Magnesium alloys: application, classification and properties

Magnesium alloys have a number of unique physical and chemical properties, the main of which are low density and high strength. The combination of these qualities in materials with the addition of magnesium makes it possible to produce products and structures that have high strength characteristics and low weight.

Characteristics of magnesium

The industrial production and use of magnesium began relatively recently - only about 100 years ago. This metal has a small mass, since it has a comparatively low density (1.74 g / cmᶟ), good stability in air, alkalis, gaseous media with fluorine content and mineral oils.

The melting point is 650 degrees. It is characterized by high chemical activity up to spontaneous combustion in air. The strength of pure magnesium is 190 MPa, the modulus of elasticity is 4,500 MPa, the elongation is 18%. The metal has a high damping ability (effectively absorbs elastic vibrations), which provides it with excellent shock tolerance and reduced sensitivity to resonant phenomena.

Other features of this element include good thermal conductivity, low ability to absorb thermal neutrons and interact with nuclear fuel. Due to the combination of these properties, magnesium is an ideal material for creating hermetic shells of high-temperature elements of nuclear reactors.

Magnesium fuses well with different metals and is one of the strong reducing agents, without which the metallothermy process is impossible.

In pure form, it is mainly used as a dopant in alloys with aluminum, titanium and some other chemical elements. In the ferrous metallurgy with the help of magnesium, deep desulphurization of steel and cast iron is carried out, and the properties of the latter are improved by means of the spheroidization of graphite.

Magnesium and alloying additives

Among the most common alloying additives used in magnesium-based alloys are elements such as aluminum, manganese and zinc. Aluminum improves the structure, increases fluidity and strength of the material. The introduction of zinc also makes it possible to obtain stronger alloys with a reduced grain size. With the help of manganese or zirconium, the corrosion resistance of magnesium alloys increases.

Addition of zinc and zirconium provides increased strength and ductility of the metal mixtures. And the presence of certain rare-earth elements, for example, neodymium, cerium, yttrium, etc., contributes to a significant increase in heat resistance and maximization of the mechanical properties of magnesium alloys.

To create ultralight materials with a density of 1.3 to 1.6 g / mᶟ, lithium is introduced into the alloys. This additive makes it possible to reduce their weight by half as compared with aluminum-metal scales. At the same time, their indicators of ductility, fluidity, elasticity and manufacturability come to a higher level.

Classification of alloys with magnesium

Magnesium alloys are subdivided according to a number of criteria. It:

• By the method of processing - on foundry and deformable;
• By the degree of sensitivity to heat treatment - on non-hardened and hardened by heat treatment;
• On properties and spheres of application - on alloys heat-resistant, high-strength and general purpose;
• By the doping system - there are several groups of non-refractable and heat-strengthened deformable magnesium alloys.

Foundry alloys

This group includes alloys with the addition of magnesium, intended for the production of various parts and elements by the method of shaped casting. They have different mechanical properties, depending on which are divided into three classes:

• Medium-strength;
• High-strength;
• Heat resistant.

The chemical composition of alloys are also divided into three groups:

• Aluminum + magnesium + zinc;
• Magnesium + zinc + zirconium;
• Magnesium + rare earths + zirconium.

Foundry properties of alloys

The best casting properties among the products of these three groups are aluminum-magnesium alloys. They belong to the class of high-strength materials (up to 220 MPa), therefore they are the best option for manufacturing parts of aircraft engines, cars and other equipment operating under mechanical and thermal loads.

To increase the strength characteristics, aluminum-magnesium alloys are alloyed with other elements. But the presence of impurities of iron and copper is undesirable, since these elements have a negative effect on the weldability and corrosion resistance of alloys.

Foundry magnesium alloys are prepared in different types of melting furnaces: in reflective, in crucible with gas, oil or electric heating or in crucible induction plants.

To prevent combustion during the melting process and during casting, special fluxes and additives are used. Castings are produced by casting in sand, gypsum and shell molds, under pressure and using melted models.

Deformable alloys

Compared with foundry, deformable magnesium alloys are more durable, ductile and viscous. They are used for production of blanks by rolling, pressing and stamping methods. As a heat treatment of products, tempering is applied at a temperature of 350-410 degrees, followed by arbitrary cooling without aging.

When heated, the plastic properties of such materials increase, so treatment of magnesium alloys is carried out by means of pressure and at high temperatures. Stamping is performed at 280-480 degrees under presses by closed stamps. During cold rolling, frequent intermediate recrystallization anneals are carried out.

When welding magnesium alloys, the strength of the seam of the product can be reduced on the segments where the welding was performed, because of the sensitivity of such materials to overheating.

Spheres of application of alloys with the addition of magnesium

By means of methods of casting, deformation and heat treatment of alloys , various semi-finished products are produced - ingots, plates, profiles, sheets, forgings, etc. These blanks are used for the production of elements and parts of modern technical devices, where the priority role is played by the weight efficiency of structures (reduced mass) while maintaining their strength characteristics. Compared to aluminum, magnesium is 1.5 times lighter, and with steel, 4.5.

Currently, the use of magnesium alloys is widely practiced in the aerospace, automotive, military and other industries, where their high cost (some brands contain fairly expensive alloying elements) is justified from the economic point of view by the possibility of creating a more durable, fast, powerful and safe technique , Which can effectively work under extreme conditions, including when exposed to high temperatures.

Due to their high electrical potential, these alloys are the optimal material for creating protectors that provide electrochemical protection of steel structures, for example, car parts, underground structures, oil platforms, sea vessels, etc., from corrosive processes occurring under the influence of moisture, fresh and marine water.

We found the use of alloys with the addition of magnesium and in various radio engineering systems, where they make sound lines for ultrasonic lines to delay electrical signals.

Conclusion

Modern industry is placing ever higher demands on materials with regard to their strength, wear resistance, corrosion resistance and processability. The use of magnesium alloys is one of the most promising directions, therefore, studies related to the search for new properties of magnesium and the possibilities of its use do not stop.

Currently, the use of magnesium based alloys in creating a variety of parts and structures allows you to achieve a reduction in their weight by almost 30% and increase the strength to 300 MPa, but, according to scientists, this is not the limit for this unique metal.