Sourcing Die Cast Parts from China: Alloys, Tooling, and Porosity Control

Die casting delivers complex, thin-walled metal parts at low per-piece cost, but the category has failure modes that do not exist in machining or fabrication: porosity hidden below the surface, tooling that wears out mid-program, and gate designs that quietly determine whether your parts leak. This guide covers alloy selection between ADC12, A380, AlSi10Mg, and zinc alloys, what to agree on about tooling before you pay for it, and how to specify porosity control and inspection so that pressure-tight and machined parts arrive usable.

Why Die Casting Is Its Own Sourcing Category

High-pressure die casting (HPDC) injects molten metal into a hardened steel die at high velocity. The process fills thin walls and fine detail that sand or gravity casting cannot, and cycle times are measured in seconds. The trade-off is that the metal front traps air and gases as it fills, so every die casting contains some level of internal porosity. Whether that porosity matters depends entirely on what happens to the part afterward: a decorative housing tolerates it, a machined sealing face or a pneumatic manifold may not. Sourcing die castings well means specifying the alloy, the tooling, and the acceptable porosity level in writing before the first quote is compared, because these three items explain most of the price spread you will see between suppliers listed in a manufacturer directory.

Choosing the Alloy

Aluminum: ADC12, A380, and AlSi10Mg

The two workhorse aluminum die casting alloys are near-equivalents from different standards systems. ADC12 is defined in the Japanese standard JIS H5302 and is the default alloy in most Chinese die casting shops; the Chinese designation YL113 in GB/T 15115 covers essentially the same composition. A380 is the American equivalent under ASTM B85, close to the Chinese YL112. Both are aluminum-silicon-copper alloys with excellent castability, good mechanical properties, and easy machinability. If your drawing calls out A380 and the supplier proposes ADC12, that is usually a reasonable substitution, but it should be documented as a formal deviation, not a silent swap, because the copper and silicon ranges differ slightly and some end customers audit material certificates line by line.

AlSi10Mg, standardized in Europe as EN AC-43400 in its iron-bearing die casting form, is a different choice: lower copper content gives it better corrosion resistance and, critically, it can be heat treated and welded in structural variants. It is the common answer when the part needs anodizing-adjacent finishes, higher elongation, or when the same geometry also exists as an additive-manufactured prototype, since AlSi10Mg is the standard alloy for laser powder bed fusion. Expect fewer Chinese foundries to stock it and quote it, and expect them to ask why you need it.

Zinc alloys

Zinc die casting alloys, commonly known by the Zamak family names (Zamak 3 and Zamak 5, standardized in ISO 301 and EN 12844), run at much lower temperatures than aluminum. That means longer die life, thinner walls, sharper detail, and excellent surfaces for plating, which is why zinc dominates locks, connectors, gears in small appliances, and decorative hardware. Zinc parts are heavier and lose strength at elevated temperature, so the choice between aluminum and zinc is usually settled by weight targets and operating temperature rather than by cost alone.

Tooling: Life, Ownership, and Gate Design

Die life and what your quote actually includes

An aluminum die casting die is a machined block of hot-work tool steel, typically H13 or its Chinese equivalent 4Cr5MoSiV1, heat treated and often nitrided. Aluminum erodes tool steel; zinc barely does. That is why die life is quoted in shots and why an aluminum die may be quoted with a guaranteed shot life while a zinc die effectively outlives the program. When you pay for tooling, get four things in writing: the guaranteed shot count, the tool steel grade and heat treatment, who owns the die and the design data, and what happens when inserts wear out. Cavity inserts, cores, and slides are the wear items; a well-structured agreement obligates the foundry to replace inserts at its own cost within the guaranteed life. Tool ownership matters if you ever need to move the program, a scenario worth planning for during supplier qualification rather than after a dispute.

Gate and overflow design decides quality before the first shot

Where the metal enters the cavity (the gate), how fast it travels, and where the displaced air escapes (vents and overflow wells) determine porosity distribution more than any process tweak later. Ask the foundry to share the gating layout and, for critical parts, a mold-flow simulation before steel is cut. Two practical review points: the gate should not feed directly into a surface that will be machined or must seal, because the last-filled and turbulent regions concentrate porosity; and overflows should sit at the end of fill so trapped gas has somewhere to go. A foundry that cannot show you a gating plan for a structural or leak-tight part is telling you how it plans to run your program.

Porosity: The Defect That Defines the Process

Machined surfaces reveal what casting hides

An as-cast surface is a fine-grained skin that looks dense. Machining cuts through that skin into the interior, where gas porosity and shrinkage voids live. This is why parts can pass visual inspection at the foundry and arrive at your CNC subcontractor with pinholes across every milled face. The mitigation is contractual and technical: define porosity acceptance on the drawing by zone, referencing ASTM E505 radiographic grades or a customer-defined maximum pore size and density in machined areas, and tell the foundry which surfaces will be machined so gating can keep those zones clean. If the foundry also machines, put the porosity criteria in the machining acceptance spec, not just the casting spec.

Pressure-tight parts need a leak spec, not a porosity hope

For manifolds, valve bodies, and housings that hold gas or liquid, specify a leak test with a pressure, a medium, a hold time, and a maximum leak rate, and require it as an in-process test rather than a final audit. Interconnected porosity that crosses a wall creates leak paths that no visual or dimensional inspection catches. Vacuum-assisted die casting reduces trapped gas at the source and is worth asking about for leak-critical geometry, though not every shop runs it.

Inspection: X-ray, CT, and Sampling Plans

Radiographic sampling is the standard tool for internal quality. Two-dimensional X-ray is fast and inexpensive per part; industrial CT gives a full three-dimensional map of porosity and is used for first article qualification, gating changes, and dispute resolution rather than routine checks. A workable scheme for most programs: CT or full X-ray coverage on first articles and after any tooling repair, then periodic X-ray sampling per lot using an AQL-based plan consistent with ISO 2859-1, tightened for safety-critical or leak-critical items. How AQL sampling plans work in practice is covered in our guide to quality inspection and AQL. Insist that radiographs are retained and traceable to lot numbers, because porosity problems tend to surface weeks later during machining or assembly.

Post-Processing: Deburring, Impregnation, Coating

Die castings leave the tool with flash at parting lines and gate remnants, so trimming and deburring are part of every quote; what varies is the method (trim die, tumbling, hand finishing) and the resulting edge condition, which should be specified if edges are cosmetic or handled by users. Vacuum impregnation, in which parts are infiltrated with a sealant resin under vacuum per specifications such as MIL-STD-276, is the accepted rescue for marginal leakers and is sometimes planned into the process for pressure-tight parts; agree in advance whether impregnation is allowed, on what percentage of parts, and whether impregnated parts must be marked. For coatings, aluminum die castings take powder coat and wet paint well after chromate or chrome-free conversion coating, but the high silicon and copper content of ADC12 and A380 means decorative anodizing yields dark, blotchy results; if anodized cosmetics matter, revisit the alloy choice early. These finishing operations are often outsourced by foundries, which is worth probing when you evaluate suppliers in the basic metal manufacturing sector.

Key Takeaways

• ADC12 and A380 are near-equivalent default alloys; treat substitutions as documented deviations, and choose AlSi10Mg or zinc deliberately for corrosion, finish, or detail requirements.
• Put die shot-life guarantees, tool steel grade, insert replacement responsibility, and tool ownership in the tooling contract before payment.
• Review the gating and overflow layout for any part that will be machined or must seal, since gate position determines where porosity concentrates.
• Define porosity acceptance by zone on the drawing and specify a leak test with pressure, hold time, and leak rate for pressure-tight parts.
• Use CT or full X-ray at first article and AQL-based X-ray sampling per lot, and agree upfront whether vacuum impregnation is permitted.

This guide is editorial reference material, not legal or transactional advice. Verify supplier claims and regulatory requirements independently. See our data sources and editorial policy.