Multi-Slide and Automated Conventional High Pressure Casting

Zamak 2, a predecessor of the more widely used Zamak 3, has the highest strength and hardness in the zinc-4% aluminum (Zamak) alloy family. Because of its relatively high copper content (3%), it is about 25% stronger, as cast, than Zamak 3, and almost 10% stronger than Zamak 5, with higher hardness than either. The high copper content, however, results in property changes upon long term aging. These changes include slight dimensional growth (.0014in/in after 20yrs), lower elongation and reduced impact performance (to levels similar to aluminum alloys) for die cast products. It does, however, provide some interesting characteristics which may assist designers. Its creep performance is rated higher than the other Zamaks and Zamak 2 maintains higher tensile strength and hardness levels after long term aging. Also, preliminary investigations suggest Zamak 2 is a good bearing material and may eliminate bushings and wear inserts in die cast designs. But it does give up impact strength and because of this limitation, Zamak 2 is used only when the strength or hardness of Zamak 3 or 5 are not sufficient for long term end use. Zamak 2 is sometimes referred to as Kirksite and is the only alloy which is used for gravity casting; mainly for metal forming dies or plastic injection tools.

Of all the zinc casting alloys, Zamak 3 is the most widely used, accounting for approx. 85% of all zinc casting tonnage. Its superb physical and mechanical properties, excellent castability and long term dimensional stability provide the basis for its broad usage. The ease with which it can be electroplated adds to the popularity of this alloy, with 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 and is, therefore, the most widely available alloy from die casting sources.

Most often, through casting design procedures, a Zamak 3 pressure die casting can be made to meet service or functional requirements. When this is not the case, especially where strength is concerned, Zamak 5 is the logical choice. Except for a nominal 1% copper addition, the chemistry of Zamak 5 is comparable to that of Zamak 3. This composition modification results in higher tensile strength and increased hardness, but with a sacrifice in elongation. Zamak 5 also has significantly better creep resistance than the other alloys in the conventional group. Zamak 5 is not as ductile as some of the other alloys, a factor to consider when post casting operations such as secondary bending, riveting, swaging or crimping are required. Because of Zamak 3’s wide availability, material specifiers often strengthen components by design modification instead of using Zamak 5. However, when an extra measure of tensile performance is needed, Zamak 5 castings are recommended. The alloy is readily plated, finished and machined, comparable to Zamak 3.

Of all the zinc alloys that can be cast in hot-chamber machines, ZA-8 is the most creep resistant (three times that of Zamak 3) and is the strongest and hardest, with the exception of Zamak 2, which is very similar in performance. It is used principally in structural or highly stressed applications. In spite of its relatively high aluminum content, it can be electroplated using conventional plating techniques and finished using standard procedures for Zamaks. When the performance of standard Zamak 3 or Zamak 5 is in question, ZA-8 is often the die casting choice because of high strength and creep properties and efficient hot chamber castability.