Mechanical Properties of Zamak Alloys in Zinc Die Casting: Technical Guide

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Selecting a zamak alloy for zinc die casting requires a thorough understanding of its mechanical properties: tensile strength, hardness, elongation, impact resistance and creep behaviour are the parameters that determine the technical feasibility and service life of a die cast component. This guide provides a detailed analysis of the four alloys standardised under EN 12844 — ZP3, ZP5, ZP2 and ZP8 — comparing their nominal properties, long-term behaviour and the criteria for choosing the right alloy based on the application.

What Do Mechanical Properties Mean for a Zinc Die Casting?

When discussing the mechanical properties of a zamak die casting, we refer to a structured set of measurable physical quantities — determined according to standardised test procedures — that describe how the material responds to both static and dynamic loads.

Tensile Strength and Yield Strength

Tensile strength (Rm) is the maximum unit load a test specimen can sustain before fracture, expressed in megapascals (MPa) and measured in accordance with EN ISO 6892-1. The 0.2% proof stress (Rp0.2) defines the threshold beyond which permanent plastic deformation occurs: for die-cast ZP3, for example, zinc.org cites a reference value of 220 MPa, which is used in design calculations including creep testing.

Elongation and Ductility

Elongation at break (A%) quantifies ductility: an alloy with a higher A% value tolerates localised plastic deformation — such as in press-fit assemblies — without cracking. Zamak die casting alloys typically exhibit A% values ranging from 2% to 10%, depending on composition and ageing.

Vickers and Brinell Hardness

Vickers hardness (HV) per ISO 6507 and Brinell hardness (HB) are complementary measures of penetration resistance, closely correlated with wear resistance and performance in applications involving threads, bearing seats or sliding surfaces.

Impact Toughness and Elastic Modulus

Charpy impact energy (the energy absorbed by a notched specimen at fracture) and the elastic modulus (E ≈ 85–90 GPa) round out the picture, describing impact toughness and structural stiffness respectively.

Not sure which alloy fits your part? See our guide on how to choose the right Zamak alloy by application (ZP3, ZP5, ZP2, ZP8).

The Four EN 12844 Zamak Alloys: ZP3, ZP5, ZP2 and ZP8

The acronym ZAMAK derives from the German names of its four constituent metals: Zink (zinc), Aluminium (aluminium), MAgnesium (magnesium) and Kupfer (copper). The alloy family was developed by the New Jersey Zinc Company in 1929 and is today standardised in Europe under EN 12844.

Nominal Chemical Composition

ZP3, ZP5 and ZP2 all share a constant aluminium content of 4%, while ZP8 stands apart with 8% aluminium. Copper is the differentiating element at equivalent aluminium levels: absent in ZP3, around 1% in ZP5 and ZP8, and up to 3% in ZP2. Magnesium is present in all four alloys at trace levels (0.02–0.06%) to inhibit intergranular corrosion.

Equivalent Designations

EN 12844	EU Trade Name	ASTM B86 (USA)	ISO 301
ZP3	Zamak 3	AG40A / Zamak 3	ZnAl4
ZP5	Zamak 5	AC41A / Zamak 5	ZnAl4Cu1
ZP2	Zamak 2	AC43A / Zamak 2	ZnAl4Cu3
ZP8	—	ZA-8 (ZA family, separate)	ZnAl8Cu1

Technical note: the European ZP8 does not correspond to any ASTM Zamak alloy. Its North American equivalent is ZA-8, which belongs to the ZA-alloys family — a separate and distinct group from the ZAMAK family. The designation “Zamak 8” should be avoided in engineering specifications.

EN 1774 and Critical Impurity Limits

EN 12844 governs the composition of castings; EN 1774 governs incoming ingot composition, applying tighter tolerances to give the foundry adequate process latitude. Critical impurities — lead, cadmium, tin and silicon — must be kept well within defined limits: exceeding those thresholds causes embrittlement, intergranular corrosion and, in severe cases, the so-called “zinc pest” phenomenon. For this reason, all zamak alloys available from Micrometal are subject to compositional verification on every incoming batch, in line with our ISO 9001 certified quality system.

Comparative Table of Nominal Mechanical Properties at 20 °C

The values below are indicative and are based on the EN 12844 Nominal Properties table and zinc.org data for die castings with a 2 mm wall thickness, measured 5–8 weeks after casting.

Property	ZP3	ZP5	ZP2	ZP8
Rm – Tensile Strength (MPa)	~280	~330	~360	~370
Rp0.2 – Proof Stress (MPa)	~220	~250	~280	~290
A% – Elongation (%)	10	7	5	8
Brinell Hardness (HB)	~82	~92	~100	~103
Charpy Impact Energy (J)	~58	~65	~50	~42
Elastic Modulus E (GPa)	~85	~85	~85	~86

Hardness Hierarchy and Wear Resistance

Hardness follows the order ZP2 ≈ ZP8 > ZP5 > ZP3: ZP2 and ZP8 are classified as heavy-duty alloys for demanding applications. Wear resistance tracks closely with hardness, making these two alloys the natural candidates for heavy-duty zinc die castings subject to continuous sliding or impact loading.

Notch Sensitivity and Elastic Modulus

Charpy impact energy decreases as copper content rises: ZP3 is the toughest alloy, while ZP8 is the most notch-sensitive. The elastic modulus, on the other hand, is essentially constant at approximately 85 GPa across all four alloys — meaning they are structurally equivalent in terms of stiffness for a given geometry, a useful consideration when defining material technical specifications.

Cooling Rate and Wall Thickness: The Role of Hot Chamber Die Casting

The mechanical properties of a zinc die casting depend not only on alloy composition but also — to a significant degree — on process conditions. As documented by zinc.org (Engineering Properties – Mechanical Properties), rapid in-die cooling produces a fine-grained microstructure that maximises tensile strength and hardness.

Thin Walls = Fine Grain = Higher Strength

Thin-walled sections cool more rapidly and therefore exhibit proportionally higher Rm and hardness values compared to thicker sections within the same casting. This is precisely why the EN 12844 nominal values are referenced to standard 2 mm test specimens: greater wall thicknesses result in a progressive reduction in the mechanical performance typically quoted.

Hot Chamber Die Casting: The Ideal Process for Zamak

The low melting point of zamak alloys (~385 °C, compared to ~1,500 °C for steel) makes them ideally suited to the hot chamber die casting process, in which the injection plunger is submerged directly in the molten metal. This translates into fast cycle times — up to approximately 1,000 shots per hour with conventional tooling — and high cooling rates, both essential conditions for achieving rated mechanical properties.

Micrometal has been operating since 1991 in Erbusco, Brescia, with a fleet of 11 die casting machines, all hot chamber, ranging from 20 to 90 tonnes of locking force — a configuration that delivers the full mechanical potential of all four ZAMAK family alloys.

Ageing and Long-Term Property Stability

Zamak die casting alloys are not “frozen” in their as-cast state: in the weeks and months following casting, microstructural transformations occur (decomposition of metastable phases) that progressively alter mechanical properties.

Behaviour of ZP3, ZP5 and ZP8

For these three alloys, natural ageing at room temperature results in a gradual reduction in Rm and hardness and a corresponding increase in elongation A%. The process stabilises after several months and explains why EN 12844 nominal values are referenced to measurements taken 5–8 weeks after casting — a representative snapshot of the component’s service life.

The Special Case of ZP2

ZP2 behaves differently: elongation decreases during the first weeks and months of ageing, before gradually recovering over the longer term. This characteristic requires careful consideration in applications where initial ductility is critical — for example, in assemblies involving controlled plastic deformation.

Dimensional Stability

The dimensional stability of zamak die castings over time is greatest for ZP3, which maintains critical dimensions more reliably than the other alloys. This is why ZP3 is frequently specified for precision components in instrumentation and sensing applications.

Creep Resistance of Zamak Alloys

Creep is the progressive plastic deformation of a material under constant load over extended periods, even at stress levels below the proof stress. It is a critical parameter for components under continuous static loading — such as brackets, die-cast threaded inserts and permanent thread seats.

Alloy Creep Hierarchy

zinc.org data indicates the following creep resistance ranking: ZP8 ≈ ZP2 > ZP5 > ZP3. ZP3 is therefore the least creep-resistant alloy in the family, and specifying it for components under sustained loading warrants particular caution.

Practical Extrapolation Rule

A useful design rule of thumb: in the absence of specific creep data for ZP5, ZP3 data can be used as a reference by adding 10 °C to the temperature being assessed. ZP2 and ZP8 exhibit essentially equivalent creep behaviour.

Test Limits and Thermal Sensitivity

Accelerated creep tests on zamak alloys must respect two constraints: applied stress below 50 MPa and test temperature below 150 °C. Nominal values at 20 °C cannot be extrapolated to service temperatures above 70–80 °C without a dedicated creep calculation.

Application Example

For a ZP3 die casting with Rp0.2 = 220 MPa, the maximum allowable stress for accelerated creep testing (50 MPa limit) corresponds to approximately 23% of the proof stress. For heavy-duty applications above 80 °C, specifying the ZP8 alloy for heavy-duty applications is the preferred approach.

Comparison with Alternative Materials: Aluminium, Brass, Steel and Engineering Polymers

The decision to specify zamak for a die cast component should always be evaluated against technologically comparable alternatives.

Property	Zamak (ZP5)	Die Cast Aluminium	Machined Brass	Engineering Polymer (PA66-GF)
Density (kg/dm³)	6.7	~2.7	~8.5	~1.4
Typical Rm (MPa)	~330	~240	~400	~180
Process	Hot chamber	Cold chamber	Machining	Plastic injection
Productivity	Up to 1,000 shots/h	~200–400 shots/h	Low, subtractive	High
Geometric Detail	Excellent	Good	Limited	Excellent
Electroplating	Yes (Cu-Ni-Cr EN 12540)	Difficult	Yes	No
EMI Shielding	Yes	Yes	Yes	No

We examine in detail the advantages of zinc die casting over aluminium: for equivalent geometry, the hot chamber process delivers 2–3 times higher productivity, finer geometric detail (wall thicknesses down to 0.5 mm), integrated threads and tighter NADCA dimensional tolerances.

Compared to machined brass, zamak eliminates swarf losses and enables complex net-shape geometries. Compared to engineering polymers, zamak offers superior mechanical and thermal performance, electromagnetic shielding and — critically — the ability to apply decorative and protective Cu-Ni-Cr electroplated finishes in accordance with EN 12540:2000.

Alloy Selection Guide: Choosing the Right Zamak for Your Application

A sound alloy selection always starts from the component’s functional requirements: load level, service temperature, dimensional stability needs, and the presence of sliding contact or impact loading.

Operational Summary of the Four Alloys

• ZP5 (Zamak 5): the European standard choice for the majority of general mechanical applications. An excellent balance of strength, hardness and ductility; ideal for lock hardware and security components.
• ZP3 (Zamak 3): best long-term dimensional stability, highest ductility, excellent weldability and surface finish receptivity. Recommended for precision components and aesthetic parts.
• ZP2 (Zamak 2): maximum hardness and creep resistance; note the initial reduction in elongation during ageing. Well suited to components under prolonged static load.
• ZP8: heavy-duty alternative with mechanical and creep performance comparable to ZP2, but with better long-term elongation retention.

Decision Flowchart

flowchart TD
    A[Primary component requirement] --> B{Sustained static load
or T > 80 °C?}
    B -- Yes --> C{Ductility required
in assembly?}
    C -- Yes --> D[ZP8]
    C -- No --> E[ZP2]
    B -- No --> F{Critical dimensional
precision required?}
    F -- Yes --> G[ZP3]
    F -- No --> H{General mechanical
application?}
    H -- Yes --> I[ZP5 – European standard]
    H -- No --> J{High sliding wear
or abrasion?}
    J -- Yes --> E
    J -- No --> I

Technical Support from Micrometal

Alloy selection is rarely straightforward: balancing strength, cost, surface finish and dimensional stability typically calls for close technical dialogue with the foundry from the earliest stages of product development. Micrometal’s co-design and die casting engineering service supports designers from material validation through to surface finish specification — including the copper undercoat (2–5 µm) followed by acid copper and nickel, which is mandatory prior to chrome plating to prevent nickel attack on zinc, in line with NADCA and zinc.org standards.

Thirty years of hot chamber zinc die casting experience across all four EN 12844 alloys, a complete machine fleet from 20 to 90 tonnes locking force, and an ISO 9001 certified quality system in place since 1991 make Micrometal a reliable technical partner for alloy specification at the design stage. For a targeted assessment of your component, you are welcome to request a direct technical consultation with our engineering team.