Zamak Alloy description
No. 3 alloy is usually the first choice when considering zinc 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 #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 alloy castings are marginally 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. #5
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.
No. 7 alloy is a modification of #3 alloy in which lower magnesium content is specified in order to increase the fluidity. To avoid problems with inter-granular corrosion lower levels of impurities are called for and a small quantity of nickel is specified. Alloy #7 has slightly better ductility than #3 with other properties remaining at the same level.
#7 The alloy is therefore popular for those special cases where the die caster is making thin walled
components requiring a good surface finish. However, research testing has shown that metal and die temperatures have a bigger effect than changing alloys. Close attention to control of the die casting process parameters is important so as to eliminate defects and achieve consistent quality.
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 die casting, 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 (0.0014 in/in/after 20 yrs.), lower elongation and reduced impact performance (to levels similar to aluminum alloys) for die cast products. #2
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. Also, preliminary investigations suggest No. 2 alloy is a good bearing material, and may eliminate bushings and wear inserts in die cast designs.
A good gravity casting alloy, ZA-8 is rapidly growing for pressure die casting. ZA-8 can be hot chamber die cast, with improved strength, hardness and creep properties over ZAMAK's, with the exception of a No. 2 alloy which is very similar in performance. ZA-8 is readily plated and ZA-8 finished using standard procedures for ZAMAK. 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.
ZA-12 is the most versatile zinc alloy in terms of combining high performance properties and ease of fabrication using either gravity or pressure die casting. ZA-12 is the best gravity casting alloy for sand, permanent mold and the new graphite mold casting process. It is also a ZA-12 good pressure die casting 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. ZA-27 is the high strength performer of the zinc alloys whether for gravity or pressure die casting (cold chamber). It is also the lightest alloy and offers excellent bearing and wear resistance properties. ZA-27, however, requires care during melting and casting to assure ZA-27 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.
41 48 41 52 54 58 61 3Ultimate Tensile Strength: psi x 10 (MPa) (283) (328) (283) (359) (374) (400) (421)
32 39 32 41 42 46 55 3Yield Strength - 0.2% Offset: psi x 10 (MPa) (221) (269) (221) (283) (290) (317) (379) Elongation: % in 2" 10 7 13 7 6-10 4-7 1-3
31 38 31 46 40 43 47 3Shear Strength: psi x 10 (MPa) (214) (262) (214) (317) (275) (296) (325) Hardness: Brinell 82 91 80 100 95-110 95-115 105-125
2222333 43 48 43 35 31 21 9Impact Strength: ft-lb (J) (58) (65) (58) (48) (42) (29) (5)
8Fatigue Strength Rotary Bend - 5x10 6.9 8.2 6.8 8.5 15 17 21 3cycles: psi x 10 (MPa) (48) (57) (47) (59) (103) (117) (145)
4 444Compressive Yield Strength 0.1% Offset: 60 93 37 39 52 60873psi x 10(600) (414) (641) (252) (269) (385) (MPa) (414)
66 666Modulus of Elasticity - psi x 10 12.4 12.4 12.412.4- - - 3(MPa x 10(85.5) (85.5) (85.5) ) (85.5)
Poisson's Ratio 0.27 0.27 0.27 0.27 0.29 0.30 0.32
.24 .24 .24 .24 .227 .218 .181 3Density: lb/cu in (g/cm) (6.6) (6.6) (6.6) (6.6) (6.3) (6.0) (5.0)
718-728 717-727 718-728 715-734 707-759 710-810 708-903 Melting Range: ?F (?C) (381-(380-(381-(379-(375-(377-(376-387) 386) 387)