What is Zamak, and should your die-cast part use Zamak 3 or Zamak 5?

What is Zamak and what are its grades?

Zamak is the trade name for the conventional zinc die-casting alloys standardized in ASTM B86 and EN 12844. Zamak 3 and Zamak 5 are the common grades, and copper is the only intended difference between them: per EN 12844, Zamak 5 carries 0.7–1.2% copper, while Zamak 3 holds copper to a trace level and shares the same aluminum, magnesium and impurity limits.

The North American Die Casting Association describes the conventional zinc alloys as having a nominal aluminum content of 4% and notes that copper in small amounts raises tensile strength and hardness but lowers ductility, particularly after aging (NADCA, zinc alloys). Magnesium is there mainly to counter the effect of trace lead, cadmium and tin, which can otherwise cause intergranular corrosion in this alloy system. That is also why the impurity ceilings are so low and why the base zinc has to be high purity.

Is Zamak 5 stronger than Zamak 3?

Yes, but only modestly: Zamak 5 is a little stronger and noticeably harder, and it gives up elongation in return. If the part was designed with a normal safety factor, Zamak 3 is usually strong enough.

The International Zinc Association publishes nominal values measured on thin flat specimens eight weeks after casting. On that basis Zamak 3 shows an ultimate tensile strength of 315 MPa against 331 MPa for Zamak 5, and a Brinell hardness of 97 against 114, while elongation at rupture is 7.73% for Zamak 3 and 3.43% for Zamak 5 (IZA, mechanical properties). The same association states that a Zamak 3 casting is highly likely to be satisfactory where a normal safety factor has been applied, and treats the two alloys as interchangeable for most applications (IZA, selecting the best zinc alloy).

Treat these as design-reference numbers, not acceptance values. The association itself warns that zinc die-casting properties depend on section thickness and cooling rate, with thin walls proportionally stronger than thick ones, and that test results from different studies are not directly comparable. If a part is strength critical, write the property requirement and the test on the drawing, or plan a test of the actual casting, rather than relying on a handbook figure. Hardness also tracks wear: the association ranks Zamak 5 ahead of Zamak 3 for wear resistance, which matters for sliding latches, gear teeth and hinge knuckles.

How does aging change the dimensions of each alloy?

Both alloys shrink slightly and lose a little strength as they age after casting, and Zamak 3 is the more dimensionally stable of the two. The difference only matters on features with very tight tolerances, and it can be largely removed with a stabilizing heat treatment.

Die casting freezes zinc alloys into a structure that is not stable at room temperature, so the metal slowly rearranges itself. NADCA gives the result as a small contraction, with total shrinkage of 0.0007 in/in and most of it occurring within five weeks at room temperature, and property changes that continue over roughly a decade (NADCA, zinc alloys). Per NADCA, an accelerated aging schedule such as 3 hours at 100 °C (212 °F) brings most of the change forward.

The zinc association’s stabilized-casting data put the contraction after two years at 0.03% for Zamak 3 and 0.037% for Zamak 5 (IZA, physical properties), and it notes that quenching a casting right after ejection delays the shrinkage rather than preventing it. For the drawing this has three consequences. Say when dimensions are to be measured relative to casting. If a bore, a pin fit or a sealing face is machined to a close tolerance, consider requiring a stabilizing treatment before machining. And do not use a first-article report taken the day after casting as proof of long-term fit. The tolerance guide explains how to set the general tolerance class for cast and machined features.

How should you call out the alloy on a drawing and RFQ?

Name one governing standard and the designation within it, for example “Zinc alloy 3 (UNS Z33525) per ASTM B86” or “ZP3 (ZP0400) per EN 12844”. Avoid “Zamak” on its own and avoid “or equivalent” unless you have decided which equivalents you accept.

When a quote comes back in a different system, map it before you accept it. A supplier in Japan or elsewhere in Asia may quote ZDC2 for Zamak 3 and ZDC1 for Zamak 5, following JIS H 5301, and the numbering runs in the opposite direction to the Zamak numbers, which is an easy way to receive the wrong alloy. Ask for a chemistry certificate for the casting lot, not only for the ingot, and compare it with the standard on your drawing.

It also helps to know how die casters work. NADCA notes that many zinc die casters run only Zamak 3, so they do not have to segregate scrap, and that some run only Zamak 5. If your part genuinely works in either alloy, say so on the RFQ: you widen the pool of shops that can quote it and avoid a changeover charge. If only one alloy is acceptable, say that just as clearly. The RFQ preparation guide covers the rest of the package, and the aluminum die-casting alloy guide covers the same naming problem for ADC12 and A380.

For programs moving tooling from one country to another, for example from China to Vietnam, check the alloy name as carefully as the tool itself. The previous supplier’s internal grade name may not appear in any standard, and the new supplier should confirm in writing which standard designation it will cast to.