Zinc Casting Alloys

This guide is to help designers and material specifiers to better understand the capabilities of zinc casting alloys for product applications.

• Descriptions

ADVANTAGES

Zinc casting alloys are versatile engineering materials. No other alloy system provides the combination of strength, toughness, rigidity, bearing performance and economical cast ability. Listed are zinc alloy attributes which can reduce component costs. Improving precision, quality and product performance are other zinc alloy design advantages discussed bellow.

Process Flexibility:

Virtually any casting process can be used with zinc alloys to satisfy virtually any quantity and quality requirement. Precision, high-volume die casting is the most popular casting process. Zinc alloys can also be economically gravity cast for lower volumes using sand, permanent mold, graphite mold and plaster casting technology.

Precision Tolerances:

Zinc alloys are castable to closer tolerances than other metals or molded plastics, therefore presenting the opportunity to reduce or eliminate machining. "Net Shape" or "Zero Machining" manufacturing is a major advantage of zinc casting.

Strength & Ductility:

Zinc alloys offer high strengths (to 60,000 psi) and superior elongation for strong designs and form ability for bending, crimping and riveting operations.

Toughness:

Few materials provide the strength and toughness of zinc alloys. Impact resistance is significantly higher than cast aluminum alloys, plastics, and grey cast iron.

Rigidity:

Zinc alloys have the rigidity of metals with modulus of elasticity characteristics equivalent to other die castable materials. Stiffness properties are therefore far superior to engineering plastics.

Anti-Sparking:

Zinc alloys are non sparking and suitable for hazardous location applications such as coal mines, tankers and refineries.

Bearing Properties:

Bushing and wear insert in component designs can often be eliminated because of zinc's excellent bearing properties. For example, zinc alloys have outperformed bronze in heavy duty industrial applications.

Easy Finishing:

Zinc castings are readily polished, plated, painted, chromated or anodized for decorative and/or functional service.

Thin Wall Castability:

High casting fluidity regardless of casting process allows for thinner wall section to be cast in zinc compared to other metals.

Machinability:

Fast, trouble-free machining characteristics of zinc materials minimize tool wear and machining costs.

Low Energy Costs:

Because of their low melting temperature, zinc alloys require less energy to melt and cast versus other engineering alloys.

Long Tool Life:

Low casting temperatures result in less thermal shock and therefore extended life for die casting tools. For example, tooling life can be more than 10 times that of aluminum dies.

Clean and Recyclable:

Zinc alloys are among the cleanest melting materials available. Zinc metal is non-toxic and scrap items are a reusable resource which are efficiently recycled.

ZINC ALLOYS

There are two basic families of zinc casting alloys: ZAMAK alloys and ZA alloys. The ZAMAK alloys were developed for pressure die casting during the 1920's and have seen widespread usage since then. It is for this reason that specifiers often relate zinc as synonymous with die casting. However, the development of the ZA (Zinc-Aluminum) alloys during the 1970's have radically changed zinc's product design and manufacturing capabilities.

ZA alloys were initially developed for gravity casting. Their mechanical properties compete directly with bronze, cast iron and aluminum using sand, permanent mold and plaster mold casting methods. Distinguishing features of the ZA alloys are their high aluminum content and excellent bearing properties.

During the 1980's, ZA alloys evolved as valuable die casting materials. It is important to note that when considering a ZA alloy for die casting, only ZA-8 can be hot chamber die cast. Hot chamber casting (which the ZAMAK alloys employ) is highly automated and the most efficient die casting process. ZA-12 and ZA-27 require special melting procedures and must be die cast like aluminum using the less efficient cold chamber die casting process. A brief description of each alloy is provided The ZAMAK alloy family is identified by their numbers 3, 5, 7, & 2. ZA alloys consist of ZA-8, ZA-12 and ZA-27.

NO.3

No. 3 alloy is usually the first choice when considering zinc for die casting. Its excellent balance of desirable physical and mechanical properties, superb castability and long-term dimensional stability are the reasons why over 70% of all North American zinc die castings are in No. 3 alloy. It is therefore the most widely available alloy from die casting sources. ZAMAK No. 3 also offers 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.

NO. 5

No. 5 alloy castings are stronger and harder than No. 3. However, these improvements are tempered with a reduction in ductility which can affect form ability during secondary bending, riveting, swaging or crimping operations. No. 5 contains an addition of 1% copper which accounts for these property changes. The alloy is widely die cast in Europe and does exhibit excellent castability characteristics as well as improved creep performance over No. 3. Because of No. 3's wide availability, material specifiers often strengthen components by design modifications instead of using No. 5. However, when an extra measure of tensile performance is needed, No. 5 alloy castings are recommended. The alloy is readily plated, finished and machined comparable to No. 3 alloy.

ALLOY SELECTION GUIDE

Numerous factors influence material selection. Most important are mechanical properties, choice of casting process, and manufacturing characteristics. Rated are the general design features of zinc alloys, which can influence material selection.