Extrusions
Rods, tubes and profiles for struts, drive shafts, frames and bicycle components. Extrusion aligns the particles and gives good longitudinal properties.
Advanced materials guide
Wrought Ceramic Aluminium Matrix Composites
Wrought aluminium matrix composites (Al-MMCs) are heat-treatable aluminium alloys containing fine ceramic particles, such as silicon carbide, alumina or titanium diboride, that are extruded, rolled or forged like conventional alloys. The particles raise stiffness, fatigue strength and wear resistance while density stays close to aluminium. This guide explains how they are made, what they can and cannot do, and how to decide whether one is worth specifying.
- Matrix alloys
- 2xxx, 6xxx, 7xxx (wrought)
- Reinforcement
- SiC, Al₂O₃, B₄C, TiB₂ particles
- Typical loading
- About 10 – 25 vol %
- Designation
- ANSI H35.5 (e.g. 6061/Al₂O₃/20p-T6)
What is a wrought aluminium matrix composite?
A metal matrix composite combines a metal with a second, much stiffer phase. In discontinuously reinforced aluminium (DRA), the second phase is ceramic particles a few micrometres across, or in newer grades much finer particles formed inside the melt. "Wrought" means the composite is supplied as billet that is then hot-worked into extrusions, plate, sheet or forgings, as opposed to cast composites poured directly into shape.
The aim is simple: aluminium alloys are light and strong but not very stiff, with an elastic modulus of about 70 GPa whatever the alloy. Strength can be raised by alloying and heat treatment; stiffness cannot. Adding ceramic particles is the only practical way to raise the modulus of an aluminium part substantially while keeping it light, and the particles also slow fatigue crack initiation and resist abrasive wear.
The trade-offs are just as real. Ductility and fracture toughness fall, machining becomes abrasive, fusion welding is difficult, and the material costs considerably more than standard 6061 or 7075. Wrought Al-MMCs are therefore engineering choices for parts where stiffness per kilogram, fatigue life or wear decide the design, not general-purpose replacements.
How aluminium composites are designated
Proprietary trade names are common in this field, which makes comparisons difficult. The neutral way to describe a composite is the Aluminum Association system in ANSI H35.5, which builds on the normal alloy and temper designations of ANSI H35.1.
| Part of the code | Example | Meaning |
|---|---|---|
| Matrix alloy | 6061 | The aluminium alloy, by its registered designation |
| Reinforcement | Al₂O₃ | Chemical formula of the ceramic phase (SiC, Al₂O₃, B₄C, TiB₂) |
| Volume fraction and form | 20p | Volume percent, with p = particles, w = whiskers, f = fibres |
| Temper | -T6 | Standard temper designation of the matrix |
| Full designation | 6061/Al₂O₃/20p-T6 | 6061 reinforced with 20 vol % alumina particles, solution treated and aged |
When you compare offers, ask for this full description and for the test data behind it. A house code tells you nothing about matrix, particle type or loading, and two materials with similar strength can differ greatly in toughness and machinability.
Ceramic reinforcements and what each contributes
| Reinforcement | Density (g/cm³) | Main benefit | Typical uses |
|---|---|---|---|
| Silicon carbide (SiC) | 3.21 | Largest stiffness gain per volume, good wear resistance, low expansion | Structural struts, aerospace and space parts, brake components |
| Alumina (Al₂O₃) | 3.95 | Chemically stable, good wear resistance, well-established extrusion grades | Drive shafts, bicycle and sports parts, wear parts |
| Boron carbide (B₄C) | 2.52 | Very hard and light; boron-10 absorbs neutrons | Neutron-absorber plate for spent-fuel storage and transport |
| Titanium diboride (TiB₂), in situ | 4.5 | Very fine particles formed in the melt; better ductility than coarse additions | High-strength extrusions and forgings, additive-manufacturing feedstock |
Composite density follows the rule of mixtures. For a 6061 matrix (2.70 g/cm³), 20 vol % SiC gives about 2.80 g/cm³, 20 vol % alumina about 2.95 g/cm³ and 20 vol % boron carbide about 2.66 g/cm³. Even with heavy reinforcement, the material stays far lighter than titanium (about 4.4 g/cm³) or steel (about 7.8 g/cm³).
How reinforcement changes the properties
Exact values depend on matrix, particle size, loading, processing route and temper, and published datasheets vary widely. The table therefore shows the direction and approximate size of the changes for a 6xxx matrix with 15 – 25 vol % SiC or alumina, compared with the same alloy unreinforced in T6. Design data should always come from the producer's qualified test results.
| Property | Effect of particle reinforcement | Comment |
|---|---|---|
| Elastic modulus | Rises from about 70 GPa to roughly 95 – 115 GPa | The main reason to use an MMC; gain is nearly linear with SiC loading |
| Specific stiffness (E/ρ) | Higher than aluminium, titanium and steel | Allows thinner, lighter sections at the same deflection |
| Tensile and yield strength | Moderate increase | Depends strongly on matrix and particle size; finer particles help |
| Elongation | Falls, often to a few percent | Design for limited ductility; avoid sharp notches |
| Fracture toughness | Falls | The key limitation for damage-tolerant structure |
| Fatigue strength | Higher, especially at high cycle counts | Benefit is largest in smooth, well-machined parts |
| Wear resistance | Much higher | Hard particles carry the load at the surface |
| Thermal expansion | Lower (towards 15 – 18 µm/m·K at high loadings) | Helps match ceramics, steel inserts or electronics |
| Thermal conductivity | Similar or slightly lower | SiC keeps conductivity reasonably high |
Claims of 800 MPa tensile strength or titanium-beating strength-to-weight should be treated with care. Such values, where real, apply to specific high-strength 7xxx-matrix grades in particular product forms and directions. Ask for the test standard, specimen direction and statistical basis before using them.
How wrought Al-MMC billet and products are made
- Billet productionEither powder metallurgy (alloy powder blended with ceramic powder, consolidated by pressing and sintering or hot isostatic pressing) or melt routes (stir casting, or in-situ reaction that forms TiB₂ particles inside the melt), followed by casting into billet.
- Hot workingBillet is extruded, rolled or forged. Working breaks up particle clusters and closes porosity, so wrought products are more uniform and tougher than as-cast composites.
- Heat treatmentThe matrix is solution treated, quenched and aged like the unreinforced alloy, giving tempers such as T6 or T8.
- FinishingParts are machined with diamond or carbide tooling and may be anodised or coated.
- InspectionParticle distribution, porosity and tensile properties are checked by metallography, ultrasonic testing and mechanical tests.
Powder-metallurgy routes generally give the most uniform particle distribution and best properties at high loadings; melt routes are more economical for large volumes. In both cases the consistency of particle distribution is what separates a reliable product from a variable one. Clusters of particles and small pores act as crack starters, so buyers of fatigue-critical parts should ask how distribution is measured, how often, and what acceptance limits apply to each lot.
Product forms and what they are used for
Plate and sheet
Rolled products for stiff panels, neutron-absorber plate and machined structural parts.
Forgings and rings
Closed-die forgings and rolled rings for highly loaded rotating or reciprocating parts.
Billet and bar for machining
Stock for precision parts in optical, semiconductor and space equipment, where stiffness and dimensional stability matter.
Powder feedstock
Composite powders for additive manufacturing and near-net-shape parts; see our composite powder guide.
Machining, joining and finishing
Machining
Ceramic particles are harder than carbide tool grades, so tool wear is rapid. Polycrystalline diamond (PCD) tooling is standard for production; coated carbide is used for short runs at reduced speed.
Drilling and threading
Use PCD or diamond-coated drills. Form-tapping is unsuitable; cut threads or use inserts.
Fusion welding
Difficult: SiC can react with molten aluminium to form brittle aluminium carbide, and particles segregate in the weld pool. Avoid fusion welds in highly stressed areas.
Solid-state joining
Friction stir welding, mechanical fastening and adhesive bonding are the usual joining methods.
Forming
Limited cold formability. Bend hot or design parts to be machined from extrusions or plate.
Surface treatment
Can be anodised, though the coating is less uniform than on monolithic alloys; conversion coatings and paints are also used.
Typical applications
- Aerospace and space: stiff struts, fan exit guide vanes, equipment racks, optical benches and instrument structures where deflection and thermal stability govern
- Automotive and motorsport: drive shafts, brake discs and drums, pistons and connecting parts where weight, stiffness and wear interact
- Rail and transport: brake components and stiff lightweight structural parts
- Electronics and semiconductor: stages, frames and housings needing stiffness with low thermal expansion
- Nuclear: B₄C-reinforced aluminium plate as neutron absorber in spent-fuel racks and casks, qualified under standards such as ASTM C1671
- Sports equipment: bicycle frames and components, where alumina- and SiC-reinforced extrusions have long been used
In each case the part is designed around the composite's limits: generous radii, smooth surfaces, solid-state joints and allowance for lower ductility.
Al-MMC or a high-strength wrought alloy?
| Need | Consider first | Why |
|---|---|---|
| Highest static strength at low cost | 7075-T6 / T651, 7050-T7451 | Proven, widely certified, easy to machine |
| Damage tolerance and fatigue crack growth | 2024-T3 / T351, 7050 | Higher toughness than particle composites |
| Weldable high-strength structure | 2219, 6061, 6082 | Fusion-weldable with established procedures |
| Maximum stiffness per weight | SiC-reinforced Al-MMC | Modulus gain that no unreinforced alloy can match |
| Wear resistance in a light part | Al₂O₃ or SiC Al-MMC, or hard-anodised alloy | Choose the composite where coatings wear through |
| Neutron absorption | B₄C-aluminium composite | Boron-10 content with aluminium thermal conductivity |
A useful rule: if the design is limited by strength, stay with a conventional high-strength alloy; if it is limited by stiffness, vibration or wear, an aluminium composite may justify its cost. Common mistakes are specifying a composite for a part that will be welded, choosing on tensile strength alone without checking toughness, and underestimating machining cost.
What to include in an enquiry
- FunctionWhat the part does, the governing requirement (stiffness, fatigue, wear, expansion) and its environment.
- MaterialFull designation if known (matrix / reinforcement / volume % / temper), or the target properties.
- Form and sizeExtrusion, plate, forging or bar, with dimensions, tolerances and quantity.
- TestingRequired tensile directions, ultrasonic class, metallography and the certificate type (EN 10204 3.1).
- DeliveryDestination and terms (EXW, FOB, CIF or DAP) for export shipment.
Metline reviews composite enquiries case by case and supplies the conventional high-strength alternatives, such as 7075, 7050, 2024 and 2219, in plate, bar, extrusion and forged forms worldwide.
References and standards
- ANSI H35.5 – Nomenclature System for Aluminum Metal Matrix Composite Materials (Aluminum Association)
- ANSI H35.1 – Alloy and Temper Designation Systems for Aluminum
- ASM Handbook, Vol. 21 – Composites (discontinuously reinforced aluminium)
- ASTM C1671 – Qualification and Acceptance of Boron Based Metallic Neutron Absorbers for Nuclear Criticality Control
- ASM Alloy Digest Al-359 – 6092/SiC/17.5p discontinuously reinforced aluminium
Wrought aluminium (aluminum) matrix composites: frequently asked questions
What is the main advantage of an aluminium matrix composite?
Higher stiffness at almost the same weight. Ceramic particles can raise the elastic modulus from about 70 GPa to around 100 GPa, which no conventional aluminium alloy can achieve, and they also improve fatigue and wear resistance.
Can Al-MMCs replace titanium?
In some stiffness-limited parts, yes, because their specific stiffness can exceed that of titanium. They have lower toughness and ductility and a lower temperature limit, so each part must be assessed individually.
Can aluminium matrix composites be welded?
Fusion welding is difficult and generally avoided in stressed areas. Friction stir welding, bolting, riveting and adhesive bonding are the normal joining methods.
Why are Al-MMCs hard to machine?
The ceramic particles are harder than most cutting-tool materials and wear tools quickly. Polycrystalline diamond tools are the standard choice for production machining.
What does 6061/Al2O3/20p-T6 mean?
It is the ANSI H35.5 designation for a 6061 aluminium matrix containing 20 % by volume of alumina particles, in the T6 solution-treated and aged temper.
Does Metline supply aluminium matrix composites?
We review Al-MMC enquiries case by case and supply conventional high-strength aluminium alloys as alternatives, all with mill test certificates and worldwide shipping.
Evaluating an aluminium composite?
Tell us the part function, form, size and quantity. We will advise on composite or conventional alloy options and what can be supplied.
