In order to smelt high-quality aluminum melt, qualified raw materials should be used first. The raw materials must be scientifically managed and properly treated, otherwise the quality of the alloy will be seriously affected. Production practices have proved that the control of raw materials (including metal materials and auxiliary materials) will cause the castings to be scrapped in batches.
(1) Raw materials must have qualified chemical composition and organization. The specific requirements are as follows:
In addition to analyzing the main components and impurity content, the alloy ingots entering the factory are also inspected for low accompanying organization and fracture. Practice has proved that the use of aluminum liquid containing severe shrinkage cavities, pinholes, and air bubbles makes it difficult to obtain dense castings, and may even cause the entire furnace and the entire batch of castings to be scrapped.
Some people have studied the influence of aluminum-silicon alloy ingot on the pinhole of aluminum alloy. It is found that there is no pinhole when using molten pure casting sand type test piece. When adding low-structure and unqualified aluminum-silicon alloy ingot, test piece pinhole Severe, and the grain size is large. The reason is due to the heritability of the material. The aluminum-silicon alloy and heredity increased with the increase of the content, and the amount of silicon reached 7%, which was genetically significant. Continue to increase the silicon content to the eutectic composition, and the heredity is slightly reduced. In order to solve the casting defects caused by the genetics of the charge, it is necessary to select aluminum ingots, intermediate alloys and other charge materials with high metallurgical quality. The specific criteria are as follows:
(1) There should be no pinholes or stomata on the fracture
The pinhole should be within three levels, and the local (not exceeding 25% of the tested area) should not exceed three levels. Those who exceed the third level must adopt the remelting method to reduce the pinhole. The remelting refining method is the same as the general aluminum alloy smelting, and the casting temperature should not exceed 660 ° C. For those aluminum ingots and alloy ingots with large original grain size, the lower ingot mold temperature should be used first to make them rapidly solidify and refine the crystal. grain.
2, charge treatment
The charge should be sandblasted before use to remove rust, grease and other dirt on the surface. The aluminum alloy ingot and the metal-type returning material with a relatively clean surface can be left without blowing, but the iron filter and the inserts mixed in the charge should be eliminated. All the charge should be pre-filled before entering the furnace. Heat to remove the moisture attached to the surface and shorten the melting time by more than 3 hours.
3. Management and storage of charge
Reasonable storage and management of the charge is important to ensure the quality of the alloy. The charge should be stored in a warehouse where the temperature does not change much and is dry.