Magnesium vs Aluminum Alloy Extrusions
Aluminum alloy extrusions are popular largely because of their light weight. But is there an extrusion material even lighter than aluminum? The answer is yes: magnesium alloy extrusions. This article provides a concise comparison between magnesium and aluminum extrusions, highlighting their key differences and applications.
Weight Comparison
Magnesium (Mg), with an atomic number of 12, is lighter than aluminum (Al), which has an atomic number of 13. Reflecting this difference, magnesium alloys have a density of 1.74 to 1.85 g/cm³, while aluminum alloys are denser, at 2.68 to 2.80 g/cm³. As a result, magnesium alloys are roughly 30% lighter than aluminum alloys.
Corrosion Resistance Comparison
Aluminum is known for its excellent corrosion resistance, which is a major reason for its widespread use. When exposed to air, aluminum forms a thin, dense, and adherent oxide layer (Al₂O₃) that acts as a protective barrier, preventing further oxidation and corrosion. This inherent property can be further improved through specific alloy compositions, such as the 5xxx series, which are designed for enhanced resistance in marine environments.
In contrast, magnesium is much more reactive. Although it also forms an oxide layer when exposed to air, this layer is neither dense nor adherent and has a lower volume than the base metal. As a result, the oxide film cracks and flakes off easily, continually exposing fresh magnesium to the environment and accelerating corrosion. Due to this vulnerability, magnesium alloys typically require special surface coatings or treatments to be suitable for most practical applications.
In comparison, aluminum’s corrosion resistance is similar to that of stainless steel, while magnesium is more comparable to iron.
Mechanical Properties Comparison
Below is a comparison of the mechanical properties of aluminum and magnesium alloys; aluminum alloys outperform magnesium alloys in all aspects.
| Property | Aluminum Alloy | Magnesium Alloy |
|---|---|---|
| Density | 2.68–2.80 g/cm³ | 1.74–1.85 g/cm³ |
| Tensile Strength | 200–600 MPa (7075-T6 maximum) | 150–350 MPa (ZK60 maximum) |
| Yield Strength | 100–500 MPa | 80–300 MPa |
| Elongation | 5–25% (excellent at room temperature) | 2–15% (brittle at room temp, improves at high temp) |
| Fatigue Performance | Good (resists repeated loading) | Lower (crack sensitive), but excellent vibration damping |
| Hardness | Higher (6061-T6 ~95 HB, 7075-T6 ~150 HB) | Lower (AZ31 around 60 HB) |
| High Temperature Performance | Strength decreases above 150°C | Maintains strength at 200–300°C (e.g., engine parts) |
| Low Temperature Performance | Remains tough to -196°C | Becomes brittle below -50°C |
| Processing Methods | Cold and hot working possible (e.g., stamping, welding) | Primarily hot working (prone to cracking at room temperature, better above 200°C) |
Cost Comparison
Firstly, the price of magnesium ingots is about 30% higher than that of aluminum ingots, making the raw material cost for magnesium extrusions more expensive from the outset.
Secondly, magnesium is more difficult to extrude due to its brittleness and low ductility, which doubles the processing cost compared to aluminum extrusions. Strict temperature control is also necessary to prevent combustion, raising manufacturing costs further.
Finally, magnesium extrusions require additional surface treatments for corrosion protection, which adds another cost not typically needed for aluminum products.
Conclusion
Magnesium alloy extrusions offer a significant advantage in terms of weight reduction. However, in almost all other respects—including corrosion resistance, strength, manufacturability, and cost—they fall short when compared to aluminum extrusions. As a result, magnesium extrusions are mainly chosen for highly specialized applications that demand the utmost weight reduction, such as in the aerospace industry and similar fields.
Aluminum alloy extrusions combine low density, excellent corrosion resistance, and high strength, making them exceptionally versatile. As a result, they are widely utilized across various sectors such as industrial, architecture, window, furniture, transportation, decoration, photovoltaic systems, and automotive manufacturing.