1.Overview 

aluminum brass can be divided into two categories. One is to add a small amount of aluminum to cast brass in order to remove impurities and increase fluidity, and to cast complex castings in which the amount of excess aluminum in the alloy does not exceed 0.5% . The other is to add aluminum to forge brass to increase corrosion resistance, often used as a condenser, the general composition range is AL1 ~ 6% , ZN24 ~ 42% , CU55 ~ 71% . There are 6 grades of aluminum brass in national standard. The main reason is to add MN, FE and other elements to improve the strength and wear resistance of the alloy. The most common types of aluminum brass are HAl77-2, HAl66-6-3-2, HAl64-3-1, HAl60-10-1, HAl59-3-2, etc. .

2.The addition of alloying elements

(1)Manganese and iron

Because the melting point of manganese and iron is very high, it is difficult to reach the melting point of manganese and iron. The solubility of manganese in copper is high, and it is easy to be dissolved in copper at high temperature. Although the solubility of iron in copper is very small, the solubility of iron in Cu-Mn alloy is large, so it can be added conveniently. Therefore, the method of adding MN and Fe at high temperature can not only ensure the composition of alloy, but also avoid the process of manufacturing intermediate alloy, so as to reduce the production cost and improve the production efficiency. MN can melt into copper in a large amount, which can play the role of solid solution strengthening, at the same time can effectively prevent brass "dezincification" , and improve the corrosion resistance of brass. The Fe-rich phase can improve the lubricity, the strength of the Matrix and the wear resistance of the alloy.

(2)Zinc and aluminum

Zinc and aluminum have a low melting point and are easily oxidized. When the alloy melt temperature is high, the addition of aluminum, zinc, it is easy to be oxidized combustion. Therefore, we use to wait for MN, Fe dissolved after adding cold (Cu or scrap) for cooling, and then add aluminum, zinc production. Because the solubility of AL and ZN IN CU is high, it is easy to dissolve in Cu, which ensures the chemical composition of the alloy. The zinc equivalent coefficient phase of aluminum, when high (N = 6) , a small amount of aluminum can make the phase of biphase brass increase, even in complex aluminum brass brittle phase formation, so that the strength and hardness of the alloy increased, while the plasticity and toughness decreased significantly.

(3)microalloying elements

The microalloyed elements are added in the last working procedure and heated to the temperature of the furnace. Adding Tin can strengthen the Matrix of the material, produce SNO2 protective film to improve the anti-corrosion ability, and can prevent the phenomenon of "dezincification" . However, excessive addition of tin will increase the number of brittle compounds and affect the properties of the materials. The addition of rare earth elements can refine the grains, strengthen the Matrix and improve the cold and hot working properties of the materials. Aluminum Brass series more complex, complex aluminum brass containing manganese, nickel, silicon, cobalt and arsenic and the third and fourth alloy elements. HAl66-6-3-2 and HAL61-4-3-1, which have a lot of alloy elements, are made up of six elements, and some of the complicated processing of aluminum brass is originated from the special-shaped casting alloy. Different alloys often have different melting properties, so different melting processes are needed.

3. How to smelt aluminum brass

First, aluminum brass in the smelting process prone to "Foam" , and easy to be contaminated by aluminum or other metal oxide inclusions, reasonable smelting process should include some preventive measures. If there is aluminum oxide film on the surface of the melt, it can protect the melt to some extent, and no covering agent can be used when melting.

Theoretical analysis: Adding Zinc into the molten pool protected by Al2O3 film can reduce the volatilization loss of zinc. In fact, since the boiling of zinc may destroy the oxide film, the burning loss of zinc can be effectively avoided or reduced only when the proper flux is used to protect the melt more reliably. CRYOLITE has become an indispensable and important component in the flux used to smelt aluminum brass. Aluminum brass melt must not be allowed to overheat, to prevent the melt a large number of oxidation and inhalation. If there is more gas in the melt, either flux overlay or inert gas refining may be used, including re-flux and re-refining prior to pouring, and a bell jar is used to press the chloride salt into the melt for refining the melt. The high melting point alloy elements such as FE, MN and SI in complex al-brass should be added in the form of Cu-fe, Cu-Mn and so on.

In general, large pieces of scrap and copper should be first added to the furnace and melted. Finely chopped burden can be added directly to the melt, and zinc is added at the end of the smelting period. When pure metals are used as charge, phosphorus should be used to deoxidize them, then manganese (Cu-Mn) , iron (Cu-Fe) , then aluminum and finally zinc should be added. The contents of iron and manganese in complex aluminum brass HAl66-6-3-2 should be controlled at 2% ~ 3% and about 3% respectively. Otherwise, when their content is too high, some properties of the alloy may be adversely affected. Because of the low density of aluminum, if the melt is not thoroughly stirred, it is possible to cause uneven chemical composition. When there is a transition melt in the furnace, aluminum and some copper can be added first, and then zinc can be added after it is melted. When aluminum is added, a large amount of heat is released due to the fusion of copper and aluminum. The exothermic process can be used to speed up the melting process. However, if not handled properly, the intense exothermic reaction may cause the local temperature of the molten pool to be too high, resulting in the intense volatilization of zinc. In severe cases, a flame may be ejected from the furnace. The normal melting temperature of HAl67-2.5 is 1000 ~ 1100 °c, the normal melting temperature of HAl60-1-1, HAl59-3-2, HAl66-6-6-2 is 1080 ~ 1120 °c, the lower melting temperature should be adopted as far as possible. The charging and melting procedure is: copper + scrap + Cu-Mn + Cu-Fe + Cu-Ni + covering agent → melting → AL + Zn → melting → adding cryolite → stirring → fishing slag → sampling → heating → stirring → discharging. 

Source: Web Collation

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