1. The first alloy melting process: The initial step involves the production of Al-Cu master alloys. A graphite crucible is preheated to approximately 200°C, and a protective paint is applied two to three times, allowing it to dry thoroughly before use. Broken aluminum ingots are then placed into the painted area. Once the crucible begins to swirl, the entire aluminum ingot can be added, followed by the introduction of charcoal powder during the heating process. After the aluminum has fully melted, preheated electrolytic copper is introduced into the molten aluminum. Continuous stirring ensures that the copper dissolves completely in the aluminum. Once the copper is fully dissolved, the power is turned off, and the refining process begins.
Commonly used refining agents include zinc chloride or hexachloroethane. Due to their lower density compared to the alloy, they are pressed into the melt using a bell-shaped tool to ensure adequate reaction with the metal. These agents are typically packed in paper and compressed for efficient application. After refining, the slag and charcoal are removed by pouring the molten metal into ingot molds. The thickness of the intermediate alloy ingot should be between 40 and 50 mm; if too thick, it becomes more difficult to crush later on.
The second stage involves melting the zinc alloy. The crucible is preheated to a dark red color, and about 90% of the zinc and return charge are added first, followed by the addition of the master alloy. The typical composition includes 5% zinc, 5% aluminum, and 25% magnesium. When the molten metal reaches a temperature above 650°C, the required amount of magnesium is added, followed by 0.5% zinc chloride for refining. The remaining zinc and return charge are then added, and the mixture is stirred and skimmed. Finally, a sample is taken for inspection, and the temperature is checked.
If the alloy composition meets the requirements and the temperature is suitable, the metal can be poured. The pouring temperature should be between 550°C and 650°C, and the fracture analysis before casting should show a silver or white color, which is acceptable.
Although this method is widely used, it has several drawbacks, including the need for high-temperature operations and a relatively complex procedure.
2. Pure metal smelting: The process starts with preheating the smelting furnace to a dark red color, with temperatures ranging from 500°C to 600°C. Charcoal is added as a covering agent to prevent oxidation. During electric melting, the furnace must be carefully monitored to avoid overheating. Once the electrolytic copper or copper ingots are added, phosphorus copper is used for deoxidation, accounting for 0.6% to 1.0% of the total copper content. After the copper melts, all the aluminum is introduced. Once the aluminum is fully melted, 90% of the zinc is added. When the molten metal reaches a temperature of 650°C or higher, a bell jar is used to press in the required amount of magnesium. Then, the refining agent is introduced, and after the reaction subsides, the mixture is left to settle for 5 to 10 minutes. The remaining zinc is then added to cool the mixture, followed by stirring and skimming. A final sample test and temperature check are conducted. If the alloy composition is within specification and the temperature is appropriate, the metal can be poured into molds.
This method requires operation at temperatures exceeding 1000°C, making it less commonly used in industrial settings due to its complexity and energy demands.
3. Low-temperature direct smelting new process: This innovative low-temperature direct smelting process involves adding the required amount of copper to a molten zinc bath, followed by the addition of aluminum and magnesium, along with the remaining zinc. This approach effectively addresses the shortcomings of the traditional methods. The alloys produced through this process have passed all quality tests, demonstrating excellent performance and consistency.
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