Zamak 3 vs Zamak 5: Choosing the Right Zinc Alloy for Die Cast Parts
In one sentence: Zamak 3 and Zamak 5 differ by about one percent of copper — and that one percent decides the trade between strength and castability, so the right choice comes from the part's function, not from a datasheet preference.
What "Zamak" actually is
Zamak is the commercial name for the zinc-aluminum alloy family used in hot-chamber die casting — the name historically stands for the German initials of its constituent metals (Zink, Aluminium, Magnesium, Kupfer). Both Zamak 3 (often labeled alloy 3, UNS Z33520 family) and Zamak 5 (alloy 5) are essentially zinc with about 4% aluminum, a trace of magnesium, and — in Zamak 5 only — about 1% copper. Both dominate the classic zinc casting applications: connectors, locks and lock bodies, gearbox and actuator housings, consumer-electronics frames, cosmetic hardware, and any small part that needs tight as-cast tolerances, thin walls or a plating-grade surface.
Zinc casting runs in hot-chamber machines, where the injection system sits permanently in the molten alloy. Compared with the cold-chamber process used for aluminum, this gives shorter cycle times, less turbulence in the shot, lower die temperatures and — because the process is gentler on the steel — dramatically longer tool life. Those process properties, more than the alloy chemistry, are why zinc castings come off the die with finer surface detail and hold tighter as-cast tolerances than aluminum castings of the same geometry.
Zamak 3 vs Zamak 5: the numbers
Typical values from published supplier datasheets (NADCA product-standards figures and major zinc suppliers' data; actual values vary with section thickness and process):
| Property (typical) | Zamak 3 | Zamak 5 |
|---|---|---|
| Tensile strength | ~283 MPa | ~331 MPa |
| Yield strength (0.2%) | ~221 MPa | ~265 MPa |
| Elongation | ~10% | ~7% |
| Hardness (Brinell) | ~82 HB | ~91 HB |
| Density | 6.6 g/cm³ | 6.7 g/cm³ |
| Castability / surface quality | Best in family | Very good |
Read the table as a trade, not a ranking. Zamak 5's copper addition buys roughly 15-20% more strength and higher wear resistance, and gives up about a third of the ductility. Zamak 3 fills thinner, more intricate sections more reliably and produces the best as-cast surface of the family — which matters directly for parts that will be plated or polished.
Choose Zamak 3 when…
- the part is intricate or thin-walled and fill reliability matters more than peak strength;
- the surface will be plated, painted or polished — Zamak 3's surface is the plating benchmark;
- the part sees impact or vibration loads where ductility absorbs energy (many consumer and lock components);
- cost and cycle time dominate — it is the default, highest-volume zinc alloy worldwide.
Choose Zamak 5 when…
- the application needs higher tensile or yield strength in the same envelope (actuator and gearbox housings, some structural brackets);
- wear or thread-galling resistance matters — the higher hardness helps on sliding or fastened features;
- the part will be machined in areas where a harder as-cast surface improves tool life.
Design notes specific to zinc
Walls go thinner. Zinc routinely casts at wall thicknesses that aluminum cannot fill — sections around 0.8-1.5 mm are normal production practice for small parts, against the ~2 mm and up that aluminum needs for the same geometry. That thickness advantage is usually where zinc's per-part economics beat aluminum, not the alloy price itself.
Tolerances tighten. The lower casting temperature means less shrinkage distortion; as-cast tolerances on small zinc features are commonly held tighter than aluminum equivalents, and features that would need machining in aluminum frequently come out of the die finished in zinc. Our machining guides on holding ±0.05 mm tolerances and machining allowance apply when features do need post-machining.
Mind the creep. Zinc alloys lose strength under sustained load at elevated temperature; long-term service above roughly 100 °C is generally avoided for load-bearing Zamak parts. Indoor electronics, hardware and mechanisms are ideal; under-hood and high-power-density applications belong to aluminum. If your part straddles that line, our article on choosing between zinc and aluminum walks the full decision.
Finishing is a zinc superpower. Chrome, nickel and zinc-alloy plating, powder coating, e-coat and painting all adhere and look excellent on Zamak — decorative hardware has been plated on zinc castings for a century. If your product spec sheet says "chrome-plated", the substrate conversation is usually already over.
How zinc fits the wider alloy decision
Zamak 3 and Zamak 5 are the two most-specified members of a broader family that also includes the ZA series (ZA-8, ZA-12, ZA-27) with higher aluminum content and correspondingly higher strength, usually cast cold-chamber. For the full cross-alloy picture — including ADC12 and A380 aluminum and where each wins on cost, weight and thermal performance — see our die casting alloy selection guide. For magnesium, the lightweight opposite end of the spectrum, our AZ91D vs ADC12 comparison covers the trade from the other direction.
OKDieCast is the die casting brand of Shenzhen Leijing Technology Co., Ltd., operating a 22,000 m² plant with hot-chamber zinc and cold-chamber aluminum/magnesium die casting, 5-axis CNC machining, surface treatment including plating-ready finishing, and ISO 9001 / IATF 16949 certified quality. Zinc programs move from drawing to sample in 7 days and series production in 30-45 days. Send your drawing for a DFM review and a quote within 24 hours.
Frequently asked questions
What is the difference between Zamak 3 and Zamak 5?
Zamak 5 carries roughly 1% more copper than Zamak 3, which raises tensile and yield strength and hardness, at the cost of ductility and some castability. Zamak 3 is the default for intricate, thin-walled or cosmetically demanding parts; Zamak 5 is preferred where higher strength or better wear behavior justifies the trade.
Can zinc die casting replace aluminum for structural parts?
Zinc wins on strength per volume and dimensional precision, but its density of about 6.6-6.7 g/cm³ is roughly 2.4 times that of ADC12 aluminum. For weight-critical structures aluminum stays the default; for small, complex, tight-tolerance or heavily plated components zinc is usually the better and often cheaper choice once machining and finishing are counted.
Why does zinc die casting hold tighter tolerances than aluminum?
Zinc is cast in a hot-chamber machine at lower injection temperature, which is gentler on the die, allows thinner walls and finer detail, and produces less thermal distortion on solidification. The result is as-cast tolerances and surface finish that aluminum cold-chamber casting approaches only with more machining.
Is Zamak suitable for parts that operate hot?
With a limit. Zinc alloys creep under sustained load at elevated temperature, so long-term service above roughly 100 °C is generally avoided for load-bearing Zamak parts. For engine-bay or power-electronics applications aluminum remains the right alloy; for indoor electronics, locks, connectors and consumer hardware Zamak performs well.
How does tooling life compare between zinc and aluminum die casting?
Hot-chamber zinc casting runs at lower injection temperature and pressure against the die, so tool life per program is typically several times longer than for aluminum cold-chamber work. For high-volume small parts this is one of the strongest cost arguments for zinc.
Related reading
Not sure whether your part is a zinc or aluminum casting? Send us the drawing — we will run the alloy trade with you and quote within 24 hours.