Zinc Die Casting
Zinc-base alloys were introduced in the late 1920’s to meet the demand for strong, stable die castings. These alloys, familiarly known as the Zamak or Mazak alloys, show a unique combination of properties which permit rapid, economic casting of strong, durable, accurate parts, and hence have dominated the market since their inception. They have many advantages over other die casting materials, such as aluminum alloys. Lowest in cost among metals most commonly used in die casting, zinc alloys are more easily cast, are stronger and more ductile, require less finishing, can be held to closer tolerances and can be cast in thinner sections. Because of low casting temperatures, die life for zinc die castings far exceeds that for other die cast metals.
Die casting with zinc-base alloys is one of the most efficient and versatile production methods which can be used for the manufacture of accurate, complex and detailed metal components. In general, the mechanical properties of zinc alloy die castings at normal temperatures are superior to sand castings of grey iron, brass and aluminum, particularly in toughness and impact strength. They are much stronger, tougher and more dimensionally stable than injection molded plastics. Many components normally manufactured in iron, copper, or aluminum alloys, or in plastics, can be produced as zinc alloy die castings and show improved properties, often at reduced cost.
Zamak 3, the standard IMG zinc alloy, is characterized by excellent retention of impact strength and long-term dimensional stability. It has been used for decades in a multitude of engineering applications and the properties and performance are excellent. The alloy 3 is die cast in a hot chamber die casting machine; that is, one in which the injection plunger sleeve and gooseneck are continuously immersed in molten zinc in the machine pot or furnace.
During the 1970’s, thin wall die casting techniques were developed. The term “thin wall,” when applied to zinc alloy die castings, is used to identify the minimum wall thickness required for an intended application. Thin wall casting technology is particularly valuable under circumstances where weight must be reduced while still retaining the advantages of zinc alloy die castings. Faster production rates can be achieved, resulting in improved cost-effectiveness.
Thin wall castings have significant increases in fracture resistance and toughness over castings with thicker sections because they are better able to withstand the complex stresses encountered during assembly and the types of static and intermittent loadings that may be encountered in service. These increases are due to the so-called “chilled skin” which is found on all die castings. This dense surface layer produces higher mechanical properties in thin wall castings than in thick wall castings where the center porosity and microshrinkage can cause poorer mechanical properties. Thin wall castings are almost entirely “chilled skin.” Besides the healthy cost savings directly related to the reduced wall sections, zinc also provides a familiar success story - "faster and more economical production...longer die life...less rejects."