Magnesium is a young metal that was developed in the 20th century; its chemical activity is strong, and its affinity with oxygen is large. It is often used as a reducing agent to replace metals such as titanium, zirconium, uranium, and beryllium. Magnesium metal is non-magnetic and has good heat dissipation. The structural properties of magnesium are similar to those of aluminum, so it has various uses as a light metal, and can be used as an alloy material for aircraft and missiles. However, magnesium is flammable at the ignition point of gasoline, which limits its application.
Due to the low mechanical strength of pure magnesium, aluminum-magnesium alloy is mainly used. It is light and has a certain strength. Used in the manufacture of cars and trains. Magnesium metal is the main alloying element in aluminum alloys, and the annual demand in the world is about 150,000 tons. my country uses magnesium as an alloying element, and the annual demand is about 10,100 tons. There are 4 main series of magnesium alloys: Mg-Al-Zn-Mn (AZ series), Mg-Al-Mn (AM series), Mg-Al-Si (AS series), Mg-Al-rare earth (AE series), They each have unique performance, can meet the needs of various functions, and will be widely used.
Applications in the defense industry
Modern warfare requires the military to have the ability to rapidly deploy movement in long distances, and requires lightweight weapons and equipment. A large number of light metal materials will be used in hand-held weapons, armored combat vehicles, transport vehicles, and aviation-guided weapons.
Lightweight is an important direction to improve the combat performance of weapons and equipment. The lightweight properties of magnesium determine that magnesium alloys are indispensable structural materials for the production of aerospace vehicles, military aircraft, missiles, high-mobility chariots, and ships, such as rocket heads, missile ignition heads, and spacecraft components. and flares etc. Therefore, vigorously developing the application range of magnesium alloys is the need for national defense modernization.
Application in the steel industry
Magnesium is currently mainly used for casting in the metallurgical industry and desulfurization of steel. With the increasing demand for high-strength and low-sulfur steel used in the automotive industry, oil and natural gas pipelines, offshore drilling platforms, bridge construction and other fields, in recent years, my country's Anshan Iron and Steel, Baosteel, Wuhan Iron and Steel, Benxi Iron and Steel, Baotou Iron and Steel, Panzhihua Iron and Steel, Shougang And other iron and steel enterprises have used magnesium powder for deep desulfurization to obtain high-quality steel, and achieved good results. Magnesium powder is used for steel desulfurization and has a huge potential market.
Magnesium is one of the lightest structural metal materials, and has the advantages of high specific strength and specific stiffness, strong damping, good machinability, and easy recycling. Magnesium alloys are used in the automotive industry at home and abroad to reduce weight, save energy, reduce pollution and improve the environment. At present, the world's largest consumption of magnesium alloys is in the automobile industry. In order to reduce the total weight of automobiles, magnesium alloy die-casting parts are used more and more in automobiles, including instrument panels, steering wheels, gearboxes, oil bottoms, cylinder covers, seats Frame and wheel hub (WheelHub) and other key components. According to statistics, in 2003, the average amount of magnesium alloy used in each automobile in the United States reached about 60 kilograms. The American Association for Automotive Materials (USAMP) expects that the amount of magnesium alloy used in each automobile produced in North America will reach about 160 kilograms by 2020. At present, the use of magnesium alloys in the automobile industry in China is still in its infancy. Except for Shanghai Volkswagen, other automobile manufacturers have no specific development plans for the manufacture of magnesium alloys. The fuel consumption of automobiles per 100 kilometers in developed countries will eventually achieve the goal of 3 liters. Magnesium used in European automobiles accounts for 14% of the total magnesium consumption, and it is expected to increase at a rate of 15% to 20% in the future. Data shows that the growth rate of global magnesium alloys in automotive die castings has remained at the level of 15% for many consecutive years, which is a new industry highlight at present and in the future. my country's Dongfeng, Changan and other automobiles have begun to use magnesium alloys. Soon, Chongqing, Chengdu and other countries will become production bases for the research, development and application of magnesium alloys for automobiles in my country. Therefore, comprehensively promoting the use of magnesium alloy products in automobiles will become an important development direction for the new material industry.
Other applications - magnesium's lightweight properties bring great prospects for magnesium applications. As one of the effective methods to prevent metal corrosion, magnesium sacrificial anodes can be widely used in underground iron pipelines, oil pipelines, storage tanks, offshore facilities, and civil use.
In addition, magnesium powder is also used in the manufacture of chemical products, pyrotechnics, signal flares, metal reducing agents, paint coatings, welding wires and nodularizing agents for ductile iron. Magnesium is flammable, so it can be used as a flare. The principle is that the flare is filled with magnesium, aluminum, sodium nitrate, barium nitrate and other substances. After detonation, magnesium burns rapidly in the air, emitting a dazzling white light containing ultraviolet rays, and at the same time releasing heat to decompose nitrates. Compared with plastic, magnesium alloy has the advantages of light weight, high specific strength, good vibration damping, good thermal fatigue performance, not easy to age, good thermal conductivity, strong electromagnetic shielding ability, very good die casting process performance, especially easy to recycle. It is a new generation of high-performance structural materials to replace steel, aluminum alloys and engineering plastics. In order to adapt to the development trend of high integration and miniaturization of electronic and communication devices, magnesium alloys are ideal for transportation, electronic information, communications, computers, audio-visual equipment, portable tools, motors, forestry, textiles, nuclear power plants and other products. Material. Developed countries attach great importance to the development and application of magnesium alloys, especially in the application of portable electronic products such as auto parts and notebook computers. The annual growth rate is 20%, which is very eye-catching and the development speed is amazing.
As a home appliance city, Qingdao, my country, has invested 210-350 million yuan successively to manufacture mobile phone casings, digital cameras, laptop computers, PDA casings, high-end audio-visual equipment casings and other products, with an annual output of 16 million castings, becoming the first magnesium alloy. Develop and apply industrialization base. Magnesium alloy profiles and pipes are also used to make bicycle frames, wheelchairs, rehabilitation and medical equipment.
New Development of Magnesium Alloys
Poor heat resistance is one of the main reasons that hinder the wide application of magnesium alloys. When the temperature rises, its strength and creep resistance drop significantly, making it difficult to be used as a material for key parts (such as engine parts) in industries such as automobiles. be more widely used. The alloying elements used in the developed heat-resistant magnesium alloys are mainly rare earth elements (RE) and silicon (Si). Rare earth is an important element used to improve the heat resistance of magnesium alloys.
The rare earth-containing magnesium alloys QE22 and WE54 have high temperature strength comparable to that of aluminum alloys, but the high cost of rare earth alloys is a major obstacle to their widespread application.
The corrosion resistance of magnesium alloys can be solved in two ways: ① Strictly limit the content of impurity elements such as Fe, Cu, and Ni in magnesium alloys. For example, the corrosion resistance of high-purity AZ91HP magnesium alloy in the salt spray test is about 100 times that of AZ91C, surpassing that of die-cast aluminum alloy A380, and much better than low carbon steel. ② Surface treatment of magnesium alloys. According to different corrosion resistance requirements, chemical surface treatment, anodizing treatment, organic coating, electroplating, electroless plating, thermal spraying and other methods can be selected. For example, the corrosion resistance of electroless plated magnesium alloy exceeds that of stainless steel.
In the process of smelting and casting magnesium alloys are prone to violent oxidative combustion of flaming alkanes. Practice has proved that flux protection method and SF6, SO2, CO2, Ar and other gas protection methods are effective flame retardant methods, but they will cause serious environmental pollution in application, and reduce alloy performance and increase equipment investment. Adding calcium to pure magnesium can greatly improve the anti-oxidative combustion ability of magnesium liquid, but because adding a large amount of calcium will seriously deteriorate the mechanical properties of magnesium alloys, this method cannot be applied to production practice. Hinge can prevent further oxidation of magnesium alloy, but when the content of hinge is too high, it will cause grain coarsening and increase the tendency of hot cracking.
The room temperature strength and plastic toughness of the existing magnesium alloys need to be further improved. Adding Ca and Zr to Mg-Zn and Mg-Y alloys can significantly refine the grains and improve their tensile strength and yield strength; adding Ag and Th can improve the mechanical properties of Mg-RE-Zr alloys, such as containing Ag's QE22A alloy has high room temperature tensile properties and creep resistance, and has been widely used as high-quality castings for aircraft and missiles; through rapid solidification powder metallurgy, high extrusion ratio and equal channel angular extrusion, the magnesium alloy can be The grains are processed very finely to obtain high strength, high plasticity and even superplasticity.
Magnesium alloy forming is divided into two methods: deformation and casting. Currently, the casting forming process is mainly used.
Die casting is the most widely used method of forming magnesium alloys.
The new magnesium alloy die-casting technologies developed in recent years include vacuum die-casting and oxygen-charged die-casting. The former has successfully produced AM60B magnesium alloy automobile wheels and steering wheels, and the latter has also been used to produce magnesium alloy parts for automobiles
Magnesium alloys are the lightest metal structural materials in engineering applications and are widely used in aerospace, military, and automotive industries. Replacing aluminum and steel with magnesium can greatly reduce structural weight. Weight reduction is of great significance to structural parts such as aerospace, aviation, electronics and communications, especially transportation tools.
my country is rich in magnesium resources, and the production capacity, output and export of primary magnesium rank first in the world. Therefore, how to make use of my country's magnesium resource advantages, transform magnesium resource advantages into technological and economic advantages, promote national economic development, and enhance the international competitiveness of my country's magnesium industry is an urgent task before us.
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