Aluminum Casting - Processes, Alloys & Applications
Aluminum casting explained: die casting, sand casting, gravity and low pressure processes compared, with alloy selection (A380, A356) and application guidance for buyers.
Mike Yao
Technical Director, Die Casting Engineering
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Aluminum casting turns the world's most-used non-ferrous metal into net-shape parts through five distinct processes - and choosing the wrong one costs you either money or performance. This guide maps the whole landscape: which process fits which part, which alloy goes with which process, and where the economic crossovers sit.
The Five Aluminum Casting Processes
| Process | How it works | Volume sweet spot | Typical parts |
|---|---|---|---|
| High-pressure die casting (HPDC) | Molten aluminum injected at 30-60 m/s into steel dies | 10,000+/year | Housings, brackets, enclosures |
| Gravity die casting (permanent mold) | Metal poured into reusable steel molds | 1,000-50,000/year | Wheels, structural parts |
| Low-pressure die casting (LPDC) | Metal pushed gently up into the die | 1,000-50,000/year | Wheels, premium structural |
| Sand casting | Single-use sand molds | 1-1,000 | Large parts, prototypes |
| Investment casting | Ceramic shell around wax pattern | 100-50,000 | Complex small parts, aerospace |
KastMfg's core is aluminum die casting (HPDC) with gravity and low-pressure for structural programs.
How to Choose: The Four Questions
1. What volume?
Volume is the first filter. HPDC dies cost $8,000-80,000 but deliver 30-second cycles; sand casting needs almost no tooling but costs 10-50x more per part. The HPDC crossover typically sits at 5,000-10,000 parts per year.
2. What mechanical properties?
This is where buyers get burned. HPDC traps gas, so standard die castings cannot be fully T6 heat treated or welded. If your part needs A356-T6 ductility (elongation 3-8%) or weldability, you need gravity or LPDC with A356 - not die casting, no matter what the per-part quote says. Vacuum die casting narrows the gap for structural HPDC.
3. What size?
- Under 30 kg: HPDC or gravity
- 30 kg to hundreds of kg: sand casting
- Thin walls under 2 mm: HPDC owns this territory
4. What surface and tolerance?
HPDC delivers ±0.05-0.10 mm and Ra 1.6-3.2 µm as-cast. Sand casting runs ±0.5-1 mm and rough surfaces needing machining. Gravity/LPDC sit in between.
Aluminum Casting Alloys by Process
| Process | Workhorse alloys | Character |
|---|---|---|
| HPDC | A380, ADC12, A383 | High fluidity, iron-bearing, as-cast use |
| Gravity/LPDC | A356 (T6) | Ductile, weldable, heat-treatable |
| Sand | A356, 319, 535 | Large parts, flexibility |
| Investment | A356, 357 | Precision + complexity |
Full breakdown in our aluminum casting alloys guide and the die casting materials hub.
What Cast Aluminum Parts Surround You
- Automotive/EV: motor housings, battery trays, transmission cases, wheels (automotive die casting)
- Electronics: heat sinks, enclosures, 5G housings
- Industrial: gearbox cases, pump bodies, compressor housings
- Consumer: furniture bases, power tool bodies, cookware
- Robotics: arm links and EOAT frames (robotics castings)
Frequently Asked Questions
Is cast aluminum strong?
Cast aluminum alloys range from 130 MPa (as-cast A356-F) to 320+ MPa (A380 HPDC, A356-T6). For reference, mild steel starts around 400 MPa - at one-third the weight. Proper alloy and process selection routinely puts cast aluminum into structural, safety-relevant applications.
Cast aluminum vs billet (machined) aluminum?
Billet (6061/7075) is stronger and fully dense - but machining from solid wastes 60-90% of the material on complex shapes. Casting wins on cost and geometry freedom at volume; billet wins for prototypes and extreme strength. See die casting vs machined aluminum.
Does cast aluminum rust?
No - aluminum forms a protective oxide layer. Cast aluminum handles outdoor service well, with chromate, powder coat, or anodizing (on low-silicon alloys) for enhanced protection or cosmetics.
What is the cheapest aluminum casting process?
Per part at volume: HPDC by a wide margin. At under 100 pieces: sand casting or machining. The crossover math depends on part complexity - send the drawing for an honest process recommendation.
Related Guides
- aluminum die casting - KastMfg HPDC capability
- types of die casting - process variants compared
- die casting vs sand casting - the most common crossover
- die casting vs investment casting - precision comparison
Casting project inquiry: yaoqingpu1983@gmail.com | +86 138 1403 4409 | No.6, Rungu Road, Nanjing, China
About The Author
Mike Yao on aluminum casting
Technical Director, Die Casting Engineering
Technical Director at KastMfg with 20+ years in high-pressure die casting, leading engineering and program management across aluminum, zinc, and magnesium programs for automotive, EV, electronics, and medical OEMs worldwide.
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