The Fascinating Properties and Uses of Magnesium Metal

Magnesium Metal

Magnesium is the lightest structural metal and the eighth most abundant element in the Earth's crust. With an atomic number of 12, magnesium is a shiny gray metal that is highly flammable and combustible in its powder form. With a density of only 1.74 grams per cubic centimeter, magnesium is less dense than aluminum yet it is 33% stronger than aluminum and even stronger than some steels. Some key properties of magnesium include its light weight, strength-to-weight ratio, castability, and electrical conductivity. These properties have led to wide applications of magnesium across many industries.

Physical and Chemical Properties

Magnesium has a hexagonal crystal structure that gives it unique physical characteristics. It has a melting point of 649°C (1200°F) and a boiling point of 1091°C (1996°F). Magnesium is highly flammable and burns with a brilliant white light when exposed to heat or flames. It readily ignites in air at 360°C (680°F) to form magnesium oxide. Magnesium has a silvery-white color and is a fairly reactive metal. It undergoes corrosion reactions when exposed to moisture, acids, alkalis and saltwater. Magnesium Metal forms a protective oxide layer in air that slows further corrosion. Its reactivity also means it can be used as a desiccant to absorb moisture and as a reducing agent in chemical reactions.

Mechanical Properties

Despite its lightness, magnesium metal has impressive mechanical properties. It has a tensile strength that ranges from 170-412 MPa depending on the alloy and heat treatment used. This translates to magnesium having a high strength-to-weight ratio that makes it attractive for applications requiring lightweight yet strong materials. Additionally, magnesium has good machinability, castability, and is recyclable without loss of properties. It also has good vibration damping properties, electromagnetic shielding, and is an excellent conductor of electricity and heat. These mechanical characteristics have led to expanding uses of magnesium in automotive, aerospace and electronics industries.

Major Alloying Elements

While pure magnesium metal has its advantages, alloying it with other elements vastly improves its strength and corrosion resistance for structural applications. Some key alloying elements include:

- Aluminum: The addition of up to 5% aluminum creates the strongest and most common Mg alloy AZ91D. Al improves strength, creep resistance and castability.

- Zinc: Zinc alloys such as ZK60 are used in die casting for their high strength and ease of casting. However, they have lower creep resistance than Al alloys.

- Manganese: Additions up to 2% Mn in alloys like AM50, AM60 impart better corrosion resistance than other alloys.

- Silver, rare earths: Minor additions refine grain structure and improve mechanical properties. Alloys such as WE54 are best for welding.

Carefully balancing these alloying ingredients allows customizing magnesium for different manufacturing techniques and end-use requirements.

Manufacturing of Magnesium

Over 75% of magnesium production is via the Pidgeon process which involves the electrolytic reduction of magnesium chloride. Other methods include the electrolysis of molten magnesium salts and the thermal decomposition of magnesium from magnesium oxide. Due to its lightness, castability and machinability, there are several ways magnesium and its alloys can be processed:

- Casting: Die casting and sand casting are widely used for complex automobile and electronic components.

- Extrusion and rolling: Used to make sheets and profiles for automotive and industrial components requiring strength and lightness.

- Powder metallurgy: Produces high strength near-net shapes for aerospace parts.

- Welding and joining: Techniques like MIG welding are suited for construction of aircraft frames and wheel rims.

The ability to cast, extrude, forge and machine magnesium opens up many design possibilities for engineers and manufacturers.

Applications of Magnesium and its Alloys

The prime advantages of light weight, strength and machinability have boosted magnesium metal use across many industries:

- Automotive: Components like engine covers, seat frames and wheels in high-end automobiles are commonly made of magnesium. Its use reduces vehicle weight and improves fuel efficiency.

- Aerospace: Spacecraft, aircraft frames, helicopter gearboxes widely employ magnesium for its high strength-to-density properties critical for flight applications.

- Electronics: Housings and casings for laptops, mobile phones, and cameras use die-cast magnesium alloys for lightweight durability.

- Industrial: Components for machinery, hand tools, lamps commonly employ sand-cast Mg alloys for strength at low weights.

- Sports equipment: Bicycles, golf club heads etc benefit from magnesium's lightness and shock absorbing qualities.

- Medical: Implants and medical instruments utilize biocompatible Mg alloys and are being researched for degradable implants.

As researchers further magnesium alloys to improve properties, its use across more industries will continue expanding to replace heavier conventional materials.

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