Cast aluminum and extruded aluminum are types of aluminum made in different ways. In cast aluminum, you pour melted metal into a mold to make a shape. Extruded aluminum is made by pushing aluminum through a hole to create shapes like tubes. Extruded aluminum is usually stronger and has a smoother surface. Cast aluminum can make more complicated shapes, but extruded is often cheaper for simple shapes

In order to select the right material for specific applications, understanding cast and extruded aluminum differences is important. Read this article to explore their specific methods, applications, pros and cons, limitations, etc.

What is Cast Aluminum?

Die casters make cast aluminum parts using molten aluminum alloys. They inject this liquid form then into the mold of the product profile. These parts are lightweight and durable because die-casting makes it that way. Cast aluminum can be used in cars, airplanes, machinery, and everyday items.

Common Aluminum Alloys

Lega A380

There are already about 8.5% silicon and 3.5% copper present in alloy A380. They exist to offer good electrical conductivity and a lower density of 2.71 g/cm³. Its fluidity is excellent. They give good castability to make thin-walled parts, and engine brackets in high-pressure die casting.

A356-T6 Alloy

This alloy has around 7% silicon and 0.3% magnesium. Parts have better strength, reaching a tensile strength of 310 MPa when they do get the proper heat treatment. These alloys contain good conductivity. Manufacturers usually use it mainly for car wheels and aerospace parts via sand casting.

319 Alloy

Generally, about 6% of this metal is silicon and 3.5% copper. This alloy is much heavier than others. It gives excellent conductivity and has a density range of 2.76 g/cm³. That makes it useful for engine blocks where heat resistance is important.

Casting Processes

Pressofusione ad alta pressione

The process in which manufacturers pour molten aluminum into a steel mold at 10–175 MPa is high-pressure die-casting. This technique works faster and produces parts within 30 seconds. It is best suited for sharply detailed parts like gearbox housings.

Pressofusione a bassa pressione

This process pushes metal into the mold at 20–100 kPa, which means at lower pressure. Slow processing like this makes fewer defect-reducing air bubbles. Their examples can be aluminum wheels that contain improved strength.

Colata in sabbia

The manufacturer pours molten metal into sand molds. This process actually does take hours per part. However, detailed parts like pump housings can make it through this.

Other Methods:

The most used process is not just die-casting or sand-casting. It also includes investment casting and permanent mold casting. In investment casting, manufacturers use wax patterns. But for permanent mold casting, they use a reusable steel mold. These techniques are those that can make medium-sized stated parts like cookware.

Microstructure and Solidification

Every time aluminum cools, tiny crystals (nucleation) and grain growth occur. This means cooling temperatures are what can impact them. That’s because fast cooling in die-casting makes very small, strong grains. Meantime, slow cooling does produce large and less durable grains. Additionally, wear resistance in alloys like A380 due to silicon particles and heat treatment in a 356-T6  actually does reduce brittle areas.

What is Extruded Aluminum?

Manufacturers use shaped dies to apply force to heated aluminum alloys. This metal then takes on profile shapes that usually are long, for instance, rods, tubes, or beams. Extruded aluminum parts are widely used across construction, automotive, and consumer goods. But their reasoning is that they are light, strong, and affordable.

Leghe comuni

6061 Alloys:

6061 alloy includes 1.0% magnesium and 0.6% silicon. These particles give it high strength (310 MPa tensile) and excellent weldability. They work well for structural and heavy-stress parts like truck frames and bicycle components.

6063 Alloys:

There is 0.7% magnesium and 0.4% silicon in 6063 alloys. It stops corrosion and gives a fine surface finish. This is why it is best for decorative and architectural profiles like window frames and door rails.

Trattamento termico

The properties of extruded aluminum get improved when manufacturers pass them under heat treatments like T5 or T6 tempering.

In T5 tempering, the extruded part is air-cooled. It increases the part’s strength with the possibility of 20–30%.

T6 tempering incorporates a solution treatment at 530°C. This is followed by artificial aging. The parts get much harder and stronger as a result. For example, you can use 6061-T6 for structural applications, balancing its optimal ductility and strength.

Extrusion Process In direct extrusion:

Manufacturers use a hydraulic ram to push the billet through a stationary die, which is referred to as direct extrusion. This kind of process performs efficiently but needs more energy just because of friction.

In indirect extrusion:

During indirect extrusion, it keeps the billet stationary while the die moves toward it. This is the reason for calling it a backward or reverse technique too. It reduces friction and energy consumption by as much as 10–30%. This technique perfectly produces precise parts like tubing.

Press Types

Among the available options, hydraulic presses give high force (up to 100 MN) for big profiles. Meanwhile, the mechanical presses work fast (up to 60 strokes/minute). It is well-suited for small parts.

Types of Extrusion

Hot extrusion:

Hot extrusion occurs at 350–500°C. It uses heat and pressure. This process actually helps in making solid or hollow parts via fixed cross-sections. For instance, I-beams or automotive chassis.

Cold extrusion:

Cold extrusion goes up to 120°C and also occurs at room temperature (20-25°C). In this process, the manufacturer does not heat the aluminum and force it to die. It makes parts with very tight tolerances up to ±0.02 mm-±0.05 mm and reduces oxidation. That, therefore, is ideal for producing fasteners, electrical connectors, and stated parts.

Key Differences Between Cast and Extruded Aluminum

1.   Mechanical Properties

Manufacturing processes have an impact on the variations in the mechanical characteristics of cast and extruded aluminum.

Forza:

Generally, the extruded arts offer higher tensile strength than those aluminum casting. For example, the tensile strength of A356-T6 cast aluminum is around 230-250 MPa. Meanwhile,  6061-T6 extruded has a tensile strength of up to 310 MPa.

Duttilità

The refined grain achieved via extruded aluminum makes it more ductile. Meanwhile, coarse grains and intermetallic phases are reasons for cast aluminum brittleness.

Durezza

Hardness is totally based on which alloy and heat treatment you pick. However, extruded parts tend to have more consistent hardness. For instance, A380 cast aluminum contains hardness around ~80 HB, but 6061-T6 extruded parts have 95 HB hardness.

Resistenza alla fatica

The finer grain structure in extruded aluminum lets them perform well under cyclic loading. Conversely, cast aluminum contains lower fatigue resistance. This is because of its porous structure. Somehow, you can improve it using proper heat treatment and better alloys.

2.   Microstructure Comparison

The microstructure in cast aluminum shows its coarse grains (ranging from 50–200 µm) and clustered intermetallic phases. This is the reason that led to the cause of brittleness and reduction in mechanical performance.

On the other hand, the extrusion process refines the grain structure as small as 10–50 µm. This is because it breaks up intermetallics and aligns grains.

For instance, the image contrasts both parts of microstructures. Wherein the cast structure exhibits coarse grains.

The extruded part (a-f) demonstrates how it refines the grain structure, leading to better performance.

3.   Tolerances

When mold expansion and solidification shrinkage happen, tolerances of cast aluminum become looser (±0.5 mm or more).

Tighter tolerances (±0.1 mm) in extruded aluminum are doable. That’s because of using a precision die for forcing metal. This means die designs and press accuracy can cause changes in tolerances.

4.   Design Considerations

Casting aluminum is mainly used for making sharply detailed shapes with internal cavities. For example, engine blocks or pump housings. But somehow, it is ill-suited for thin-walled or long profiles.

The extrusion technique produces the best long parts and uniform profiles with consistent cross-sections. For instance, beams or tubes. Besides, these parts can also take on specific design requirements.

5.   Joining Methods

Manufacturers can join both cast and extruded aluminum together. For this, they use techniques like welding, bolting, or adhesive bonding.

Wherein, cast aluminum is not easy to weld. The reason is the presence of porosity, intermetallic phases and also high silicon content in some alloys (e.g., A380. This can cause cracking.

Extruded aluminum parts are much easier to weld and machine. They contain a uniform structure. That therefore, makes them more versatile for assembly.

Advantages and Disadvantages of Cast Aluminum

Vantaggi

• It allows you to make deeply detailed and complex shapes with internal cavities. For instance, cylinder heads, transmission cases, or pump housings.
• Cast aluminum alloys like A356-T6 provide great tensile strength while being less than average weight.
• These parts are affordable if they are produced in bulk.

Svantaggi

• Trapped gas or shrinkage during solidification will cause the other parts to lose strength and fatigue resistance. But this issue can be fixed using vacuum casting or degassing agents.
• Both liquid and solid shrinkage cause parts to shatter or crack. Use proper mold design and controlled cooling to tackle this.
• Cast aluminum has a looser tolerance compared to extrusion.

Advantages and Disadvantages of Extruded Aluminum

Vantaggi

• Extruded aluminum gives excellent finishes. The part after undergoing a mill finish to anodized or powder-coated coating would be more strong. They contain improved corrosion resistance and durability.
• You can achieve tighter tolerances using precision dies.
• These parts are cost-effective at high volumes.
• Ideal for long, invariant profiles like ladder rails or multi-hollow tubes.

Svantaggi

• These parts are limited to simple shapes and do not work well for complex designs.
• Need special dies for making hollow or multi-channel profiles.
• Extrusion is not suitable for parts with multiple cross-sections or intricate internal features.

Applicazioni e settori

Specific Examples

Generally, cast aluminum is used for automotive applications. The parts include engine blocks, transmission housings, and wheel hubs.

The given image shows the engine block die design. It highlights the key components. For instance, a gating system (pathways of molten metal), overflows (collect excess material), vacuum lines (remove air), and the final cylinder block casting.

Meanwhile, manufacturers use extruded aluminum for window frames, door rails, and structural beams. In transportation, they use it for railcar bodies, truck frames, and bicycle components.

Electric Vehicles (EVs)

The usage of both cast and extruded aluminum in EVs makes them more popular. Wherein, manufacturers use cast aluminum for battery housings and motor casings. Conversely, extruded aluminum produces lightweight chassis and structural components.

Additive Manufacturing

The integration of 3D printing in cast aluminum enables it to handle more difficult shapes. They facilitate lightweight parts for aerospace and medical industries.

Additionally, innovative designs become possible with additive techniques for extruded aluminum. That makes these parts suitable to use in hybrid manufacturing processes.

Conclusione:

Cast and extruded aluminum do not contain a resemblance. Their strength, microstructure, tolerance, and design levels are different. If you pick them randomly, that means the selection can ruin the whole project. So wisely choose the right material and manufacturing process based on the application needs.