Die Casting in China: Aluminum and Zinc Parts Explained

Die casting injects molten alloy at high pressure into a reusable steel mold — the die. It cools in seconds, the die opens, and a near-net-shape part comes out. Done well, it produces complex metal parts with fine detail at very low per-part cost. Done badly, it produces porous parts that crack, leak, or fail plating.

China is one of the world's main sources of die-cast parts: aluminum for automotive, lighting, and equipment; zinc for hardware, locks, and small parts. It works when three things line up — volume justifying a steel die, suitable geometry, and a supplier controlling the variables that cause defects.

Without an engineering team on the ground, a sourcing agent like CN Ally can identify candidate die casters, compare tooling quotes, and verify process control before you commit to a mold. Vetting before tooling prevents most expensive mistakes.

How does die casting actually work — and what is hot-chamber vs cold-chamber?

Molten metal is forced into a steel die cavity at high pressure, held there while it solidifies, then ejected when the die opens — a cycle of seconds to about a minute. Whether a shop runs hot-chamber or cold-chamber equipment depends on the alloy's melting point, and it decides which parts they can make for you.

In a hot-chamber machine, the injection system sits inside the furnace: a gooseneck nozzle stays submerged in molten metal and a plunger pushes each shot into the die. No ladling step, so cycles run 5 to 15 seconds and output reaches several hundred parts per hour. The constraint is chemistry — machine components bathe in the melt — so this suits only lower-melting-point alloys like zinc, tin, and lead. Molten aluminum attacks the gooseneck and nozzle, so aluminum cannot run this way.

In a cold-chamber machine, the furnace stands apart. Each shot is ladled into a shot sleeve and a plunger drives it into the die. Keeping hot metal away from the machine's internals is what makes aluminum, magnesium, and copper alloys possible — at the cost of slower cycles and much higher injection pressures.

Hot-chamber die casting · Cold-chamber die casting

• Typical alloys: Zinc, tin, lead · Aluminum, magnesium, copper
• Metal temperature: Roughly 400–450°C · Roughly 600–700°C
• Injection pressure: Roughly 7–15 MPa · Roughly 30–150 MPa
• Cycle time: About 5–15 seconds · About 20–60 seconds
• Output rate: Roughly 300–700 parts/hour · Roughly 100–300 parts/hour
• Tooling cost: Lower · Higher
• Part size and complexity: Small to medium, simple to moderate · Larger, more complex

These are representative ranges from a published supplier comparison, not guarantees. The sourcing takeaway: aluminum parts need a cold-chamber shop; small zinc parts at volume belong on hot-chamber lines. A supplier quoting aluminum on hot-chamber equipment is a red flag.

Aluminum vs zinc vs magnesium: which die casting alloy should you choose?

Pick aluminum (usually A380 or ADC12) for lightweight structural parts, zinc (usually Zamak 3) for small, thin, highly detailed parts with an excellent as-cast surface, and magnesium (usually AZ91D) only when every gram matters. Most buyers end up with one of the first two.

Aluminum (A380 / ADC12) · Zinc (Zamak 3) · Magnesium (AZ91D)

• Casting process: Cold chamber · Hot chamber · Cold chamber
• Density: 2.70 g/cm³ · 6.60 g/cm³ · 1.81 g/cm³
• Minimum wall thickness: 1.5–2.0 mm · 0.5–1.0 mm · 1.0–1.5 mm
• Reported die life: Around 100,000 shots · Over 1,000,000 shots · Roughly 300,000–500,000 shots
• Thermal conductivity: Good (A380 ≈ 96 W/(m·K)) · Moderate (Zamak 3 ≈ 105–114 W/(m·K)) · Good
• Strengths: Light, strong, corrosion-resistant, widely available · Thin walls, fine detail, superb as-cast finish · Lightest structural metal, fast machining
• Watch out for: Shorter die life than zinc · Heavy; creep risk above ~120°C · Flammable dust — controlled foundry needed

Die-life figures come from a Chinese die caster's engineering guide — approximate, but the ordering is well established: zinc runs far cooler, so dies last dramatically longer, often an order of magnitude. For small parts at millions of units, that can outweigh zinc's weight penalty. Zinc also plates beautifully — hence its dominance in decorative hardware.

But zinc has a temperature ceiling: published data recommends keeping Zamak 3 and 5 at or below roughly 120°C in continuous service, since the alloy can creep under load above that. Parts near engines or high-power LEDs belong in aluminum.

Magnesium is the lightest structural die casting alloy, but its chips and dust are flammable, demanding special foundry controls. Unless weight dominates, aluminum serves most buyers better — A380 remains the worldwide default for its strength-to-weight ratio and broad availability in China.

What do die casting molds cost in China — and how long do they take?

Expect quotes from a few hundred dollars for a small, simple zinc die to tens of thousands — and beyond — for large, complex aluminum dies; most mid-size aluminum molds land in the low-to-mid thousands. Tooling lead times of 20 to 60 days are commonly quoted, with first trial samples typically 15 to 45 days after drawing approval. These are published supplier ranges as of late 2026; they move with steel prices and shop workload.

Your quote moves with part size, complexity (every slide and undercut adds mold components and machining hours), cavity count, die steel grade (H13 and SKD61 are standard), surface texture, and tolerance demands.

Two contractual points matter more than the headline number. First, who owns the die — ownership disputes are common in China, so put ownership, maintenance, and transfer terms in writing before paying. Second, what the quote includes: mold, trial shots (T1), and at least one dimensional report. Suspiciously cheap quotes often exclude trials and corrections.

On die life, treat supplier claims with skepticism. Listings advertise 60,000 to over 1,000,000 shots; one sourcing agent working with Chinese die casters calls 60,000 to 70,000 cycles the realistic figure for typical aluminum tooling. Plan unit economics on the conservative end, and ask how the shop tracks shot counts and schedules die maintenance.

What tolerances and surface finishes can you realistically get?

The NADCA standard is the industry reference: for aluminum, zinc, and magnesium, standard linear tolerance is ±0.25 mm for the first 25 mm of a dimension, plus ±0.025 mm for each additional 25 mm — so a 100 mm feature carries roughly ±0.33 mm. Precision grade tightens the base to ±0.05 mm per 25 mm, but costs more and shortens the interval before die maintenance. Full tables are published on Engineers Edge.

Design to standard tolerance wherever function allows; reserve precision grades for bores, sealing surfaces, and mating faces. Features formed across the parting line or by moving cores need additional tolerance — your supplier's DFM feedback should flag them. Critical dimensions are routinely cast slightly oversize and finished on a CNC machine, a workflow most established Chinese die casters run in-house.

Zinc takes electroplating exceptionally well — chrome, nickel, zinc over polished or blasted surfaces. Aluminum anodizes (Type II is standard), powder-coats, and paints well, though high-silicon A380 anodizes less evenly than A360 — settle the alloy first if cosmetics matter.

One caution: finishes magnify surface defects rather than hiding them. A part with subsurface porosity can blister under plating when trapped gas expands during heating. Specify finish requirements and porosity acceptance together, not as separate line items.

Porosity: the defect that decides whether your parts survive QC

Porosity — small voids trapped inside the casting — is the most common reason die-cast parts fail strength, pressure, or leak tests, and the defect buyers discover last: a part can look perfect outside while being spongy inside. The two types have different causes and fixes.

Gas porosity · Shrinkage porosity

• Appearance: Round, smooth-walled bubbles · Irregular, jagged voids, often interconnected
• Location: Scattered through the part · Thick sections and hot spots — last areas to solidify
• Root cause: Air trapped during injection; dissolved gas (hydrogen in aluminum) released as metal freezes · Thick sections contract with no liquid metal left to feed them
• Prevention: Melt degassing, controlled injection speed, proper venting and overflows, vacuum-assisted casting · Balanced wall thickness, cooling design, intensification pressure, mold-flow simulation

Detection determines what you can enforce. X-ray or CT inspection finds internal voids without destroying the part — several established Chinese die casters list X-ray as standard equipment. Sectioning and polishing a sample is destructive but definitive. For pressure-tight parts, leak or pressure testing a defined sample percentage is the practical acceptance criterion.

Ask prospective casters: mold-flow simulation before cutting steel? Vacuum-assisted casting for pressure-tight parts? How do they degas aluminum melts, and what porosity level do they verify? A shop answering concretely is process-controlled; one claiming "no porosity problem" without describing controls is one to walk away from (the Engineer has a deeper technical overview).

Where porosity or leak-tightness is contractual, verify it independently. A quality control inspection covering the agreed acceptance test catches problems before parts ship, while fixes are still the supplier's responsibility.

When does die casting beat CNC machining or injection molding?

Die casting wins for medium-to-high volumes of complex metal parts, where one steel die replaces hours of machining on every part. Below that volume, CNC usually wins because it needs no tooling. If the part can be plastic, injection molding is a different process with its own economics — compare on material requirements, not just cost.

Die casting · CNC machining · Plastic injection molding

• Tooling investment: Steel die: hundreds to tens of thousands of dollars · None (fixtures only) · Steel mold: comparable or higher
• Per-part cost at scale: Very low · High — every part consumes machine time · Very low
• Design freedom: Complex shapes, thin walls, integrated features · Almost anything, but each feature costs cycle time · Complex shapes, but plastic only
• Material: Aluminum, zinc, magnesium, copper alloys · Almost any metal or plastic · Thermoplastics
• Best for: Thousands to millions of metal parts per year · Prototypes, low volumes, ultra-tight tolerances · High volumes of plastic parts

Decision rule: multiply expected annual volume by per-part machining cost, and compare against the tooling quote. Payback within roughly one to two years favors die casting; five years favors CNC, which stays flexible and keeps cash out of a die you might need to modify. A heuristic — alloy prices and finish costs shift the math.

There is also a middle path: die cast plus CNC. Cast the complex geometry, machine only critical bores, threads, and sealing faces. Most established Chinese die casters run CNC in-house for this, delivering precision where it matters at near-casting economics.

How do you vet a die caster in China before paying for a mold?

Ask for evidence, not promises. A capable die caster shows certifications, equipment, inspection records, and marked-up drawings. A weak one shows a nice office and a low quote. Work through this checklist before any tooling payment:

1. Certifications matched to your industry. ISO 9001 baseline; IATF 16949 for automotive. Ask for the certificate number and verify it.
2. In-house tooling or outsourced? An own mold workshop means faster iteration and direct die quality control. If outsourced, identify the mold maker.
3. Inspection equipment. CMM or 3D measurement, X-ray for internal integrity, spectrometer for alloy verification. Ask what gets inspected and how often.
4. DFM feedback quality. A serious shop marks up your drawing — wall thickness, draft angles, parting line, tolerance feasibility. A shop quoting without a single question didn't read it.
5. Sampling discipline. T1 samples, dimensional report, your approval, corrections, T2 if needed. Agree upfront how many rounds are included and what "approved" means measurably.
6. Relevant references. Parts in the same alloy and similar complexity — not just any metal part.
7. Tooling contract terms. Die ownership, maintenance responsibility, shot-count tracking, and what happens to the mold if you move production. In writing, before payment.
8. An independent factory audit. Verify the facility matches the brochure before committing to tooling. A factory audit is inexpensive insurance against the costliest mistake — paying for a mold at a shop that cannot run it.

Match machine tonnage to your part: roughly 160–250 tons clamping force for 100 × 100 mm parts, 400–650 tons for 300 × 300 mm, 800–2000 tons for 500 × 500 mm. A shop whose largest machine is 180 tons cannot run your 400 mm housing.

Frequently asked questions

How much does a die casting mold cost in China?

Published listings quote a few hundred dollars for a small zinc die up to tens of thousands for large aluminum dies, with some automotive tools near $100,000. Most mid-size aluminum molds land in the low-to-mid thousands. Get an itemized quote — mold, trials, dimensional reports — and confirm tooling ownership in writing.

How long does it take to get the first die-cast samples from China?

Tooling lead times of 20 to 60 days are commonly quoted; T1 samples often follow 15 to 45 days after drawing approval, complex parts at the long end. Add time for your dimensional review and T2 corrections.

What is the thinnest wall you can die cast in aluminum?

Around 1.5 to 2.0 mm for aluminum, per published die caster data; zinc goes thinner at 0.5 to 1.0 mm. Below these ranges the metal freezes before filling the cavity, causing misruns and cold shuts.

Can die-cast aluminum parts be anodized?

Yes — Type II anodizing is standard for die-cast aluminum. But high-silicon A380 anodizes less evenly than lower-silicon alloys, so cosmetic parts may need A360 or extra prep. Settle the alloy before parts are cast.

Can you weld die-cast aluminum parts?

Technically yes, but most designers avoid it. Trapped gas and porosity expand under welding heat, causing pinholes and weak joints. Standard practice is mechanical fastening, adhesive bonding, or self-clinching hardware instead.

Does die casting make sense for 10,000 parts a year?

Often yes, depending on complexity. Per-part savings over CNC usually repay a mid-size die within one to two years at that volume — but run your own numbers. Simple parts may stay cheaper on CNC; complex thin-wall parts strongly favor die casting.

Your next move: a three-step die casting checklist

First, confirm alloy and volume math: aluminum for structural parts, zinc for small detailed ones, tooling payback inside roughly two years. Second, get DFM feedback and itemized quotes from two or three shops — compare what they asked you, because the questions reveal the competence. Third, lock sampling criteria, porosity or leak-test requirements, and tooling ownership in writing before paying.

Get those three right and die casting in China is among the most cost-effective ways to make metal parts at scale. For a second pair of eyes on quotes or vetting: hi@cnally.com.