Discussion on the Causes of Porosity in Aluminum Alloy Die Casting
Because aluminum alloy die casting has severe oxidation and gas absorption tendency, it is in direct contact with furnace gas or the outside atmosphere during the smelting process. Therefore, if there is a slight improper control during the smelting process, the aluminum alloy can easily receive gas and form pores. The most common is pinholes.
Pinholes usually refer to the precipitation pores less than 1mm in the casting, the tension is round, and the distribution is uneven across the entire section of the casting, especially in the thicker section and the lower cooling rate. According to the distribution and shape characteristics of the precipitated pores in aluminum alloys, pinholes are divided into three types.
1. Mesh pinholes: In the macro layout, the pinholes are closely connected to form a network, and there are some large holes, which is not convenient to check the number of pinholes on the unit area, and it is also difficult to measure the diameter of the pinholes.
2. Point-shaped pinholes: In the macro layout, the pinholes are dot-shaped, and the outline is clear and does not continue. The number of pinholes per square centimeter can be calculated, and the diameter can also be measured. This pinhole is easily distinguished from shrinkage and looseness.
3. Comprehensive stomata: the middle type of point pinholes and net pinholes. From the macro layout, there are many large pinholes, but they are not dots, but polygons. The production practice of aluminum alloy die-casting proves that the gas component of the pore tight gas formed by aluminum alloy due to inhalation is hydrogen, and there is no inevitable discipline to follow. Aluminum alloy die casting often presents pinholes in the same furnace, and the material is no exception. Various components of aluminum alloy are prone to pinholes.