What are the most common zinc alloys used in die casting?

The short answer

The seven grades at a glance

Zinc die casting looks like a smaller field than aluminium because it is, and that is an advantage: the grades are well characterised and the differences between them are predictable. Two families matter. The Zamak family is based on about 4 percent aluminium and runs in hot-chamber machines. The ZA family raises aluminium to 8, 12 or 27 percent, which raises strength and hardness and, at the top end, forces a change of process.

The Zamak family: 3, 5, 2 and 7

All four contain roughly 3.9 to 4.3 percent aluminium, which is the near-eutectic composition where the alloy is most castable. What separates them is copper and, for Zamak 7, nickel.

Zamak 3 is the default and the most widely used zinc die casting alloy in the world. It has the best combination of castability, dimensional stability and cost, machines and plates well, and holds about 10 percent elongation, which is enough ductility for most hardware. If a drawing does not name a grade, the quote is probably Zamak 3.

Zamak 5 adds roughly 0.7 to 1.1 percent copper, which lifts tensile strength from about 283 to 331 MPa and improves hardness, creep resistance and wear behaviour. The price is a little of the ductility and a slightly narrower process window, which is why it is specified for gears, levers and parts that carry load rather than for general housings.

Zamak 2 raises copper to roughly 2.7 to 3.3 percent and is the strongest and hardest of the Zamak family at about 359 MPa. Its dimensional stability is slightly lower than Zamak 3, so it is reserved for bearings, wear surfaces and small high-load parts where strength matters more than long-term stability.

Zamak 7 is the ductility grade. It keeps copper at the impurity level but adds a small nickel content and tightens the magnesium range, which produces about 13 percent elongation, the best in the family. That combination makes it the choice for thin, intricate, impact-resistant parts and for components that must take a high-quality plated finish.

The ZA family: 8, 12 and 27

The ZA alloys trade castability for strength by raising aluminium. ZA-8 at about 8 percent is the most useful of the three in die casting: it runs hot chamber like the Zamak grades, reaches roughly 372 MPa and offers excellent bearing characteristics, so it is often used for bushings and small machine elements that would otherwise need a pressed insert. ZA-12 at about 12 percent aluminium reaches roughly 404 MPa and is used for structural and heavy-duty parts, though it needs cold-chamber processing. ZA-27, at roughly 27 percent aluminium, is the strongest zinc casting alloy at about 426 MPa with the lowest density of the family, but its aluminium content makes it unsuitable for pressure die casting in practice and it is normally gravity or sand cast.

Purity limits matter more than the headline numbers

The composition table hides the specification that actually governs whether zinc parts survive. Every die casting grade requires high-purity zinc and caps three elements tightly: lead at 0.005 percent maximum, tin at 0.003 and cadmium at 0.004. Those limits exist for a specific failure mode. Above them, the alloy becomes susceptible to intergranular corrosion, and a part that passes inspection today can swell, crack or lose strength months into service, particularly in warm humid conditions.

The practical consequence is that grade substitution between suppliers is not as safe as it looks. A Zamak 3 ingot made from high-purity zinc to the published limits is not interchangeable with a generic zinc alloy of similar appearance. Ask for the ingot specification and the certificate with each heat, especially where parts are safety-related, exposed to moisture or expected to last decades.

How to pick a grade in four questions

1. What is the load? Static loads and general service point to Zamak 3. Wear, pivoting or gear contact points to Zamak 5 or Zamak 2. Impact or flexing points to Zamak 7, because elongation is what absorbs energy.
2. How thin is the wall? Below about 0.8 mm the answer is almost always Zamak 7 for ductility or Zamak 3 for general work; the higher-aluminium ZA grades do not fill as easily.
3. Which chamber is available? Zamak grades and ZA-8 run hot chamber with 5 to 20 second cycles. ZA-12 and ZA-27 need cold chamber, which is slower and costs more per part.
4. What finish is required? Bright chrome and nickel plating favour Zamak 3 or Zamak 7. ZA-27 will plate but its high aluminium content makes bright finishing harder, and it is rarely chosen for decorative work.

Where a grade change is not free

• Strength and ductility trade against each other. Moving up the table from Zamak 3 to ZA-27 roughly doubles tensile strength but cuts elongation from 10 percent to about 3. A part redesigned for the stronger grade without checking impact loading can fail in a different way.
• Hot-chamber capability is lost above ZA-8. ZA-12 and ZA-27 need cold-chamber machines, which removes the cycle-time and energy advantage that justified zinc in the first place.
• Dimensional stability varies. Zamak 3 is the most dimensionally stable; Zamak 2 and the ZA grades grow slightly as the alloy ages, which matters on long close-tolerance assemblies.
• Service temperature is capped near 100 C for the whole family, so a high-strength grade does not make zinc suitable for hot applications. Grade does not change that physics.
• Purity is not negotiable. A cheaper ingot outside the lead, tin and cadmium limits will eventually show up as corrosion failures rather than as a casting defect.

Getting the grade right in the quotation

Tell us what the part does rather than only what alloy you have in mind. The load path, the operating temperature and environment, the wall thickness, whether the part is plated and the annual volume are enough to select between Zamak 3, 5, 2 and 7 and the ZA grades, and where two grades both work we will quote both so the strength you gain and the ductility you give up are visible on the page. Related processes are aluminium die casting, surface finishing for plating and coating, and laser cutting or metal stamping where a formed sheet part is the better answer.