Smelting is the first key link in the casting of aluminum-magnesium alloy, if it is not well controlled in this link, any subsequent process can not harvest qualified castings.
When melting, in addition to taking the means of low temperature rapid melting, the most important thing is to prevent the oxidation of aluminum magnesium alloy, so the isolation of oxygen is crucial. Because the chemical reaction between magnesium and gas occurs very fast, as long as the alloy liquid is in contact with the air, it will immediately generate a layer of black magnesium oxide, which has a melting point of about 2800 ° C, and is gradually included in the interior during the solidification of the casting, resulting in a gradual serious decline in mechanical properties.
Therefore, when the magnesium alloy ZL301 begins to melt, it must be ensured that it is in a vacuum state and cannot contact with air, and the consistency and thickness of the covering layer must be strictly controlled during the whole smelting process. If the covering agent is too thick, it is easy to form a hard shell, resulting in some voids containing gas, and if it is too weak, it will make the cover is not strict, resulting in the liquid surface exposed to the air.
The covering agent must be melted in advance and prepared to remove moisture and other impurities that are easy to produce gas. After cold grain solidification, it is broken and screened, and strictly sealed and stored.
The main raw material of smelting magnesium alloy ZL301 is 2° magnesium ingot or special 1° aluminum ingot. Before smelting, it must be baked at a temperature of 300-350 ° C, and the baking time is about 2 to 4 hours. If there is serious oxidation on the surface of the ingot, the oxide should be removed before baking.
After the preparation work is done, it is necessary to melt, and different melting operation procedures are different. Using a single smelting, no beryllium, titanium, and no refining method is the most ideal. The main melting steps of this method are: control the range of the covering agent at any time during the melting process, especially control the consistency and thickness of the covering agent, and pay attention to the stirring method after the addition of pure magnesium. In addition, the temperature of melting must be controlled well, and the temperature should not be too high or too low. This smelting method has the advantages of convenience, safety, low cost and good quality.