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Characteristic Of Magnesium Alloy

Adding some useful alloying elements in pure magnesium alloy can be obtained in different kinds of magnesia, they not only have the characteristics of magnesium, physical, chemical and mechanical properties and can greatly improve the magnesium, expand its application. At present, dozens of different properties of magnesium alloys have been developed, forming a magnesium alloy system.

 

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Most Magnesium Alloys Have The Following Characteristics:

(1) the density of magnesium alloy is slightly higher than that of pure Mg (1.738g = cm-3), and is 1.74-1.85g = cm-3, which is 36% lower than that of aluminum alloy, 73% lower than that of zinc alloy, and is only 1/4 of steel, so its specific strength and specific stiffness are very high. Magnesium alloy is a structure material of the world's most light, making parts made of magnesium alloy, which can reduce the structural weight, reduce energy consumption, reduce emissions, load and increase the speed of transport machinery, is a good material for lightweight aerospace and transportation.
(2) the specific elastic modulus of magnesium alloy is approximately the same as that of high strength aluminum alloy and alloy steel. It is very advantageous to make a rigid component with magnesium alloy. The weldability and fatigue resistance of the magnesium alloy are also good.
(3) the elastic modulus of magnesium alloy is low, and the stress distribution is more uniform when the external force is acted on, so as to avoid excessive stress concentration.
(4) magnesium alloy has high vibration damping capacity, that is, high vibration damping and low inertia.
(5) magnesium alloys have some plasticity in high temperature and normal temperature, so the method can be used for processing all kinds of pressure bars, tubes, profiles, forging, forging and stamping, die casting, sheet metal and powder material etc..
(6) magnesium alloy has excellent cutting performance, and its cutting speed is much higher than other metals. Because of its high stability, casting has a high precision in casting and machining.
(7) magnesium is stable in alkaline environment and has resistance to salt fog corrosion.
(8) the reaction between magnesium and iron is low, the casting loss is less, the service life is long, and the die casting speed of magnesium is higher than that of aluminum.
(9) magnesium has great adaptability in foundry industry. Almost all special casting processes can be cast.

Compared With 0ther Alloy Materials, Magnesium Alloys Also Have The Following Disadvantages:

(1) the chemical activity of magnesium is very strong, it is easy to be oxidized in air, easy to burn, and the oxide film is loose. Therefore, magnesium alloy must be melted under special flux or protective atmosphere. Special attention should be paid to fire prevention in processing workshop and milling workshop.
(2) resistance to salt water is poor; therefore, antiseptic treatment must be carried out.
(3) it is easy to produce electrochemical corrosion when contacted with iron and steel materials.
(4) the properties of materials such as young's modulus, fatigue strength and impact value are lower than those of aluminum. In contemporary aluminum alloy parts, the thickness increases and sometimes the desired light weight is not achieved.
(5) the casting of magnesium alloy is poor. It is easy to produce micro pores during solidification, thus reducing the mechanical properties of castings.
(6) the comprehensive cost of magnesium alloy casting is higher than that of aluminum alloy, and the price of processing parts is much higher than that of aluminum alloy.

In foreign countries, wrought magnesium alloys are basically made from 5-12t flame furnaces or crucible furnaces. In China, large flame reverberatory furnace and power frequency crucible furnace are adopted. Crucible furnace is more conducive to improve metal quality and improve production conditions.

Casting technology characteristics of magnesium alloy

Magnesium alloy heat treatment
Magnesium alloy casting and deformation for two kinds, two kinds of alloy can be annealing, quenching and artificial aging and natural aging and heat treatment, the state symbols and application scope and casting Aluminum Alloy are basically the same, but the slow diffusion rate of Mg alloy, the quenching sensitivity is low, can be static or flowing air quenching, in individual cases also with hot water quenching (such as T61), cooling air cooling T61 high strength ratio. It is worth pointing out that the majority of Mg alloys are insensitive to natural aging and can remain quenched at room temperature for long periods of time, even if they are artificially aged, and the aging temperature is higher than that of AL alloy (up to 175-250 DEG C). In addition, the oxidation tendency of Mg alloy is higher than that of AL alloy. In order to prevent combustion, the furnace should maintain neutral atmosphere or pass through SO2 gas protection (0.5% to 1% SO2).
Mg alloy is different from AL alloy and can be treated by hydrogenation (gas) to improve its microstructure and properties.

Magnesium alloy application
Application of magnesium alloy in transportation system
The application of magnesium alloy including aviation: at present various civilian and military aircraft engine parts, propeller, gear box, support structure and the Rockets, missiles and satellites of some parts in the field of aviation.
Automotive applications: magnesium alloy die castings are the lightest in all die casting alloys, and now a large number of magnesium alloy parts have been produced in the automotive industry to replace plastics, aluminium alloys and even steel parts.
Motorcycle and bicycle application: if the whole car is applied, it is lighter than the aluminum alloy die casting. Bicycle is a new application field of magnesium alloy, which is mainly used as bicycle frame.
Wheelchair application: AZ31 magnesium alloy is used to make wheelchair frame or wheel, and the rest parts are made of magnesium alloy.
Application of ship: magnesium alloy in shipbuilding industry and ocean engineering, mainly used in marine instruments, underwater weapons, sea water batteries, diving suits, sacrificial anodes, timing devices, etc..

(1) the chemical activity of magnesium is very strong, and it is easy to react with oxygen, nitrogen and water vapor in molten state. In the melt surface, if not strictly protected, near 800 degrees of temperature, will soon be oxidized combustion. In order to reduce the loss of combustion, the safety of production and the quality of the metal, the melt is always protected by flux in order to avoid contact with oxygen, nitrogen and moisture in the furnace gas and air. Therefore, a lot of problems have been brought into the process, for example, a great deal of molten salt has brought a lot of trouble to the quality of products, the health of people and the safety of production.
(2) in addition to a small number of components (elements), such as Cd, Zn, Al, Ag, Li etc., other components in the magnesium solubility is very small; in addition, the refractory component is easy to form high melting point compounds and precipitation, therefore in the process of joining difficult. Because iron is difficult to dissolve in magnesium, it is possible to use iron tools without any coating in the process of casting magnesium alloys.
(3) in some magnesium alloy ingots, local grain size is easy to occur. At the same time, the grain size is large, the grain shape is easy to appear columnar crystal and fan-shaped crystal, which seriously affects the pressure processing performance and the mechanical properties of the products. Therefore, the corresponding modification methods should be adopted to refine the grain and change the grain shape properly. As the grain coarsening tendency of magnesium alloy is larger, the size and shape of the grain of magnesium alloy ingot are not strictly required.
(4) the oxidation inclusions, fluxes, slag inclusions and gas solubility of magnesium alloy are much more than that of aluminum alloy. Therefore, purification is needed. At present, flux refining method is adopted in our country. In some countries, gas refining method is adopted, and some new purification technologies are developed. The cleaning agents of magnesium alloys are of the settling type, which is different from aluminum alloys and other non-ferrous metals, which brings a lot of trouble to the quality of the process and the products. Therefore, there is a need for adequate settling time after purification. In the bottom still need to separate the discharging port, the process will not be ignored PA slag. In the casting process, the need to use a lot of flux, at the same time with a large number of chemical materials (adding components and modification), the quality of them, directly affect the quality of the alloy, and molten salt flux should be strict with.
(5) [H] has some influence on magnesium alloys. In addition to the influence of zirconium - solubility of zirconium in magnesium alloy, when the hydrogen content exceeds a certain amount (16 cm 3/100g mg), there will be different degrees of porosity in ingot. Therefore, the amount of hydrogen should not be neglected.
(6) as the heat content of magnesium alloy is lower, the melt temperature will be greatly lowered when the high melting point component or larger batch chemical material is added. Therefore, the melting temperature of magnesium alloy should be higher than that of aluminum alloy. The overheating of the melt will lead to the coarsening of the grain, and the oxidation, nitridation and tendency of hot cracking tend to be serious with the increase of superheat temperature. Therefore, Melt Overheating should be avoided in the process. The effect of metal superheating on grain refinement in mg Al alloys. But refining the grain in this way will cause other defects, but it will not work well. At the same time, the refining effect time is short, and the residence time of the melt is longer when the residence time of the melt is longer.
(7) the smelting process of magnesium alloy is much more complicated than that of aluminum alloy, but it is worse than that of aluminum alloy in the research. Therefore, many mechanistic problems remain to be confirmed. Such as the properties of molten salt, purification mechanism, modification and other important processes, there are many hypotheses about the mechanism, some of which have not yet been confirmed.
(8) the safety technical problem of magnesium alloy is very important. Most of the molten salt deliquescence, most chemical materials have water of crystallization. In the process, the liquid metal directly see water, resulting in splash explosion, must pay careful attention. In addition, harmful gases and dust should be properly handled.
(9) metal elements, metal magnesium and most of the chemicals added are mostly expensive and scarce raw materials. In the process, the burning loss is large and the yield is low, which seriously affects the economic effects of the products.
(10) in order to guarantee the high and uniform performance of magnesium alloy products, the density and component segregation of ingot should be paid more attention to.
(11) the tendency of hot cracking of magnesium alloy is large, so the crystallization speed should not be too high. But when the crystallization rate is small, it will promote the formation and development of metal intermediate compounds. Therefore, there is a contradiction between the two processes of thermal cracking and intermetallic compound, which is also the reason why the process is complex and difficult. Must be fully considered and appropriately chosen. But because of the elastic modulus of the magnesium alloy is much smaller than Aluminum Alloy (mg E=45000MPa, Al E=72000 MPa), therefore, should be much smaller than the Aluminum Alloy magnesium alloy ingot, the cold crack tendency is much smaller than Aluminum Alloy.

Characteristics of wrought magnesium alloys

Many magnesium alloys can be used as cast magnesium alloys as well as wrought magnesium alloys. The wrought magnesium alloy has higher mechanical properties than the cast magnesium alloy of the same composition after extrusion, rolling and forging. Wrought magnesium alloy products include rolled sheets, extruded parts (such as bars, profiles and tubes) and forgings. These products have the advantages of more cost, higher strength and ductility, and diversified mechanical properties.

Magnesium Alloy Classification

There are many classification methods for magnesium alloys, and different countries are not unified. But in general, nothing more than the three principles of magnesium, including the main elements (chemical composition), the forming process (or product form) and whether they contain zirconium.

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(I) classification according to alloy composition
Magnesium alloy can be divided into two categories: Al Mg alloy and no Al Mg alloy. Most of the alloys without al contain zirconium to refine the grain structure (except for Mg-Mn alloy). Therefore, the industrial magnesium alloy series can be divided into two categories, namely, zirconium magnesium alloy and zirconium free magnesium alloy. The five main alloying elements Mn, Al, Zn, Zr and rare earth based basic magnesium alloys: Mg-Mn Mg-, Al -Mn, Mg- Al- Zn -Mn, Mg-Zr Mg-, Zn -Zr, Mg- RE, Mg-Ag- - Zr RE - Zr, Mg- - Zr Y-RE. Th is also a major alloying element in magnesium alloys. It can also form a magnesium alloy system: Mg-Th-, Zr, Mg-Th-, Zn-, Zr, Mg-Ag-Th-, RE - Zr. But because of the radioactivity of Th, it has rarely been used except for individual cases.
(two) classification according to processing technology or product form;
Industrial magnesium alloys can be divided into two major categories: Cast Magnesium Alloys and wrought magnesium alloys:
(1) cast magnesium alloy:
1. common cast magnesium alloys: Mg-, Al-, Zn, II, Mg-, Zn - Zr, Mg-, Zn-Al, Mg-, Zn-Al-Ca (ZAX), IV, Mg-, RE, Mg-RE-Mn
2. pressure casting magnesium alloy:
(1) Mg-, Al-, Zn (AZ91), II, Mg-, Al - Mn (AM50, AM60), Mg-, Al - Si (AS41, AS21)
Mg-, Al-, RE (AE42), Mg-, Al-, Ca (AX51),:Mg-, Al-, Ca-RE (ACM522) and Mg- Zn-Al-Ca
(2) Mg-, RE-, Zn (MEZ);
2. wrought magnesium alloy:
The extrusion forging II: 1. Mg- Al- Zn 2. Mg- Zn 3. Mg- - Zr Zn - Mn 4. Mg- Mn 5. Mg-Li, Mg-Li-Al: Mg-Li-Al-MM and Mg-Li-Al-Si, both no strict distinction between rolling, casting magnesium alloy AZ91, AM20, AM50, AM60, AE42 etc. can also be used as wrought magnesium alloy.

Cast magnesium alloy

There are many methods for casting magnesium alloys, including gravity casting and pressure casting, which can be subdivided into sand casting, permanent mold casting, semi permanent die casting, investment casting, squeeze casting, low pressure casting and high pressure casting. Commonly referred to as die casting refers to high-pressure casting to distinguish between gravity casting and low-pressure casting. For the specific material, the proper casting method should be chosen according to its chemical composition and process requirements. Important effects of alloy composition and casting process. Alloying elements, especially rare earth element RE, cause complex changes in mesophase structure, which have a great influence on the microstructure and properties of magnesium alloys.
Cast magnesium alloys can be divided into general casting (sand casting, permanent mold casting), magnesium alloy and pressure casting (die casting) magnesium alloy. Magnesium alloys are common: Mg-Al-Zn, Mg-Zn-Zr, Mg-Zn-Al (Mg-Zn-Al-Ca) and Mg-RE-Mn alloy; die cast magnesium alloy are common: Mg-Al-Zn Mg-Al-Mn, Mg-Al-Si, Mg-Al-RE, Mg-Al-Ca, Mg-Al-Sr and Mg-RE-Zn alloys.

Magnesium alloy smelting method

According to the characteristics of wrought magnesium alloy, its smelting equipment is divided into two major categories: flame reverberatory furnace and crucible furnace. There are two kinds of crucible furnaces: Electric crucible furnace and fuel crucible furnace. The electric crucible furnace is divided into two types, namely the frequency division crucible furnace and the resistance crucible furnace.

 

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Two. Application of magnesium alloy in electronic industry
At present, the electronic products made of magnesium alloy parts include cameras, cameras, digital cameras, laptops, mobile phones, televisions, plasma displays, hard drives, etc..
Three. Application of magnesium alloy in national defense industry
Magnesium and its alloys are widely used in national defense and aerospace products due to their light weight. Mainly used in weapons and tanks, armored vehicles, air defense, anti missile systems, tactical missiles, photoelectric equipment, fuses and communications equipment.
Four. Magnesium alloy used as sacrificial anode
Widely used in extended family or industrial water heaters, underground pipelines, cables, iron tower, oil tank, water distiller, ship shell and marine environments such as the life of steel pile.
Five, other aspects
Magnesium and magnesium alloys are also used in the power industry, home consumer goods, furniture, office equipment, optical equipment, sports equipment, lathe equipment and other fields. Such as suitcase, typewriter frame, pencil sharpener, printing machine parts, binoculars, table tennis bat and so on.

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