Pure Magnesium is the lightest structural metal in commercial use, valued for its exceptionally low density, high specific stiffness, excellent damping capacity, and good electromagnetic shielding. While it has limited absolute strength, its strength-to-weight advantages and unique physical behavior make it important in chemical, metallurgical, sacrificial, and specialty engineering applications.
Chemical Composition
| Element | Typical Content (%) |
|---|---|
| Magnesium (Mg) | ≥ 99.8 |
| Aluminum (Al) | ≤ 0.05 |
| Zinc (Zn) | ≤ 0.02 |
| Manganese (Mn) | ≤ 0.03 |
| Silicon (Si) | ≤ 0.01 |
| Iron (Fe) | ≤ 0.005 |
| Copper (Cu) | ≤ 0.01 |
| Nickel (Ni) | ≤ 0.001 |
Crystal Structure & Metallurgical Behavior
Crystal Structure: Hexagonal Close-Packed (HCP)
Slip systems are limited at room temperature, resulting in reduced ductility at ambient
conditions but excellent ductility at elevated temperatures (>200 °C).
Metallurgical Insight:
The HCP structure gives magnesium directional properties, making texture control critical
during rolling and extrusion.
Strengthening Mechanisms
Pure magnesium is not heat-treatable. Strength is derived from:
✔ Grain size refinement (Hall–Petch effect)
✔ Minor solid solution effects (trace impurities)
✔ Limited cold work due to HCP crystal structure
Key Mechanical Properties
| Property | Typical Value |
|---|---|
| Tensile Strength | 90 – 110 MPa |
| Yield Strength (0.2%) | 20 – 35 MPa |
| Elongation | 5 – 15% |
| Hardness | ~30 HB |
| Fatigue Strength | Low |
| Creep Resistance | Poor |
| Modulus of Elasticity | ~45 GPa |
Physical Properties
| Property | Value |
|---|---|
| Density | 1.74 g/cm³ |
| Melting Point | 650 °C |
| Boiling Point | 1090 °C |
| Thermal Conductivity | 155 – 160 W/m·K |
| Electrical Conductivity | ~38% IACS |
| Thermal Expansion | 26 ×10⁻⁶ /°C |
| Damping Capacity | Excellent |
| EMI Shielding | Very good |
Corrosion & Surface Behavior
Forms a thin MgO/Mg(OH)₂ surface film but is susceptible to chlorides and marine environments. Corrosion resistance improves significantly with high purity and protective coatings.
Common protection methods include conversion coatings, anodizing, organic coatings, and controlled atmospheres.
Refining & Production Processes
Primary Production
Thermal reduction (Pidgeon Process)
Electrolytic MgCl₂ process (higher purity)
Refining
Flux refining, vacuum distillation, and filtration to remove oxides and inclusions
Processing & Fabrication
| Process | Performance |
|---|---|
| Casting | Good (requires protective atmosphere) |
| Forming | Poor cold, excellent hot |
| Machining | Excellent (fire precautions required) |
| Welding | Possible (TIG, laser) |
| Fastening | Common |
Available Forms
Ingots
Billets
Rods & bars
Sheets & plates
Powders & granules
Sacrificial anodes
Cast shapes
Applications
Metallurgical
Aluminum alloying, steel desulfurization, nodular cast iron
Chemical & Cathodic Protection
Sacrificial anodes, chemical reduction
Aerospace & Defense
Pyrotechnics, flares, lightweight components
Automotive & Electronics
Lightweight housings, EMI shielding enclosures
Advantages of Pure Magnesium
✔ Lightest structural metal
✔ Excellent strength-to-weight ratio
✔ Superior vibration damping
✔ High thermal conductivity
✔ Easy machining
✔ Highly recyclable
Limitations
❌ Low absolute strength
❌ Limited room-temperature ductility
❌ Poor corrosion resistance without protection
❌ Fire risk in fine forms
❌ Poor creep resistance
Why Choose Pure Magnesium?
Pure magnesium is chosen when weight reduction, damping, conductivity, and machinability are critical and when magnesium’s reactivity is beneficial in chemical or metallurgical applications.