Aluminum alloy, which is made by adding some metal or non-metal elements to pure aluminum, is a new type of alloy material. Because of its small specific gravity, high specific strength and good comprehensive performance, it is widely used in the aviation industry and automobile manufacturing. Industry, power instrument, tools and civil appliance manufacturing and so on. With the development of the national economy and the advancement of the process of economic integration, its production and consumption have greatly exceeded that of steel. Strengthening the research on the properties of aluminum alloy materials and ensuring the excellent quality of aluminum alloy castings is not only the obligatory responsibility of each of our scientific and technological workers, but also the top priority that is closely related to our daily life. Combined with the author's practical experience in the production of aluminum alloy castings, this article discusses the problems of pores and prevention of aluminum alloy castings.
Type of stomata
Because aluminum alloy has a serious tendency to oxidize and inhale, and it is in direct contact with the furnace gas or the outside atmosphere during the smelting process, if the control is not properly controlled during the smelting process, the aluminum alloy can easily absorb gas and form pores. The most common is a pinhole. Pinhole (gas porosity/pin-hole), usually refers to the precipitation pores less than 1mm in the casting, which are mostly circular and unevenly distributed on the entire section of the casting, especially in the thick and large section of the casting and the cooling rate is small. part. According to the distribution and shape characteristics of aluminum alloy precipitation pores, pinholes can be divided into three categories ①, namely:
(1) Dot-shaped pinholes: In low-magnification tissue, the pinholes are in the shape of dots, and the outlines of the pinholes are clear and discontinuous. The number of pinholes per square centimeter can be counted and their diameters can be measured. Such pinholes are easily distinguished from shrinkage cavities and shrinkage porosity.
(2) Mesh pinholes: In the low magnification tissue, the pinholes are densely connected to form a network, 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 the pinholes.
(3) Comprehensive stomata: It is an intermediate type between point pinholes and mesh pinholes. From the perspective of low magnification, there are many large pinholes, but they are not dot-shaped, but polygonal.
The practice of aluminum alloy production has proved that the main gas component of the pores formed by the aluminum alloy due to inhalation is hydrogen, and there is no certain rule to follow. No exception, aluminum alloys of various compositions are prone to pinholes.