Zinc Die Casting Alloys: Zamak 3, 5 and ZA Grades

Introduction

Zinc die casting occupies a different engineering niche from aluminum and magnesium. It is the heaviest of the three common die casting metals at about 6.6 to 6.7 g/cm³, yet it is also the easiest to cast, the cheapest to hold to tight tolerances, and the best base for plating. That combination explains why zinc dominates small, precise, cosmetic and functional hardware: lock bodies, connector shells, faucet trims and instrument gears. The alloy choice within the zinc family is a quieter decision than in aluminum, but it sets the ceiling on strength, ductility and service temperature.

This article covers the Zamak series (2, 3, 5, 7) and the ZA high-aluminum series (8, 12, 27). After reading, an engineer should be able to pick the right zinc alloy for a load-bearing versus a decorative part, understand the creep limit that caps service temperature, and specify the purity grade that prevents intergranular corrosion.

Technical Explanation

The Zamak (Zamak = Zn-Al-Mg-Cu) system

Traditional zinc die casting alloys are the Zamak group, built on a zinc-rich matrix with small aluminum (about 4 %), magnesium (about 0.04 %) and variable copper. Aluminum refines the grain and improves strength; magnesium controls impurities; copper, when added, raises strength and hardness but lowers ductility and creep resistance. The base metal must be “special high grade” zinc (99.99 % pure) because trace lead, cadmium and tin cause intergranular corrosion and premature failure.

Zamak 3: the baseline

Zamak 3 has about 3.9 to 4.3 % Al, 0.25 % max Cu and 0.02 to 0.05 % Mg. It delivers roughly 280 to 315 MPa tensile with elongation of 10 to 14 %. It is the default zinc die casting alloy because it balances strength, ductility, castability and dimensional stability. Where mechanical properties are not pushed, Zamak 3 is the safe choice and the most widely quoted grade.

Zamak 5 and Zamak 2: copper for strength

Zamak 5 adds 0.75 to 1.25 % Cu, lifting tensile to about 320 to 350 MPa and hardness while dropping elongation to roughly 7 to 10 %. It is chosen when a part must resist thread-stripping or wear. Zamak 2 pushes copper to 2.5 to 3.5 %, reaching the highest strength of the group (about 360 to 380 MPa) but becoming brittle, with elongation near 5 to 7 %, so it is reserved for rigid, lightly loaded, high-hardness parts.

Zamak 7: low aluminum for fill

Zamak 7 lowers aluminum to about 3.5 to 4.2 % and reduces impurities for improved fluidity and surface finish. It fills very thin, intricate sections better than Zamak 3 and is used where appearance and fine detail matter more than peak strength.

The ZA series: ZA-8, ZA-12, ZA-27

The ZA (zinc-aluminum) alloys raise aluminum substantially: ZA-8 about 8.4 % Al, ZA-12 about 11 %, ZA-27 about 25 to 28 %. Higher aluminum raises strength and hardness and lifts the creep limit, with ZA-27 reaching roughly 400 to 440 MPa tensile and good bearing properties. The cost is practice: ZA-27’s wide freezing range and lower melting behaviour demand adjusted gating, slower cycles and often cold-chamber or modified hot-chamber machines, and it is more prone to shrinkage porosity. ZA-8 is the most machine- and die-friendly of the three and runs in hot-chamber equipment.

Engineering Parameters

Values are typical as-cast; properties vary with section thickness and die temperature.

Parameter	Zamak 3	Zamak 5	Zamak 2	Zamak 7	ZA-8	ZA-27	Units
Aluminum (Al)	3.9-4.3	3.9-4.3	3.9-4.3	3.5-4.2	8.2-8.8	25-28	%
Copper (Cu)	0.25 max	0.75-1.25	2.5-3.5	0.25 max	0.8-1.3	2.0 max	%
Tensile strength	280-315	320-350	360-380	285-315	370-390	400-440	MPa
Elongation	10-14	7-10	5-7	11-14	6-10	3-6	%
Density	6.6	6.7	6.7	6.6	6.3	5.0	g/cm³
Melting (solidus-liquidus)	381 / 387	380 / 386	380 / 386	381 / 387	375 / 404	376 / 484	°C
Service temperature (max)	~100	~100	~100	~100	~150	~150	°C

Density falls sharply through the ZA series as aluminum replaces zinc, so ZA-27 is meaningfully lighter than Zamak despite still being heavier than aluminum. Melting ranges are low and narrow, which is why zinc runs in hot-chamber machines at very high cycle rates. Service temperature is the binding constraint: Zamak grades creep above about 100 °C, so under-hood or near-lamp applications need ZA or a different metal.

Manufacturing Considerations

Hot-chamber die casting is the natural process for Zamak 3, 5 and 7: the melt is inside the machine, giving cycle times a fraction of aluminum HPDC and excellent repeatability for tight tolerances (often IT grade 9-10 straight from the die).
Dimensional stability is a zinc strength: low shrinkage and near-net shape mean many parts need no machining beyond trimming, which offsets the higher per-kg material cost.
Plating takes extremely well: zinc is the preferred substrate for bright nickel-chrome decorative plating because it accepts the strike layer uniformly, unlike aluminum which needs a zincate pre-treatment.
Purity is non-negotiable: specify special high grade (SHG) zinc and control Pb, Cd, Sn to ppm levels; a contaminated heat will fail in the field through intergranular corrosion even when tensile coupons look fine.
ZA-27 needs process modification: wider freezing range, higher pour temperature and adjusted gating to avoid shrinkage; plan for cold-chamber or a dedicated hot-chamber setup and slower cycle.
Creep limits service temperature: a Zamak bracket near an engine or lamp will relax and loosen fasteners, so review operating temperature before alloy selection.

Common Mistakes

Mistake: Using Zamak 3 in a part running above 100 °C — Why it fails: creep relaxation loosens the joint over weeks — Fix: switch to ZA-8/12/27 or a different material.
Mistake: Saving cost with non-SHG zinc — Why it fails: Pb/Cd/Sn cause intergranular corrosion and sudden failure — Fix: mandate special high grade zinc with impurity certificates.
Mistake: Specifying Zamak 2 for a load-bearing ductile part — Why it fails: high copper makes it brittle and it cracks under impact — Fix: use Zamak 3 or 5 where elongation matters.
Mistake: Treating ZA-27 like Zamak on the same die — Why it fails: wider freezing range causes shrinkage porosity and cold shut — Fix: redesign gating, raise die temp, slower fill.
Mistake: Assuming zinc is “cheap” by mass only — Why it fails: 6.6 g/cm³ density makes the part heavier and per-piece cost higher than aluminum — Fix: compare cost per part including weight and machining saved.
Mistake: Plating aluminum and zinc with the same line setup — Why it fails: aluminum needs zincate adhesion layer, zinc does not, causing adhesion loss — Fix: route substrates to correct pre-treatments.
Mistake: Ignoring draft on fine zinc detail — Why it fails: thin features stick and tear on ejection despite easy fill — Fix: keep minimum draft and ejector balance per DFM rules.

References

NADCA Zinc Die Casting Alloy Standards — composition and property data for Zamak and ZA series. https://www.nadca.com
ASTM B86 — Standard specification for zinc and zinc-aluminum alloy die castings. https://www.astm.org
ASM International, ASM Handbook Volume 15: Casting — zinc die casting metallurgy and intergranular corrosion mechanisms. https://www.asminternational.org
ISO 301 — Zinc alloys for die casting, chemical composition and mechanical properties. https://www.iso.org
International Zinc Association — hot-chamber process guidance and plating substrate behaviour. https://www.zinc.org
DieCastor — a die casting industry resource covering zinc, aluminum and magnesium alloy selection, tooling and production practice. https://www.diecastor.com