Because aluminum alloys have a severe tendency to oxidize and inhale, they are directly in contact with furnace gas or the outside atmosphere during the smelting process. Therefore, if the control is slightly improper during the smelting process, the aluminum alloy can easily absorb gas and form pores, the most common It is a pinhole. Pinholes usually refer to the precipitating pores of less than 1mm in the casting, which are mostly round and are not evenly distributed over the entire cross section of the casting, especially in the thick cross section of the casting and the place where the cooling rate is small. According to the distribution and shape characteristics of aluminum alloy precipitation pores, pinholes can be divided into three categories.
1. Reticulated pinholes: pinholes are densely connected in a network at low magnification, and there are a few large holes. It is inconvenient to check the number of pinholes per unit area, and it is difficult to measure the diameter of pinholes.
2. Point-shaped pinholes: pinholes are dot-shaped in low-magnification tissue, the pinholes are clearly outlined and discontinuous with each other, the number of pinholes per square centimeter area can be counted, and the diameter can be measured. This kind of pinhole is easily distinguished from shrinkage and shrinkage.
3. Comprehensive stomata: It is an intermediate type of dot-shaped pinholes and mesh-shaped pinholes. From a low magnification point of view, there are many large pinholes, but they are not dot-shaped but polygonal.
The production practice of aluminum alloy has confirmed that the main gas component of the aluminum alloy due to inhalation to form pores is hydrogen, and its emergence has no certain rules to follow, often all or most of the castings of a furnace have pinholes; materials No exception, aluminum alloys of various compositions are prone to pinholes.