Characteristics of Zinc Alloys
When impurity elements such as lead, cadmium, and tin exceed standard limits in the alloy composition, it causes the casting to age and deform, manifesting as volume expansion and a significant decline in mechanical properties—particularly plasticity—and may even lead to fracture over time. Lead, tin, and cadmium have very low solubility in zinc alloys and therefore concentrate at grain boundaries, acting as cathodes, while the aluminum-rich solid solution acts as an anode. In the presence of water vapor (electrolyte), this promotes intergranular electrochemical corrosion. Die-cast parts age due to intergranular corrosion.
The microstructure of zinc alloys primarily consists of zinc-rich solid solutions containing Al and Cu, and Al-rich solid solutions containing Zn. Their solubility decreases as temperature drops. However, due to the extremely rapid solidification rate of die-cast parts, the solubility of these solid solutions is largely saturated by the time the part reaches room temperature. After a certain period of time, this supersaturation gradually dissipates, causing slight changes in the casting's shape and dimensions.
Zinc alloy die-castings should not be used in high-temperature or low-temperature (below 0°C) operating environments. Zinc alloys exhibit good mechanical properties at room temperature. However, tensile strength decreases significantly at high temperatures, and impact strength decreases significantly at low temperatures.
Types of Zinc Alloys
| Alloy Type | Characteristics & Applications |
|---|---|
| Zamak 3 | Good fluidity and mechanical properties. Used for castings with low mechanical strength requirements, such as toys, lighting fixtures, decorative items, and certain electrical components. |
| Zamak 5 | Good fluidity and excellent mechanical properties. Used for castings with moderate mechanical strength requirements, such as automotive parts, electromechanical components, mechanical parts, and electrical components. |
| Zamak 2 | Used for mechanical parts with special mechanical performance requirements, high hardness requirements, and general dimensional accuracy requirements. |
| ZA8 | Good fluidity and dimensional stability, but relatively poor fluidity. Used for die-casting small-sized workpieces with high precision and mechanical strength requirements, such as electrical components. |
| Superloy | Optimal fluidity, used for die-casting thin-walled, large-sized, high-precision, and complex-shaped workpieces, such as electrical components and their enclosures. |
Different zinc alloys possess distinct physical and mechanical properties, providing flexibility in the design of die-cast parts.
Selection of Zinc Alloys
The choice of zinc alloy is primarily determined by three factors:
Tensile strength, which is the maximum resistance of a material before fracture; elongation, which measures the balance between brittleness and ductility; and hardness, which is the resistance of a material's surface to plastic deformation caused by indentation or friction from a hard object.
Operating temperature, humidity, media with which the workpiece comes into contact, and airtightness requirements.
Achievable accuracy and dimensional stability.
Control of Zinc Alloy Composition
| Element | Zamak 2 | Zamak 3 | Zamak 5 | ZA8 | Superloy | AcuZinc 5 |
|---|---|---|---|---|---|---|
| Aluminum | 3.8 ~ 4.3 | 3.8 ~ 4.3 | 3.8 ~ 4.3 | 8.2 ~ 8.8 | 6.6 ~ 7.2 | 2.8 ~ 3.3 |
| Copper | 2.7 ~ 3.3 | <0.030 | 0.7 ~ 1.1 | 0.9 ~ 1.3 | 3.2 ~ 3.8 | 5.0 ~ 6.0 |
| Magnesium | 0.035 ~ 0.06 | 0.035 ~ 0.06 | 0.035 ~ 0.06 | 0.02 ~ 0.035 | <0.005 | 0.025 ~ 0.05 |
| Iron | <0.020 | <0.020 | <0.020 | <0.035 | <0.020 | <0.075 |
| Lead | <0.003 | <0.003 | <0.003 | <0.005 | <0.003 | <0.005 |
| Cadmium | <0.003 | <0.003 | <0.003 | <0.005 | <0.003 | <0.004 |
| Tin | <0.001 | <0.001 | <0.001 | <0.001 | <0.001 | <0.003 |
| Zinc | remainder | remainder | remainder | remainder | remainder | remainder |
Post time: Apr-23-2026
