Cast Zinc Material Properties Guide

Die casting grades are almost never pure zinc. Commercial alloys sit between roughly 3.5% and 27% aluminum by weight, with copper, magnesium, and small amounts of iron and lead controlled tightly. Aluminum raises strength and hardness. Copper improves creep resistance and wear behavior but slows the casting cycle. Magnesium controls grain growth and limits intergranular corrosion. Iron keeps the melt from attacking the die steel, and lead, tin, and cadmium are held very low because they cause intergranular corrosion and dimensional growth over time.

That balance matters more than the base metal. A 4% aluminum alloy with 3% copper behaves very differently from a 4% aluminum alloy with almost no copper. The first resists creep under a sustained load. The second is cheaper, casts faster, and machines more easily, but it will slowly deform in a warm, loaded application.

Typical as-cast density lands near 6.6 g/cm³ for the Zamak family and closer to 5.0 g/cm³ for the high-aluminum ZA-27. Compare that with 2.7 g/cm³ for aluminum and 7.8 g/cm³ for steel. The mass penalty versus aluminum is real, and it is often the first reason a project moves away from zinc.

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  AluminumRaises strength and hardness, lowers ductility as content climbs.
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  CopperImproves creep resistance and wear; slows cycle time.
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  MagnesiumRefines grain structure, limits intergranular corrosion.
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  Lead, tin, cadmiumHeld very low. They cause corrosion and dimensional growth.

The useful properties cluster in a way that suits small, thin-walled, detailed parts. Zinc melts around 380–390 °C, far below aluminum at roughly 660 °C. That lower melting point means less thermal shock to the die, longer die life, and thinner walls. Walls down to 0.5 mm are common in Zamak 3, and 0.25 mm is achievable in short sections. Aluminum die casting usually cannot go below about 1 mm without trouble.

As-cast tensile strength for Zamak 3 is about 283 MPa, and Zamak 5 reaches roughly 328 MPa. ZA-27 pushes past 400 MPa. Elongation for Zamak 3 is around 10%, which gives it enough ductility to survive crimping and staking without cracking. Impact resistance is modest compared with brass or steel, so parts that take direct hits need a thicker section or a different material.

Thermal conductivity sits near 113 W/m·K for Zamak 3, about ten times that of stainless steel. That is why zinc housings often double as heat spreaders for small electronics. Electrical conductivity is roughly 27% IACS, enough for shielding and grounding but not for current-carrying conductors.

Machining behavior is a genuine strength. Zinc chips break cleanly, cutting speeds are high, and the as-cast surface can be finished to Ra 0.8–1.6 μm without a lot of effort. On our 5-axis centers we hold ±0.005 mm on zinc parts when the fixture supports the thin sections. The metal is soft, so clamping pressure has to be watched or the part will deform before the cutter touches it.

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  Melting point380–390 °C, roughly 270 °C below aluminum.
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  Minimum wall0.5 mm typical, 0.25 mm in short sections.
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  As-cast tensile283 MPa for Zamak 3, 328 MPa for Zamak 5.
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  Thermal conductivityAbout 113 W/m·K for Zamak 3.

Zamak 3 is the default for a reason. It casts easily, plates well, and has the best combination of ductility and surface finish in the family. If a part is a decorative housing, a connector shell, a zipper pull, or a bracket that sees no sustained load, Zamak 3 will usually be the cheapest correct answer.

Zamak 5 trades a little ductility for strength and creep resistance. The 1% copper addition makes it the standard choice for automotive hardware, lock components, and parts that carry a load for years. Zamak 7 is the low-magnesium version, used when the part must be plated or when thin walls need extra fluidity in the die.

The ZA alloys enter when loads rise. ZA-8 is a drop-in upgrade for Zamak 5 in many bearing and bushing applications because its higher aluminum content gives it better wear resistance at elevated temperature. ZA-27 has the highest strength and the best creep behavior, but it also has the lowest density in the group, the highest melting point, and a sharper casting window. It is harder on tooling and needs more careful gate design.

A practical rule: start with Zamak 3. Move to Zamak 5 or ZA-8 only when the load case demands it. Pick ZA-27 when you need strength and creep resistance together and you can accept the tooling cost. If the part is large, thin, and heavily loaded all at once, zinc is probably the wrong family and you should be looking at aluminum or steel.

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  Zamak 3Default for housings, brackets, plated parts.
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  Zamak 5Automotive hardware, lock parts, sustained loads.
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  ZA-8Bearings and bushings running warm.
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  ZA-27Highest strength and creep resistance, tighter process.

Creep is slow deformation under a constant load at a temperature well below the melting point. In zinc it becomes measurable above about 60 °C and accelerates sharply past 100 °C. A bolt boss that holds a 200 N load at 80 °C may look fine on day one and be visibly shorter after two years. Nothing cracks. The part just moves.

The mechanism is grain boundary sliding. At higher temperatures, zinc grains slide past each other and the alloy deforms without any increase in stress. Copper additions pin those boundaries, which is why Zamak 5 and ZA-27 outperform Zamak 3 under sustained load. Aluminum content helps too, but copper is the stronger lever.

Design against creep with geometry, not just alloy choice. Increase section thickness at the load path. Add ribs so the stress spreads over a larger area. Avoid long unsupported spans that carry a steady load. If the joint is bolted, use a washer or a steel insert to spread the clamp force. Where the service temperature stays above 100 °C, treat zinc as a candidate only after a creep check, and consider aluminum instead.

Fasteners are a common trap. A threaded zinc boss that is torqued once and left alone will relax over time. A through-bolt with a steel nut and washer on the far side removes the creep path entirely. When the design allows it, that is the cheaper fix.

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  Below 60 °CCreep is negligible for most Zamak parts.
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  60–100 °CMeasure it. Copper content matters most here.
• 3
  Above 100 °CAvoid sustained loads or switch material.
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  Bolted jointsUse washers or steel inserts to spread clamp load.

Electronics use zinc for shielding cans, connector housings, and heat-spreading enclosures. The high thermal conductivity and the ability to cast thin walls make it a good match for small devices that need both structure and heat paths. EMI shielding benefits from the 27% IACS conductivity, and the as-cast surface takes plating and powder coating without much prep.

Automotive and EV applications lean on Zamak 5 and ZA-8 for lock bodies, seat hardware, sensor housings, and brackets that see vibration but modest temperature. Zinc handles vibration well because of its damping capacity. The limits show up near exhaust components, motor windings, and underhood areas that soak above 100 °C.

Consumer products use zinc where feel and finish matter: knobs, buckles, housings, and decorative hardware. The weight is part of the appeal. A zinc knob feels solid in a way that a plastic one does not, and it can be polished, brushed, or plated to a wide range of finishes.

Zinc is the wrong choice for large structural parts, high-temperature service, and anything that must be welded. It is also a poor fit for parts that need very high impact toughness, such as safety-critical brackets. For those, aluminum or steel is the better path, and we will say so during the DFM review.

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  Good fitThin housings, connectors, knobs, lock hardware.
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  WorkableBrackets and bushings below 100 °C.
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  Poor fitHigh-temperature, welded, or high-impact parts.