Aluminum is stronger than magnesium in absolute terms. A common aluminum alloy (6061-T6) has a yield strength of about 276 MPa, while a widely used magnesium alloy (AZ91) yields at roughly 160 MPa. But “stronger” depends on what you’re measuring, and magnesium has a compelling advantage when you factor in weight.
Raw Strength: Aluminum Wins
When you compare the two metals head to head, aluminum alloys consistently outperform magnesium alloys in tensile and yield strength. Yield strength is the point where a material permanently deforms instead of springing back, and it’s the most practical measure of how much load a part can handle. At 276 MPa, 6061-T6 aluminum can take about 70% more stress than AZ91 magnesium before it starts to bend out of shape. High-performance aluminum alloys like 7075 push even further, reaching yield strengths above 500 MPa.
Magnesium is also significantly less stiff. Its elastic modulus (a measure of rigidity) is around 44 to 45 GPa, compared to about 69 GPa for aluminum. That means a magnesium beam of the same dimensions will flex roughly 50% more under the same load. For applications where deflection matters, like structural beams or load-bearing frames, aluminum holds its shape better.
Strength Per Unit Weight: Magnesium Closes the Gap
Magnesium’s density is only 1,830 kg/m³, about two-thirds that of aluminum at 2,700 kg/m³. This changes the math considerably. When engineers compare materials, they often care less about raw strength and more about specific strength: how strong something is relative to how much it weighs.
On a per-kilogram basis, standard magnesium alloys are competitive with aluminum alloys, and advanced magnesium formulations can surpass them. Researchers at Science Advances reported a magnesium-lithium-aluminum alloy (LA147) with a density of just 1.32 g/cm³ and a specific yield strength of 470 to 500 kN·m/kg, exceeding nearly every other engineering alloy tested. That includes aerospace-grade aluminum-lithium alloys and titanium alloys. For industries obsessed with cutting weight, like automotive and aerospace, this ratio is often more important than absolute strength numbers.
This is why magnesium castings are popular in car parts like steering wheels, instrument panels, and seat frames. The material shaves weight without requiring a proportionally larger part to compensate for its lower raw strength.
Heat Performance and Durability
Aluminum handles heat better than magnesium in two important ways. First, aluminum alloys like 6061-T6 hold their mechanical properties reasonably well up to about 150°C. Above 200°C, they weaken substantially, but they do so gradually and predictably. Magnesium alloys also lose strength at elevated temperatures, but the bigger concern is surface degradation. Magnesium reacts aggressively with oxygen at high temperatures, forming a brittle oxide layer. In extreme cases, magnesium can ignite, something that simply doesn’t happen with aluminum. Aluminum forms a thin, protective aluminum oxide film that actually shields the metal from further damage.
This thermal stability is one reason aluminum dominates in engine components and exhaust-adjacent parts, while magnesium is used in cooler, less exposed areas of a vehicle.
Corrosion Resistance
Magnesium corrodes far more easily than aluminum, especially in the presence of moisture and salt. When magnesium contacts aluminum or steel directly, it creates a galvanic cell where the magnesium rapidly deteriorates while the other metal stays intact. This is because magnesium sits very low on the galvanic series, making it the “sacrificial” metal in any mixed-metal assembly.
Aluminum also corrodes, but its natural oxide layer provides meaningful protection in most environments. Magnesium parts almost always need protective coatings, anodizing, or careful isolation from other metals to survive long-term outdoor or marine exposure. This adds manufacturing steps and cost that aluminum parts can often avoid.
Cost and Practical Tradeoffs
Magnesium costs significantly more than aluminum. As of recent U.S. market data, magnesium metal runs about $5.00 per pound on the spot market, while aluminum typically sits between $1.00 and $1.50 per pound. The U.S. Geological Survey notes that magnesium’s high cost is a recognized disadvantage relative to aluminum and zinc, even in applications where its lighter weight is beneficial.
About 64% of primary magnesium consumption goes into castings, mostly for the automotive industry. Magnesium is excellent for die casting because it flows well in molds and solidifies quickly. But the raw material premium, combined with the need for corrosion protection and more careful handling during machining (magnesium chips can ignite), means it only makes economic sense when weight savings justify the extra expense.
For most everyday structural applications, aluminum offers a better balance of strength, durability, corrosion resistance, and affordability. Magnesium earns its place in specialized roles where every gram matters and the operating environment can be controlled.