Zinc Alloys

Choosing A Zinc Alloy For Miniature Die Casting

ZAMAK # 2
This is the only ZAMAK alloy used for gravity casting; mainly for metal forming dies or plastic injection tools. It is sometimes referred to as KIRKSITE. For die casting, it offers the highest strength and hardness of the ZAMAK family, but long-term aging applications should be reviewed. It has some interesting characteristics that may assist designers. Its creep performance is rated higher than any of the commercially available ZAMAKS (EZAC- High Creep Resistance Alloy still in development), and it maintains a higher strength and hardness level after which makes it a very good choice for bearing applications.

ZAMAK # 3
Usually the first choice when considering zinc for die casting, ZAMAK # 3 offers an excellent balance of desirable physical and mechanical properties, superb castability and long-term dimensional stability. No. 3 also offers excellent finishing characteristics for plating, painting and chromate treatments. It is the "standard" by which other zinc alloys are rated in terms of die casting.

ZAMAK # 5
The addition of 1% copper makes castings from ZAMAK # 5 marginally stronger and harder than # 3, but also causes a reduction in ductility, which can affect formability during secondary bending, riveting, swaging or crimping operations. The # 5 alloy offers excellent castability characteristics and improved creep performance over # 3. Because of # 3's wide availability, material specifiers often strengthen components by design modifications instead of using # 5. However, when an extra measure of tensile performance is needed, # 5 alloy castings are recommended. The alloy is readily plated, finished and machined.

ZAMAK # 7
A modification of # 3 alloy, # 7 has a lower magnesium content to increase fluidity. To avoid problems with intergranular corrosion, lower levels of impurities are called for and a small quantity of nickel is specified. Alloy # 7 has slightly better ductility than # 3 with other properties being comparable. Traditionally the alloy is popular for casting thin-walled components requiring good surface finish. Note, however, that research testing has shown metal and die temperatures have a bigger effect than changing alloys. Close attention to control of the die-casting process parameters is important to eliminate defects and achieve consistent quality.

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