Quick Answer
Aluminum casting — aluminum casting produces lightweight, corrosion-resistant metal parts by melting aluminum alloy and shaping it in a mold. The main processes are sand casting (lowest cost, largest range), investment casting (high precision), gravity die casting (moderate volume, pressure-tight), and high pressure die casting (HPDC, highest volume). For OEM buyers, choosing the right aluminum casting process depends on volume, tolerance, surface finish, and part size.
Why Aluminum Casting for OEM Parts?
Aluminum casting combines unique advantages that make it the most widely used non-ferrous casting material:
- Lightweight: 2.7 g/cm³ — one-third the weight of steel, ideal for automotive, aerospace, and portable applications
- Corrosion resistance: Aluminum forms a stable oxide layer that protects against atmospheric and mild chemical corrosion
- High thermal conductivity: 150–200 W/m·K — excellent for heat sinks, engine components, and thermal management
- Good strength: Tensile strength 220–330 MPa (as-cast) up to 400 MPa (heat treated); excellent strength-to-weight ratio
- Excellent castability: Low melting point (660°C), good fluidity, fills thin sections well
- Recyclable: Aluminum is 100% recyclable with no property loss; recycled aluminum requires only 5% of the energy of primary aluminum
Aluminum Casting Processes Compared
| Process | Tooling Cost | Best Volume | Tolerance | Surface | Max Size | Porosity |
|---|---|---|---|---|---|---|
| Sand Casting | $500–$5,000 | 10–500 | ±0.5–1.0 mm | Ra 12.5–25 µm | Unlimited | Low |
| Investment Casting | $5,000–$30,000 | 50–5,000 | ±0.1–0.3 mm | Ra 3.2–6.3 µm | ~50 kg | Low |
| Gravity Die Casting | $10,000–$50,000 | 500–10,000 | ±0.2–0.5 mm | Ra 3.2–12.5 µm | ~100 kg | Low |
| Low Pressure Die Casting | $20,000–$80,000 | 1,000–10,000 | ±0.1–0.3 mm | Ra 1.6–6.3 µm | ~100 kg | Very low |
| High Pressure Die Casting | $30,000–$150,000 | 10,000+ | ±0.1–0.25 mm | Ra 0.8–3.2 µm | ~20 kg | Moderate (VAD needed for pressure-tight) |
Aluminum Casting Alloys
Aluminum casting alloys are designated by a three-digit number followed by a decimal (e.g., A356.0, A380.1):
Common Aluminum Casting Alloys and Properties
| Alloy | Process | Tensile (MPa) | Yield (MPa) | Elongation (%) | Key Properties | Applications |
|---|---|---|---|---|---|---|
| A356 | Sand, Investment, Gravity, LP | 220–260 | 150–180 | 3–6 | Good castability, weldable, moderate strength | Automotive wheels, structural |
| A357 | Sand, Investment, Gravity, LP | 260–320 | 200–260 | 2–5 | High strength (T6), pressure-tight | Engine, aerospace, structural |
| 319 | Sand, Gravity, LP | 180–230 | 110–150 | 1.5–3 | Good castability, machinable | Engine brackets, pump housings |
| A380 | HPDC | 220–330 | 150–200 | 1–4 | Best HPDC castability, good strength | Engine covers, housings, brackets |
| A413 | HPDC | 180–230 | 90–130 | 2–4 | Excellent castability, thin walls | Complex thin-wall housings |
| B390 | HPDC | 200–270 | 200–270 | <1 | High wear resistance, low expansion | Pistons, compressors, dry cylinder blocks |
Choosing the Right Alloy
- General purpose, good castability: A356 (sand/investment/gravity), A380 (HPDC)
- High strength required: A357 (T6 heat treatment gives up to 310 MPa tensile)
- Pressure-tight applications: A357 or A356 with proper process control
- Thin wall HPDC: A413 or A380
- Wear resistance: B390 (high silicon content)
- Welding required: A356 or 6061 (wrought equivalent)
Sand Casting Aluminum
When Sand Casting Wins
- Large parts (over 10 kg) where die casting tooling is prohibitively expensive
- Low-to-moderate volume (under 500/year)
- Tolerance of ±0.5 mm or looser is acceptable
- Rough surface (Ra 12.5–25 µm) acceptable or will be machined
- Unique or custom alloy required
Design Rules
- Minimum wall thickness: 3–5 mm (small to medium parts)
- Draft angle: 1–2° minimum
- Machining allowance: 1.5–3.0 mm on machined surfaces
- Uniform wall thickness: avoid 3:1+ transitions
Investment Casting Aluminum
When Investment Casting Wins
- High precision required (±0.1–0.3 mm)
- Complex geometry with undercuts (using ceramic cores)
- Good surface finish needed (Ra 3.2–6.3 µm as-cast)
- Thin walls (1.5–3 mm)
- Moderate volume (50–5,000/year)
Design Rules
- Minimum wall thickness: 1.5–2 mm
- Draft angle: 0.5–1.5° (less than sand casting)
- Fillet radii: minimum 1–2 mm internal
- Excellent surface finish achievable (Ra 3.2–6.3 µm)
Die Casting Aluminum
Gravity Die Casting vs HPDC
Gravity die casting fills the die by gravity only (ladle pour). HPDC injects at 1,000–10,000 bar. Key differences:
- Gravity die: Lower tooling cost, lower porosity, pressure-tight natural, slower cycle, good for Al and Cu alloys
- HPDC: Higher tooling cost, higher production rate, excellent surface finish, thin walls possible, inherent porosity (needs VAD for pressure)
When HPDC Wins
- Volume is 10,000+ parts/year
- Excellent surface finish needed (Ra 0.8–3.2 µm)
- Very thin walls (0.8–1.5 mm)
- Tight tolerance (±0.1–0.25 mm)
- Automotive or consumer electronics housings
When Gravity/LP Die Casting Wins
- Pressure-tight parts (hydraulic, automotive engines)
- Non-aluminum alloys (copper, brass)
- Moderate volume (500–10,000/year)
- Lower tooling budget
Heat Treatment for Aluminum Castings
| Condition | Heat Treatment | Effect | Tensile Increase |
|---|---|---|---|
| T5 | Cool from casting + artificial age | Moderate strength improvement | +20–30% |
| T6 | Solution treat + quench + artificial age | Peak strength and hardness | +40–60% |
| T7 | Solution treat + quench + overage | Stable strength, reduced hardness | +30–50% |
Surface Treatment and Finishing
- Anodizing: Creates hard, corrosion-resistant oxide layer; excellent for appearance and wear resistance. Available in clear, black, and colors.
- Powder coating: Thick, durable finish; wide color range; excellent corrosion protection.
- Wet painting: Good appearance, moderate protection; less durable than powder coat.
- Electroplating: Zinc, nickel, chromium plating for appearance and corrosion resistance.
- Mechanical polishing: Buffing and polishing for decorative appearance.
- Shot blasting/peening: Clean up surface, improve fatigue strength, create uniform matte appearance.
Real Buyer Sourcing Scenarios
Scenario 1: Automotive Bracket (1,000 Parts/Year)
Requirement: 1,000 aluminum brackets per year, A356 alloy, 500g each, general structural use.
Analysis: At 1,000/year, sand casting is competitive due to low tooling ($1,500). Investment casting is overkill. HPDC would require $50,000+ tooling that does not amortize. Sand casting with A356 gives good strength, tolerance acceptable at plus/minus 0.5 mm.
Decision: Aluminum sand casting, A356 alloy, wood pattern ($800), production in 3 weeks, approximately $6 per part.
Scenario 2: Electronic Housing (20,000 Parts/Year)
Requirement: 20,000 aluminum electronic housings per year, A380 alloy, thin walls (1.2 mm), good appearance surface for powder coating.
Analysis: 20,000/year justifies HPDC. Thin walls (1.2 mm) are achievable only with HPDC. Excellent surface finish means minimal post-processing. A380 is the standard HPDC alloy for this application.
Decision: HPDC, A380 alloy, single-cavity die ($60,000), production in 12 weeks.
Scenario 3: Hydraulic Manifold (200 Parts/Year)
Requirement: 200 aluminum hydraulic manifolds per year, must hold 200 bar, complex internal passages.
Analysis: 200/year is below HPDC threshold. Complex internal passages rule out simple sand casting. Investment casting with ceramic cores can produce the passages. A357 provides pressure-tightness after heat treatment.
Decision: Investment casting, A357 alloy, T6 heat treatment, 200 parts in 8 weeks.
Buyer Decision Checklist
- What is the annual volume? (Determines best process)
- What tolerance is required on each feature?
- What surface finish is required?
- Is pressure-tightness required?
- What is the maximum part size and weight?
- Is heat treatment required for strength?
- What surface treatment is needed (anodize, paint, powder coat)?
- Have you compared total cost across at least two processes?
- Has DFM review been completed with the foundry?
Before finalizing the sourcing decision, many OEM buyers also compare Sand Casting, Gravity vs HPDC, Casting Tolerances, and Surface Finish to clarify process fit, cost trade-offs, tolerance expectations, and supplier risk.
If you need application-specific guidance, drawing review, or a quotation, you can Contact YCUMETAL.
FAQ
What is the strongest aluminum casting alloy?
A357 with T6 heat treatment achieves the highest strength: up to 320 MPa tensile and 260 MPa yield. For comparison, structural steel is ~250 MPa yield. A357’s strength-to-weight ratio is exceptional.
Can aluminum castings be welded?
Yes — aluminum castings are weldable. A356 and A357 are the easiest to weld (low hydrogen risk). Use ER4043 or ER5356 filler wire for general welding, ER4047 for silicon alloy castings. Pre-weld heat treatment may be needed depending on the alloy and application.
How do I choose between sand casting and die casting?
Volume is the primary driver. Under 500/year: sand casting wins on total cost. 500–10,000/year: gravity or low pressure die casting wins. 10,000+/year: HPDC wins. Beyond volume, consider: tolerance required (die casting wins), surface finish (die casting wins), part size (sand casting wins for large parts), and pressure-tightness (gravity/LP wins).