Specific Heat and Thermal Conductivity of Zamak

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When engineering a die cast component, attention usually goes to mechanical strength, tolerances, and finish. Yet two less visible properties — specific heat and thermal conductivity of zamak — directly determine how quickly a casting solidifies inside the die, how much it costs to produce, and whether it can serve a heat-dissipation function. This guide breaks down the technical meaning of these two parameters, the typical values for zamak alloys (ZP3, ZP5, ZP2, ZP8), and their implications for hot chamber die casting mold design.

Specific heat and thermal conductivity: definitions applied to zamak

Specific heat (measured in J/kg·K) expresses the amount of energy required to raise the temperature of one kilogram of alloy by one degree. It is a heat capacity property: it tells you how much “heat” a zamak casting stores or releases during heating and cooling. A higher specific heat means more energy is needed to bring the alloy up to pouring temperature, but it also means the metal retains more heat that must be removed during solidification.

Thermal conductivity (in W/m·K), by contrast, describes how quickly heat moves through the material. It is a transport property: it quantifies how fast thermal energy migrates from hot to cold regions of a casting. In die casting, this translates into how quickly heat from the molten metal reaches the die walls and is carried away by the cooling system.

In metals, thermal and electrical conductivity tend to move together: both largely depend on the motion of free electrons. As reference sources on the subject summarize, metals show high values of both, with notable exceptions such as diamond, which conducts heat well but electricity poorly. This correlation explains why zinc — the base of zamak alloys and their composition — is attractive both for thermal applications and for electromagnetic shielding.

Typical values for zamak alloys (ZP3, ZP5, ZP2, ZP8) and ZA alloys

Pure zinc has excellent thermal conductivity at room temperature. Zamak alloys, which add mainly aluminum (~4%) along with smaller amounts of magnesium and copper, retain good thermal behavior, though somewhat lower than the pure metal: the alloying elements introduce barriers to electron motion, slightly reducing both thermal and electrical conductivity.

Composition has a direct effect on these values. Copper, present in Zamak 5 with its copper addition (~1%) and even more so in Zamak 2 (~3%), increases strength and hardness but tends to reduce thermal conductivity compared with Zamak 3, the base alloy. The high-aluminum ZA family (such as ZA-8, ~8% Al) shows a different thermophysical profile again, with lower density (~6.3 g/cm³ versus ~6.6 g/cm³ for conventional zamak).

Alloy	Distinctive elements	Expected thermal effect	Design note
Zamak 3 (ZP3)	base ~4% Al, Cu ≤0.10%	Reference thermal conductivity, the highest in the ZP family	Most ductile alloy, standard for over 70% of North American castings
Zamak 5 (ZP5)	~4% Al + ~1% Cu	Slightly lower conductivity than ZP3	+10% strength versus ZP3
Zamak 2 (ZP2)	~4% Al + ~3% Cu	Reduced conductivity due to the higher copper content	The hardest and strongest, the least ductile
ZP8 / ZA-8	~8% Al + ~1% Cu	Thermal profile modified by higher aluminum content	Lower density (~6.3 g/cm³)

Why they matter in hot chamber die casting mold design

In hot chamber die casting, molten metal is injected into the cavity and must solidify in a controlled way before the die opens. How fast this happens depends on the alloy’s thermophysical properties: thermal conductivity and specific heat determine how much energy must be extracted and how quickly.

Cooling channel sizing is the practical translation of these parameters. A liquid circulation system inside the die ensures the part cools down: the designer must calibrate its diameter, position, and flow rate based on the heat load to be removed. An alloy with higher specific heat stores more thermal energy, requiring more efficient circuits or longer cooling times.

The impact on cycle time is direct: the more effectively heat is removed, the sooner the die can open and the part be extracted, boosting productivity. Hot chamber casting is particularly advantageous because zamak is well suited to this process: below ~450°C, the aluminum content in the alloy dramatically reduces the corrosive attack of molten metal on the die’s ferrous components, making it possible to submerge the injection unit in the metal bath. Mold design must therefore balance thermal extraction, casting integrity, and tooling life.

Effect of cooling rate on microstructure and final properties

The mechanical and physical properties of zamak castings depend not only on alloy composition but also on the casting conditions that influence cooling rate. This is a well-established metallurgical principle: conditions that favor rapid cooling in the die produce the highest values of strength and hardness.

This leads to a surprising practical consequence: thin sections turn out proportionally stronger than thick ones. A thin wall cools faster, develops a finer microstructure, and therefore performs better mechanically. This behavior is governed precisely by the thermophysical properties discussed above: high conductivity and moderate specific heat favor rapid thermal transients.

The relationship between thermophysical properties and casting conditions is therefore two-way: material properties set the thermal limits, while process parameters — injection temperature, die temperature, cooling efficiency — determine how much of that potential translates into final casting performance.

Thermal diffusivity: linking specific heat, density, and conductivity

To predict a casting’s transient thermal behavior, a single parameter summarizes all three fundamental quantities: thermal diffusivity. In thermodynamics it is defined as thermal conductivity divided by the product of density and specific heat at constant pressure, with units of m²/s.

α = k / (ρ · c_p)   [m²/s]

Diffusivity measures how quickly a temperature change propagates through the material. A material with high diffusivity reaches thermal equilibrium quickly; one with low diffusivity responds more slowly to changes. This is critical for thermal transients: how fast a zamak casting cools in the die, but also how quickly an in-service component responds to a heat spike that needs dissipating.

Material	Approximate density	Qualitative thermal behavior
Zamak	~6.6 g/cm³	Good conductivity, high density: balanced thermal response, ideal for complex geometries
Aluminum	~2.7 g/cm³	Very high conductivity, low density: high diffusivity, fast dissipation but requires cold chamber
Iron / steel	~7.8 g/cm³	Lower conductivity than the two above: slower thermal response

This comparison is qualitative: exact values vary with temperature and composition. The point is conceptual — diffusivity explains why two materials with different density and zamak alloy density can behave differently even at comparable conductivity.

Zamak as a heat sink material: comparison with aluminum

Zinc’s excellent thermal and electrical conductivity, combined with precise casting tolerances, makes zamak alloys an ideal choice for heat sinks, electrical components, and applications requiring electromagnetic shielding. This isn’t just theory — it’s the reason zamak competes directly with aluminum in electronics applications.

Criterion	Zamak (hot chamber)	Aluminum (cold chamber)
Thermal conductivity	Good	Very high
Casting tolerances	Very tight	Looser
Geometric complexity	High, thin walls	More limited
EMC shielding	Excellent	Good
Process	Hot chamber, fast cycle	Cold chamber

Zamak’s decisive advantage in thermal management is not raw conductivity — where aluminum leads — but the combination of adequate conductivity, tight tolerances, and the ability to produce complex thin-wall geometries cost-effectively. A heat sink or housing with dense fins, undercuts, and integrated details is produced more efficiently in zamak via hot chamber die casting than in aluminum. We cover the differences between zamak and die cast aluminum in a dedicated article.

Choosing zamak becomes the natural option when a component must integrate multiple functions: heat dissipation, electromagnetic shielding, dimensional precision, and mechanical fixings in a single casting. This is typical of many instrumentation and sensor housings.

Impact of finishing (Cu-Ni sequence) on heat dissipation

A zamak component intended to dissipate heat is almost always coated, for both corrosion-resistance and aesthetic reasons. The reference electroplating sequence for decorative nickel plating is the copper-nickel (Cu-Ni) cycle: a copper undercoat is essential because, without it, nickel would attack the zinc. Copper acts as a barrier layer and as an adhesion base.

Each layer adds a degree of contact thermal resistance: heat must pass through the coatings before reaching the surroundings or the dissipation interface. Copper and nickel are both conductors, but the overall deposit thickness affects the thermal path. For components whose primary function is heat dissipation, surface protection and desired conductivity must be balanced against each other.

From a design standpoint, this means discussing coating thickness, thermal contact area, and possible masking of functional surfaces early in the project. Our electroplated finishes for zamak castings are outsourced to qualified partners, while the Cu-Ni cycle remains the technical foundation of every durable decorative finish on zamak.

Micrometal case studies: thermal management in electronics and automotive

Since 1991, Micrometal, based in Erbusco (Brescia, Italy) and ISO 9001 certified, has translated these thermophysical properties into concrete production choices. Our machine fleet includes 11 units — 7 hot chamber presses (Agrati, Italpresse, and Frech) and 4 robotic cells — with clamping forces from 20 to 90 tonnes.

Our technical team designs the die’s cooling circuits with the selected alloy’s specific heat and conductivity in mind, to optimize cycle times without compromising casting integrity. This is the stage where thermophysical properties stop being table values and become coolant flow rate, channel position, and cavity geometry.

Typical applications include electronics housings with EMC shielding and dissipation requirements, and components for cooling systems where zamak combines dimensional precision, geometric complexity, and controlled thermal behavior. In both cases, the combination of alloy conductivity and Cu-Ni finishing offers a design advantage, alongside aesthetic and corrosion-resistance benefits.

If you’re evaluating zamak for a component with thermal management requirements, our technical team can support you in alloy selection and mold design: request a technical consultation or call +39 030 7760830.

Technical review: Marco Sega