Magnesium: Definition, Composition, Properties, and Applications
Magnesium alloys, whether cast or wrought, offer exceptional strength-to-weight ratios. They are useful for a wide range of engineering endeavors. It provides a weight reduction of up to 70% compared to stainless steel and 33% compared to aluminum. These alloys are cost-effective, highly workable, and possess the highest damping capacity among structural metals. Their applications include: automotive, aerospace, electronic, defense, biomedical, manufacturing, and green energy technologies.
This article will explore the definition, composition, applications, chemical and physical properties, advantages and limitations of magnesium and its alloys, and more.
What Is Magnesium?
Magnesium (Mg) is a silvery-white alkaline earth metal that resembles aluminum in appearance. Magnesium is also the 8th most abundant metal on our planet, constituting about 2.4% of the Earth’s crust. It is also considered to be the lightest structural metal, with a density of 1.74 g/cm3.
Magnesium has a hexagonal close-packed (hcp) crystalline arrangement. Similar to the majority of metals with this structure, magnesium exhibits reduced ductility when subjected to lower temperatures during processing. Furthermore, in its unalloyed state, it lacks the requisite strength for the majority of structural applications. However, the introduction of alloying elements improves its mechanical properties, making both wrought and cast magnesium alloys useful for applications demanding a combination of low weight and high durability. Industries that routinely use magnesium alloys include: aerospace, automobile, and electronics.
What Is the History of Magnesium?
In 1808, British chemist Sir Humphrey Davy produced magnesium metal by first passing electricity through a magnesium sulfate/mercury mixture, and then heating the resulting amalgam to remove the mercury and leave the magnesium. Subsequently, in 1828, French scientist Antoine Bussy managed to produce the first metallic magnesium. His approach involved reducing melted magnesium chloride with potassium vapor. The year 1833 saw English scientist Michael Faraday's successful production of magnesium via electrolysis of molten magnesium chloride, with his experiments later replicated by the German chemist, R. Bunsen.
The journey towards industrial-scale magnesium production began in Germany in the year 1886 with the company Aluminium und Magnesiumfabrik Hemelingen. This company made significant advancements in magnesium production processes in the 1920s and '30s. Notable contributions included the development of the IG Farben process, which produced substantial quantities of nearly water-free magnesium chloride, electrolyzing it to extract chlorine and magnesium metal. This era also witnessed the development of various magnesium alloys, refining techniques, wrought products, and applications in the aviation and automotive industries.
What Is the Other Term for Magnesium?
Magnesium is often referred to by its chemical symbol, "Mg." The name originates from Magnesia, a region situated in Eastern Thessaly, Greece. Initially, magnesium was recognized primarily through compounds such as Epsom salts (magnesium sulfate), magnesia or magnesia alba (magnesium oxide), and magnesite (magnesium carbonate). The silvery-white element in its pure form is not found in nature.
What Is Magnesium Made Of?
Magnesium is a chemical element with the symbol "Mg" and atomic number 12 on the periodic table. It is an elemental metal, which means that its composition consists solely of magnesium atoms. Each magnesium atom has 12 protons in its nucleus and a corresponding number of electrons orbiting around the nucleus.
How Is Magnesium Processed?
Pure magnesium is not found in nature, so all magnesium is produced by extractive chemical processes. The main sources of magnesium are seawater and natural brines (approximately 1.3 kg/m3 of dissolved magnesium), and minerals such as magnesite (MgCO3) and dolomite (MgCO3.CaCo3).
The extraction of magnesium from raw source materials is an energy-intensive process. It begins with concentrating the source material into a form that can be used in one of the two primary methods: the thermal reduction (Pidgeon process) method and the electrolytic process.
In the Pidgeon process, dolomite ore is crushed and heated (calcined) in a kiln, resulting in a mixture of magnesium and calcium oxides. These oxides are combined with crushed ferrosilicon. The mixture is made into briquettes which are heated in a vacuum until the silicon in the ferrosilicon reduces the magnesium oxide to magnesium. This process is conducted at a temperature above the vaporization temperature of magnesium. The pure element is collected as a gas and then condensed, cooled, and cast into ingots. This method yields magnesium with a purity of up to 99.99%, slightly higher than the purity delivered by the electrolytic processes.
The electrolytic process involves two stages: (1) obtaining pure magnesium chloride from seawater or brine, and (2) electrolysis of fused magnesium chloride.
For stage 1, the production of pure magnesium chloride, seawater, or brine is treated with calcined dolomite to generate magnesium hydroxide. The Mg(OH)2 is then transformed into oxide. Conversion to magnesium chloride is achieved by heating the oxide with carbon in the presence of chlorine at high temperatures in an electric furnace.
Stage 2 is the electrolysis of the fused anhydrous magnesium chloride the output of the previous step. The MgCl2 is continuously fed into electrolytic cells, where it is melted to conduct electricity. Electrolysis leads to the production of magnesium and chlorine gas (see Figure 1).
The electrolysis process of magnesium chloride.
Image Credit: https://www.essentialchemicalindustry.org/metals/magnesium.html#:~:text=Magnesium%20is%20the%20lightest%20structural,the%20automotive%20and%20aircraft%20industries
The molten magnesium is cast into ingots, while the chlorine gas is recycled to the chlorination furnace. After the extraction of magnesium through the electrolytic process described, it is often further processed and utilized primarily as an alloying element.
What Are the Characteristics of Magnesium?
Magnesium possesses several distinctive characteristics that influence its properties and applications. These are listed below.
- Low density
- Highly flammable
- Susceptible to oxidation and corrosion
- Reasonable electrical conductivity
- Can form a variety of alloys with other elements
- High strength-to-weight ratio (this property is especially pronounced in magnesium alloys)
- Good thermal conductivity (magnesium alloys maintain this property)
- Excellent castability (primarily attributed to magnesium alloys)
- Biocompatible and biodegradable (mainly relevant to biodegradable magnesium alloys)
- Relatively soft and ductile (this property varies depending on the specific alloy composition)
Take note that the properties listed pertain to pure magnesium unless stated otherwise.
What Is the Color of Magnesium?
Freshly exposed surfaces of pure magnesium have a silvery-white color, similar to many other metals. However, over time, when exposed to air, magnesium can develop a dull gray patina due to the formation of a thin layer of magnesium oxide on its surface. This oxide layer can give magnesium a slightly grayish appearance. Additionally, magnesium alloys can vary in color depending on their composition and surface treatment.
What Does Magnesium Look Like?
Magnesium is solid at room temperature and has a solid, dense texture. Pure magnesium typically appears as a shiny, silvery-white metal when freshly cut or polished. It has a metallic luster and reflects light in a manner similar to other metals. Figure 2 is an example of magnesium:
Magnesium.
Image Credit: Shutterstock.com/Miroslav Halama
However, the appearance of magnesium can change over time due to oxidation. This can lead to the development of a grayish patina on its surface. Additionally, magnesium is often used in alloy forms, which can influence its visual characteristics based on the specific alloy composition and any surface treatments applied.
What Are the Physical Properties of Magnesium?
The physical properties of magnesium are given in Table 1:
| Property | Value/Description |
|---|---|
Property Color | Value/Description Silvery-white |
Property Density | Value/Description 1.74 g/cm^3 at 20 °C |
Property Brinell hardness | Value/Description 30 |
Property Tensile strength | Value/Description up to 280 MPa (cast alloys), up to 360 MPa (wrought alloys), up to 20 MPa (pure cast) |
Property Yield strength | Value/Description up to 160 MPa (cast alloys), up to 300 MPa (wrought alloys), up to 20 MPa (pure cast) |
Property Young’s Modulus | Value/Description 44-45.5 GPa |
Property Ductility | Value/Description 0.12-0.2 |
Property Poisson’s Ratio | Value/Description 0.28-0.295 |
Property Melting point | Value/Description 650 °C (alloys will have different values) |
Property Boiling point | Value/Description 1107 °C (alloys will have different values) |
Property Flammable | Value/Description Yes |
Property Electrical conductivity | Value/Description 2.3×107 S/m |
Property Corrosion resistance | Value/Description Poor |
Property Thermal conductivity | Value/Description 156 W/mK |
| Property | Value/Description |
|---|---|
Property Atomic number | Value/Description 12 |
Property Atomic mass | Value/Description 24.30 g/mol |
Property Atomic radius | Value/Description 0.160 nm |
Property Structure | Value/Description hexagonal close-packed (HCP) crystal structure in pure form |
Property Isotopes | Value/Description 3 natural isotopes with mass numbers 24,25 and 26 |
Property Valence electrons | Value/Description 2 |
Property Recyclable | Value/Description Yes |
Magnesium, with its lightweight nature and high strength-to-weight ratio, offers several advantages, particularly in industries like aerospace and automotive. It also exhibits excellent thermal conductivity, making it suitable for applications requiring efficient heat dissipation. However, magnesium's susceptibility to corrosion, especially in aqueous environments, is a significant drawback. It readily reacts with water and oxygen to form magnesium hydroxide and magnesium oxide, compromising its structural integrity. Additionally, when in contact with certain metals like steel or aluminum, magnesium can induce galvanic corrosion, further accelerating its degradation. Pitting corrosion and stress corrosion cracking are other concerns, particularly in environments containing chlorides or corrosive substances. To address these weaknesses, various strategies such as surface treatments, protective coatings, alloying, and careful design considerations are employed, ensuring the material's long-term performance and durability in the intended application.
What Are Some of the Applications of Magnesium?
Listed below are some common applications of magnesium:
1. Pyrotechnics
Magnesium is commonly used in fireworks and flares due to its intensely bright, white light when burned. It enhances the visual effects of pyrotechnic displays.
2. Luggage
Some high-end luggage manufacturers use magnesium alloys to create lightweight yet durable suitcase frames. The lightweight nature of magnesium helps reduce the overall weight of the luggage.
3. Sports and Recreation Equipment
Magnesium alloys are used in the production of sports equipment such as: tennis rackets, golf clubs, and bicycle frames. The lightweight and stiffness properties of magnesium contribute to improved performance.
4. Cameras
Magnesium is used in the production of camera bodies, particularly in high-end cameras, due to its light weight and durability.
5. Power tools
Magnesium is often used in producing power tool housings due to its lightweight nature and good impact resistance. This makes the tools more user-friendly and less fatiguing to use. In addition to this, magnesium's ability to dampen vibrations is an attractive attribute for hand-held power tools. Vibration damping is crucial in power tools because it helps reduce operator fatigue and discomfort during prolonged use.
6. Car Seats
Some car manufacturers use magnesium in the construction of car seat frames. Its lightweight nature helps improve fuel efficiency and overall vehicle performance.
7. Laptops
Magnesium is used in the construction of laptop casings, primarily in high-end models. It provides a balance among weight, strength, and heat dissipation, contributing to the overall design and performance of the laptop.
Why Is Magnesium Used in Stainless Steel?
Magnesium is a crucial component in the production of steel, primarily due to its role in desulfurization. Sulfur is typically considered an unwanted impurity in steel rather than an intentional alloying element. Sulfur, when present in steel, can have detrimental effects on its mechanical properties. It is also regarded as detrimental to both the surface and internal quality of steel. With concentrations exceeding 0.05%, sulfur can lead to increased brittleness and reduced weldability of steel. Besides making steel more brittle, it plays a role in reducing its melting point and diminishing its intergranular strength and cohesion. Also, in the presence of elemental sulfur, steel can experience both general and localized forms of corrosion. However, intentionally adding small amounts of sulfur, typically ranging from 0.10% to 0.30%, can actually enhance the steel's machinability.
Magnesium can reduce the sulfur content of steel to extremely low levels, as little as 0.0002%.
To learn more, see our guide on the Composition of Stainless Steel.
Why Is Magnesium Not Used in the Building Industry?
Magnesium is not used in the building industry because magnesium and its alloys are prone to galvanic corrosion, particularly when exposed to moisture and corrosive agents prevalent in construction environments. This susceptibility to corrosion raises durability concerns for long-term structural integrity. Moreover, the cost of producing magnesium and its alloys can be relatively high compared to established building materials like steel or aluminum.
Can Magnesium Be Used in Die Casting?
Yes, magnesium can be used in die casting. Pure magnesium is not used, but magnesium alloys such as AZ91D are very popular die casting material choices. This alloy has castability and toughness, rendering it a good choice for crafting lightweight components with sufficient ductility that demand lasting performance. Other common magnesium die casting alloys include: AM60B, AM20, and AM50A.
Magnesium die casting designs can incorporate thin walls in regions where strength isn't a critical factor, and sturdier walls in zones necessitating heightened strength. The high-pressure die casting process enables the production of thinner walls with magnesium (ranging from 1 to 1.5 mm) than with aluminum alloys (typically around 2 to 2.5 mm).
To learn more, see our guide on the Die Cast Process.
What Are the Benefits of Magnesium?
Magnesium offers a range of benefits across various aspects of industrial applications:
- With a density of 1.74 g/cm³, magnesium is the lightest structural metal. Magnesium offers a weight advantage of about 30% over aluminum and an impressive 50% over titanium.
- Magnesium is the 8th most plentiful element found on Earth. It is an economical choice when balancing all factors, such as weight in weight-critical applications.
- Has excellent strength-to-weight and stiffness-to-weight ratios. Magnesium is inherently strong due to its hexagonal, closely packed crystal structure.
- Exhibits good thermal conductivity.
- Can provide effective electromagnetic shielding in applications like aerospace and electronics.
- Can be engineered to offer good corrosion resistance.
- Offers high specific strength, which is the strength of a material relative to its weight.
- Recycling of magnesium requires significantly less energy than primary extraction.
- Has the highest known damping capacity among structural metals, outperforming aluminum, titanium, and steel by a factor of ten.
- Can be easily alloyed with other metals and elements.
- Certain magnesium alloys are biocompatible and can be used for implants and medical devices.
- Some magnesium compounds can offer flame-retardant properties, making them useful in applications where fire safety is a concern.
- When used in contact with other metals, especially in the presence of an electrolyte (like moisture), magnesium can act as a sacrificial anode to protect the other metal from galvanic corrosion.
What Are the Limitations of Magnesium?
While magnesium offers numerous benefits in industrial applications, it also has some limitations that need to be considered such as:
- It is highly flammable, particularly in its pure form as a powder or shaved strips. Bulk magnesium does not pose such a great flammability risk compared to finely divided magnesium material. Certain magnesium alloys are also flammable.
- Despite the availability of some corrosion-resistant alloys, magnesium is generally more prone to corrosion than other metals such as aluminum and stainless steel.
- Processing magnesium can be more complex compared to processing other metals due to its lower melting point and reactive nature. Specialized equipment and techniques are often required for casting, machining, and forming magnesium components.
- Some magnesium alloys can exhibit brittleness, particularly at low temperatures.
- While magnesium compounds are abundant in nature, the extraction and refining process can be energy-intensive.
- When used in contact with other metals, especially in the presence of an electrolyte (like moisture), magnesium is susceptible to galvanic corrosion.
- The production and processing of magnesium can be more expensive than for other metals such as aluminum and steel.
- Magnesium's relatively low melting point, compared to materials like steel, nickel, and titanium, can be a disadvantage in applications requiring true high-temperature performance.
Is Magnesium Rust Proof?
No. “Rusting" is a term that is applied only to the corrosion of iron and steel, whose iron oxide is less dense than the metal itself, and therefore is not tightly adherent or protective. However, both magnesium and its alloys are susceptible to galvanic corrosion, a process that can lead to significant deterioration in the metal. This is especially true in applications where magnesium is exposed to aqueous solutions. This corrosion can lead to diminished mechanical strength and undesirable visual deterioration. In contrast to the reddish-brown rust commonly seen on corroded iron surfaces, magnesium corrosion typically manifests as a subdued gray film. For this reason, magnesium is commonly used as a sacrificial anode, where magnesium corrodes to protect the other metals.
Can Magnesium Form Alloys?
Yes, magnesium can form alloys. An alloy is a mixture of two or more elements, at least one of which is a metal. It has properties distinct from those of its individual components. Magnesium can alloy with various other elements, such as: aluminum, zinc, and manganese. These alloying elements are added to magnesium to create magnesium alloys that exhibit specific properties tailored for various applications. Among the most common cast magnesium alloys, you'll find: Elektron 21, ZE41, QH21, HK31, ZC63, ZK61, AM50, AZ91, AZ81, AZ63, HZ32, QE22, WE54, WE43, and ZK51. On the wrought magnesium alloys side, the frequently used ones are: ZC71, ZE41, HM21, Elektron 675, ZK60, AZ80, HK31, M1A, AZ61, and AZ31.
Is Magnesium a Metal?
Yes, magnesium is a chemical element classified as an alkaline earth metal. Magnesium has the characteristic properties of metals, such as: metallic luster, high thermal and electrical conductivity, malleability (ability to be shaped without breaking), and ductility. It's an important industrial metal and has applications in fields ranging from the aerospace industry to the automotive, due to its lightweight and strong properties.
To learn more, see our guide on What is An Alloy.
Is Magnesium a Solid, a Liquid, or a Gas?
Magnesium is a solid at room temperature and normal atmospheric pressure. It is a metallic element with a silvery-white appearance. Like many other elements, magnesium can exist in different states under different conditions and different temperatures and pressures. However, under typical conditions found on Earth's surface, magnesium is solid.
What Is the Difference Between Magnesium and Metal?
Magnesium is one of the metallic elements, meaning it falls under the broad category of metals. Metals are a group of elements characterized by their metallic luster, ability to conduct electricity, and generally high melting and boiling points. Besides being a metal, magnesium is also classified under the group alkaline earth metals. They are found on the left side of the periodic table.
To learn more, see our guide on the Most Common Metalloids.
What Is the Difference Between Magnesium and Aluminum?
The primary difference between magnesium and aluminum lies in their densities. Magnesium boasts a lower density than aluminum, which contributes to its lighter weight for a given volume of material. Moreover, magnesium has lower melting and boiling points when contrasted with aluminum.
To learn more, see our guide on What is Aluminum Metal.
Summary
This article presented magnesium, explained it, and discussed its composition and properties. To learn more about magnesium, contact a Xometry representative.
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