Re-moval Mechanism of Oxide Film on Aluminum during Brazing, Shenyang North really brings you to know, China’s professional vacuum furnace manufacturers, complete after-sales service, to protect your rights, contact Tel: 0086-13998872066

Disruption of Oxide Film on Aluminum by Metal Vapor in Vacu-um Environment

  • Since Milled*^1 found that magnesium vapor promotes the fluidity of solder in K-space brazing, this method of using magnesium as an activator has become the official process for conventional Vacuum brazing furnace. Investigating the role of magnesium vapor in vacuum brazing and what kind of metal vapours besides magnesium can play a similar role. Alcoa’s experimental slaughter did a systematic job. TVrrill 184′ reports on the content of this work. The report shows that under vacuum conditions, in addition to further eliminating residual oxygen and water, the main thing is to reduce the A1203 film and cause damage. The experiment investigated the effect of the vapor of 16 elements on the brazing process: the order of Pr, Sc, Sm, Ca, Be, La, Ce, Nd, Mg, Sr, U || Ba, Na, Zn, Sb, Bi In the middle, the || line to the left can play the role of reducing and destroying A1203 and promoting brazing, while the right side of the twisting line cannot. Experiments have also shown that there is a relationship between the concentration of active metal vapor and the ability to promote vacuum brazing.
  • When the brazing temperature is 600T, since the vapor pressure of Mg is the largest among the left elements of the twist line, the promotion effect is optimal, and for those metals with a small vapor pressure, a higher vacuum is required, and even It is necessary to add these Jincheng as a trace additive to the Al-Si-clad solder layer on the surface of the base material to obtain a better effect. StnniP [M] et al. reported in detail the results of the use of mixed rare earths and Sc, Y and U-based metals as vacuum brazing activators.
  • Regarding the film removal process of vacuum brazing, Zou Wei believes that in addition to eliminating the harmful effects of oxygen and water vapor in the environment, Mg vapor also infiltrates the surface layer of the base metal under the human film, and together with the silicon diffused into the human body, the surface layer is formed low. The melting point of the Al-Si-Mg alloy melts, thereby breaking the combination of the surface vaporized film and the base material, so that the molten solder wets the base material, spreads under the film along the base material, and floats the surface film. Remove.
  • In the vacuum brazing process, no flux is used other than Mg. Where does the power of the A1-Si solder wet the base material come from? How is the interfacial tension reduced? It can be seen that the vapor of magnesium acts as a “flux”. The vapor of magnesium infiltrates the base material to produce mass transfer, which reduces the interfacial tension between the base metal and the magnesium vapor. At the same time, the magnesium vapor also penetrates into the sinter solder, which also produces mass transfer, which in turn reduces the interfacial tension between the molten solder and the magnesium vapor. It can be known from the formula (1-8) in
  • Chapter I that the interfacial tension between the molten solder and the base material is roughly the sum of the interfacial tensions of the former two at the start of the wetting. At this time, the interfacial tension between the nail and the base metal is obviously reduced by the mass transfer of the magnesium vapor. The greater the mass transfer rate, the more the interfacial tension is reduced. Thus, under the action of Mg vapor, the molten solder is allowed to wet the base material well.

Brazing Filler Metals and Solders for Aluminum Alloys

  • The overheating temperatures of different aluminum alloys, so in order to braze different aluminum alloys, it is necessary to have a series of solders with different liquidus. It should range from brazing of pure aluminum (m. p. 660) liquidus up to 6301 C to solder of only 156 T for low temperature soldering. Some foreign manuals often consider aluminum alloys with a relatively large amount of Mg to be uncomfortable. Brazing, the main thing is that it is difficult to break its oxide film, so it is rarely considered to be suitable for the development and application of medium temperature aluminum brazing alloy of 400 ~ 500 <C. It has been proven that some special fluxes are effective in removing Mg-containing oxide films, so it is important to consider solders of different liquidus ranges. For aluminum brazing alloys, in addition to the common requirements for general brazing filler metals, such as wettability, fluidity of brazing joints, bonding ability with base metal, thermal stability of brazing filler metal, strength of brazing joints and heat of brazing filler metal In addition to processability, because aluminum is a very active element, the choice of solder alloy elements has a great relationship with the galvanic corrosion of solder joints. Furthermore, the alloying properties of aluminum alloys have to be an important consideration. For aluminum brazing alloys, aluminum alloys should first be considered. This is undoubtedly solved at 45 CTC with hard brazing filler metal. It is not difficult, and as the melting temperature of the solder is lowered, a low-melting heavy metal has to be added to the solder alloy, and the above various contradictions become prominent here. The following sections cover the full temperature range of brazing in the liquidus of the solder.

Filler Metals of Al-Si Series (melting range 570 – 630^ )

  • The Al-Si based brazing filler metal described in the present invention mainly refers to a brazing material based on the Al-Si eutectic composition, and also includes hypoeutectic, hypereutectic and additive elements not less than 5% (mass ft fraction). Al-Si alloy. This series of brazing filler metal is excellent in brazing property, strength, base material color consistency, plating property and corrosion resistance. It is a rare and excellent brazing filler metal, especially this series of brazing filler metal can be deteriorated ( The modification process can greatly increase the toughness and bending properties of the brazing filler metal and the brazing joint, and is therefore a fixed product. Table 2-11 lists the basic data for Al-Si solders.
  • A silver-white base metal, the color of the solder and the plating properties of the joint between the brazing seam and the base metal have to be an important consideration. For aluminum brazing alloys, the aluminum-based alloy should be considered first. It is not difficult to solve the brazing filler metal at 45 CTC. As the melting temperature of the brazing filler metal is lowered, a low-melting heavy metal has to be added to the brazing alloy, and the above various contradictions become more prominent here. The following sections cover the full temperature range of brazing in the liquidus of the solder.
  • Table 2-11 The basic data of Al-Si series filler metals
  • Brand Alloying element content (mass fraction, %) Melting temperature
    domestic AA AWS-ASTM Si Cu Zn Be Other elements | total A1 Solid line Liquidus
    4043 BAlSi-1 4.5 -6.0 0.3 0.1 ? <1.0 margin 577 629
    BA192Si 4343 BAlSi-2 6.8-8.2 <0.25 <0.20 ? <1.0 margin 575 615
    BA190Si 4045 BAlSi-5 9.0-11.0 彡0.30 <0.10 ? <1.0 margin 575 590
    BA186SiCu 4145 BAlSi-3 9.3-11.7 3.3 -4.7 <0.20 ? <1.0 margin 520 585
    BA188Si 4047 BAlSi^ 11.0-13.0 <0.30 0.20 ? <1.0 margin 575 585
    6M 13.0 ? ? 0.4-0.8 Sr:0.03

    La:0.03

    margin 570 575
  • The Al-Si alloy phase cabinet is shown in Figure 2-21. This system is a eutectic, eutectic point; (Si) = 12_6%, temperature 577 弋. The Si phase in the eutectic structure exhibits a curled sheet shape in the as-cast state, and the metallographic section has a linear cross section (u, but this has a special property, and can accept the modification of certain micro-® elements such as Na, Sr, La, etc. 1961, The Si phase thus becomes dendritic, and the metallographic section is early and creepy. If the heat treatment is repeated, the Si phase will further become spheroidal l?n. Since the deteriorated brazing material can still be brazed after brazing Maintaining some metamorphic structure 1<(5], the strength of the brazing joint is thus greatly improved. Al-Si-Bc solder, the phase diagram of this system [W1 indicates that there is a twin-eutectic point in this system, ?(Si =13%, to(Bc) =0.5%, the composition is the peritectic-eutectic point, the temperature is 571T, which is 6弋 lower than the Al-Si eutectic. The joint deterioration of Sr and 丨_a After that, the tensile strength of the joint (see Figure 2-23) is higher than that of the base metal 3003. The butt joint has a particularly strong bending ability and can be hammered into a dead bend of 1801 without breaking.
  • The 6M solder in Table 2-11 was originally from 1977 to 978, and the research team provided the research results of a satellite I: plant for the aluminum waveguide on the brazing satellite. However, because the factory is worried about the toxicity of a small amount of antimony, the ingredients of the crucible are eliminated, and the popular Al-Si-Sr-La aluminum brazing filler metal is later formed, but its properties, regardless of processability and joint strength. And the toughness is much different than the 6M solder.
  • The cooling rate after brazing has a great influence on the structure of the Al-Si eutectic brazing filler joint. After adding some modifier elements, the effect is more sensitive. The blank Al-Si eutectic accelerates with the cooling rate. -Since only the Si phase structure is thinned, but the shape of the flaky crystal is not changed; after adding some minor impurities (deterioration) elements, the Si phase morphology begins to change from flake to as the cooling rate increases. Root branches. More than 20 kinds of added elements have this effect, but the most sensitive addition elements are Na, Sr and U, and the addition amount is only 0.1% -0.01% (mass fraction). In general, after the welding, the cooling at a faster speed is beneficial to refining the crystal beam and increasing the strength of the brazing seam.
  • The Al-Si sizing materials described in this section are excellent in processing properties and can be easily processed into filaments or foils.
  • A quenching technique has led to new developments in the performance of Al-Si solders. Yan Juqi et al [100] obtained a thin strip solder for Al-Si based alloys using single-roll and two-roll quenching techniques. It is reported that this quenched solder has a lower liquidus than the as-cast solder and has higher wettability and joint strength.

Filler Metals of Al-Si-Cu-Zn Series ( melling range500 ~577t)

  • The phase diagram of the A1 angle of the Al-Si-Cu system is shown in Fig. 2-24_TMw. There is a ternary eutectic point in the bismuth binary system of Al-CuAl2-Si, ie(Cu) = 26.7%, w(Si) = 5.1%, and the degree of 525″C. This composition is often used as a brazing fluid. The flux of the brazing filler metal is significantly increased after the addition of Cu to the eight-Si brazing filler metal in the lower phase aluminum alloy brazing filler metal; JB11001 o the binary eutectic solder, the towel in CuAl, and the intermetallic compound Very high, so it is very brittle, only suitable for casting into strips and difficult to process into silk and foil. However, if the increase of t?Al) is 3% -5%, leaving the eutectic point and entering the liquid phase of A1 The hot workability of the solder can be improved, but the liquidus point is correspondingly raised to about 5,401.The partial phase diagram of the Al-Si-Zn system is shown in Figure 2-25 for U3.KBUH0]?. The composition of the ternary eutectic point E is 揂丨) = 5. 10%, w(Si) =0. 04%, w(Zn) = 94. 86%. After the addition of Zn to the A1-Si eutectic solder, the wettability and fluidity of the solder are enhanced. As the concentration of Zn increases, the solubility of Si rapidly decreases. The relationship between the composition of the Al-Si-Zri system and the temperature of the liquidus is shown in Table 2-12. Since the solder has no compound in the system, the hot-worked part of the solder can be much stronger than the Al-Si-Cu system, and can be easily formed into a wire or a belt. When formulating this alloy, the Al.Si alloy should be prepared first, then Zn is added under the protection of the flux, and the addition of Si to the Al-Zn alloy is not easy to dissolve. Nishimura llM reported that in such solder alloys, “Cu, b丨 is added to reduce the color difference from the base metal, and the addition of less Mg can improve the corrosion resistance.
  • Table 2-13 The basic data of Al-Si-Cu-Zn series filler metals
    Brand Alloying element content (%) Melting temperature / t
    Domestic code AA AWS-ASTM w( Si) ?;(Cu) w(7n) Other elements w(M) Solid line Liquidus
    BA167CuSi

    HI403

    4245 6

    9.3 〜10.7

    28

    3.3 -4.7

    9.3-10.7 ? <1

    <1

    margin

    margin

    525

    516

    535

    560

    B62 3.5 20 25 0.3 <1 margin 480 500
    Y-1 9-11 3 ~6 5-7 Yb 彡 0.04 Ti^0.04 margin 525 560
  • l-Cu-Ag-Zn solder (liquidus temperature range 400 ~ 500X: ) Filler Metals of Al-Cu-Ag-Zn Series (melting range 400 -50010) Al-Cu-Ag system A1 angle phase Figure 2-26 shows the sunny town. The ai_A丨2Cu_AgjAl ternary system at the A1 angle has a ternary eutectic point with a composition of u?Al) = 40. 0%, ?Cu) = 19.3%, w(Ag) = 40.1%, and the temperature is 5001. . The eutectic point component has great advantages as a brazing material, and its color is consistent with that of the A1 base metal. The fluidity of the sizing welding is excellent, the plating performance is good, and the disadvantage is that it is brittle and the bismuth ratio is
  • Al-Si-Cu. The brittleness is low. 01%。 Lithium is the best soldering agent to increase the wettability of titanium.
  • Another ternary used as a brazing material in this system is Al-Cu-Zn, and the phase diagram is shown in Figure 2-27 [102W, “_61. The AI-C丨i-Zn phase diagram is more complicated and suitable for use. The composition and temperature of several non-change points of the solder are shown in Table 2-14. There is a patent report “981 used this kind of solder, and added 0.05% – 0_ 08% (mass fraction) of Mg, 0 05% (Quality Score) of Ni or & can improve its corrosion resistance. The color of the solder is relatively close to the base material, and the processing performance is good.
  • A1-Cu-Ag-Zn solder can be prepared by adding Zn to Al-Cu-Ag eutectic alloy [23]. As the Zn content increases, the liquidus temperature of the alloy decreases linearly when it is <70%. The relationship is as follows: t(Zii) (%) 0 10 20 30 40 50 60 70 80 90 liquidus /T』500 485 475 465 455 446 436 424 396 380 Figure 2-27 Al-Cu-Zn phase diagram [丨02]9丨•丨丨]161 Fig. 2-27 Phase diagram of Al-Cu-Zn System
  • Table 2-14 Composition and temperature of nonvariant points in system Al-Cu-Zn
    point composition(%) Temperature / t
    m;(A1) w( Cu) w(Zn)
    44.3 50.0 5.7 580
    26.5 16.6 56.9 420
    % 15.9 9.1 75.0 396
    E 5.8 4.2 90.0 377
  • After removing the coating layer from the 2024 aluminum alloy base material and the above-mentioned solder as a pair of electrodes, the potential of the electrolyte is measured by using a 3% solution of NaCl as the electrolyte. When (Zn) = 20% to 30%, the potential difference between the two is zero. If the Zn is less than this value, the solder is positive, and more than this value, the solder is negative. This solder l>(Zn) = 20% -30% has good corrosion resistance and color.
  • Al-Ge-Si solder (liquidus temperature range 425 ~ 500Tl) Filler Metals of Al- Ge-Si Series (melting range 425 ~ 500t:)The basic alloy of this series of solders is Al-Ge, and the phase diagram of the system is shown in Figure 2-28. For a simple eutectic system, the eutectic point = 55% ‘, temperature 423 弋. The eutectic solder has good fluidity and excellent spreadability, and can be distributed along a large area of ​​the surface of the base material. Darker color is a disadvantage.
  • Although no compound is formed in the system, the eutectic point t?Ge) is as high as 55%, which is extremely brittle, and the cast strip has almost no strength, and the landing breaks. Since the eutectic temperature of 423 弋 is just in the rare medium temperature aluminum brazing range and the brazing process performance is excellent, it is still highly valued. Some special measures need to be taken during use. For example, the gap should be reduced, and should not exceed 0. lmrn. After brazing, the brazing joint is properly heat-treated at the brazing temperature, and high strength can be obtained after thermal diffusion.
  • Ge and Si are in the same family in the periodic table, and their physicochemical properties are very similar, and AUSi and Al-Gc are both eutectic. The former can obtain the metamorphic structure by adding some metamorphic elements, thereby greatly improving the strength of the brazing filler metal and the brazing joint; while the latter proves that it is impossible to obtain the metamorphic structure of si from the practical and theoretical U09’ll(l] However, in the case of refractory metals such as Ti, the Ge plate crystals tend to aggregate into block crystals.
  • When Ge is added to the Al-Si binary system, the eutectic temperature of Al-Si decreases as the amount of G? increases, thus forming the Al-Ge-Si ternary system. The phase diagram of the Al-Ge-Si ternary system is shown in Figure 2-29 [1111. Since the Ge-Si binary system is a continuous solid solution system, only one binary eutectic line in the phase diagram is connected from the Al-Si-based e to the Al-Ge-based e2. The composition and temperature of each point on this line are shown in Table 2-15. On the line, as the Si content increases, the tendency of the Ge-Si solid solution dispersed phase to be deteriorated is also enhanced. w(Ge) <41. The 8% alloy has the potential to produce a more pronounced metamorphic structure |KN1. The alloys of the series from 3 to 6 which have been modified by Na, Si• or La have proved to be very important needle alloys, and the brazing process performance is very good. The liquidus temperature range is 480 -5501. Kayamot J”21 reported that the Al-Mg and Al-Mg-Si alloys were successfully brazed with this brazing filler metal.
  • On the basis of Al-Si-Ge solder, the literature [113] reported the formation of Al-Si-Ge-Cu quaternary solder after adding Cu. Since the brazing material is very brittle, it has been reported that a strip of spoilage having a thickness of 90 to 150 pm is prepared by a rapid cooling process, and Bf is used to apply a lower brazing temperature.
  • Table 2-15 Compositions and temperatures of binary eutectics in system Al-Ge-Si
    Serial number Composition (quality score, %)
    temperature A1 Ge Si
    511 87.4 12.6
    1 572 82.3 7.2 10.5
    2 548 75.3 16.7 8.0
    3 536 69.2 25.2 5.6
    4 504 63.5 32.6 3.9
    5 490 59.0 38.2 2.8
    6 472 56.0 41.8 2.2
    7 454 52.0 46.6 1.4
    ? 424 47.0 53.0