Magnesium alloys: application, classification and properties

Characteristics of magnesium

Industrial production and use of magnesium began relatively recently - only about 100 years ago. This metal has a low mass, as it has a relatively low density (1.74 g/cmᶟ), good stability in air, alkalis, gaseous environments containing fluorine and in mineral oils.

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

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

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

In its pure form, it is mainly used as an alloying additive in alloys with aluminum, titanium and some other chemical elements. In ferrous metallurgy, with the help of magnesium, deep desulfurization of steel and cast iron is carried out, and the properties of the latter are also improved through spheroidization of graphite.

Read also

Copper and alloys

Copper and alloys Quite often, home mechanics prefer copper (specific gravity 9.0 g/cm2), since its softness and ductility allow them to achieve precision and high quality in the manufacture of all kinds of parts and products. Pure (red) copper is excellent

LECTURE No. 5. Alloys

LECTURE No. 5. Alloys 1. Structure of metals Metals and their alloys are the main materials in mechanical engineering. They have many valuable properties, mainly due to their internal structure. A soft and ductile metal or alloy can be made hard and brittle, and vice versa.

Copper alloys

2. Copper alloys Copper is one of the metals known since ancient times. Man's early acquaintance with copper was facilitated by the fact that it occurs in nature in a free state in the form of nuggets, which sometimes reach significant sizes. Currently

Aluminum alloys

3. Aluminum alloys The name “aluminum” comes from the Latin word alumen - so 500 years BC. e. called aluminum alum, which was used for pickling when dyeing fabrics and tanning leather. In terms of prevalence in nature, aluminum ranks third

Titanium alloys

4. Titanium alloys Titan is a silver-white metal. It is one of the most common elements in nature. Among other elements in terms of abundance in the earth’s crust (0.61%), it ranks tenth. Titanium is light (its density is 4.5 g/cm3), refractory

Zinc alloys

5. Zinc alloys An alloy of zinc and copper - brass - was known to the ancient Greeks and Egyptians. But zinc smelting on an industrial scale began only in the 17th century. Zinc is a light gray-bluish metal, brittle at room temperature and at 200 °C, when heated to

Gold alloys

Gold alloys Pure metals are not always used to make jewelry and other products. This happens due to the high cost of precious metals, their insufficient hardness and wear resistance, therefore, in practice, alloys are most often used

7.4. Copper alloys simulating gold and silver alloys

7.4. Copper alloys that imitate gold and silver alloys In order to reduce the cost of artistic products, tombac, brass, cupronickel, and nickel silver are widely used in the production of inexpensive jewelry; in the manufacture of artistic products - bronze. Copper alloys with zinc,

Aluminum alloys

8. Aluminum-based alloys Aluminum alloys are classified according to manufacturing technology (wrought and cast), ability to heat treatment (hardenable and non-hardenable) and properties (Fig. 8.1). Rice. 8.1. State diagram of aluminum - alloying element

Silver and its alloys

10. Silver and its alloys Silver is a chemical element, a metal. Atomic number 47, atomic weight 107.8. Density 10.5 g/cm3. The crystal lattice is face-centered cubic (fcc). Melting point 963 °C, boiling point 2865 °C. Brinell hardness 16.7. Silver – white metal

10.4. Silver alloys for solders

10.4. Silver alloys for solders Solder is a very important auxiliary material in jewelry. To connect various elements of jewelry to each other, when working in filigree and granulation techniques, silver solders are used - silver-based alloys. Basics

Gold and its alloys

11. Gold and its alloys Gold is a chemical element, a metal. Atomic number 79, atomic weight 196.97, density 19.32 g/cm3. The crystal lattice is face-centered cubic (fcc). Melting point 1063 °C, boiling point 2970 °C. Brinell hardness – 18.5. Gold – yellow metal

11.1. Two-component gold alloys

11.1. Two-component gold alloys In the jewelry industry, two-component alloys are sometimes used: gold - copper and gold - silver. Rice. 11.1. State diagram Cu - Au. Gold and copper have unlimited solubility in liquid, and at high temperatures in

11.2. Multicomponent gold alloys

11.2. Multicomponent gold alloys In the jewelry industry, for the manufacture of gold products, in most cases, alloys of the gold - silver - copper system are used, which may contain additives of other metals: nickel, palladium, zinc, platinum. Chemical

11.6. Gold alloys for solders

11.6. Gold alloys for solders In the manufacture of jewelry and art products from gold alloys, soldering is used. The composition and melting temperature range of jewelry solders for soldering gold alloys is given in Table. 11.9. Marking of gold solders is carried out as follows:

Magnesium and alloying additives

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

The addition of zinc and zirconium provides increased strength and ductility of metal mixtures. And the presence of certain rare earth elements, for example, neodymium, cerium, yttrium, etc., helps to significantly increase the heat resistance and maximize the mechanical properties of magnesium alloys.

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

Content

• 1 Designation 1.1 Cast alloys
• 1.2 Wrought alloys
• 1.3 Named alloys 1.3.1 Aluminum alloys with magnesium

Casting alloys

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

• medium strength;
• high strength;
• heat resistant.

Based on their chemical composition, alloys are also divided into three groups:

• aluminum + magnesium + zinc;
• magnesium + zinc + zirconium;
• magnesium + rare earth elements + zirconium.

Casting properties of alloys

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

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

Cast magnesium alloys are prepared in various types of melting furnaces: in reflective furnaces, in crucible furnaces with gas, oil or electric heating, or in crucible induction installations.

To prevent combustion during the melting process and during casting, special fluxes and additives are used. Castings are produced by sand, plaster, shell, pressure and lost wax casting.

Manufacturing [edit]

Hot and cold processing[edit]

Magnesium alloys harden quickly under any type of cold working and therefore cannot be subjected to extensive cold work without repeated annealing. Sharp bending, rotating, or drawing must be done at 260 to 316 °C (500 to 600 °F), although smooth bending around large radii can be done cold. Slow molding gives better results than fast molding. Press – The press is preferred to hammer forging because the press allows more time for the metal to flow. The range of plastic forging is 500 to 800 °F (260 to 427 °C). Metal processed outside this range breaks easily.

Casting[edit]

Magnesium alloys, especially dispersion-hard ones, are used in casting. Sand casting, permanent mold and injection molding methods are used, but plaster of Paris casting has not yet been perfected. Sand casting requires special techniques because magnesium reacts with moisture in the sand to form magnesium oxide and release hydrogen. The oxide forms blackened areas called burns on the surface of the casting, and the hydrogen released can cause porosity. Inhibitors such as sulfur, boric acid, ethylene glycol or ammonium fluoride are mixed with wet sand to prevent the reaction. All gravity-fed molds require a very high column of molten metal so that the pressure is great enough to force gas bubbles out of the casting and force the metal to grip the mold part. The wall thickness of the casting should be at least 5/32 inch in most conditions. Very large fillets should be provided at all reentrant corners, since stress concentrations in magnesium castings are especially dangerous. Permanent mold castings are made from the same alloys and have approximately the same physical properties as sand castings. Since the solidification shrinkage of magnesium is about the same as that of aluminum, aluminum molds can often be adapted to produce magnesium alloy castings (although the closure may need to be modified). Cold chamber pressure castings are used for mass production of small parts. The rapid solidification caused by the contact of the liquid metal with the cold matrix produces a casting with a dense structure and excellent physical properties. Finishing and dimensional accuracy are very good and machining is only necessary where maximum precision is required. These castings are not usually heat treated.

Welding, soldering and riveting[edit]

Many standard magnesium alloys are easily welded using gas or resistance welding equipment, but cannot be cut with an oxy-fuel torch. Magnesium alloys are not welded with other metals because brittle intermetallic compounds may form or because the combination of metals may promote corrosion. If two or more parts are welded, their composition must be the same. Soldering of magnesium alloys is possible only for sealing surface defects of parts. Solders are even more corrosive than aluminum and the parts should never be able to withstand stress. Riveted: Connections in magnesium alloy structures typically use aluminum or aluminum-magnesium alloy rivets. Magnesium rivets are not often used because they must be driven in while hot. Rivet holes should be drilled, especially in thick sheets and extruded profiles, as stamping tends to produce a rough hole edge and cause stress concentrations.

Processing[edit]

The special attractiveness of magnesium alloys lies in their extremely good processing. Their properties surpass even threaded brass. The power required to cut them is low, and extremely high speeds (5,000 feet per minute in some cases) can be used. The best cutting tools have a special shape, but tools for cutting other metals can be used, although their efficiency is slightly lower. When cutting magnesium at high speed, tools must be sharp and must always cut. Dull, dragging tools operating at high speeds can generate enough heat to ignite fine chips. Since chips and dust from grinding can pose a fire hazard, grinding should be carried out with coolant or using a dust concentration device under water. A magnesium grinder should also not be used on ferrous metals, as a spark could ignite accumulated dust. If a magnesium fire breaks out, it can be extinguished with cast iron shavings or dry sand, or other materials specially prepared for this purpose. Water or liquid fire extinguishers should never be used because they may spread the fire. In fact, magnesium chips and dust are much more difficult to ignite than is generally assumed, and for this reason they present little difficulty in handling. The special methods that must be used in the production of magnesium (processing, casting and joining) significantly increase the cost of production. When choosing between aluminum and magnesium or a given part, the base cost of the metal may not give much advantage to either, but typically manufacturing operations make magnesium more expensive because they tend to dissipate fire. In fact, magnesium chips and dust are much more difficult to ignite than is usually assumed, and for this reason they do not present much difficulty in handling. The special methods that must be used in the production of magnesium (processing, casting and joining) significantly increase the cost of production. When choosing between aluminum and magnesium or a given part, the base cost of the metal may not give much advantage to either, but typically manufacturing operations make magnesium more expensive because they tend to dissipate fire. In fact, magnesium chips and dust are much more difficult to ignite than is usually assumed, and for this reason they do not present much difficulty in handling. The special methods that must be used in the production of magnesium (processing, casting and joining) significantly increase the cost of production. When choosing between aluminum and magnesium or a given part, the base cost of the metal may not give much advantage to either, but generally the manufacturing operations make magnesium more expensive and compound) significantly increase the cost of production. When choosing between aluminum and magnesium or a given part, the base cost of the metal may not give much advantage to either, but generally the manufacturing operations make magnesium more expensive and compound) significantly increase the cost of production. When choosing between aluminum and magnesium or a given part, the base cost of the metal may not give much advantage to either, but typically manufacturing operations make magnesium more expensive.[1] There is perhaps no group of alloys in which extrusion is more important than this, since the comparatively coarse grain structure of the cast material makes most of them too susceptible to cracking to be worked in other ways until sufficient deformation has occurred. was given the task of cleaning the grain. Therefore, with the exception of one or two soft alloys, machining is always a preliminary step to other forming processes.

Hot extrusion[edit]

Not much pure magnesium is extruded as it has somewhat poor properties, especially regarding its yield strength. Currently, the main focus is on alloying elements: aluminum, zinc, cerium and zirconium; Manganese is usually also present because although it has little effect on strength, it plays an important role in improving corrosion resistance. One important binary alloy, containing up to 2.0% manganese, is widely used for sheet metal production. It is relatively soft and easier to extrude than other alloys, and is also one of the few alloys that can be directly rolled without pre-extrusion. In the UK, extrusions are made from 2.87–12 in (73–305 mm) diameter blanks. On presses of various capacities from 600 to 3500 tons; Normal maximum pressure on the workpiece is 30-50 t/sq.m. In the US, chemical company Dow recently installed a 13,200-ton press capable of processing workpieces up to 32 inches in size. The extrusion technique is generally similar to that of aluminum-based alloys, but according to Wilkinson and Fox, die design requires special attention and, in their opinion, should include short supports and a sharp die. records. Pipe extrusion of AM503, ZW2 and ZW3 alloys is now done using bridge dies. (Aluminum alloys do not weld well.) In contrast to the previous practice of using drilled blanks, mandrel piercing is now used when extruding large diameter ZW3 alloy pipe. AM503, ZW2 and ZW3 alloy pipe are now extruded using bridge dies. (Aluminum alloys do not weld well.) In contrast to the previous practice of using drilled blanks, mandrel piercing is now used when extruding large diameter ZW3 alloy pipe. AM503, ZW2 and ZW3 alloy pipe are now extruded using bridge dies. (Aluminum alloys do not weld well.) In contrast to the previous practice of using drilled blanks, mandrel piercing is now used when extruding large diameter ZW3 alloy pipe.

The extrusion hardness of alloys increases in proportion to the number of reinforcing elements they contain, and the temperature used is usually higher the greater the number. The workpiece temperature is also affected by the size of the sections, being higher for heavy reductions but typically in the range of 250–450 °C (482–842 °F). The temperature of the container should match the temperature of the workpiece or only slightly exceed it. Preheating of the workpieces should be carried out uniformly to promote, as far as possible, a homogeneous structure by absorbing compounds such as Mg4Al present in the alloys.

Fox points out, and this also applies to aluminum alloys. The original structure of the workpiece is important, and casting methods that result in fine grains make sense. Coarse material contains larger particles of compounds that are less easily dissolved and tend to cause a solution gradient. In magnesium alloys this causes internal stress as the solution undergoes slight compression and can also affect the uniformity of response to subsequent heat treatment.

Binary magnesium-manganese alloy (AM505) is easily extruded at low pressures over a temperature range of 250 to 350 °C (482 to 662 °F). The actual temperature used depends on the reduction and length of the workpiece, not the desired properties. which are relatively insensitive to extrusion conditions. Good extrusion surface condition is achieved only at high speeds of the order of 50-100 feet per minute.

Alloys containing aluminum and zinc, and especially higher aluminum content alloys such as AZM and AZ855, have difficulty at high speeds due to their heat resistance. Under near-equilibrium conditions, magnesium is capable of dissolving about 12% aluminum, but in cast billets 4-5% usually represents the solubility limit. Consequently, alloys containing 6 percent Al or more contain Mg4Al3, which forms a melting eutectic at 435 C. Extrusion temperatures can range from 250 to 400 °C (482 to 752 °F), but at higher values ​​rates are limited to approximately 12 feet per minute. Continuous casting improves the uniformity of these alloys, and water-cooling the dies or heating the cone of the blanks further facilitates their extrusion.

The introduction of magnesium-zinc-zirconium alloys, ZW2 and ZW3, represents a significant advance in magnesium alloy technology for a number of reasons. They have high strength, but because they do not contain aluminum, the casting contains only small amounts of the second phase. Because the solidus temperature is raised by approximately 100 °C (180 °F), the risk of hot shorts at relatively high extrusion speeds is greatly reduced. However, the mechanical properties are sensitive to preheating time of the preform, temperature and extrusion speed. Long preheat times, high temperatures and speeds provide properties similar to older aluminum alloys. The heating time must be short and the temperature and speed must be low to achieve high temperatures. characteristics. Increasing the zinc content to 5 or 6 percent, as in US alloy ZK60 and ZK61, reduces the sensitivity to extrusion speed in terms of mechanical properties.

Alloying of zirconium-containing materials has been a major problem in their development. Zirconium is usually added from salt and careful control can give good results. Dominion Magnesium Limited in Canada has developed a traditional addition method via ligature.

The explanation for the low extrusion speeds required for successful extrusion of some magnesium alloys is not related to the reasons put forward for other metals. Altwicker believes the most important reason is related. With a degree of recovery from crystal deformation that is less rivaled by rapid application of work, causing higher stresses and exhausting the sliding ability of the crystals. This is noteworthy because the rate of recrystallization varies from one metal to another and with temperature. It is also a fact that metal processed within what is considered its operating range can often exhibit noticeable work hardening when quenched immediately after deformation—this shows that a temporary loss of ductility can easily accompany rapid processing. [10] [ full citation required

]

Wrought alloys

Compared to casting alloys, wrought magnesium alloys are characterized by greater strength, ductility and toughness. They are used to produce blanks using rolling, pressing and stamping methods. As a heat treatment of products, hardening is used at a temperature of 350-410 degrees, followed by random cooling without aging.

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

When welding magnesium alloys, the strength of the weld of the product can be reduced in the sections where back welding was performed due to the sensitivity of such materials to overheating.

Designation [edit]

The names of magnesium alloys are often given by two letters after two numbers. The letters represent the main alloying elements (A = aluminum, Z = zinc, M = manganese, S = silicon). The numbers indicate the corresponding nominal compositions of the main alloying elements. The AZ91 marking, for example, coats a magnesium alloy with approximately 9 weight percent aluminum and 1 weight percent zinc. The exact composition must be confirmed by reference standards.

The designation system for magnesium alloys is not as standardized as for steels or aluminum alloys; most manufacturers follow a system using one or two prefix letters, two or three numbers, and a suffix letter. The prefix letters designate the two primary alloying metals according to the following format developed in ASTM B275 specification: [1]

Aluminum, zinc, zirconium and thorium promote dispersion hardening: manganese increases corrosion resistance; and tin improves casting. Aluminum is the most common alloying element. The numbers correspond to the rounded percentages of the two main alloy elements in alphabetical order as the compositions become standard. Character The designation is almost the same as that of aluminum. Using –F, -O, -H1, -T4, -T5 and –T6. Sandblasting and injection molding are well developed for magnesium alloys, with injection molding being the most popular. Although magnesium is about twice as expensive as aluminum, its hot chamber injection molding is simpler, more economical, and 40-50% faster than the cold chamber process required for aluminum. Poor molding behavior at room temperature, but most conventional processes can be done when the material is heated to 450–700 °F (232–371 °C). Because these temperatures are easily achieved and usually do not require a protective atmosphere, many molded and drawn products are made from magnesium. The machinability of magnesium alloys is the best of any industrial metal, and in many cases the savings in machining costs more than offset the increased cost of the material. [ Citation

] However, it is necessary that the tools are sharp and that there is enough space for the chips. Magnesium alloys can be spot welded almost as easily as aluminum, but brushing or chemical cleaning is necessary before forming the weld. Fusion welding is most easily accomplished using an inert protective atmosphere of argon or helium gas. There is considerable misinformation regarding fire hazards when processing magnesium alloys. It is true that magnesium alloys are highly flammable in fine form such as powder or fine shavings, and this danger should never be ignored. Above 800 °F (427 °C), a non-flammable, oxygen-free atmosphere is required to suppress combustion. Casting operations often require additional precautions due to the reactivity of magnesium with sand and water in sheet, rod, extruded or cast form; however, magnesium alloys do not pose a real fire hazard. [1]

Cast alloys [edit]

Magnesium casting proof strength is usually 75-200 MPa, tensile strength 135-285 MPa and elongation 2-10%. The typical density is 1.8 g/cm3 and Young's modulus is 42 GPa. [2] The most common cast alloys are:

AZ63 AZ81 AZ91 [3] AM50 AM60 ZK51 ZK61 ZE41 ZC63 HK31 HZ32 QE22 QH21 WE54 WE43 Electron 21

Forged alloys[edit]

Magnesium wrought alloy proof strength is usually 160-240 MPa, tensile strength is 180-440 MPa [ edit

] and relative elongation 7-40%.
The most common wrought alloys are: AZ31 AZ61 AZ80 Electron 675 ZK60 M1A HK31 HM21 ZE41 ZC71 ZM21 AM40 AM50 AM60 K1A M1 ZK10 ZK20 ZK30 ZK40
Forged magnesium alloys have a special feature. Their compressive strength is less than their tensile strength. After forming, wrought magnesium alloys have a fibrous texture in the direction of deformation, which increases tensile strength. When compressed, the proof of strength is less due to twinning [ edit]

], which occurs more easily under compression than under tension in magnesium alloys due to the hexagonal lattice structure.

Extrusions of fast-hardening powders achieve tensile strengths of up to 740 MPa due to their amorphous nature [4], which is twice as strong as the strongest traditional magnesium alloys and comparable to the strongest aluminum alloys.

Named alloys[edit]

• Electron
• Magnox
• Magnuminium
• Mag-Thor
• Metal 12

Aluminum alloys with magnesium [edit]

• Birmbright
• Magnalium

(codes: A = aluminum, C = copper, E = rare earth elements, usually obtained by adding mischmetal to a melt, H = thorium, K = zirconium, L = lithium, M = manganese, O = silver, S = silicon, T = tin, W = yttrium, Z = zinc)

Thorium-containing alloys are not generally used because thorium contents greater than 2% require the component to be treated as a radioactive material, although thoriated magnesium was used in military and aerospace applications in the 1950s.

Magnesium alloys are used for both cast and forged parts, with aluminum-containing alloys typically used for castings and zirconium-containing alloys for forgings; Zirconium-based alloys can be used at higher temperatures and are popular in the aerospace industry. Magnesium + yttrium + rare earth + zirconium alloys such as WE54 and WE43 (the latter with a composition of Mg 93.6%, Y 4%, Nd 2.25%, 0.15% Zr) can operate without creep at temperatures up to 300 °C and are quite resistant to corrosion. .

Composition table [edit]

Areas of application of alloys with the addition of magnesium

Through the 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 4.5 times lighter than steel.

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

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

Alloys with the addition of magnesium have also found application in various radio engineering systems, where they are used to make sound ducts for ultrasonic lines to delay electrical signals.

Application area

Magnesium alloys have a number of useful properties that other materials do not provide. These properties provide widespread use in industry:

Based on their properties, magnesium alloys find application:

With the development of technology, magnesium alloys will receive additional applications. The trend towards lighter weight of finished products is already regularly increasing interest in these alloys. If we take into account how rapidly robotics, the production of computers, and various gadgets are developing, we can understand that the need for magnesium grades of metals will be limited only by the amount of mined magnesium.

Source