1. When the melting temperature of aluminum is too high, the reaction between iron crucible and zinc solution is accelerated, and the oxidation of iron on the crucible surface generates Fe2O3 and other oxides; iron also reacts with zinc solution to generate fezn13 compounds (zinc slag), which are dissolved in zinc solution. The burning loss of aluminum and magnesium element, the oxidation rate of metal, the amount of burning loss and the content of zinc slag increase. The hammer head will get stuck due to thermal expansion. The reaction of zinc and iron accelerated at high temperature. It will form hard particles of iron aluminum intermetallic compound, causing excessive wear of hammer head and gooseneck. The reaction of zinc and iron accelerated at high temperature. It will form hard particles of iron aluminum intermetallic compound, causing excessive wear of hammer head and gooseneck. Fuel consumption has increased accordingly. The higher the temperature is, the larger the crystallization is and the lower the mechanical properties are.
2. The melting temperature is moderate, the melting point of die-casting zinc alloy is 382-386 ℃, and the proper temperature control is an important factor for the composition control of aluminum alloy. In order to ensure the good filling fluidity of the alloy liquid, the temperature of the metal liquid in the zinc tank of the die casting machine is 415 ~ 430 ℃, the upper limit of the die casting temperature can be used for the thin-walled parts and the complex parts, and the lower limit can be used for the thick walled parts and the simple parts. The temperature of molten metal in smelting furnace is 430-450 ℃. The temperature of liquid metal entering into gooseneck is basically the same as that of zinc pot. The pouring temperature can be controlled by controlling the liquid metal temperature of the zinc pot.
3. When the melting temperature is too low, the fluidity of the alloy is poor, which is not conducive to forming and affects the surface quality of aluminum castings. The oil must be removed before the aluminium castings are treated. If there is oil stain on the aluminum casting, it will affect the treatment process. In the cleaning process of aluminum casting, the acid alkali property of cleaning agent is low. The cleaning agent shall be soluble in water, have good stability and good flushing performance, its pH value shall be between 9-11, and buffer shall be added to ensure the stability of the cleaning agent, so as to reduce the corrosion of metal. Acid degreasing shall be carried out after cleaning. Acid degreasing can remove the oil stain on the surface of aluminum casting, but it has higher requirements on the corrosion protection of parts. Aluminum casting manufacturers can prepare degreaser with moderate acidity, including corrosion inhibitor with sodium polyphosphate as the main component and active agent with low alkalinity to remove oil stains, so as to achieve good degreasing and cleaning effect.
3. Alkali corrosion of aluminum castings. Because there are many impurities in the aluminum castings of zinc fittings, it is easy to produce white corrosion products due to oxidation during the treatment process, thus affecting the effect of the treatment process. The oxide and corrosion products on the surface of aluminum casting can be transformed into black or gray black loose layer by alkali corrosion solution. After acid treatment, the surface of aluminum casting is bright and bright. In addition, cast aluminum also needs the role of chemical conversion film. Because of its porosity, the chemical conversion film can increase the combination with the bottom layer, thus improving the corrosion resistance.