Nondestructive flaw detection
Brass is widely used in the manufacture of mechanical equipment, such as heat exchanger copper pipe, automobile water tank, etc. because of its good mechanical properties, technological properties, conductivity, heat conduction and corrosion resistance. However, there is selective corrosion dezincification phenomenon in the use of brass. How to prevent dezincification corrosion is very important to improve the service life of the equipment. At present, the mechanism of dezincification corrosion of brass is not very clear. The main theories are: preferential dissolution mechanism, dissolution redeposition mechanism, double vacancy mechanism and percolation mechanism. Some researches have found that selective dissolution is a common form of dezincification corrosion of brass, especially in seawater. The measures to prevent dezincification of brass are mainly from metallurgical aspects, such as adding a small amount of as, B, Sb, rare earth and other elements in copper alloy can inhibit dezincification corrosion; in addition, corrosion inhibitor can also be used to slow down dezincification corrosion of brass. There are two forms of dezincification of brass: (1) layer dezincification: it refers to the preferential removal of zinc elements on the whole surface of copper alloy materials, the overall thinning of components, the gradual weakening of strength, and generally less destructive than plug dezincification. It mostly occurs in brass with high zinc content. (2) plug dezincification: the corrosion develops along the local area to the depth, and the local corrosion rate can reach 5 mm per year, but there is no obvious corrosion sign in the area around the hole, which is easy to cause brass pipe perforation or sudden brittle fracture. Most of them occur in brass with low zinc content or under weak oxidation conditions.