Zinc Alloy Die Casting Basics You Should Know

Zinc Alloy Die Casting Basics You Should Know

I. Characteristics of Die Casting with Zinc Alloys

Zinc alloys exhibit superb mechanical and electroplating properties. The surface roughness, strength, and ductility of die-cast zinc alloy parts are all excellent.

Due to the exceptional fluidity of zinc, it can be used to create thinner products, with wall thicknesses achievable down to 0.5mm.

The primary drawback of zinc is its high density, which results in heavier and more costly products, making it more suitable for small parts. Additionally, zinc alloys lack dimensional stability.

1) Density:

  • Pure zinc: 6.6g/cm3;
  • Die-cast zinc alloy: 6.7-6.9g/cm3;

2) Melting point:

  • Pure zinc: 419°C;
  • Zinc alloy: 387-390°C;
  • Die casting temperature: 390-410°C

3) The most commonly used die-cast zinc alloy is ZAMAK 3.

II. Models of Die-Cast Zinc Alloys

The international standards and models corresponding to ZAMAK 3 are as follows:

United KingdomBS:1004-1972 Alloy A
United StatesASTM:B240-74 Alloy AG40A; SAE:903
JapanJIS:H2201 Na 2(ZDC2)
GermanyDIN 1743:1978 GB ZN A14
AustraliaAS 1881-1977 Zn A14
TaiwanCNS: ZAC1
ChinaGB: Z ZnAl4

III. Composition of Die-Cast Zinc Alloys

The chemical compositions of several commonly used zinc alloys are as follows:

 ZAMAK 2ZAMAK 3ZAMAK 5
Al3.8-4.23.8-4.23.8-4.2
Cu2.7-3.3≤0.0300.7-1.1
Mg0.035-0.060.035-0.060.035-0.06
Pb≤0.03≤0.003≤0.003
Fe≤0.020≤0.020≤0.020
Cd≤0.003≤0.003≤0.003
Sn≤0.001≤0.001≤0.001
Si≤0.02≤0.02≤0.02
Ni≤0.001≤0.001≤0.001

IV. Dimensional Stability of Zinc Alloys

Zinc alloy products will continuously shrink after molding, stabilizing essentially after six months. The shrinkage of zinc die castings is as follows:

Casting ProcessingTimeAlloy No. 3
mm/m
Alloy No. 5
mm/m
Standard Aging Variation5 weeks later
6 months later
5 years later
8 years later.
0.32
0.56
0.73
0.79
0.69
1.03
1.36
1.41
After Stabilization Treatment5 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 perform 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)

Die-cast zinc alloys typically contain 3.9-4.3% aluminum. Aluminum enhances the strength of the castings, but the strength is optimal only at 3.5% and 7.5%.

Meanwhile, the addition of aluminum affects the fluidity of the zinc alloy. The fluidity of the zinc alloy is best when the aluminum content is 0% and 5%.

Due to the relative contradictions in the impact of aluminum content on zinc alloy castings, the control of aluminum content in zinc alloys is strict. This can be clearly seen from the following two charts:

1) From the analysis, it is evident that in the production process, the amount of aluminum mixed into the zinc alloy should be strictly controlled.

2) Magnesium (Mg)

Trace amounts of magnesium in the zinc alloy can mitigate grain corrosion (micro-corrosion) caused by impurities.

However, an excess of magnesium can increase the brittleness of the casting. In production, magnesium tends to burn off easily, so 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 the zinc alloy.

However, if its content exceeds the specified range, the dimensional stability of the casting decreases. Given copper’s high melting point, its content in production should be controlled.

4) Iron (Fe)

Iron in zinc alloy readily reacts 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 die-casting performance of the casting. However, hard compounds can affect polishing and machining tools.

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Shane
Author

Shane

Founder of MachineMFG

As the founder of MachineMFG, I have dedicated over a decade of my career to the metalworking industry. My extensive experience has allowed me to become an expert in the fields of sheet metal fabrication, machining, mechanical engineering, and machine tools for metals. I am constantly thinking, reading, and writing about these subjects, constantly striving to stay at the forefront of my field. Let my knowledge and expertise be an asset to your business.

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