Properties and Characteristics of Magnesium
Magnesium is a shiny gray metal that is the lightest structural metal. With a density of 1.738 grams per cubic centimeter, magnesium is lighter than aluminum and about two-thirds the weight of steel or nickel. Magnesium has remarkable physical properties that make it ideal for applications where weight reduction is critical. It has a hexagonal-close-packed crystalline structure that gives it good creep resistance at elevated temperatures as well as excellent castability. Magnesium also has high specific strength, meaning it can withstand high stresses considering its low density.
Magnesium metal has a melting point of 649°C and a boiling point of 1,090°C. It is ductile and can be readily machined, cast, rolled or drawn into wires. However, magnesium is highly flammable and reactive, readily igniting in air at temperatures over 360°C. It must therefore be protected from moisture and oxidizing environments during storage, handling, and processing to prevent corrosion. Finished magnesium components also require protective coatings or alloying to prevent ignition.
Major Alloying Elements and Their Effects
To enhance the mechanical and corrosion resistance properties of Magnesium Metal, it is usually alloyed with other metals. Aluminum is the most common alloying element for magnesium. Adding 4-12% aluminum to magnesium improves its strength, hardness, and corrosion resistance without significantly increasing its density. Aluminum-magnesium alloys are widely used for aircraft applications due to their high specific strength.
Zinc is another important alloying element for magnesium. Adding 1-5% zinc increases the strength and hardness of magnesium more than aluminum alone. Magnesium-zinc alloys have better casting properties than pure magnesium or magnesium-aluminum alloys. Common magnesium-zinc alloys include ZK60, which contains 5-6% zinc and is used for die casting auto parts.
Manganese is added in small amounts, around 0.2-1%, primarily to enhance the creep resistance of magnesium alloys at elevated temperatures. Rare earth elements such as neodymium and mischmetal (a cerium-containing alloy) are also sometimes added in minute quantities to refine magnesium grain structure for improved strength and plasticity.
Applications of Magnesium and Its Alloys
Due to its low density, high specific strength, castability, and machinability, magnesium finds diverse industrial applications where weight reduction is important. Some of magnesium’s major application areas are discussed below.
Automotive Applications – Magnesium die castings are increasingly used in auto interiors, housings, steering wheels, and casings. Reducing vehicle weight with magnesium improves fuel economy. Common magnesium die casting auto alloys include AM50, AZ91, and ZK60.
Aircraft Applications – Magnesium metal is a critical structural metal for aircraft applications. It is used in wings, fuselages, engine mounts, and other airframe components to reduce aircraft weight. Popular aerospace magnesium alloys include AM60, Elektron 21, and Elektron 651. The B-2 stealth bomber utilizes more than 4,700 lbs of pure magnesium in its structure.
Electronics Applications – Computer housings, portable device casings, mobile phones, digital cameras all utilize magnesium die castings and extrusions to achieve light yet durable construction. Magnesium is corrosion resistant enough for these applications. Common electronic magnesium alloys include Elektron 21 and AM50A.
Other Industrial Applications – Areas such as power tools, portable machinery, medical and sports equipment benefit from lightweight magnesium construction. Additional uses include desk lamps, flashlights, and bicycle frames and parts. Magnesium’s unique blend of properties enables many custom engineering solutions.
Ongoing R&D and New Developments
Research into developing new magnesium alloys with even better mechanical properties at high temperatures, corrosion resistance, and castability continues. Some recent advancements include rare earth containing alloys such as Elektron 21, which exhibit high creep strength up to 200°C, enough for elevated automotive applications. Additions of calcium or strontium improve castability by modifying grain structure during solidification. New processing methods such as thixomolding and rheocasting allow near-net shape magnesium component manufacturing.
As sustainability concerns rise, magnesium production using secondary recycling from scraps is increasing to reduce energy costs and emissions from primary magnesium extraction. Novel hybrid composite materials combining magnesium metal matrix with fibers or particles also show promise for balancing strength, weight and manufacturability needs. With its diverse properties and lightweight potential, magnesium and its alloys remain important industrial metals for applications demanding structural efficiency well into the future.
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