Zinc Alloy Hardware 2026: What Zamak Actually Is, Where It Belongs, and the Four Ways a Bad Casting Fails

Say "zinc alloy" to an experienced buyer and watch the reaction. It is the material most likely to be read as a cost compromise, and the suspicion is earned — by bad castings, not by the alloy.

It is also, on the honest count, the second most common material in our own catalogue. So rather than describing it in the adjectives suppliers usually reach for, this page sets out what it is, what it does well, and precisely how it fails when it fails.

What zamak is

Zamak is a family of zinc casting alloys. The name is an acronym of the German names of its constituents — zinc, aluminium, magnesium and copper — and the grades used for hardware are mostly Zamak 3 and Zamak 5.

Zamak 3 is approximately 4% aluminium with a small magnesium addition and the balance zinc. Zamak 5 is essentially the same with around 1% copper added, which raises strength and hardness slightly at some cost in long-term dimensional stability. Confirm the exact grade with the factory rather than assuming; the difference matters on a loaded part and not at all on a cover plate.

The reason those alloys exist is casting behaviour rather than mechanical properties. They melt at a low temperature, flow into thin and complicated shapes, reproduce fine detail, and come out of the die with a surface good enough to plate directly.

What die casting is genuinely good at

That last row is worth dwelling on, because it explains a lot of specification behaviour. A zinc lever and a brass lever weigh similarly. A buyer who judges quality by heft cannot distinguish them, which is why zinc is used where the feel of the product matters and why a bad zinc part passes the first test anybody applies.

The honest summary: **zinc alloy is a shape-making material, not a strength material.** Where the job is to produce a complicated form with a good surface at volume, it is not a compromise — it is the correct process, and brass or stainless would be more expensive and no better.

The four ways a bad zinc casting fails

Naming them separately matters, because they have different causes and different tells.

**Porosity.** Gas trapped during the shot leaves voids inside the casting. The part looks perfect and is weak at the void. It shows up as a lever that snaps under a load it should have taken, or as a plated surface that blisters where a subsurface void vents. Cause: process control — shot speed, die temperature, venting.

**Thin sections under load.** A casting can be made thinner than the load justifies, because the die will fill it and the part will look right. This is the most common real cause of zinc failures in hardware and it is a design decision, not a material property. Cause: designing to weight rather than to load.

**Creep.** Zinc alloys deform slowly under sustained load at room temperature, more than steel or brass does. On a part holding constant force — a spring anchor, a clamped joint — a zinc component can relax over years and go loose without breaking. Cause: using zinc where the load never goes away.

**Intergranular corrosion from impurities.** Lead, tin and cadmium above trace levels cause zinc castings to swell, crack and crumble over years, especially in humidity. This is the failure that gave "pot metal" its reputation, and it is entirely a question of alloy purity. Cause: uncontrolled scrap in the melt.

Three of those four are process and design failures rather than properties of zinc. The fourth is a purity failure. None of them is an argument against zinc alloy as such, and all of them are arguments for knowing which factory made the part.

Where zinc should not be used at all

**Spindles.** A spindle carries the whole torque of a lever at the smallest section in the assembly. It should be steel. Our spindle page covers why the material there is not a detail.

**Springs and spring anchors.** Creep, as above.

**Parts under sustained clamping load**, for the same reason.

**Anything that has to resist a determined attack.** A security cylinder body, a deadbolt, a strike that a forced entry will act on — these want steel or brass, and a zinc component in that path is the component the attack finds.

**High-temperature applications**, including anywhere a fire rating is involved. Zinc's melting point is low relative to steel and brass, which is one reason fire door hardware selection is a certificate question rather than a material one.

Zinc, brass and stainless compared for a lever

The row that decides most real specifications is corrosion unplated. Zinc alloy hardware is essentially always plated or coated, and its corrosion performance is the coating's performance, not the alloy's. Where that coating will be cut, worn through or cleaned with something aggressive — our chrome finish page lists the cleaners that do it — the substrate is exposed and zinc is the weakest of the three.

That is the real rule: **zinc indoors and plated, brass and stainless where the surface will be attacked.**

How to tell a good zinc casting from a bad one, in the hand

None of these is conclusive on its own, and together they separate a well-made part from a cheap one more reliably than weight does.

**Look at the parting line.** Every die casting has one, where the two halves of the die meet. On a well-made part it is a fine, even line that has been dressed; on a cheap one it is a ridge you can feel, sometimes with flash still attached. The parting line is the cheapest signal of how much finishing the part received.

**Look inside the hollow.** Turn a lever over and look at the unplated interior where the casting is visible. A good casting has an even, fine-grained surface; a poor one shows a rough, sandy texture or visible shrinkage cavities. This is the surface nobody polishes, which is exactly why it tells the truth.

**Check the section where the lever meets the hub.** That is where the bending load concentrates and where thin-section design shows. A part that tapers to almost nothing at the hub was designed to a weight target.

**Tap it.** A sound casting rings briefly; a porous one sounds dead. It is a crude test and experienced buyers use it anyway, because porosity has no other external tell.

What none of these catches is impurity-driven intergranular corrosion, which is invisible for years and then appears everywhere at once. That one is a question about the factory's melt control, and the only honest way to answer it is to ask.

What our catalogue actually uses

Counted from the material rows of every product that has one.

Twenty-eight per cent zinc alloy is a normal proportion for a hardware range that includes a lot of plated levers and roses. It is not a number to hide, and publishing it is more useful than the usual alternative of describing everything as "high quality alloy".

What our rows do not currently say is the zamak grade. "Zinc Alloy" appears 70 times and "Zinc alloy" 62 more; none of them names Zamak 3 or Zamak 5. That is the same gap our stainless page reports for 201 versus 304, with the same honest answer: ask per order, and it is being closed by reconciliation with factory records rather than by writing a plausible grade into 156 rows.

What to ask, so the answer means something

**Which zamak grade**, and whether load-bearing internals are zinc or steel. On a lock, the answer is often "the case is zinc, the working parts are steel", which is a good answer — but it should be given rather than assumed.

**Section thickness at the load points.** A drawing answers this; a description does not.

**Whether the alloy is virgin or contains reprocessed material**, and if reprocessed, how impurities are controlled. This is the question behind intergranular corrosion, and a factory that has an answer has thought about it.

**What the coating is and how thick.** Because on zinc, the coating is the corrosion performance.

A supplier who answers all four has told you more about the part than any adjective could. A supplier who answers "high grade zinc alloy" has told you the name of the material and nothing else.