Zinc Aluminum (ZA) alloys are modified zinc alloys with higher levels of aluminum than in traditional zinc alloys. The percentage of aluminum mixed in the zinc is greater than can remain in solution at normal casting temperatures.
The ZA number is the approximate percentage of aluminum included (i.e. ZA27 has 27% AL). The aluminum having less than half the density of zinc tends to rise to the surface of the metal bath. Because of this there is a need to agitate the material while in its molten state to ensure the consistent composition during casting. This makes it more difficult to cast as well as a more expensive raw material.
ZA is a very high performance alloy in terms of strength and hardness. It is stronger and has better wear resistance than either zinc or aluminum alloys.
ZA 12 is an alloy with good die casting characteristics with 20-25% greater strength and hardness than typical aluminum alloys. It requires periodic agitation during its molten state and special foundry practice during transfer and melting. It is widely used for structural castings where high tensile and shear strength is worth the extra expense of the material and labor involved. Being a composite of aluminum (11%) and zinc its density approximately double that of aluminum and a quarter less than zinc. It can sometimes be used to replace bronze bearing/die casting assemblies by eliminating the need for an inserted bearing. ZA should only be used where the additional cost and weight are out weighed by the increased mechanical performance.
ZA 27 is the strongest of the ZA series. It is extremely difficult to handle and has poor die filling characteristics, which can be offset somewhat by simplifying the casting design. Frequently surface defects are common on ZA 27 castings. It has 30-45% greater strength and hardness than typical aluminum die cast alloys. Its density is less than double that of aluminum (27% of its composition is aluminum). We advise against its use unless strength is the most important criteria of product performance.