I. Characteristics of die casting with zinc alloys
Zinc alloys have excellent mechanical and electroplating properties. The surface roughness, strength and ductility of zinc alloy castings are excellent.
Due to zinc's exceptional fluidity, it can be used to create thinner products with wall thicknesses of up to 0.5 mm.
The main disadvantage of zinc is its high density, which results in heavier and more expensive products, making it more suitable for small parts. Furthermore, zinc alloys lack dimensional stability.
1) Density:
- Pure zinc: 6.6 g/cm 3 ;
- Cast zinc alloy: 6.7-6.9 g/cm 3 ;
2) Melting point:
- Pure zinc: 419°C;
- Zinc alloy: 387-390°C;
- Casting temperature: 390-410°C
3) The most commonly used cast zinc alloy is ZAMAK 3.
II. Cast Zinc Alloy Models
The international standards and models corresponding to ZAMAK 3 are as follows:
| UK | BS:1004-1972 League A |
| U.S | ASTM: Alloy B240-74 AG40A; SAE:903 |
| Japan | JIS:H2201Na2(ZDC2) |
| Germany | DIN 1743:1978 GB ZN A14 |
| Australia | AS 1881-1977 Zn A14 |
| Taiwan | CNS: ZAC1 |
| China | GB: ZZnAl4 |
III. Composition of cast zinc alloys
The chemical compositions of several commonly used zinc alloys are as follows:
| ZAMAK 2 | ZAMAK 3 | ZAMAK 5 | |
| Al | 3.8-4.2 | 3.8-4.2 | 3.8-4.2 |
| Ass | 2.7-3.3 | ≤0.030 | 0.7-1.1 |
| mg | 0.035-0.06 | 0.035-0.06 | 0.035-0.06 |
| Pb | ≤0.03 | ≤0.003 | ≤0.003 |
| Faith | ≤0.020 | ≤0.020 | ≤0.020 |
| CD | ≤0.003 | ≤0.003 | ≤0.003 |
| Sn | ≤0.001 | ≤0.001 | ≤0.001 |
| Yes | ≤0.02 | ≤0.02 | ≤0.02 |
| No | ≤0.001 | ≤0.001 | ≤0.001 |
4. Dimensional Stability of Zinc Alloys
Zinc alloy products will shrink continuously after molding, essentially stabilizing after six months. The shrinkage of zinc castings is as follows:
| Casting Processing | Time | League no. 3 mm/m |
League No. 5 mm/m |
| Standard Aging Variation | 5 weeks later After 6 months 5 years later 8 years later. |
0.32 0.56 0.73 0.79 |
0.69 1.03 1.36 1.41 |
| After stabilization treatment | 5 weeks later 3 months later 2 years later |
0.20 0:30 0:30 |
0.22 0.26 0.37 |
Due to the pronounced continuous shrinkage phenomenon of zinc alloys, it is recommended to carry out stabilization post-processing (100-120°C, 2-4H) for products with strict size requirements.
V. The role of chemical composition in zinc alloys:
1) Aluminum (Al)
Cast zinc alloys typically contain 3.9-4.3% aluminum. Aluminum increases the strength of castings, but the strength is ideal only at 3.5% and 7.5%.
Meanwhile, the addition of aluminum affects the fluidity of zinc alloy. The fluidity of zinc alloy is better when the aluminum content is 0% and 5%.
Due to the relative contradictions in the impact of aluminum content in zinc alloy castings, the control of aluminum content in zinc alloys is strict. This can be clearly seen in the following two graphs:
1) From the analysis it is evident that in the production process the amount of aluminum mixed with zinc alloy must be strictly controlled.
2) Magnesium (Mg)
Traces of magnesium in zinc alloy can mitigate grain corrosion (microcorrosion) caused by impurities.
However, an excess of magnesium can increase the brittleness of the casting. In production, magnesium tends to burn easily, therefore, the more recycled the production, the lower the magnesium content.
3) Copper (Cu)
The role of copper in zinc alloys is similar to that of magnesium. It can reduce grain corrosion and increase the strength of zinc alloy.
However, if its content exceeds the specified range, the dimensional stability of the casting decreases. Given the high melting point of copper, its content in production must be controlled.
4) Iron (Fe)
The iron in zinc alloy reacts readily with aluminum to produce a compound (FeAl3) that is lighter than zinc and can be removed during slag cleaning.
Iron has no impact on the mechanical properties and pressure casting performance of the casting. However, hard compounds can affect polishing and machining tools.
