1 Foreword  Cold shrinkage cable terminal,Low pressure cold shrinkage terminal, Low pressure cold shrinkable intermediate connector, Cold shrinkable insulated straight pipe ShenZhen FUJI Electric Material Co., Ltd , https://www.sinofuji.com
Magnesium is the lightest engineering metals, but the mechanical properties and corrosion resistance of pure magnesium can be low, its application is less, the mechanical properties can be improved by adding a certain amount of magnesium alloying elements and corrosion. As the lightest engineering metal material, magnesium alloy has a specific strength higher than that of engineering plastics, and has a series of advantages such as good castability, machinability, thermal conductivity, damping, electromagnetic shielding ability and easy recycling. As an alternative to aluminum alloy magnesium alloy, steel and plastics materials to achieve the desired reduction in weight, wherein the maximum potential to replace aluminum alloy. In recent years, with the increasing awareness of energy conservation and environmental protection, the use of magnesium alloys has been expanding. In addition to applications in the aerospace industry and the automotive industry, it is also widely used in electronic products, power tools, household appliances, medical and sports equipment, Leisure goods and other fields.
2 Research progress of magnesium alloy
Magnesium alloys can be classified into magnesium-aluminum alloys, magnesium- zinc alloys, magnesium-rare earth alloys, magnesium- lithium alloys, and the like, depending on the chemical composition. Although magnesium alloys have many advantages, they are limited in their use due to their shortcomings such as high temperature resistance, poor corrosion resistance and poor toughness. To this end, researchers at home and abroad have done a lot of work to improve and improve the performance of magnesium alloys.
2.1 Improvement of high temperature performance
Most magnesium alloys belong to a close-packed hexagonal structure with only four independent slip systems and poor plastic deformation. According to the Von Mises criterion, if a polycrystalline material is plastically deformed and maintains its integrity at the grain boundaries, each grain must have at least five independent slip systems. Creep is a slow plastic deformation process under high temperature conditions. Compared with the normal temperature stretching process, not only the slip system but also the grain boundary slip is observed in the microscopic mechanism. Grain boundary slip during creep will provide two other effective slip systems, in which case the alloy will undergo high temperature creep 1 when the Von Mises criterion is met. The main means of strengthening the magnesium alloy matrix to improve the high temperature creep properties of magnesium alloys are solid solution strengthening, precipitation strengthening and dispersion strengthening. All of the magnesium alloys currently in use are precipitation-type strengthening alloys. The development of dispersion-strengthened heat-resistant magnesium alloys is a potential way to expand the high-temperature applications of magnesium alloys. The Canadian ITM has developed two dispersion-strengthened alloys in the laboratory. In addition, at the grain boundary, the diffusion rate of the atom is accelerated due to the large number of lattice defects, resulting in a decrease in grain boundary strength. The measures to strengthen the grain boundary are: forming a large number of fine precipitation hardening phases at the grain boundaries; increasing the grain size to increase the atomic diffusion distance, but according to the Hall Petch effect, increasing the grain size reduces the mechanical properties of the alloy; The surface active elements collected on the surface of the crystal grain and the grain boundary position fill the lattice vacancies at the grain boundary to improve the morphology of the structure near the grain boundary. Surface active elements such as Ce, Ca, Sr, Ba and Sb have been found to improve the high temperature properties of magnesium alloys.
In recent years, the high temperature performance of magnesium alloys has been significantly improved. For example, the Mg-Zr alloy not only greatly improves the mechanical properties at room temperature, but also greatly improves its high-temperature performance. In the past, it was only able to withstand 150 ° C and is now resistant to 300 ° C. At the same time, Mg-Th alloys ZT and ZT6 can maintain high temperature creep resistance at 350 °C. This alloy is mainly used in the manufacture of aircraft engines, aluminum and titanium alloy as a high temperature alternative materials. [next ]
稀土 Because rare earth elements have a unique extranuclear electronic arrangement, it can form high melting point compounds at the grain boundaries to pin the grains, thereby increasing the high temperature strength and creep strength of the alloy. Therefore, by adding rare earth (cerium misch typically rich) elements to obtain a more excellent high-temperature strength of magnesium alloy series AE. 
Because Si mainly forms Mg 2 Si phase in the alloy, it is dispersed around the grain boundary, and Mg 2 Si has higher melting point and thermal stability, and becomes unstable only at 400 ° C. Therefore, it is in Mg-Al alloy. The addition of a certain amount of Si can also significantly improve the high temperature creep resistance of the alloy. But to date, the most successful high-strength, heat-resistant magnesium-based alloys are Mg-Y-Nd-based WE54 (Mg-5.1% Y-3.3% RE(Nd)-0.5% Zr) and WE43 (Mg). - 4.0% Y-3.3% RE (Nd) - 0.5% Zr) alloy.
2.2 Improvement of corrosion resistance
Due to the high specific strength and other excellent properties of magnesium alloys, it has broad prospects for use as structural materials, but the poor corrosion resistance of magnesium alloys has become one of the main factors that restrict its performance advantages. Therefore, it is of great practical significance to carry out proper surface treatment to enhance the corrosion resistance of existing magnesium alloys. Since the magnesium anodized film has strong bonding force with metal matrix, good electrical insulation, excellent optical properties, thermal shock resistance, wear resistance and corrosion resistance, the anodizing process has become the most commonly used one for magnesium and magnesium alloys to improve corrosion resistance. Sexual surface treatment. The addition of Mn element to the magnesium alloy is also advantageous for improving the corrosion resistance because Mn can be eliminated as a slag with Fe in the alloy, and the harmful effect of Fe on the corrosion resistance of the magnesium alloy is eliminated. Therefore, magnesium-aluminum alloys generally used for corrosion resistance contain a certain amount of Mn. However, as the amount of Mn increases, a brittle α-Mn phase will appear in the structure, which reduces the ductility of the alloy. Therefore, the content is generally limited to 0.6%.
The Al content of the Mg-Al alloy commonly used in the industry is less than 10%, and the structure at room temperature is α (Mg) and β (Mg 17 Al 12 ) due to unbalanced crystallization. When the Al content in the Mg-Al alloy is more than 4%, more Mg 17 Al 12 phase is precipitated due to the increase of the amount of Al, which is more resistant to corrosion than the α-Mg matrix; Al reacts with Fe to form a compound, which lowers the alloy. The content of Fe reduces the harmful effects of impurity elements on corrosion resistance; and Al forms an aluminum oxide protective film on the surface of the alloy, thereby improving the corrosion resistance of the alloy.
 By strictly controlling the content of impurity elements in the alloy and maintaining a certain Fe/Mn ratio in the alloy to suppress the harmful effects of Fe, various high-purity die-cast magnesium alloys having excellent corrosion resistance and good mechanical properties have been developed. The corrosion resistance of the high-purity AZ91E alloy in the salt spray test is about 100 times that of the AZ91C, and it also exceeds the die-cast aluminum alloy A380, which is much better than the low carbon steel. [next]
2.3 Improvement of plastic deformation ability
The crystal structure of the hexagonal hexagonal alloy of magnesium alloy determines its plastic deformation ability is poor, and solving this problem is one of the keys to the application of magnesium alloy. Practice has shown that fine equiaxed grains can improve the plastic deformation ability of magnesium alloys. In 1937, Zr was found to have a significant refinement effect on magnesium alloys, and research on grain refiners for magnesium and magnesium alloys began. Since Zr has little solubility in liquid magnesium, Zr and Mg do not form compounds. Zr is first precipitated as a mass point during solidification, and α-Zr and Mg are hexagonal crystal forms, and their lattice constants are very close (Mg The lattice constant a is 3.200 Å, c is 5.200 Å; the lattice constant a of α-Zr is 3.230 Å, and c is 5.140 Å), which conforms to the principle of "size and structure matching" as the core of grain nucleation, so It becomes the crystalline core of α-Mg. When the Zr content is more than 0.6%, the α-Zr formed in the magnesium liquid has a large amount of dispersed particles, so that the crystal grains are remarkably refined. However, the amount of Zr added is unlikely to be large because only 0.7% Zr can be dissolved in the magnesium solution when the temperature reaches 900 °C. In addition, Zr dissolved in the matrix also plays a certain strengthening role. However, for the Al-containing magnesium system, since Zr and Al are easy to form a stable compound (Al-3Zr), the crystal structure of Al-3Zr is body-center square, the lattice constant is very different from that of Mg, and the Al and Zr in the system are caused. Loss, so for the Mg-Al alloy, Zr cannot be used to refine the grains, and the carbonaceous inoculation method should be used to refine the grains.
2.4 Improvement of toughness and flame retardancy
Among the Mg-Al alloys, the Mg-Al-Mn alloy formed by adding an appropriate amount of Mn has the highest elongation in the Mg-Al alloy, and is called a high-toughness magnesium alloy. The addition of Ca element in the Mg-Al-Si alloy can improve the morphology of the dispersed phase Mg-2Si around the grain boundary of the alloy, thereby improving the toughness of the alloy.
The application range of bismuth magnesium alloy is more and more wide, but the magnesium alloy is easily oxidized and burned in the air during smelting and processing, so production is very difficult. At present, magnesium alloys are generally smelted by flux coating and gas protection at home and abroad, but there are disadvantages such as environmental pollution and complicated equipment. To this end, researchers have been working hard to find a better way to flame retardant. According to the data, rare earth and high content of lanthanum are added to the magnesium alloy to obtain Ignition-proof magnesium alloy (IPMA) which can be directly smelted in the atmosphere and has good casting properties and mechanical properties. .
2.5 Magnesium Matrix Composites
Magnesium-based composites are newly developed products with granular silicon carbide as the reinforcing phase, with a 40% increase in modulus of elasticity and a density of only 2.0 g/cm 3 . Magnesium-based composites have better wear resistance and lower coefficient of thermal expansion than ordinary magnesium alloys. [next]
3 Research direction
Due to the unique properties of magnesium alloy materials, especially its high recovery rate, it not only effectively utilizes resources, but also reduces environmental pollution. International companies have started research on magnesium alloys and continuously improve the performance of magnesium alloys to make high. Performance of magnesium products. As a main component of magnesium alloy, the production method is divided into two major categories: electrolysis and thermal reduction. The world's largest magnesium producing country is the United States, with an annual output of about 150,000 tons, most of which are produced by electrolysis. However, due to the production process of electrolysis, the toxic gas, chlorine gas, whose waste gas, waste water and waste residue pollute the environment, some developed countries gradually changed from their own production to import from the third world. 
The magnesium salt resources in the world are extremely rich, mainly in the form of liquid ore and solid ore. The liquid ore is mainly composed of seawater, underground brine and salt lake brine. The solid ore includes magnesite , dolomite, serpentine, talc , brucite and a small amount of other sedimentary minerals. China is a famous "magnesium power" in the world. It is rich in magnesium resources, accounting for more than 50% of the world. But it is not a strong magnesium country, magnesium products are still stuck in the development of primary products. China's magnesite and dolomite are rich in resources, and their distribution is spread all over the country. Among the salt lake resources, liquid mineral resources are in a very important position. The salt lakes that have been developed on a large scale in the world almost all use their brines, and the development of salt lake solid mines is rare. Because brine (including seawater and salt lake brine) is a renewable resource, and magnesite is a non-renewable resource, the development of brine magnesium salt industry is required for China's sustainable economic development strategy.
工艺 The process of producing magnesium metal or (high-purity) magnesia from salt lake magnesium resources mainly includes potassium carnallite dehydration electrolytic magnesium smelting and bischofite dehydration electrolytic magnesium smelting. There are many countries that use magnesium salt products to produce magnesium compound products. For example, Israel Dead Sea Magnesia Company introduced Austrian technology in 1993, using magnesium chloride mother liquor after salting the caramel as raw material, and preparing magnesium chloride by pyrolysis of the reaction furnace. Acid, the annual output of magnesia reached 70,000 tons in 1998, producing nearly 100,000 tons of hydrochloric acid; the Ruthner branch of Andritz, Austria, used spray calcination pyrolysis to produce magnesium oxide; and Germany, Mexico, Norway, the United States, Russia, etc. The country also produces various types of magnesium salt products. However, only the National Magnesium Company is used to produce magnesium metal from salt lake brines. From the development trend of the world magnesium salt industry, the prospect of developing brine magnesium salt industry is very broad. It should make full use of the renewable resources of salt lake brine, and retain more non-renewable resources, which will save the long-term development of China's magnesium industry and magnesium alloy. power.
The Dead Sea is the salt lake with the largest reserves of magnesium salt. The magnesium resources in the Qinghai Salt Lake sub-region are also abundant, and the reserves and concentrations are among the top four lakes in China. The Chaerhan Salt Lake in Qinghai Lake District is the largest potassium salt lake in China. Its magnesium salt reserves account for 74% of the national magnesium salt resources, and it has the characteristics of symbiosis of many useful components. The development of salt lake resources began in 1958. For several decades, every 1 t of potassium chloride was extracted, and 8 to 11 tons of magnesium chloride was discharged back to the salt lake, resulting in local enrichment of magnesium salts, which caused the phase balance of the salt lake to be destroyed. Within a certain range, it has been disadvantageous to the extraction of potassium and the comprehensive utilization of other beneficial components, forming a "magnesium hazard". Considering the comprehensive utilization of magnesium resources in salt lakes to solve the problem of “magnesium damage†caused by the development of potash resources, we should start low-temperature, non-polluting extraction of magnesium resources in salt lakes and prepare high-performance, high-value magnesium. Research on alloy technology allows magnesium resources to be fully utilized. With the development of national economies, the lack of resources will become an important factor restricting the development of a country. Today, when economically processed mineral resources are almost exhausted, mankind is bound to move toward the ocean. The seawater contains abundant salt resources, which is an inexhaustible resource treasure compared with the proven reserves of magnesite, potash and lithium salt in the world. It is a sustainable and sustainable for human society. Development plays a huge role. The comprehensive processing and utilization of salt lake brine can be said to be the prelude to the processing and utilization of sea water resources. If the technical and environmental problems encountered in the comprehensive processing and utilization of salt lake brine water resources are solved, it will provide very important evidence for the large-scale development of future sea water resources. Therefore, the development of salt lake brine water resources for magnesium industry and other The development of industry has invaluable value.