Die casting alloy melting process
The die-casting alloy melting process is a key factor in determining the quality of die-cast products. By precisely controlling the melting temperature, alloy composition, impurity content, and melt processing, it provides a stable molten metal for subsequent die-casting. The melting characteristics of different alloys vary significantly. For example, aluminum alloy melting requires strict control of hydrogen content (the solubility of hydrogen in molten aluminum increases sharply with increasing temperature), while zinc alloy melting requires attention to the content of heavy metal impurities such as lead and cadmium (due to increasingly stringent environmental protection requirements). A high-quality melting process can control the fluctuation of the alloy’s mechanical properties to within 5%, significantly improving the consistency and reliability of castings.
The selection and optimization of melting equipment has a profound impact on process performance. Commonly used die-casting alloy melting equipment includes crucible furnaces, reverberatory furnaces, and induction furnaces. Induction furnaces are the preferred choice for high-precision die-casting production due to their rapid heating speed and excellent temperature uniformity (temperature differentials can be controlled within ±5°C). Induction furnaces utilize electromagnetic induction heating principles to uniformly stir the melt, effectively reducing segregation. Furthermore, their excellent airtightness reduces alloying element burn-off. For example, in aluminum alloy melting, the use of vacuum induction furnaces can reduce magnesium burn-off rates from 15% in traditional crucible furnaces to below 3%. Furthermore, modern melting equipment is generally equipped with automatic temperature measurement and control systems, achieving a temperature control accuracy of ±2°C, meeting the melting requirements of various alloys.
Precise control of alloy composition is at the heart of the smelting process. The performance of die-cast alloys depends largely on their chemical composition. For example, the silicon content in aluminum alloys directly affects fluidity (optimal fluidity is achieved when the silicon content is between 7% and 12%), while the copper content affects strength (increasing copper content increases strength but decreases corrosion resistance). During the smelting process, alloy composition must be monitored in real time through spectral analysis, and adjustments must be made promptly if deviations exceed the standard. Taking ADC12 aluminum alloy as an example, its silicon content is required to be 9.6%-12.0%, and its iron content is ≤1.3%. Through online composition testing and an automatic batching system, the composition qualification rate can be increased to over 99%. At the same time, the content of impurity elements must be strictly controlled. For example, if the iron content in zinc alloy exceeds 0.07%, it will cause brittleness in the casting, which requires the addition of manganese to neutralize it.
Melt treatment is a key step in improving the quality of die-cast alloys. For aluminum alloys, melt treatment primarily involves degassing, slag removal, and modification. Degassing typically involves bubbling an inert gas (such as argon). As the bubbles rise through the melt, they absorb hydrogen, reducing the hydrogen content to below 0.1 mL/100 g. Slag removal involves adding refining agents (such as hexachloroethane) to aggregate and float non-metallic inclusions. After slag removal, the inclusion content can be controlled to below 0.01%. Modification primarily targets eutectic aluminum alloys. Adding sodium or strontium refines the eutectic structure, increasing the elongation of the casting by over 20%. For magnesium alloys, melt treatment also requires consideration of oxidation protection. Typically, a mixture of SF6 and N2 (1:99 by volume) is introduced during the smelting process to form a protective film that prevents combustion of the magnesium liquid.
Energy-saving and environmentally friendly transformation of smelting processes is a key trend in industry development. Traditional smelting processes are energy-intensive and polluting. For example, crucible furnaces have a thermal efficiency of only 30%-40%, and emit large amounts of dust. Modern smelting processes achieve energy conservation and consumption reduction through waste heat recovery and clean energy substitution. For example, installing a waste heat boiler in the flue of the smelting furnace can recover more than 30% of the flue gas waste heat, which can be used to preheat combustion air or heat circulating water, reducing overall energy consumption by 20%-30%. At the same time, using natural gas instead of coal as fuel can reduce sulfur dioxide emissions by more than 90%. The use of dust collection systems (such as bag filters) can control dust emission concentrations to below 30mg/m³, meeting strict environmental standards. In the future, with the popularization of intelligent smelting systems, die-cast alloy smelting will achieve energy conservation, environmental protection, and high efficiency throughout the entire process.
