Study on Silver Degassing Process of AgCu28 Vacuum Solder Raw Material

1 Introduction Vacuum solder is an indispensable solder in the production of electric vacuum instruments, meters and components. It is widely used in the fields of electronics, aerospace, aerospace and military. AgCu28 vacuum solder is a silver-copper eutectic alloy. It has good wettability and spreading ability for copper and copper alloys, high electrical conductivity, and the solder does not contain volatile elements. It is suitable for brazing and vacuum brazing in furnaces with protective atmospheres. Welding, and thus the most widely used in vacuum solder.

Cleanliness and spattering are the two main properties of AgCu28 vacuum solder. The oxygen content of raw material silver and copper directly affects the sputterability of AgC:u23 vacuum solder. For raw copper, oxygen-free copper is usually used. The national standard GB/T 52311985 specifies that it contains oxygen; I-ft 0.0020% (mass fraction), such oxygen containing ft can meet the production requirements of AgCu28 vacuum solder. For raw material silver, commonly used silver ingots on the market or silver scraps produced by scraps recovered by production companies, the oxygen content of silver ingots varies greatly, and some of them are. 0010%.0020%, and some are more than 0.0100%; and the silver powder prepared by the production company's recycled material has a higher oxygen content, usually. 0250% 0.0300%, therefore, raw material silver must be degassed. In this paper, the degassing process of AgCu28 vacuum solder raw material silver is studied.

2 Test methods 2.1 Degassing of silver ingot degassed silver ingots Vacuum degassing degassing method, activated carbon degassing method and vacuum graphite crucible melting degassing method are used, respectively.

2.2 Silver powder degassing Silver powder degassing uses silver powder vacuum degassing method, silver powder billet vacuum degassing method and silver powder billet vacuum helium melting degassing method.

3AgCu28 vacuum solder cleanliness and spattering of the determination of oxygen-free copper and degassed by different processes silver ingot or silver powder, respectively, preparation of AgCu28 vacuum solder, according to the provisions of the national standard GB/T4907-1985 sampling for cleaning and spattering The determination.

3 Test results and analysis 1 Degassing of silver ingots 3.1.1 Vacuum smelting method Degassing Using 25kg vacuum induction melting furnace and corundum smelting three furnaces, 14kg per furnace, the vacuum degree is 1.2Pa, and the heat preservation and degassing time are lOmin and 15min, respectively. , 20min, cooling casting. The ingots were analyzed for oxygen content. The silver ingots treated with the above process and the oxygen-free copper were respectively made into AgCu28 vacuum solder. Samples were taken from the alloy ingots and the cleanliness and spatterability were analyzed according to the national standard GB/T 4907-1985. The results are shown in Table 1. Show.

Table 1 Degassing effect of vacuum smelting method and the effect on the performance of AgCu28 Sample number Thermal degassing time Min oxygen content mass fraction.

Clean Dispersion (Silver Bars) Disqualification As can be seen from Table 1, degassing by vacuum melting can be deoxygenated. When the heat preservation degassing time is less than 20min, its spattering property does not meet the standard requirements. With the increase of time for heat preservation and degassing, the oxygen content of the silver ingot gradually decreases. According to this trend, if the time of heat preservation and degassing is further prolonged, the oxygen content of the silver ingot may be reduced to. 0020% or less, to meet the vacuum solder AgCu28 production requirements. Theoretically, during melting, the dissolved oxygen in the molten metal can enter the gas from the surface of the liquid, and the oxygen in the gaseous phase is drawn out of the furnace. In an ideal state, this process should be continued, but due to the vacuum The influence of factors such as temperature and temperature will eventually reach a dynamic equilibrium state. Therefore, as long as a high degree of vacuum and a long time for heat preservation and degassing are maintained, the oxygen content of the silver ingot can be less than 20%, but Taking into account actual production efficiency and raw material consumption, this method is not only time-consuming but also causes the volatilization of silver to increase under high vacuum, which increases raw material consumption and pollutes the vacuum equipment. Therefore, this method is not desirable in practical production.

3.1.2 Activated carbon method Degassing Using 25kg vacuum induction melting furnace, corundum, activated carbon (three granular activated carbon furnaces, powdered activated carbon three furnaces), vacuum degree 1.2Pa, insulation degassing time lOmin , 15min, 20min, cooling Rao casting. The cast lake was analyzed for oxygen content. The AgCu28 vacuum solder was prepared from the silver ingots and the oxygen-free copper respectively, and was sampled from the alloy ingots. The cleanliness and spattering properties were analyzed according to the national standard GB/T4907-1985. The results are shown in Table 2.

Table 2 Degassing effect of activated carbon method and its effect on the performance of AgCu28 Insulation degassing time/min oxygen content/mass fraction. AsCu28 Cleanability AgCu28 Sputtering Sample No. Particulate powdered activated carbon Activated carbon Particulate activated carbon Powdered activated carbon Particulate activated carbon Powdered activated carbon 0 (silver ingot) 160-1 A3152081AA Dispersive analysis, results Table 3 shows.

As can be seen from Table 2, degassing with activated carbon, degassing granular and powdered activated carbon is better than degassing with vacuum melting, and powdered activated carbon is better than granular activated carbon.

From the theoretical analysis, after adding activated carbon, there is the following chemical reaction: the solubility of carbon monoxide and carbon dioxide in silver is lower than the solubility of oxygen in silver, which is more conducive to being pulled out of the furnace under vacuum, so the degassing effect is good . In addition, because the granular activated carbon has a much smaller surface area than powdered activated carbon, the surface area in contact with oxygen is also much smaller. In the same period of time, the granular activated carbon and oxygen react insufficiently and cannot be played. The degassing effect is very good. If the time of heat preservation and degassing is prolonged, the granular and powdery activated carbon should have equivalent deoxidation effect. Tests have found that when degassed with powdered activated carbon, the carbon volatilizes severely, contaminating the vacuum equipment, and affecting the cleanliness of the AgCu28 vacuum solder to varying degrees.

3.1.3 vacuum graphite crucible melting degassing using 25kg vacuum induction melting furnace, graphite crucibles r high purity, high strength, high density), vacuum degree is 1. The heat preservation degassing time is lOmin, 15min, 20min cooling casting. The ingots were analyzed for oxygen content. The AgCu28 vacuum solder was prepared from the above silver ingots and oxygen-free copper respectively. Samples were taken from the alloy ingots, and the degassing effect and cleanliness of the vacuum graphite crucible melting method were evaluated according to the provisions of 497-1985. The effect of AgCu28 performance, vrl insulation degassing time / min oxygen content mass fraction, cleaning grazing (silver ingot) can be seen from Table 3, the use of "three high" graphite crucible, degassing of silver ingot, its effect Similar to the addition of activated carbon, the graphite crucible in the test process has low carbon volatilization and almost no pollution to the vacuum equipment, ensuring the cleanliness of the AgCu28 vacuum solder. This method not only achieves a good degassing effect without pollution, but also can increase the production efficiency and reduce the cost, and it is the most suitable method for practical production.

3.2 Degassing of silver powder 3.2.1 Vacuum degassing of silver powder ingots) Vacuum degassing ingots in a K vacuum annealing furnace (temperature of 500°C, vacuum degree of 2°C for 1h, 3h, t; h for degassing treatment. Analysis of oxygen content of deaerated ingots Preparation of AgCu28 vacuum solder (two furnaces) using degassed ingots and oxygen-free copper, sampling from alloy ingots, and analysis of U cleanliness and dispersion in accordance with national standard GB/T-1907-1985, and the results are as follows: Table i - Table 4 Degassing effect of vacuum degassing method for silver powder ingot and its influence on the performance of AgCu28 sigma heat preservation degassing time / h oxygen content mass fraction, cleanability spatter (silver powder) disqualification from Table 4 It can be seen that the effect of vacuum degassing with silver powder is not obvious and takes a long time. Since the silver powder presses the ingot, the oxygen is squeezed inside the spindle, and at the same time, a dense film is formed on the surface of the silver powder ingot so that when degassing, the gas is not easy. Escape, so degassing effect is not good.

3.2.2 Silver powder vacuum degassing The silver powder is placed in a vacuum annealing furnace (temperature 500'C, vacuum degree 2Xl (T3Pa)) for 1h, 3h, 6h respectively for degassing treatment. The degassed silver powder is analyzed for oxygen content. AgCu28 vacuum solder (three furnaces) was prepared using degassed silver powder and oxygen-free copper. Samples were taken from the alloy ingots and the cleanliness and spattering properties were analyzed according to the national standard GB/T4907-1985. The results are shown in Table 5.

Table 5 Effect of silver powder vacuum degassing method on degassing effect and performance of AgCu28 Sample heat preservation degassing time/h Oxygen-containing gas fraction, cleaning spattering (silver powder) It can be seen from Table 5 that silver powder is used for vacuum stripping. The gas treatment method has a good effect, and the silver powder with 6 hours of heat preservation can fully meet the production requirements of the AgCu28 vacuum solder. The reason is that the silver powder is loose and the gas easily escapes under vacuum.

3.2.3 Silver powder ingot vacuum graphite crucible melting degassing The silver powder ingot after the ingot in the vacuum melting furnace graphite crucible, vacuum degree of 1. 2Pa, insulation degassing time for the oxygen content analysis. AgC28 vacuum solder (five furnaces) was prepared with treated silver ingots and oxygen-free copper. Sampling from alloy ingots was performed according to the national standard GB/T 49071985, and the results were shown in Table 6.

Table 6 Degassing effect of vacuum-graphite crucible degassing method with silver powder ingot and its influence on the performance of AgCu28 Sample No. heat preservation degassing time/min Oxygen content mass fraction, cleanability Spatter (silver powder) unsatisfactory Seen from the data of Table 6 The vacuum degassing method of vacuum graphite crucible melting degassing with silver powder ingot is not obvious and takes a long time, during the test process. It was found that when the silver powder ingot was melted, a large number of bubbles escaped, causing splashing of the molten metal, resulting in a short circuit in the vacuum equipment. This method is not desirable in production.

4 Conclusions a) Degassing by vacuum melting and activated carbon degassing all have the effect of deoxidation. However, due to the serious volatilization of silver during degassing by vacuum melting, the volatilization of carbon during degassing of activated carbon is severe, and both are seriously polluted. Vacuum equipment does not guarantee the cleanliness of AgCu28 vacuum solder, so it should not be used in actual production.

12) The use of "three high" graphite crucible vacuum melting smelting silver ingot, the effect of deoxidation is good, the pollution of the vacuum equipment is also small, the processed silver ingot for the production of AgCu28 vacuum solder, its spattering up to A level, cleanability up to I-I level. This method can fully meet the production requirements of AgCu28 vacuum solder, and the production cost is low.

The degassing and deoxidation effects of the vacuum degassing and the vacuum melting of the silver ingots are not obvious, which not only takes a long time, but also the vacuum degassing degassing method of the silver powder ingots has great harm to the equipment, so both of them are not suitable for use.

The degassing effect of the silver powder vacuum degassing method is good, and the AgCu28 vacuum solder produced can have an A-level spattering property and a cleanability of 111 grades. It can be used to produce AgCu28 vacuum solder.

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