Magnesium Metal Matrix Composites (Mg-MMCs) are advanced engineering materials in which a magnesium or magnesium-alloy matrix is reinforced with ceramic or carbon-based phases to overcome the inherent limitations of conventional magnesium alloys.
Mg-MMCs deliver the lowest density among structural MMC systems while providing significantly enhanced stiffness, strength, wear resistance, and thermal stability.
Matrix Materials
| Matrix Alloy | Reason for Use |
|---|---|
| Pure Magnesium | Maximum lightweight potential |
| AZ31 / AZ91 | Good castability and availability |
| AM50 / AM60 | Improved ductility |
| ZK60 | High strength and grain refinement |
| WE43 / WE54 | High-temperature performance |
Reinforcement Types
| Reinforcement | Typical Content | Purpose |
|---|---|---|
| SiC Particles | 5 – 30 vol% | Strength and wear resistance |
| Al₂O₃ Particles/Fibers | 5 – 25 vol% | Stiffness and hardness |
| B₄C | 5 – 20 vol% | Ultra-light stiffening |
| Carbon Fibers | 5 – 60 vol% | Very high stiffness |
| CNTs / Graphene | 0.1 – 2 wt% | Nano-scale strengthening |
| Fly Ash / Cenospheres | 5 – 25 wt% | Cost reduction |
Mechanical Property Comparison
| Property | Mg Alloy (AZ31) | Mg-MMC (AZ31 + 15% SiC) |
|---|---|---|
| Density | 1.78 g/cm³ | 1.85 – 1.95 g/cm³ |
| Tensile Strength | 250 MPa | 300 – 380 MPa |
| Yield Strength | 150 MPa | 220 – 280 MPa |
| Elastic Modulus | 45 GPa | 70 – 110 GPa |
| Hardness | 60 HB | 90 – 140 HB |
| Wear Resistance | Moderate | Excellent |
Physical Properties
| Property | Typical Value |
|---|---|
| Density | 1.8 – 2.1 g/cm³ |
| Melting Range | 600 – 650 °C |
| Thermal Conductivity | 60 – 130 W/m·K |
| Electrical Conductivity | 15 – 30% IACS |
| CTE | 12 – 20 µm/m·K |
| Magnetic Behavior | Non-magnetic |
Strengthening Mechanisms
Load transfer strengthening
Orowan dislocation strengthening
Grain refinement
Thermal mismatch strengthening
Precipitation strengthening (matrix-dependent)
Processing & Machining Behavior
Reinforcement agglomeration and oxidation control are key challenges. Machining requires carbide or diamond tooling with reduced cutting speeds.
Corrosion Behavior
Reinforcements may improve or degrade corrosion resistance depending on type. Protective coatings are commonly applied. Rare-earth magnesium matrices show best performance.
Available Forms
Billets
Extruded rods and bars
Plates and sheets
Tubes
Near-net shape castings
Custom MMC profiles
Applications
Aerospace
Aircraft brackets, satellite structures, UAV frames
Automotive
Brake components, pistons, engine blocks, transmission housings
Defense & Electronics
Lightweight armor, missile components, EMI shielding
Advantages
✔ Lightest structural MMC system
✔ Exceptional stiffness-to-weight ratio
✔ Superior wear and creep resistance
✔ Improved high-temperature capability
✔ Excellent dimensional stability
Limitations
❌ Higher cost than magnesium alloys
❌ Processing and machining complexity
❌ Limited large-scale availability
❌ Corrosion management required
Why Choose Magnesium MMCs?
Mg-MMCs are selected when weight is the dominant constraint and high stiffness, wear resistance, and dimensional stability are required beyond conventional magnesium alloy capabilities.