For decorative hardware that will be plated, handled and looked at, Zamak 3 is the default. Move to Zamak 5 when the part carries load, takes a thread, or wears against another metal. Move to ADC12 only when the part is large, must be light, or runs hot — and accept thicker walls and a paint finish instead of plating.
That order settles most arguments before they start. The rest of this guide is the reasoning and the numbers behind it.
The three alloys, side by side
| Property | Zamak 3 | Zamak 5 | ADC12 |
|---|---|---|---|
| Common designations | ZnAl4, ZDC2, AG40A, ZP3 | ZnAl4Cu1, ZDC1, AG41A, ZP5 | A383, YL113, EN AC-46100 |
| Nominal composition | Al 3.9–4.3 %, Cu ≤ 0.1 %, Mg 0.02–0.06 % | Al 3.9–4.3 %, Cu 0.75–1.25 %, Mg 0.03–0.08 % | Si 9.5–12 %, Cu 1.5–3.5 % |
| Density | 6.6 g/cm³ | 6.7 g/cm³ | ≈ 2.74 g/cm³ |
| Tensile strength (typical) | 280–320 MPa | 320–380 MPa | 235–310 MPa |
| Elongation (typical) | 7–20 % | 2–7 % | 1.5–3.5 % |
| Hardness (typical) | 80–90 HB | 90–100 HB | Roughly 70–90 HB |
| Melting range | ≈ 380–390 °C | ≈ 380–390 °C | ≈ 580–600 °C |
| Machine type | Hot chamber | Hot chamber | Cold chamber |
| Practical minimum wall | 0.5 mm | 0.5 mm | 0.8–1.2 mm (sources differ) |
| Typical linear tolerance | ± 0.05 mm | ± 0.05 mm | ± 0.1 mm |
| Typical die life | 1 million+ shots | 1 million+ shots | 100,000–150,000 shots |
| Decorative plating | Excellent | Very good | Requires zincate first |
| Decorative anodising | Not applicable | Not applicable | Not recommended |
Strength and elongation figures are typical values from public alloy data, not minimum guaranteed values. If a drawing needs a guaranteed number, quote the standard (ASTM B86 for zinc, ASTM B85 / EN 1706 for aluminium) and let the certificate carry it.
Why Zamak 3 is the default for anything you will look at
Three properties matter for decorative parts, and Zamak 3 wins all three.
It fills thin sections and fine detail. Zamak 3 is the most fluid of the common zinc alloys, which is why it is the alloy used for thin walls, sharp relief, small lettering and long, narrow cores. A logo plate, a zipper pull or a cosmetic cap with 0.3 mm relief is a Zamak 3 job.
It plates cleanly. Zinc alloy has no silicon phase to interrupt the surface, and Zamak 3's fine grain polishes to a good base for copper–nickel–chrome. This matters more than most buyers expect: the same plating line produces visibly fewer pits and rejects on Zamak 3 than on a coarser casting, because plating does not hide casting defects — it magnifies them.
It is cheap to run. At a melting range around 385 °C, zinc runs on hot-chamber machines with long die life (commonly quoted at a million shots or more, against 100,000–150,000 for aluminium), so tooling amortises over a much larger quantity. That is the real reason small zinc hardware is affordable at a few thousand pieces.
When Zamak 5 earns its extra copper
Adding roughly 1 % copper raises tensile strength by about 20 %, improves hardness, wear resistance and creep resistance, and is the standard choice for parts that see load or motion: buckles, ladder locks, latch bodies, hinge halves, caster brackets, threaded bosses.
The trade is ductility. Elongation drops from 7–20 % to 2–7 %. That has two practical consequences:
- Do not specify Zamak 5 for parts designed to be bent after casting. If the function is "bends and springs back", it is a stamped steel part, not a casting.
- Impact and drop requirements must be tested, not assumed. A Zamak 5 buckle is stronger in tension and more brittle in impact than Zamak 3. If the buyer's spec includes a drop test, cast both and test both before committing the tool.
For a plated decorative part with no load path, Zamak 5 buys nothing you can see, and costs slightly more in metal and machining. Use it for function, not for prestige.
ADC12 is a different decision, not a drop-in substitute
Aluminium is 2.4 times lighter per unit volume, which is why buyers ask for it. The saving is smaller than the density ratio suggests, for three reasons:
- Walls must be thicker. Where zinc casts at 0.5 mm, aluminium needs roughly 0.8–1.2 mm. A part redesigned at 1.5× the wall recovers much of the weight advantage.
- Tolerance is looser. Typical as-cast tolerance is around ± 0.1 mm against ± 0.05 mm for zinc, so more features end up machined — and machining cost eats the material saving.
- Die life is shorter. 100,000–150,000 shots is normal, so tooling amortisation per part is higher unless the volume is large.
ADC12 (A383) is the right answer when the part is large, weight-sensitive, or thermal: enclosures, brackets, heat-sink bodies, outdoor painted housings. It is the wrong answer for a 3-gram decorative plate, and it is specifically the wrong answer if the buyer expects a bright decorative anodised finish — the 9.5–12 % silicon in ADC12 does not anodise into a uniform colour, and comes out grey and blotchy against an extruded-aluminium sample. If the finish is paint or powder coat, ADC12 is fine; if the finish is mirror chrome, it needs a zincate pre-treatment before plating.
What about Zamak 2 and ZA-8?
Two alloys come up often enough to mention.
- Zamak 2 (2.5–3 % copper) is the hardest and least ductile of the family. It is used for wear parts and bushings, not for decorative parts, and it is a poor candidate for decorative plating.
- ZA-8 (8–8.8 % aluminium) is chosen for better creep strength and performance at slightly elevated temperature. It is normally run cold-chamber, so it carries aluminium-like tooling economics rather than zinc's.
Neither belongs in a first quote for apparel hardware. They belong in the conversation when the service temperature or the wear duty is unusual.
Two failure modes that outrank the alloy choice
Intergranular corrosion ("zinc pest"). Zinc alloy contaminated with lead, tin or cadmium corrodes along grain boundaries, swells, cracks and eventually crumbles — sometimes a year after delivery, in a warehouse. The cause is almost always contaminated melt, typically recycled scrap that included solder or bearing metal. ASTM B86 caps these impurities at thousandths of a percent (lead 0.004 %, cadmium 0.003 %, tin 0.002 % for Zamak 3 — confirm against the current standard text before writing it into a contract). The control is a certified ingot and a certificate of analysis per heat, not a visual inspection. If a supplier cannot produce an ingot certificate, the alloy question is academic.
Plating blister from casting skin defects. Cold shuts, cold laps, porosity and polishing-compound residue on the casting surface turn into blisters after plating, and they usually appear two to four weeks after shipment, not at final inspection. This is why "can it be plated" should be answered by looking at the casting's cosmetic grade first.
Both failure modes are casting-quality issues, not alloy-selection issues — which is the useful point for a buyer: arguing about Zamak 3 versus Zamak 5 is pointless if the melt and the die are not under control.
Choosing by part
| Part | Alloy | Why |
|---|---|---|
| Decorative logo plate, badge, nameplate | Zamak 3 | Fine relief, best plating base |
| Cosmetic cap, perfume cap | Zamak 3 | Thin wall, high polish, plated or painted |
| Zipper pull, cord end, small trim | Zamak 3 | Detail and finish decide; load is low |
| Belt buckle, ladder lock, side-release buckle | Zamak 5 | Load path, wear, thread or spring contact |
| Hinge half, caster bracket, latch body | Zamak 5 | Strength and creep |
| Large enclosure, bracket, heat sink | ADC12 | Size, weight, thermal |
| Painted outdoor housing | ADC12 | Paint hides the silicon, weight matters |
| Mirror-chrome part | Zamak 3 | Aluminium would need zincate and still pit more |
Write the alloy, not the trade name
A drawing that says "zinc alloy" and "chrome plated" leaves the supplier free to choose both, and the buyer has no remedy when the parts blister. Specify three things separately:
- Alloy and standard — e.g. "Zamak 5, ASTM B86 / ZnAl4Cu1, EN 1774", plus ingot certificate per lot.
- Casting tolerance and cosmetic grade — which surfaces are cosmetic, which may carry ejector marks.
- Plating class and test — a separate clause, because plating is a different supplier and a different acceptance test. The companion guide on plating specifications covers how to write that clause.
Next step
If you have a drawing, a 3D model, or even a photo of a part you want to copy, send it to 13928445679@163.com with your target annual quantity and the finish you have in mind. We will come back with a DFM review on wall thickness, draft and alloy choice, plus a quote that separates tooling, part price and finish — so you can see which line item the alloy decision actually moves.