2-10 shows LiCI-KCl-AlF, phase diagram U11. Figure 2-10a shows the isotherm diagram of this system, and Figure 2-10b shows the center projection of the system on the multi-temperature side of LiCl-KC1. The numerical value in the bracket below the data point number is A1F; the molar fraction of the graph, the abscissa of the graph is KC1: LiCl, so that it is easy to draw different serial points on the binary eutectic line in the ternary system from the graph. The composition of the liquidus and the temperature of the melting.

2.5.1.2 Fluoroaluminate flux (Mocolok flux)

  • The moisture absorption of the vaporized flux not only makes it difficult to store and use, especially the post-weld cleaning is very laborious and polluted by waste water. The 1% 3-year Dutch patent first proposed the use of
  • A1F3-KF eutectic as a flux. KF-A1F, the phase diagram is shown in the figure, and its details are shown in Figure 2-12.
  • This flux was rapidly developed in the 1970s. 21: Later, Alcan of Canada applied it and named it No > colok, meaning non-corrosive-look. The solubility of the agent in water is very small, and the water suspension is sprayed on the workpiece during use. After drying, a very thin film is formed, and then the furnace is brazed. Of course, it is also like ordinary flux. use.
  • The most widely used fluoroaluminate flux is the potassium salt system. Because its melting temperature is 558T, it is high and can only be applied to pure aluminum and a few aluminum alloys, such as 3003. In recent years, strontium salt and strontium salt fluxes having a lower melting temperature have also been developed.
  • Preparation and testing of potassium cyanurate flux; this application of KF-A1F, two intermediate compounds K3A1F4 and KA1F, fa] E, molten salt of point eutectic composition (see Figure 2-11 and Figure 2-12 >, * ( A1F,) = 44. 5% or “; (A1F)) = 53.7%, melting temperature is 558T; the composition of the flux must be very accurate to get the lowest point of 558 * 1: It is the key to the preparation of flux. If the KF is too high, the melting temperature will rise rapidly and cannot be used. There are three components with zero degree of freedom in this system, namely Ez KA1F4 and £, and the melting temperatures are 5581 and 5751 respectively. : and 572<C. and their melting intervals are zero. That is to say, when heating, a small amount of flux is melted at the beginning and end of the melt, without any dragging. If the composition of the flux is inaccurate, it is not in the three. Point, but between them, especially between -kmf4, at this time because the melting interval is about 101, it will be a little dragy when melting. The composition of the composition if the A1F3 content is high, the surface exceeds the & point composition h(AlF3) = 5丨% or “;(乂&)= 60» ;, then the melting temperature will rise rapidly and cannot be used
  • (1) Preparation of potassium cyanoaluminate flux A preparation method of potassium fluoroaluminate flux, comprehensive literature reports about the following various types: using A1F3 and 1^ of water to grind into a paste, and then in ft at 200^ Dry lh; 2i:, or add A1F3 and KF to 50T water, stir well to complete the reaction, and evaporate the product to 1000 and heat at 100 ~ 5501 temperature].
  • The mixture was heated and melted with a quantitative amount of A1F3 and 1^’, and the cooled material was ground to a 50-200 mesh.
  • Synthesize 1^, ^6% and KA1F/51], and then mix them in proportion to the composition of £2 in Figure 2-1.
  • The dry powder of anhydrous A1F and KF was mixed and ground in proportion, and calcined at SOOt for 1 h.
  • 5> The quantitative Al(OH>3 is dissolved in HF, and then the temperature is maintained at 30~丨00, and the amorphous A1(0H)3 is added to HF and KF by setting the known concentration of KOH solution. Or a mixture of
  • KOH, K2CO, or the like, a temperature of 50 to 60, and a pH of 5 to 10. Thus, a flux having a fine particle size, a large specific surface, and being easily suspended in water can be obtained.
  • A*(0H), or pure aluminum metal shavings, are dissolved in a fixed amount of K0H solution to form a mixture of KA102 and K0H, and an excess of H1•’ is converted to a potassium fluoroaluminate flux.
  • The quantitative Al(OH)3 was dissolved in a slight excess of HF to obtain a sputum solution, which was treated with a quantitative solution, and the final reaction solution was pH < 4 [381.
  • Among the above methods, the four methods of 5) to 8) are more convenient for silver production. For accurate weighing, the Ai(on)3 should be absolutely dry, otherwise it should be dried at 100~110T beforehand. In addition to KOH drying, it is also necessary to seal the product that does not absorb co2, otherwise it is not easy to be accurate. At this point, the advantage of using K2C03 instead of KOH is that K2CO is stable and not very moisture-absorbing, and the price is also cheaper.
  • The above can only be regarded as a rough description of the preparation. Strictly speaking, it should be combined with chemical analysis to accurately control the amount of AP and K’ to obtain a flux of accurately composed of £2, K3A1F4 or t’3 points.
  • During the synthesis reaction, the appropriate temperature should be maintained and the mixture should be stirred for a long time to complete the reaction. The product of the reaction is a Q-colored paste. In order to prevent hydrolysis, a slightly more HF is allowed in the clarified liquid. It is best not to take the method of filtering to obtain the precipitate, but rather to steam the soup. In order to prevent the corrosion of the acid solution in the evaporation vessel (such as the non-pound steel vessel), it is advisable to add a small amount of NH4OH to the emulsion and adjust the emulsion to pH=6.
  • In order to prevent local hydrolysis during evaporation, the final stage of evaporation should be vacuum evaporation below 80 ,, which is important for obtaining high quality, melting temperature accurate products.
  • If the above product is subjected to XR1) analysis, it can be seen that the product is mainly composed of a mountain K2A1F5 (sj(, 2KF • A1F,) phase and a relatively small amount of KA1F4 phase. This can be seen from the phase diagram of Figures 2-11. It is clear that if the product is not thoroughly dehydrated, K2A1F5, H20 phase will also appear. Only when the temperature is raised above 505<C or heat treatment is performed above this temperature, the mixed crystal of K3A1F6 and KA1F will be obtained.
  • Of course, the composition is K3A1F6 + KA1F, and the flux of eutectic point is the most ideal choice. If the solder is composed of an accurate KA1F4 (m.P. 575t) or S3 (melting temperature 572^) point, it will also have a good effect, but the melting temperature is too high and the process is not easy.
  • Industrial raw material A1 (() H), the inevitable Si impurity is a beneficial “beating” active agent, the largest impurity of S 是 is iron, not more than 0.1%, no other strict limits on other common impurities Demanding.
  • Regardless of the method used to prepare the flux, the following basic requirements should be met:
  • The composition is accurate.
  • Free of free KF.
  • The melting temperature is about 560^, the maximum temperature is 565弋, and there is no obvious temperature interval when melting.
  • When heated on the aluminum surface, the flux is spread out quickly, no refractory residue is accumulated, and the flux is not blackened. (There is a shiny alloy G in the center of the flux melting. It is A precipitated impurity
  • Si and an Al-Si liquid alloy layer formed of a base material).
  • It has a fine particle size, is larger than the surface, and is easy to suspend in water.
  • The test composition and melting temperature of the potassium fluoroaluminate flux are correct. To test the nailing agent, it is necessary to precisely measure its melting temperature, preferably by visual measurement or
  • DTA method 1 w1. To test whether it contains free KF, the flux can be washed 1 to 2 times with deionized water or distilled water, and the melting temperature is measured after drying at 100 rpm. If the melting temperature after washing is increased, or the melt + transparent, the original flux contains free KF.
  • The particle size of the flux is required to be in the range of 2 to 50) xm. In addition, the determination of the sedimentation rate of the flux in water should also be made.吋 In a graduated test tube, mix the flux with deionized
  • water in a mixture of 5% by mass and shake it vertically for 10 s. No obvious solid deposits should be seen at the bottom of the tube.
  • The physicochemical properties of potassium cyanoaluminate flux are potassium fluoroaluminate flux with KA1F4 as the main component. The solubility in water is very small (0.2%~0.4%), but the thermal stability is not good. When heated in air, the degree is different. There are: 2KA1F4 +3H20=2KF + A120, +6HF| and 4KA1F4 +30, =4KF+2A120j +6F2 t reaction occurs. The first reaction occurs mainly in moist air, and the moisture in the air significantly hydrolyzes the flux at the brazing temperature (600T), leaving the infusible residue AI20. The second reaction is mainly carried out in absolutely dry air or oxygen. It is not essential in the brazing process and can only be noticed more clearly above SOOt.
  • The other component K3A1F6 (potassium cryolite) present in the flux also reacted similarly during heating, but was much more stable than KA1F4. The hydrolysis of the flux is mainly produced by KA1F.
  • Both KAIF and K3A1F6 are weak acid salts, which are easily destroyed by strong acid. Therefore, if the flux residue after brazing needs to be removed, it can be removed by dilute nitric acid. The strong acid has the least damage to aluminum base material with hno3.
  • The solid Nocolok flux is very stable, does not absorb moisture, is hardly soluble in water, and is insoluble in organic solvents. However, the molten Nocolok flux strongly sterilizes silicates such as glass and ceramics.
  • The molten Nocolok flux has an ultra-low viscosity and an ultra-low surface tension. The melt in the platinum crucible will automatically climb out of the wall and have a “superfluidity” like liquid helium. Experiments have shown that the molten KA1F is a molten salt with a high molecular structure ratio; <°], and many ionic fluoride salts are difficult to dissolve in them.
  • The KA1F4 solid crystal belongs to the tetragonal system, a = 35. 58 nm, C = 61.49 nm, and is a solid-liquid aliquot compound. Koaocob 1241 studied the vapor pressure of the KK-A1F3 system at 838 K (565 T;). It is shown that the vapor pressure of the composition KA1F4吋 is much larger than the vapor pressure of other compositions, and is more than three orders of magnitude larger. The vapor consists of a combination of KA1F, a single molecule and a (KA1F4)2 molecule. This fact stipulates that the molten KA1F4 has the molecular structure and also shows that KA1F may be used as a gas flux.