Materials

Discover Our Different Zinc Die-Cast Components

At Connecticut Precision Castings in Claremont, New Hampshire, we use various materials and techniques in producing our small to medium-sized castings. Browse through our website for additional information.

Die-Cast Finishing

Another major advantage that zinc has over other materials is the variety of high-quality surface finishes. Listed below are the various finishes we can offer.

Zinc die-castings offer excellent plating characteristics. Electroplating is generally a multi-layered coating consisting of one or two copper layers, one or two layers of nickel, and a final layer of chromium, brass, gold, or any other palatable metal. Chromium plating is the most popular decorative finish when corrosion and high abrasion resistance are required.

Chromating is a low-cost chemical treatment that provides additional corrosion protection against "white rust." This form of zinc corrosion is caused by prolonged exposure to damp conditions. Chromate finishes are produced by simple dip methods, which deposit a thin chromate coating.

Phosphate coatings are primarily used to provide a good base for painting or powder coating.

Conventional high-luster polishing or brush finishing techniques can produce appearances similar to chrome plating or stainless steel. When lacquered, these finishes are suitable for decorative interior applications.

All zinc alloys form an excellent base for paints. To aid paint adhesion, phosphate or chromate pretreatments are often utilized. Zinc alloys can also be electrostatically painted.

Powder coating involves electrostatic spraying of the zinc castings with an epoxy or polyester powder. The parts are then immediately oven-cured for a hard, durable finish. The result is an even, inexpensive, corrosion-resistant plastic coating. Powder coatings are available in a wide range of colors.

Electrocoating (E-Coat) is the process by which a metal object is subjected to a positive charge while submerged in a solution of deionized water and negatively charged paint ions.

Zinc Alloys

Below is a list of the zinc alloys that Connecticut Precision Castings currently utilizes in their die-casting projects.

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 alloy.

No. 5 alloy castings are marginally stronger and harder than No. 3. However, these improvements are tempered with a reduction in ductility, affecting formability during secondary bending, riveting, swaging, or crimping operations.

No. 7 alloy is a modification of No. 3 alloy in which lower magnesium content is specified to increase the fluidity. To avoid problems with inter-granular corrosion, lower impurities are called for, and a small quantity of nickel is specified.

No. 2 is the only ZAMAK alloy 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.

A good gravity casting alloy, ZA-8 is rapidly growing for pressure die casting. ZA-8 can be a hot chamber die cast with improved strength, hardness, and creep properties over ZAMAK's, except for a No. 2 alloy, which is very similar in performance. ZA-8 is readily plated and 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 its high strength, creep properties, and efficient hot chamber castability.

Die-Cast Selection

Die-Casting vs. Other Processes

Die-Casting vs. Plastic Molding

Die-casting produces stronger parts with closer tolerances with greater stability and durability. Die-cast parts have greater resistance to temperature extremes and superior electrical properties.

Die-Casting vs. Sand Casting or Permanent Mold

Die-casting produces parts with thinner walls, closer dimensional limits, smoother surfaces, or even a pattern finish. Production is faster, and labor costs per casting are lower. Finishing costs are also less.

Die-Casting vs. Forging

Die-casting produces more complex shapes with closer tolerances, thinner walls, and lower finishing costs. Cast coring holes are not available with forging.

Die-Casting vs. Stamping

Die-casting produces complex shapes with variations possible in section thickness. One casting may replace several stampings, resulting in reduced assembly time.

Zinc Die-Cast Advantages

Today's zinc casting alloys are strong, durable, and cost-effective engineering materials. Their mechanical properties compete with cast aluminum, magnesium, bronze, plastics, and most cast iron. Together with their superior finishing capabilities, these characteristics make zinc alloys a preferred material choice for today's industries because they'll save you time and money.

Zinc's superior casting fluidity, strength, and stiffness permit the design of thin wall sections for reduced weight and material cost savings.

Due to the superior net-shape casting capability of zinc die cast alloys, machining can be eliminated or drastically reduced.

Entire assemblies can be cast as a single unit, eliminating the need for expensive manual assembly operations.

Die-cast manufacturing rates for zinc are typically much faster than for aluminum or magnesium. Factor in that tool life will often exceed 1 million casting cycles, tooling, and machine usage charges are dramatically reduced.

Zinc takes less energy to melt with a melting point of only 787°F compared to aluminum's melting point at 1,221°F. This also gives zinc an advantage over aluminum on the recycling end because it takes less time and energy to melt zinc down than aluminum.

Zinc castings come out with a much smoother surface than aluminum castings, making them easier for various finishes. Aluminum castings usually have to be buffed before they can be finished, representing a significant increase in processing costs.

Advantages of Zinc Over Aluminum Die-Casting

If you're considering aluminum die-casting, there are several reasons why zinc die-casting could be a better option for you.

A zinc die's tooling life can be more than 10 times longer than an aluminum die's! Lower casting temperatures for zinc are easier on tools because they create minimal thermal shock and prolong die-casting tool life. With dies costing as much as $40,000 each, having a long-lasting tool can represent significant cost savings.

Zinc is a better conductor of heat than aluminum, making it perfect for applications like heat sinks or electrical components. This means zinc can absorb and dissipate heat better than aluminum.

Zinc melts at 787.2°F, whereas aluminum melts at 1,221°F. This gives zinc an advantage because casting can use a process called "Hot Chamber" casting, which is quicker and less costly than "Cold Chamber" methods.

Using the Hot Chamber process also gives zinc a major advantage over aluminum because the Hot Chamber process goes so much quicker than the Cold Chamber's. In a Cold Chamber, aluminum needs to be manually poured into the die either by hand or using a robot. Using hot chamber casting, the molten liquid zinc is shot into the die using a highly pressurized "plunger" which systematically shoots the zinc through the die.

ZAMAK alloys have exceptional casting fluidity. It's possible to cast walls in ZAMAK as thin as .050 inches. Thinner, stronger walls result in smaller and lighter products with lower costs.

Zinc die casting has tighter tolerances than aluminum or plastic die casting, which often eliminates the need for additional machining. When no additional machining is needed, it's called "Zero Machining" manufacturing. This is one of the major advantages of zinc die casting.

ZAMAK alloys have a better surface for finishing because zinc comes out of casting with smoother skin. Because aluminum has to be hotter than zinc, the thermal shock from being put in a die produces a part with a surface that can be more pitted. The chrome finish amplifies every defect in a part, making zinc much easier to finish than aluminum. Zinc die casts can be easily polished, plated, painted, chromated or anodized.

Zinc alloys are some of the strongest and toughest materials for die casting. Neither plastic, gray cast iron, nor aluminum withstands impacts as well as Zinc alloys do.

ZAMAK alloys have exceptional casting fluidity. It's possible to cast walls in ZAMAK as thin as .25 inches. Thinner, stronger walls result in smaller and lighter products with lower costs.

Zinc die casting has tighter tolerances than aluminum or plastic die casting, which often eliminates the need for additional machining. When no additional machining is needed, it's called "Zero Machining" manufacturing. This is one of the major advantages of zinc die casting.

ZAMAK alloys have a better surface for finishing because zinc comes out of casting with smoother skin. Because aluminum has to be hotter than zinc, the thermal shock from being put in a die produces a part with a surface that can be more pitted. The chrome finish amplifies every defect in a part, making zinc much easier to finish than aluminum. Zinc die casts can be easily polished, plated, painted, chromated or anodized.

Zinc alloys are some of the strongest and toughest materials for die casting. Neither plastic, gray cast iron, nor aluminum withstands impacts as well as Zinc alloys do.

Data Tables

Mechanical Properties

  Zamak 3 Zamak 5 Zamak 7 Zamak 2 ZA-8
Ultimate Tensile Strength: psi x 103 (MPa) 41 (283) 48 (328) 41 (283) 52 (359) 54 (374)
Yield Strength - 0.2% Offset: psi x 103 (MPa) 32 (221) 39 (269) 32 (221) 41 (283) 42 (290)
Elongation: % in 2" 10 7 13 7 6-10
Shear Strength: psi x 103 (MPa) 31 (214) 38 (262) 31 (214) 46 (317) 40 (275)
Hardness: Brinell 82 91 80 100 95-110
Impact Strength: ft-lb (J) 432 (58) 482 (65) 432 (58) 352 (48) 313 (42)
Fatigue Strength Rotary Bend - 5x108 cycles: psi x 103 (MPa) 6.9 (48) 8.2 (57) 6.8 (47) 8.5 (59) 15 (103)
Compressive Yield Strength 0.1% Offset: psi x 103 (MPa) 604 (414) 874 (600) 604 (414) 934 (641) 37 (252)
Modulus of Elasticity - psi x 106 (MPa x 103) 12.46 (85.5) 12.46 (85.5) 12.46 (85.5) 12.46 (85.5) -
Poisson‘s Ratio 0.27 0.27 0.27 0.27 0.29

Physical Properties

  Zamak 3 Zamak 5 Zamak 7 Zamak 2 ZA-8
Density: lb/cu in (g/cm3) .24 (6.6) .24 (6.6) .24 (6.6) .24 (6.6) .227 (6.3)
Melting Range: °F (°C) 718-728
(381-387)		 717-727
(380-386)		 718-728
(381-387)		 715-734
(379-390)		 707-759
(375-404)
Electrical Conductivity: %IACS 27 26 27 25 27.7
Thermal Conductivity: BTU/ft/hr/°F (W/m/hr/°C) 65.3 (113.0) 62.9 (108.9) 65.3 (113.0) 60.5 (104.7) 66.3 (114.7)
Coefficient of Thermal Expansion:68-212°F; μin/in°F
(100-200°C μm/mm/°C)		 15.2 (27.4) 15.2 (27.4) 15.2 (27.4) 15.4 (27.8) 12.9 (23.3)
Specific Heat: BTU/lb/°F (J/kg/°C) .10 (419) .10 (419) .10 (419) .10 (419) .104 (435)
Pattern of Die Shrinkage: in/in .007 .007 .007 .007 .007

Compositions

Chemical Specification (per ASTM) (% by Weight) for ZAMAK Alloys
  Zamak 3 Zamak 5 Zamak 7 Zamak 2
  Ingot Casting Ingot Casting Ingot Casting Ingot Casting
Al 3.9-4.3 3.7-4.3 3.9-4.3 3.7-4.3 3.9-4.3 3.7-4.3 3.9-4.3 3.7-4.3
Mg .03-.06 .02-.06 .03-.06 .02-.06 .01-.020 .005-.020 .025-.05 .02-.06
Cu .10 max .1 max .7-1.1 .7-1.2 .10 max .1 max 2.7-3.3 2.6-3.3
Fe (max) .035 .05 .035 .05 .035 .035 .035 .05
Pb (max) .0040 .005 .0040 .005 .0030 .003 .0040 .005
Cd (max) .0030 .004 .0030 .004 .0020 .002 .0030 .004
Sn (max) .0015 .002 .0015 .002 .0010 .001 .0015 .002
Ni (other)x10 - - - - .005-.020 .005-.020 - -
Zn Bal. Bal. Bal. Bal. Bal. Bal. Bal. Bal.
Chemical Specification (per ASTM) (% by Weight) for ZA Alloys
  ZA-8
  Ingot Casting
Al 8.2-8.8 8.0-8.8
Mg .02-.03 .01-.03
Cu 0.9-1.3 .8-1.3
Fe (max) .035 .075
Pb (max) .005 .006
Cd (max) .005 .006
Sn (max) .002 .003
Ni (other)x10 - -
Zn Bal. Bal.

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