Designing for Zinc/Zinc Specifications
Casting components with seven different zinc alloys provides designers with the flexibility needed to meet their design objectives. With a specific gravity of 7.0, Zinc is among the heavier of the common structural metals. When used as a base for die casting zinc is typically alloyed with aluminum, copper and magnesium.
There are four alloys in the conventional zinc group, which are often referred to commercially as the "Zamak" alloys (an acronym for zinc, aluminum, magnesium and copper). These alloys are:
- Zinc 2 - offers the highest strength and hardness. Due to the high copper content, changes to the material properties occur with long-term aging. Changes include slight dimensional growth, lower elongation and reduced impact performance.
- Zinc 3 - is the workhorse alloy and, with its cost advantage over Zinc 5, is the one most frequently specified.
- Zinc 5 - offers high tensile strength, hardness, and better creep resistance than Zinc 3, as well as lower ductility.
- Zinc 7 - is a high purity form of Zinc 3 with higher ductility and lower hardness. Its other mechanical properties are identical to zinc 3. The alloy also exhibits higher fluidity than Zinc 3 or 5, which allows higher production rates and thinner walls.
- The other group of alloys is zinc-aluminum, known as ZA alloys. The number following the hyphen in ZA alloys indicates the approximate aluminum content. The two most common alloys from this group are:
- ZA-8 - with a nominal aluminum content of 8.4% and copper of 1%, has the lowest aluminum content, the lowest melting point and the highest density.. It has the greatest strength of any hot-chamber zinc alloy and the creep resistance of any zinc alloy and it can be chrome plated using the same processes employed for zinc alloys.
- ZA-12 - with a nominalac aluminum content of 11% and copper 1%, has aluminum content higher than ZA-8 and lower than ZA-27. Its properties fall between the two. It can be chrome plated, but the aluminum content makes it advisable to modify somewhat the processes employed for zinc alloys.
- We also use a specialty alloy called ACuZinc, originally developed by General Motors Research and Development engineers. ACuZinc alloys were developed to improve the wear resistance and creep properties in the zinc alloy family. Today there are two ACuZinc alloys: ACuZinc 5 (5% Copper), and ACuZinc 10 (10% Copper), that are used in a variety of automotive applications. ACuZinc 5 is HOT chamber die cast due to its lower melting temperature, whereas ACuZinc 10 is COLD chamber die cast.