ZAMAK: Zinc Alloys With Great Design Flexibility and Cost Effectiveness

Zinc Alloys

Zinc can be alloyed with metals such as aluminum, magnesium, copper, lead, and cadmium, usually at a content less than 1%, due to the metals' extremely low solubility level. Larger

concentrations of iron, lead, cadmium and tin could have an adverse effect on corrosion resistance which results in structural weakening of the die casting [1]. Two types of zinc alloys, ZAMAK (Zinc-Aluminum-MAgnesium-Kupfer... German for Copper) and ZA (Zinc-Aluminum) were developed during the 1920's and 1970's, respectively. The ZAMAK alloys contain ~ 4% aluminum and are widely used for casting automotive, motorbike, and electrical parts as well as in the manufacturing of household products including door and window frames, hinges and bathroom accessories. The ZAMAK alloys are identified by their numbers 3, 5, 7.

COMPOSITION	ZAMAK 3	ZAMAK 5	ZAMAK 7
Aluminum %	3.9 - 4.3	3.9 - 4.3	3.9 - 4.3
Magnesium %	0.025 - 0.050	0.03 - 0.06	0.01 - 0.02
Copper %	0.10 max.	0.75 - 1.25	0.10 max.
Iron (Max.) %	0.075	0.075	0.075
Lead (Max.) %	0.004	0.004	0.002
Cadmium (Max.) %	0.003	0.003	0.002
Tin (Max.) %	0.002	0.002	0.001
Nickel %			0.005 - 0.020
Zinc %	Balance	Balance	Balance
Source: Pe�oles, S.A. de C.V [2].

There are only two Zinc alloys, AG 40A ( ~ ZAMAK 3 ) and AC 41A ( ~ ZAMAK 5), covered by ASTM (American Society for Testing and Materials) specification B86. In comparison to ZAMAK alloys, ZA (Zinc-Aluminum) alloys, ZA-8 and ZA-27, contain a much higher percentage of aluminum ( between 8 and 27 % ) and copper (up to 2.5%). Therefore, the ZA alloys are much lighter and possess superior mechanical properties to the ZAMAK alloys, both in tensile strength and hardness.

ZAMAK Die Casting

ZAMAK die casting can be quite inexpensive due to the fact that the casting operation is done at low temperatures and hence the casting mold can be used continuously for years

without degradation due to thermal fatigue or liquid metal erosion [1]. The casting is performed by injecting molten ZAMAK alloy into a casting die or mold under high pressure and at a controlled temperature. The casted part is then rapidly cooled and removed from the mold. Over 70% of all North American zinc die castings are done using ZAMAK 3 alloy, because parts having close tolerances, complex details, and thin wall sections can be economically produced [3]. ZAMAK 3 alloy also offers excellent finishing characteristics for plating, painting and chromate treatments.

ZAMAK 5 alloy casting, which is widely used in European countries, has the highest impact strength, approximately 10% higher tensile strength, but is less ductile than ZAMAK 3 alloy casting due to an addition of 1% copper. The fact that the ZAMAK 3 alloy is widely availabile and costs less than ZAMAK 5, a design modification to strengthen a part using ZAMAK 3 alloy is often recommended, instead of using the ZAMAK 5 alloy with a higher strength.

REFERENCES

[1] Kenneth Budinski, Engineering Materials: Properties & Selection, Prentice-Hall, Virginia, USA 1979.
[2] Pe�oles, S.A. de C.V, Mexico.
[3] Eastern Alloys, Maybrook, New York, USA

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About the Author: Dr. Ed Wijaranakula is the Chief Technical Officer and co-founder of Infotix Systems, Inc. Prior to Infotix Systems, he has worked with Intel, Hewlett-Packard and Texas Instruments and has held senior as well as managerial positions in semiconductor manufacturing companies and worked at Daimler-Chrysler and Air Bus in Germany. He has a Ph.D. in Materials Science and Engineering and published over 80 technical papers. He holds 12 U.S. and foreign patents.