Because the aluminum alloy has a severe oxidation and gas tendency, in the process of melting directly with the gas furnace or outside air contact. Therefore, such as smelting process control slightly improper, aluminum alloy very easily absorbed by the gases and the formation of porosity, the most common is pinhole. Pinhole is usually less than 1mm separation of porosity in castings, assumes the circular, uneven distribution in the whole section of castings, especially in the casting of thick section and cooling rate smaller parts. According to the characteristics of distribution and shape of aluminum alloy separation of porosity, pinhole and divided into three categories.
1 mesh pinhole: in the low magnification of the organization in a dense network of holes, a small number of large holes, the size of the unit area to check the number of holes, it is difficult to measure the diameter of the pinhole.
2. Point pinhole: in the low times microstructure pinhole is round point, contour pinhole clear and discrete, count the number of pinholes per square centimeter area, and it is measured that the diameter. The pinhole easily and the shrinkage hole, shrinkage and other to be distinguished.
3. Comprehensive stomatal: it is punctate pinhole and reticular pinhole in the middle, from the point of view of the low times microstructure, more large pinhole, but is not a dot shaped and were polygonal.
Aluminum alloy production practice proved, aluminum alloy due to the suction and the formation of porosity of gas compositions is hydrogen and its appearing no certain rules to follow, is often a furnace all or most of the castings are pinhole phenomenon; materials is no exception, the various components of the aluminum alloy easy generation pinhole.