Special metal materials refer to metal materials with special properties, which are made by special molding methods or by composition design. For example, amorphous metal is a metal material with high strength, high magnetic permeability and high corrosion resistance that passes molten metal or alloy through a special device. For example, superalloys are metal materials with excellent heat resistance obtained through composition design, including iron-based austenitic heat-resistant steels, nickel-based alloys, and cobalt-based alloys.
Powder sintered alloy is a metal material or part with a certain shape made by powder sintering by powder metallurgy technology. Powder metallurgy is a relatively old technology. People used this method to make multi-pore oil bearings in 1870, tungsten wires in 1909, hard alloys in 1927, and magnetic materials later. my country’s powder metallurgy industry has developed rapidly since 1958, both in quantity and variety. In 1971, the output of iron-based powder sintered alloy mechanical parts was 10 times that of 1966. In recent years, China’s powder metallurgy industry and technology have shown a trend of rapid development, and it is one of the fastest growing industries in China’s general machinery parts. The annual output value of the powder metallurgy industry is increasing at a rate of 35%.
Powder metallurgy technology is a less and non-cutting process, which can reduce the processing amount of parts, save materials and improve labor productivity. It can manufacture materials and parts that cannot be manufactured or are difficult to manufacture by other processes, such as high melting point metal materials (W, Mo and some metal compounds), composite materials (cermets and other composite materials), etc. Powder metallurgy is widely used in the manufacture of various mechanical parts, tool parts, electromagnetic components, heat-resistant workpieces, etc., but limited by pressing equipment and sintering equipment, the production efficiency is not high enough.
Typical porous metal materials include aluminum foam, magnesium foam, nickel foam, and the like.
Due to the special functions of porous metal materials such as small volume density, sound insulation, sound absorption, shock absorption, heat insulation, electromagnetic wave shielding and non-combustibility, some developed countries have widely used porous metal materials in transportation, transportation, machinery, construction, electronics and communications industries. For example, aluminum foam materials are applied to automobiles, tanks, armored vehicles, motor vehicles, military vehicles, subway trains, and high-speed trains to make floors, shells, and partition walls to achieve sound insulation, shock absorption, and heat insulation effects; On submarines, it can absorb and insulate sound, so that the submarine runs silently and is not easy to be found by the enemy; it can be used to make car bumpers, which can absorb the impact force, protect people and cars from harm when they are hit, and improve safety; It is used to make sound insulation screens for elevated rails, highways and railways to reduce noise pollution to the environment.
There are three main methods for manufacturing foamed aluminum materials: infiltration casting method, powder manufacturing method and aluminum direct melting and foaming method. The through-hole foam aluminum material is produced by infiltration casting method, which has low sound insulation ability and high density, and is suitable for filtering high-temperature liquid and gas. The powder metallurgy method can be used to produce foamed aluminum materials with small pores, which can be used to make car engines and trunk covers, car parts, etc. The direct aluminum melting and foaming method can be used to prepare foamed aluminum materials with low density, strong sound insulation ability and low thermal conductivity, which is suitable for sound insulation, heat insulation and energy absorption materials. This method has low production cost and is suitable for large-scale production.
Application
Cemented carbide is mainly used for knives, cold working molds, measuring tools and wear-resistant parts in the mechanical casting industry, but the largest amount is used for knives. Tungsten-cobalt (YG) alloys are mainly used to cut and process brittle materials, such as cast iron, non-ferrous metals and alloys, colloids and other non-metallic materials; tungsten-cobalt-titanium (YT) alloys are mainly used to process tough materials, such as various steel material. In addition, our country also produces a new variety of alloy steel YW1 and YW2, also known as general “tungsten carbide” (also called universal alloy), because it can be used as YG alloy to cut cast iron and non-ferrous metals, and can be used to cut various kinds of steel. In addition to being used for cutting tools, cemented carbide is also used to make cold drawing dies, cold stamping dies, cold extrusion dies and cold heading forging dies. In addition, after using cemented carbide, the life of tools and parts is greatly improved, which can greatly improve productivity and product quality.
Shape memory alloys have many wonderful practical uses. The hemispherical antenna with a diameter of several meters placed on the moon by the Apollo lunar module of the United States is made of shape memory alloy material. Then use the temperature of sunlight to re-deploy the antenna and restore its original shape. In dangerous places such as aviation, aerospace, nuclear industry and submarine oil pipelines, in order to ensure the safety of the system, memory alloy sleeves are often used at the joints of the pipelines. The shape memory alloy is used to process the casing with an inner diameter 4% smaller than the outer diameter of the pipe to be connected, and then insert both ends of the casing at low temperature. When the temperature rises to normal temperature, the casing returns to its original shape and forms a tight bond.
In life, memory alloys can be used to open doors and windows to achieve the purpose of automatically adjusting the temperature. It is believed that the application prospects of shape memory alloys will be broad.
