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Solders of Zn-Al Se-ries (melting range 382 – 400X1)
- The solder with a liquid phase melting temperature in the range of 380 – 4501 can only be a Zn-Al alloy. The phase diagram of this system is shown in Figure 2-30. It is a binary eutectic system forming a large solid solution on the A1 side, the eutectic point u; (Zr丨)=95%, the temperature is 382<C0. Because the Zn is a dense hexagonal lattice, the lattice constant C axis is closer to the ^ axis. It is easy to break on the C-axis, so the as-cast properties of pure zinc are very poor. The multi-rolling by hot working mashes the oriented grains, which greatly enhances the plasticity. The mesomorphic point has the same mechanical processing properties as pure zinc.
- Although it can be hot processed into silk and sheet solder, long-term storage is more likely to cause grain growth and become brittle than pure zinc. With the most increase in the content of A1, the forming and processing properties of the alloy are significantly improved. For example, w(Zn) = 90% (420^), 80% (4751), and 15% (490^C) are easy forming processes. The composition of the solder.
- From Fig. 2-30, the melting range of the solid solution zone of t^Zn) <80% is not large, and it seems to be used continuously as the composition of the brazing material, but the cooling rate is faster under brazing conditions, and this binary melting interval (L + a) is much wider than the phase icon. In practical application, the solder melts and solidifies and is not sticky, and it is only used under rapid heating.
- Zn-Al eutectic solder and A1-rich hypoeutectic solder have much lower fluidity than Al-Si eutectic because Zn and A1 have high mutual solubility and the solder is in the braze. While flowing, it penetrates into the base metal at a relatively fast speed. • This affects the rate at which the liquid solder enters the needle gap. In addition, Schoern (4) reported that the viscosity of the solder in the molten state is large, which is also the cause of the fluidity. When M is added; (Be) = 0.01% to 0.06%, the fluidity can be improved.
- The corrosion problem of Zn-Al solder is much more difficult to control than Al-Si solder. It is necessary to pay great attention to the temperature control of brazing, and it is difficult to flow long distance in the brazing joint after melting, it is better to use the brazing wire. The flux paste sticks to the crease and implements the method of “in-place lying down” into the brazing seam.
- The corrosion resistance of Zn-Al solder is far less than that of Al-Si solder. A report 1151 examined the effects of the addition of trace elements on the corrosion resistance of Zn-Al eutectic alloys. The experiment is based on the eutectic Zn-Al alloy, adding different elements of Dong to make the brazing filler metal, soldering the solder joints on the pure aluminum and 2024 aluminum alloy test pieces, soaking in 50 °, 3% NaCl solution. 96h, then recorded its weight loss and observed the metallographic surface and section. For example, the weight loss of the blank Al-Zn eutectic solder joint is 10, and the comparison results of other solder joints are shown in
- Figure 2-31. The results show that the addition of alkaline earth and rare earth metals with a mass fraction of about 0.1% to the Zn-Al eutectic solder improves corrosion resistance. The most significant additive element is
- Be, followed by Si• and Mg. In the periodic table, IB, IHA, IV, VA and precious metals have a sharper decline in corrosion resistance, including Cu, Ag, Sn, Ph, Bi, Pt, Ga, Tl, and the like. Therefore, the preparation of such brazing filler metal should be as high as possible. Metallographic studies have also shown that the presence of trace additives such as Sn, Ph, Bi, Cu, Cd mainly produces intergranular corrosion, of which Bi is the most serious. The recommended solder composition is AI-Zn(95)-Sr(0.1) with a liquidus temperature of 385 Å.
- Zn-Al eutectic solder has a tensile strength of about 170 MPa and an elongation of about 1% [U6]02*7,6 Cd zn solder (liquidus temperature range 265 to 350T:) Solders of Cd-Zn Series (melting range 265 ~ 350^) Cd-Zn solder is a (^ based solder, eutectic point w (Zn) = 17.5%, melting temperature is 2651. Cd-Zn phase diagram shown in Figure 2 As shown in Fig. 32, the brazing temperature of such a common solder does not exceed 300 ，so the use of the nail flux can be much less corrosive to the base material than the inorganic reactive flux. The amount of T is also greatly reduced. The eutectic solder brazing process performance and joint strength are superior. The solder can be processed into silk: the mutual solubility of the main component Cd and the base material AI is extremely small, and the Zn content is Not high, so the erosion is easy to control. The disadvantage is the ambiguity and darker color of Cd.
- There are many reports on the further improvement of the properties of Cd-Zn solders. Hirosenm pointed out that adding “) (Ag) = 3% can greatly improve the strength and impact resistance of the joint. In order to increase the fluidity of the solder, lwanaga reported that the addition of Ca) or yttrium Mg in the eutectic enamel is 0.0001% -0.3% 11,81, which not only greatly improves the paving performance of the molten solder, but also It can effectively improve the shear and tensile strength and corrosion resistance. It is pointed out that adding ui(Cu) = 0.05% ~1% and w(Ti) = 0.05% ~ 0.55% can maximize the spreadability. Shear strength and brazing rate are also mentioned.
- In addition to eutectic solders, Cd70Zn, CdSOZn, Cd30Zn, and CdlOZn are also commonly used as solders. The relevant parameters are: Cd30Zn, liquidus MSOT, tensile strength = 130MPa, medium length ratio -15%; CdlOZn, liquidus ~395’€, tensile strength “l20MPa, elongation ~ 2%; CHOZn, Liquidus “292SC? Tensile strength? 130MPa, elongation = 50% [1161 2.7.7 Sn-Zn solder (liquidus temperature range 198 ~ 260^) Solders of Sn-Zn Series (melting) Range 198 ~ 260t:)
- The Sn-Zn eutectic solder is a Sn-based solder, Un) = 8.8%, and the phase is shown in Fig. 2.33. The biggest advantage of this solder is that not only the brazing process is good, but also the color of the base material is almost the same. Because it contains a considerable amount of 7,n, and Cd-Zn system, ‘the brazed joint with A1 is very strong, although the tensile strength of Sn-Zn is only about 50MPa [1丨61, but by 3003 aluminum.
- When the standard lap joint of alloy brazing is subjected to tensile, shear and tear tests, it is broken on the base metal. Why does Sn-Zn solder have such a large bonding strength as 1f A1? Chen Rong et al.  studied the interface of the joint by SEM and metallographic method. It was found that Zn in the brazing filler metal not only solid-dissolved with A1, but also grew a large number of thorn-like solid solution whiskers inserted into the brazing material for embedded bonding. This is not visible in other types of connectors. Not only Sn-Zn eutectic solder, other Sn-Pb-Zn and solder containing both Zn and Sn have this phenomenon, but Zn-Al solder does not have this phenomenon [“5], visible whisker generation It is related to the coexistence of Zn and Sn. Although the strength of the Sn-Zn joint is very low, the corrosion resistance of the joint is not good. The joint of Sn-Zn brazed aluminum is soaked in tap water, room temperature, usually 3 – 4 weeks That is, the corrosion is broken; it is immersed in 3% salt water, and the simple Sn-Zn eutectic joint is not suitable for the hot and humid environment until less than – week. Many literatures improve the corrosion resistance of Sn-Zn. A positive effort was made. Bouko [1211 believes that adding i?Ge to the Sn-Zn co-product) = 0.5% ~ 1% can greatly improve the corrosion resistance. Yasuda1122] pointed out that the composition is Sn90, Mg3, Zn5, Ag2 solder 100mm2 overlaps A1 and Cu, its joint can withstand a load of 4. 5kN, sprayed by artificial seawater for 100h without breakage. Ries-mcycrL123j series report, in the Sn-Zn eutectic 屮 add people w (Ni =0. 1% ~ 0. 5% or ui ( Mn) = 0. 05% ~ 0. 5% or w (Cd) = 0.5% ~ 4% can effectively improve the corrosion resistance of the solder.In addition to eutectic materials, SnMZn, Sn80Zn (liquidus lines of 250 and 280t, tensile strength of ~50MPa, elongation = 75%) are also commonly used as Vacuum brazing furnace „Experiments show that The corrosion resistance of these Zn-rich hypereutectic nail alloys on aluminum joints is much higher than that of eutectic solder joints; in tap water, it can withstand immersion for more than 2 months.
Solders of Sn-Pb Se-ries (melting range 183 -210X.)
- The Sn-Pb system is also a eutectic system with a eutectic point of <(Sn)=61.9% and a eutectic temperature of 183T: the phase diagram is shown in Figure 2-34. The alloys of the various compositions in this system are widely used for soldering in the electronics industry and are not used much in brazed aluminum. This is because the mutual solubility of Sn and Pb to A1 is extremely low, and there is no compound bovine, the bonding with
- A1 is very weak, and the electrode potential difference with A1 is very large, and the corrosion caused by electrochemical action is quickly carried out along the interface. . Although the %-Pb solder wets well on the aluminum surface under the action of the flux, the fluidity in the brazing seam is also good, but the strength of the brazing seam is very low. After 2~3 days of Sn-Pb solder joint on the aluminum halide, the solder joint is separated from the aluminum when the aluminum surface is bent; the joint is destroyed after being soaked in 3% brine for several days. Therefore, if the Sn-Pb solder is to be used for aluminum soldering, the bonding force between the solder and the aluminum and the corrosion resistance of the joint must be solved.
- Arbibr 12412511974 ~ 1978, in a number of patent reports, adding Ag can effectively improve the turbidity resistance of Sn-Pb solder joints when brazing aluminum = his patent report ft Heng became a multicore company’s commercial aluminum solder wire The basis of the Alu-Sol 45D. The report gives the relationship between the corrosion resistance of the 揟” joint in the artificial seawater and the content of Pb. Sn and Ag in the brazing filler metal (see Figure 2-35). The corrosion resistance zone is above the curve 4 in Fig. 2-35. The curve below H is a non-corrosion-resistant zone. It can also be seen from the figure. If the content of Sn increases, the content of Ag also increases if the content of Sn increases. The following Sn and Ag are given. Relationship: i?Ag)(%)0.51247»(5>1)(not more than %)18 25 35 45 60 It is also pointed out that if the solder contains Bi, CiK Sb or 7.n, it will be greatly The corrosion resistance of the brazed joint is lowered, but Cu is the exception, and the above-mentioned brazing material containing Cu may have corrosion resistance.
- Fig. 2-35 Corrosion-resistant relationship of Sn-Pb-Ag solder to the compositions of the Pb, Sn, Ag components in solder immersed in salted water 1231One joint break below 25 days □ One joint breaks between 25 and 50 days O—more than 200 days joint damages Multicore Alu? Sol 45D The actual composition of the solder wire is: u) ( Sn) = 18%, i?(Ag) = 1.9%, u) (Pb) = 80. 1%, melting temperature 丨78 -2701:, is a high-lead solder with a liquidus of up to 270 。.
- The 45D nail wire is a j core or a core, which is filled with a liquid flux. The filter paper is cut by the filter wire to detect the outflow of the liquid flux. In recent years, as the lamp caps of incandescent lamps have been changed to aluminum, the demand for such brazing wires has increased. The Alu-Sol 31D solder wire produced by Miillicore in a Malaysian company seems to have used solid flux, three-core filling and elimination of f/Vg, and the composition is only Pb (80)Sn (20), which seems to reduce costs. At the same time, on the very hot lamp head, the corrosion caused by moisture will not be necessary.
- Ag of solder crucible; combined with the trapping of A1, it has high bonding strength and corrosion resistance. Since Sti and Ag form a gold-to-phase interphase and y-phase compound in the Sn-Pb solder, this partially offsets the partial Ag-Al bonding in the molten solder, which also explains why the content of Sn increases. Need to add more Ag. It can be seen from the phase diagram of Ag-Al that Ag has a considerable solid solubility in A1, so that the brazing joint of the brazing filler metal and the base metal is prepared with a gradual transition of different concentrations of A1-CU solid solution, rather than a tissue eliminator. Different base metal-brass transitions, which may be the reason for the excellent performance of brazing aluminum alloys containing Ag. However, it is incomprehensible that Zn has a greater mutual solubility in A1, and the electrode potential difference between Zn and A1 is much smaller than that between Ag and A1, while the ‘Zn-Al joint is very resistant to turbidity. Chen Rong et al. described in another report n261 that there is a larger undulation at the interface between the Ag-containing solder and A1 and a thin layer of solid solution, but it is still not sufficient to illustrate the specificity of the bonding between Ag and AI.
- The bonding strength between the simple Sn-Ph solder and the aluminum base material is not good. However, if the concentration in the flux is high, the precipitation of a large amount of metal Zn participates in the interfacial reaction between Sn-W> and A1. Effectively increase the strength of the joint
Solders of Pb-Bi Series(melting range 124 ~200t)
- Whether Ph or Bi and AI binding ability is extremely weak. The liquid metal has no mutual enthalpy with A1 at the brazing temperature (below 3001 C) and no intermetallic formation. The Pb-Bi phase diagram is shown in Figure 2-36. It is also a eutectic system with a common point of u>(Bi)= 55.5% and a melting temperature of 124<C. There is a large body of literature reported that this is used in aluminum soldering, mainly considering its lower melting temperature. In order to properly improve the toughness of the brazing filler metal, it is often appropriate to increase the Pb content. Increasing the bonding strength and corrosion resistance of this solder *fAl is the key to the application of this solder. Stokes [m] reported that 0.5% ~ 5% of m is added in w(Pb) = 55% ~ 85% and w(Bi) = 11% ~ 40%; (Ag) or 0.5% ~ 10% w (In) can greatly improve the corrosion resistance of the joint.
- Using a specific composition of ui (Pb) = 78. 5%, ?; (Hi) = 18. 5%, ?; (Ag) = 3% brazing aluminum crucible, soaked in NaCl solution for 1000 h, aluminum foil corrosion The joints are flawless.Since neither Ag nor Bi nor 1>b forms a gold intermetallic compound, only eutectic action is applied, so Ag added in Pb-Bi is not consumed by the bovine compound inside the needle, so when brazing, The action and effect of the Ag 4 A1 base material in the brazing filler metal are particularly clear. The boundary structure between Pb-Bi-AK-Al was analyzed by scanning electron microscopy and EDS spectroscopy. The results show that there is a layer of non-fixed compound C formed on the interface. The electrode potential of the S phase is more positive than the phase on both sides. The authors believe that the base electrode aluminum of the three materials is the most negative, and acts as an anode in the formed primary battery, which is preferentially corroded, thereby protecting the solder and the interface from corrosion.
- An insurmountable defect of this spoilage is that the color is too dark and has a great contrast with the base metal AI. In addition, lead-free solders are also fashionable today, and unless the joints have special corrosion resistance requirements, the solders are probably not the first choice for brazing processes.