Selecting between magnesium and aluminum for die casting can be a challenge, especially for parts requiring specific performance characteristics like strength, weight, corrosion resistance, and thermal properties. In this article, we break down the differences between magnesium and aluminum alloys, their properties, casting processes, and real-world applications to help you make the best decision for your parts.
Magnesium vs Aluminum in Die Casting
Both magnesium and aluminum are popular materials in die casting, but they offer different benefits depending on the specific needs of your part.
Aluminum alloys are metallic materials primarily made of aluminum mixed with other metals like copper, magnesium, manganese, silicon, or zinc. Magnesium is the lightest structural metal, making it a popular choice for weight-sensitive applications such as automotive and aerospace components. It has a lower melting point, which results in easier flow during casting and quicker cycles in high-volume manufacturing. Magnesium’s strength-to-weight ratio is outstanding, which makes it ideal for parts that need both lightness and moderate strength.
Magnesium alloys are lightweight alloys made by adding magnesium to aluminum and other metals. Aluminum is slightly heavier but offers better strength, thermal conductivity, and corrosion resistance. It is also widely used in high-performance parts that need to endure extreme temperatures or corrosion, such as engine components and structural frames. Aluminum alloys are favored for their versatility and durability in a wide range of industries.
Magnesium and aluminum alloys are both die-castable and have their strengths in different industries and applications. Your choice between the two depends on the part’s design, performance needs, and cost considerations.
Key Properties of Aluminum and Magnesium Alloy
To understand why one material may be more suitable for a particular part, it’s important to compare the key properties of aluminum and magnesium alloys. The table below shows a side-by-side comparison of the most important properties for both materials.
| Property | Magnesium Alloy (e.g., AZ91D) | Aluminum Alloy (e.g., A380, ADC12) |
|---|---|---|
| Density (g/cm³) | 1.74 | 2.70 |
| Tensile Strength (MPa) | 150–250 | 250–350 |
| Yield Strength (MPa) | 100–200 | 150–250 |
| Elongation (%) | 2–10 | 3–15 |
| Thermal Conductivity (W/m·K) | 156 | 160–200 |
| Coefficient of Thermal Expansion (µm/m·°C) | 25 | 22 |
| Hardness (HV) | 60–80 | 80–110 |
| Corrosion Resistance | Moderate | Excellent |
| Melting Point (°C) | 650 | 660 |
| Strength-to-Weight Ratio | Excellent | Good |
| Wear Resistance | Moderate | High (with T6 treatment) |
Other Common Alloys
While A380 and AZ91D are widely used in die casting, there are other commonly used alloys:
- A356 Aluminum Alloy: This alloy is commonly used for aerospace and automotive components. It offers excellent castability and strength after heat treatment (T6).
- AM60B Magnesium Alloy: Known for its lightweight and moderate strength, AM60B is often used in automotive components, including housing, wheels, and other structural parts.
Magnesium vs Aluminum Strength and Weight in Real Parts
The primary reason for choosing magnesium over aluminum is weight reduction. Magnesium alloys, like AZ91D, are 33% lighter than aluminum alloys, making them ideal for parts that require a high strength-to-weight ratio.
In automotive parts, such as engine blocks or transmission housings, reducing weight while maintaining strength is crucial. Magnesium parts can offer the same strength as aluminum but at a lower weight, leading to improved fuel efficiency and lower emissions.
Real-world weight and strength comparison:
- Magnesium alloy (AZ91D): 1.74 g/cm³, UTS 230 MPa, YS 150 MPa
- Aluminum alloy (A380): 2.70 g/cm³, UTS 310 MPa, YS 270 MPa
For example, if you’re casting a chassis component, the difference in material weight could be substantial, leading to a lighter vehicle with improved performance. However, aluminum may be the better choice for parts that need high strength and durability, especially for high-temperature applications.
Casting Feasibility for Aluminum and Magnesium Alloy
Both magnesium and aluminum alloys can be used in die casting, but each material has its own design considerations that affect its castability, part geometry, and mold setup.
Magnesium die casting:
- Advantages: Magnesium die casting is known for its ease of flow, which allows for the production of thin-walled parts and complex geometries.
- Challenges: Magnesium’s high reactivity with oxygen requires careful control of the melt atmosphere, particularly during the pouring process. Magnesium alloy melts are also prone to oxidation, so maintaining an inert atmosphere during pouring is critical.
Aluminum die casting:
- Advantages: Aluminum is preferred for high-performance parts requiring strength and corrosion resistance. It also has better heat resistance, which makes it suitable for parts exposed to high temperatures, such as engine components and structural frames.
- Challenges: Aluminum die casting is more sensitive to shrinkage, so well-designed feeders and gating systems are required.
Key design rules for magnesium:
- Wall thickness: Magnesium works best for walls between 1.5–4 mm. Thin-walled parts are easy to produce due to better fluidity.
- Draft angles: Magnesium requires 1.5–2.5 degrees for easy mold release.
- Radii: Fillets should be at least 3 mm to reduce stress concentrations and improve moldability.
Key design rules for aluminum:
- Wall thickness: Ideal wall thickness for aluminum is between 2–6 mm for die casting.
- Draft angles: Use 2–3 degrees for most parts.
- Radii: Minimum 2 mm fillet radii to avoid casting defects.
Thermal & Electrical: Aluminum vs Magnesium for Heat and EMI
Both aluminum and magnesium have distinct thermal and electrical properties that influence their performance in different applications.
- Thermal conductivity: Magnesium’s lower thermal conductivity (156 W/m·K) makes it a better material for lightweight heat sinks and parts that need to dissipate heat in low-heat applications. However, aluminum has a higher conductivity (160–200 W/m·K) and is better suited for heat-exchanging parts like automotive radiators and electronic enclosures.
- Electrical conductivity: Aluminum’s electrical conductivity is significantly better than magnesium, which is why aluminum is preferred for electrical housings and battery enclosures.
Magnesium vs Aluminum Cost and Lead Time
When deciding between magnesium and aluminum for die casting, the cost and lead time play an important role. While magnesium alloys are generally cheaper on a per-pound basis, they often come with higher tooling costs due to the specialized equipment required for magnesium die casting. Aluminum, on the other hand, is slightly more expensive, but its tooling costs are lower.
- Magnesium: Lower material costs, but higher tooling and finishing costs than aluminum.
- Aluminum: Generally more expensive on a per-pound basis, but tooling costs are lower, and it can handle more cycles before mold wear becomes an issue.
Lead time for magnesium castings may also be longer due to the specialized equipment and additional steps like vacuum casting or inert gas shielding.
Alloy Picker: AZ91D & AM60B vs A380, ADC12, A356-T6
Below is a quick comparison of some of the most popular magnesium alloys and aluminum alloys used in die casting. Knowing the properties of these alloys helps in selecting the right one for your application.
| Alloy | Strength (MPa) | Elongation (%) | Density (g/cm³) | Applications | Process |
|---|---|---|---|---|---|
| AZ91D (Magnesium) | 240 | 3–5 | 1.74 | Automotive, Aerospace, Lightweight Parts | Die-Casting, Sand Casting |
| AM60B (Magnesium) | 230 | 6 | 1.75 | Automotive, Wheels, Housing | HPDC, LPDC |
| A380 (Aluminum) | 310 | 2.5–3 | 2.7 | Automotive, Industrial Equipment | HPDC |
| A356-T6 (Aluminum) | 310 | 10 | 2.68 | Aerospace, Engine Components | LPDC, Sand Casting |
| ADC12 (Aluminum) | 250 | 6 | 2.7 | Electronics, Housing Components | HPDC, GPM |
When to Choose Magnesium vs When to Choose Aluminum
Choose Magnesium when:
- Lightweight is critical (e.g., reducing weight in automotive or aerospace parts).
- Cost-sensitive parts that require moderate strength.
- You need to dissipate heat in low-thermal applications.
- Die-cast parts with thin walls and complex geometries are required.
Choose Aluminum when:
- High strength and corrosion resistance are critical (e.g., engine blocks, heat exchangers).
- Durability and temperature resistance are important for your parts.
- You need better machinability and weldability.
If you’re still unsure about which material best suits your project, contact us today for a free DFM (Design for Manufacturing) review.
Engineering FAQ on Magnesium vs Aluminum
- Is magnesium stronger than aluminum?
Magnesium alloys can achieve higher strength-to-weight ratios, but aluminum alloys are generally stronger and more durable in structural applications. - What is the density of magnesium vs aluminum?
Magnesium is about 35% lighter than aluminum, with a density of 1.74 g/cm³ compared to 2.7 g/cm³ for aluminum. - How does the strength of magnesium compare to aluminum?
Magnesium alloys like AZ91D are typically stronger per weight than aluminum alloys but have lower absolute strength. - Can die-cast magnesium be welded or riveted like aluminum?
Yes, magnesium can be welded with specialized techniques. It requires careful control of heat to avoid porosity and flammability. Aluminum, however, is more commonly welded in standard manufacturing processes. - What is the best aluminum alloy for die casting?
A380 and A356-T6 are great choices for die casting, offering a good balance of strength, corrosion resistance, and casting properties. - Is magnesium more expensive than aluminum?
Magnesium tends to be cheaper per weight, but its higher tooling and finishing costs can increase overall part costs compared to aluminum. - Can you machine magnesium parts?
Yes, magnesium can be machined, but it requires careful handling due to its flammability. Specialized techniques are used to ensure safe machining.
Ready to Choose the Right Material?
Now that you have a clearer idea of magnesium vs aluminum, it’s time to get your parts cast with the best material. If you’re still unsure or need guidance on your specific design, contact us today for an expert consultation. We specialize in die-casting aluminum and magnesium parts, and we can help you choose the right alloy, process, and finish for your needs.
Get a Quote: Send your drawings to yongzhucasting@gmail.com for a detailed analysis, DFM feedback, and a quote.
