Calcium-aluminum alloy plays a key role in the formation of bubbles during smelting and casting, with metal oxides and other impurities.

　　During the forging process, there will be the occurrence of gas holes. So what is going on, and how can we prevent it? The Henan calcium-aluminum alloy network will provide an in-depth analysis for everyone, hoping to be of some help to you. Let's take a look together. Because calcium-aluminum alloys have serious oxidation and respiratory tendencies, they come into direct contact with furnace gas or external air during the melting process. Therefore, if the control during the melting process is not good, calcium-aluminum alloys can easily absorb gas and produce gas holes. The most common is pinholes. Pinholes refer to soluble gas holes in castings that are less than 1mm, mostly round, and unevenly distributed across the entire cross-section of the casting, occurring in the thicker cross-sections of the casting and areas with lower cooling rates. According to the distribution and appearance characteristics of soluble gas holes in calcium-aluminum alloys, pinholes can be divided into three categories.

　　(1) Spot-like pinholes: In high magnification, pinholes appear as small circles, with clear outlines that are continuous with each other. The number of pinholes per cubic centimeter can be counted, and their diameter can be measured. These pinholes can easily be distinguished from shrinkage, casting defects, etc.

　　(2) Network structure pinholes: In high magnification, pinholes are clustered and connected in a network structure, with a few large holes. It is difficult to check the number of pinholes over the total area, and the diameter of the pinholes cannot be measured.

　　(3) Composite gas holes: This is an intermediate type between spot-like pinholes and network structure pinholes. From high magnification, there are more large pinholes, but they are not round; they appear polygonal. Practical experience with calcium-aluminum alloys confirms that the main gas component causing gas holes due to respiration in calcium-aluminum alloys is radon, and its occurrence has no specific regularity. Usually, all or most castings from a single furnace have pinhole conditions; the same goes for materials, as various compositions of calcium-aluminum alloys can easily produce pinholes.

　　The formation of Henan calcium-aluminum alloys occurs when calcium-aluminum alloys absorb a lot of radon gas during melting and pouring, and continue to dissolve due to the decrease in solubility during cooling. Some materials introduce that the hydrogen dissolved in calcium-aluminum alloys is more, and its solubility increases with the rise in the temperature of the aluminum alloy liquid and decreases with the drop in temperature. When transitioning from liquid to solid, the solubility of hydrogen in calcium-aluminum alloys decreases by 19 times. Therefore, during the cooling and solidification process of the calcium-aluminum alloy liquid, at a certain moment, the hydrogen content exceeds its solubility and dissolves in the form of bubbles. The radon bubbles generated due to saturated hydrogen dissolution cannot be expelled in time, resulting in fine, dispersed gas holes during the solidification process, commonly referred to as pinholes. The contrast before the formation of radon bubbles is a function of the number of nucleation of radon bubbles, while metal oxides and other impurities play a key role in bubble formation.

　　Under normal manufacturing conditions, especially in thick sand mold castings, it is impossible to prevent the occurrence of pinholes. When melting and pouring calcium-aluminum alloys in a humid atmosphere, pinholes in the castings are particularly severe. This is why many people are often confused in production, as pinhole defects in calcium-aluminum alloy castings are less during dry seasons compared to rainy and humid seasons.

　　Generally speaking, for calcium-aluminum alloys, if the crystallization temperature range is large, the probability of network structure pinholes occurring is also much higher. This is because under normal forging manufacturing conditions, castings have a wide solidification temperature range, allowing calcium-aluminum alloys to easily develop well-developed dendritic crystal structures. In the later stages of solidification, the residual aluminum liquid in the voids of the network structure crystals may be isolated from each other, existing in similar closed small spaces. Due to the relatively small effects of external atmospheric pressure and the negative pressure of the aluminum liquid, when the residual aluminum liquid further cools and shrinks, a certain degree of vacuum may be generated (i.e., the compensation shrinkage channel is blocked), leading to the dissolution of saturated radon gas in the aluminum alloy and the formation of pinholes.