Zinc
pressure die casting alloys
Originally
developed in the 1930's, zinc casting
alloys are made from high purity zinc, combined with small amounts
of aluminum, magnesium, and sometimes, copper. These
small amounts of alloying materials transform zinc, which in
its pure form is a brittle, low-strength metal, into an engineering
material, with high strength and hardness, good ductility and
excellent castability. The physical and mechanical properties
of zinc alloys can be negatively affected by impurities, so
international specifications have been developed for zinc die
casting alloys, insuring consistent chemical quality.
Zinc casting alloys were originally used in decorative and non-structural
applications, but over the last several decades have gained
acceptance as a material for engineered components and structures.
The castability and strength of zinc alloys
provide excellent design flexibility, expanding the capabilities
of the die casting process.
Mechanical properties (strength and ductility) are comparable,
or even superior, to many other cast materials such as aluminum,
magnesium, brass and cast iron. Zinc alloys
have good bearing and wear resistance; performing like
traditional bronze bearing alloys in both dry and lubricated
conditions. Zinc alloys perform exceptionally well under conditions
of moderate, continuous loading (like threaded connections)
or short term, high stresses. These alloys are typically not
used in applications where high continuous stresses or elevated
temperatures are encountered.
Zinc alloys are corrosion resistant
under normal atmospheric conditions, in neutral to alkaline
pH aqueous solutions and in contact with petroleum products.
Like many other metals, the use of chromate or phosphate dip
coatings enhances corrosion resistance.
The commonly used zinc alloys (normally referred to as #3, #5,
or #7) have a unique combination of properties
that allow for rapid, cost-effective production of strong,
durable and accurate components. In comparison to other non-zinc
die casting alloys (such as aluminum and magnesium), they are
more easily cast, require less finishing, can be held to tighter
tolerances, are cast in thinner sections and are generally superior
in strength and hardness. Zinc alloy die castings are stronger,
tougher and more dimensionally stable than injection
molded plastics. The development of a family of high strength
(ZA) zinc alloys in the 1970's created the opportunity for expanded
zinc pressure die casting use in higher performance applications,
replacing cast iron, brass and bronze.
Zinc alloys are environmentally sound.
They require less energy to convert from ore to ingot to finished
product than most competing materials. When properly handled,
zinc alloys do not create airborne pollutants or toxic waste
products. An infrastructure is actively in place to recycle
zinc by-products and cast zinc alloy products at the end of
their useful life.
