Processing technology of Zirconium alloy materials

Basics of Zirconium alloy materials

The earth's crust contains about 0.026% zirconium, and the total content is 2.5 times that of copper. Zirconium has high melting point, moderate density, excellent strength, low expansion coefficient and small elastic modulus, and has good corrosion resistance in various media at high temperature. Zirconium and zirconium alloys have excellent pressure processing and machining properties, and can be processed into a variety of zirconium forgings and profiles required by modern industry.

At present, the production processes of Zr Sn and Zr NB zirconium alloys are relatively mature. The common brands of Zr Sn series include Zr-2 and ZrV. The typical brand of Zr NB series is zr-2.5nb. In Zr Sn alloys, the addition of alloy elements tin, iron, foil and nickel can improve the strength, corrosion resistance and thermal conductivity of corrosion-resistant film, and also weaken the corrosion sensitivity of the material surface.

Processing technology of forging zirconium

Zirconium alloy extrusion

Zirconium alloy is mainly used for cladding parts of structural materials in nuclear reactors. It is one of the core materials used in reactors. Most of these cladding components are zirconium alloy pipes and zirconium bars, accounting for about 75%~80% of their total use. These tubes and zirconium bars are obtained by extrusion forming, and most zirconium alloys have good extrusion forming properties.

Zirconium alloy materials commonly used in nuclear industry generally have poor fluidity, which is easy to produce product quality defects or excessive extrusion pressure in the extrusion process, resulting in stuffy cars. Therefore, the extrusion process of zirconium alloy requires that ingots and dies should be lubricated sufficiently before extrusion. Therefore, China Heavy Machinery Research Institute Co., Ltd. has researched and found a special lubricant for zirconium alloy extrusion, which mainly includes aluminum disulfide, glass powder, graphite, water and adhesive. The reasonable lubrication process can effectively avoid the metal sticking to needle, cylinder and die in the extrusion process.

Zirconium alloy forging

As an important step in the production of zirconium alloy products, forging is mainly used to break the as cast structure and improve the comprehensive properties of the metal, that is, while obtaining a reasonable billet size, it provides the necessary organizational basis for the subsequent quenching, extrusion and rolling process. In actual production, in order to ensure the quality of forgings, appropriate heating specifications should be formulated for the heating of ingots and deformed billets, and the atmosphere in the heating furnace should be well controlled. When other process parameters are kept unchanged, different pre forging heating systems have important effects on the microstructure and properties of zirconium alloy billets.

Zirconium ingots obtained after high-temperature melting of sponge zirconium have poor microstructure and properties due to casting defects such as inclusions and looseness. Therefore, zirconium alloy ingots also need to undergo large forging deformation and heat treatment process to obtain ideal internal microstructure for further processing and forming. According to the current research and production results, zirconium and zirconium alloys have good free forging properties.

Due to the high chemical activity of zirconium and zirconium alloys in hot state, considering the heating quality before forging, zirconium and zirconium alloys widely used in industrial production are generally heated by medium and high temperature resistance furnaces, which can accurately control the furnace temperature and heating speed. Zirconium alloy ingots generally adopt two-stage heating specification. When their surface temperature reaches the predetermined heating temperature, they can be kept warm for a certain period of time. The holding time cannot be too long to avoid excessive oxidation of zirconium alloy surface.

Zirconium alloy has relatively good high-temperature deformation performance. There are no special requirements for the equipment used for forging. Common forging equipment for ferrous metals and non-ferrous alloys can be selected, such as forging hammer, mechanical press and hydraulic press.