Alloy

NO.3 | NO.5 | NO.7 | NO.2 | ZA-8 | ZA-12 | ZA-27 | ACuZinc 5

NO.3

No. 3 alloy is usually the first choice when considering zinc for diecasting. 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 diecasting. 

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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 formability 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. 

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NO. 7

No. 7 alloy is a modification of No. 3 alloy. Lower magnesium content and tighter impurities specification result in improved casting fluidity, ductility and surface finish. Most No. 7 is used for special hardware applications, or when castings require extra formability during assembly operations. Higher fluidity is sometimes desirable, however, it does present special casting considerations. No. 7 alloy requires good die fit, casting temperature and machine control to avoid excessive flashing along parting lines. Because of high ductility, flash break-off in vibratory and automated deburring equipment is more difficult. Also, better fits on trim dies may be required to obtain a clear trim. 

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NO. 2

No. 2 is the only ZAMAK alloy which is used for gravity casting mainly for metal forming dies or plastic injection tools. This alloy is sometimes referred to as KIRKSITE. For diecasting, No. 2 offers the highest strength and hardness of the ZAMAK family. However, its high copper content (3%) results in property changes upon long-term aging. These changes include slight dimensional growth (0.00 14 in./in./ after 20 yrs.); lower elongation and reduced impact performance (to levels similar to aluminum alloys) for die cast products. , Although No. 2 alloy exhibits excellent castability it has seen limited use by die casters in North America. It does, however, provide some interesting characteristics which may assist designers. Its creep performance is rated higher than the other ZAMAKS and No. 2 maintains higher strength and hardness levels after long-term aging. Preliminary investigations suggest No. 2 alloy is a good bearing material, and may eliminate bushings and wear inserts in die cast designs. 

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ZA-8

A good gravity casting alloy, ZA-8 is rapidly growing for pressure diecasting. ZA-8 can be hot chamber die cast with improved strength, hardness and creep properties over ZAMAKS, with the exception of a No. 2 alloy which is very similar in performance. ZA-8 is readily plated and finished using standard procedures for ZAMAKS. When the performance of standard No. 3 or No. 5 is in question, ZA-8 is often the die casting choice because of high strength and creep properties and efficient hot chamber castability. 

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ZA-12

ZA-12 is the most versatile zinc alloy in terms of combining high performance properties and ease of fabrication using either gravity or pressure diecasting. ZA-12 is the best gravity casting alloy for sand, permanent mold and the new graphite mold casting process. It is also a good pressure diecasting alloy (cold chamber), which provides a sounder structure than ZA-27, as well as higher die cast elongation and impact properties. For these reasons die cast ZA-12 often competes with ZA-27 for strength application. An excellent bearing alloy, ZA-12 is also platable, although plating adhesion is reduced compared to the ZAMAK alloys. 

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ZA-27

ZA-27 is the high strength performer of the zinc alloys whether for gravity or pressure diecasting (cold chamber). It is also the lightest alloy and offers excellent bearing and wear resistance properties. ZA-27, however, requires care during casting to assure sound internal structure, particularly for heavy wall sections. It may also need a stabilization heat treatment when tight dimensional tolerances are required. ZA-27 is not recommended for plating. However, when brute strength or wear resistant properties are needed ZA-27 has demonstrated extraordinary performance. 

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ACuZinc 5

ACuZinc 5 is a member of the new patented family of zinc casting alloys developed at the General Motors Research and Development Center. Parts may be produced in ACuZinc 5 using the highly cost-effective hot chamber diecasting process. ACuZinc 5 exhibits excellent strength, hardness and creep properties. 

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