01One element apart, more than one consequence
Zamak 3 and Zamak 5 are often treated as interchangeable zinc alloys because both are widely available, easy to die cast, and suitable for detailed parts. That shortcut can create problems after tooling: a housing may creep under load, a cosmetic part may show a different plating response, or a tight assembly may move more than expected over time. The difference is mainly chemistry, but the engineering consequences are broader. Zamak 3 contains only a small amount of copper, while Zamak 5 contains roughly 0.7–1.2% copper. That extra copper generally increases strength, hardness, wear resistance, and creep resistance. It also reduces ductility and can change dimensional and property stability. For a buyer, the right question is not “Which grade is stronger?” It is “Does this part need the extra strength enough to accept the trade-offs in ductility, stability, and cost?” This article connects NADCA data with tooling, machining, finishing, inspection, and supplier selection.
02What Zamak means
According to the 2024 NADCA Product Specification Standards, Zamak is the traditional zinc alloy family containing nominally 4% aluminum plus a small amount of magnesium. The aluminum supports castability and strength; magnesium improves strength and hardness and helps protect against intergranular corrosion. Zinc remains the balance of the composition. Zamak alloys are normally cast on rapid-cycling hot-chamber machines. NADCA notes that zinc allows thin sections, close tolerances, high impact strength, long die life, and reduced die maintenance. These benefits suit miniature hardware, knobs, brackets, housings, decorative fittings, and parts with cast-in detail.
03Composition comparison
The following values are from NADCA Table A-3-13. Single values are maximum limits unless a range is shown. According to NADCA, the higher copper content of Zamak 5 strengthens the alloy and improves wear resistance, but reduces dimensional and property stability. NADCA describes Zamak 3 as the most widely used zinc alloy in North America because of its balance of properties, castability, and economics. The alloy names on international drawings may vary. A supplier may quote “Zamak 3,” “Zinc No. 3,” or “AG-40A”; these refer to the same NADCA/ASTM family designation. The same applies to “Zamak 5,” “Zinc No. 5,” and “AG-41A.” The purchase order should still state the governing standard and chemical limits rather than relying on a trade name alone.
| Element | Zamak 3 / No. 3 / AG-40A | Zamak 5 / No. 5 / AG-41A | Why it matters |
|---|---|---|---|
| 铝 Al / Aluminum | 3.7–4.3% | 3.7–4.3% | 支撑锌铝压铸组织 / Supports the zinc-aluminum die-casting structure |
| 镁 Mg / Magnesium | 0.02–0.06% | 0.02–0.06% | 强度、硬度与防腐蚀 / Strength, hardness, and corrosion protection |
| 铜 Cu / Copper | ≤ 0.10% | 0.7–1.2% | 主要差异：提高强度、硬度、耐磨与抗蠕变 / Main differentiator; raises strength, hardness, wear and creep resistance |
| 铁 Fe / Iron | ≤ 0.05% | ≤ 0.05% | 保持低含量以保护延展性与铸件质量 / Kept low to protect ductility and casting quality |
| 铅 Pb / Lead | ≤ 0.005% | ≤ 0.005% | 为合规与长期稳定而受控 / Controlled for compliance and long-term stability |
| 镉 Cd / Cadmium | ≤ 0.004% | ≤ 0.004% | 为合规而受控 / Controlled for compliance |
| 锡 Sn / Tin | ≤ 0.002% | ≤ 0.002% | 痕量污染即可影响性能，须极低 / Kept very low because trace contamination can affect performance |
| 锌 Zn / Zinc | 余量 / Balance | 余量 / Balance | 基体金属 / Base metal |
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04Typical material performance
According to NADCA Table A-3-14, the typical values below are based on separately die-cast specimens, not specimens cut from production castings. The pattern is clear: Zamak 5 is stronger and harder, while Zamak 3 retains more elongation and is generally more forgiving under impact, bending, press-fit variation, or assembly stress. The aged values also show why the buyer must define the test condition; as-cast and aged values are not interchangeable. NADCA rates both alloys highly for casting ease, part complexity, machining, polishing, electroplating, anodizing protection, and chemical coating protection. Zamak 3 receives a more favorable pressure-tightness rating than Zamak 5, while both are rated similarly for dimensional accuracy and corrosion resistance. These ratings are selection guidance, not a guarantee that every geometry will be pressure tight or dimensionally stable without process control.
| Property | Zamak 3 as-cast | Zamak 3 aged | Zamak 5 as-cast | Zamak 5 aged |
|---|---|---|---|---|
| 抗拉强度 / Ultimate tensile strength | 283 MPa | 241 MPa | 331 MPa | 269 MPa |
| 屈服强度（0.2%）/ Yield strength, 0.2% offset | 221 MPa | 224 MPa | 228 MPa | 245 MPa |
| 伸长率（51 mm 标距）/ Elongation in 2 in. (51 mm) | 10% | 16% | 7% | 13% |
| 硬度 / Hardness | 82 BHN | 72 BHN | 91 BHN | 80 BHN |
| 密度 / Density | 6.6 g/cm³ | 6.6 g/cm³ | 6.6 g/cm³ | 6.6 g/cm³ |
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05Why this matters in real production
The copper difference matters when the part carries a sustained load. Zamak 5 is often preferred for gears, latches, brackets, lever arms, and gearbox housings where hardness, wear resistance, or creep resistance matters. It may allow a thinner section, but the design still needs radii, uniform transitions, and a realistic load path. Zamak 3 is often the safer choice for general housings, decorative hardware, fittings, and complex thin-wall parts where castability, ductility, appearance, and cost dominate. It is the normal baseline for a general-purpose Zamak callout. Dimensional behavior deserves special attention. NADCA notes that additional copper can reduce Zamak 5's dimensional and property stability. The supplier should validate geometry, cooling pattern, aging condition, and inspection timing, especially for cover fits, bearing seats, snaps, and threaded interfaces. Surface finishing is another reason to specify the grade early. NADCA considers both Zamak 3 and Zamak 5 very good for polishing, electroplating, anodizing protection, and chemical coating protection. However, a bright chrome finish still depends on die steel condition, surface porosity, trimming, polishing sequence, pretreatment, and bath control. The alloy does not compensate for poor casting or an undefined cosmetic acceptance sample. Zinc's low melting and injection temperatures affect total cost. Hot-chamber production can deliver fast cycles and long die life, but the die, plunger, gooseneck, metal temperature, and lubrication system must match the alloy and part size. Chemistry cannot rescue a poor gate layout or unstable settings.
06From our experience: riveting, polishing, ageing and the ZA alloys
If the part will be bent, riveted, crimped or hemmed in assembly — anything that plastically deforms the metal — we normally recommend Zamak 3. Seven per cent against ten per cent elongation does not sound decisive, but in a riveting operation, where the deformation is local and large, those few points can be the line between cracking and not cracking. One situation we have met: Zamak 5 was chosen for strength, the riveting station started cracking parts, a long time went into fixtures and rivet settings, and the answer turned out to be the grade. Asked at selection, the question takes a sentence. A second consideration on cosmetic parts is polishing time. In our experience Zamak 5 is harder and takes longer to bring to the same mirror; on a part that needs a mirror or high-gloss finish, that labour difference can exceed the difference in metal price. On a satin, painted or matt finish the gap largely disappears. On precision parts with fits of a few tens of microns, we plan a stabilising treatment into the process from the start — we commonly use three to six hours at 100 ℃ — so the dimensional movement happens before finishing and final inspection. It costs little, but adding it afterwards disrupts the schedule. If Zamak 5 still is not strong enough, in our experience the next step is to evaluate the ZA alloys, or to cost the aluminum alternative in full. On our tooling figures a ZA-8 die runs around 300,000–600,000 shots and a ZA-12 die around 150,000–300,000, clearly shorter than Zamak; much of zinc's cost advantage goes, and the answer is often aluminum.
| Condition | We usually suggest | Why |
|---|---|---|
| 后续需铆接 / 折弯 / 压接 / Riveted, bent or crimped later | Zamak 3 | 伸长率更高 / Higher elongation |
| 镜面电镀外观件 / Mirror-plated cosmetic part | Zamak 3 | 抛光工时更低 / Less polishing time |
| 长期承载、抗蠕变 / Sustained load, creep | Zamak 5 | 铜提高抗蠕变性 / Copper raises creep resistance |
| 齿轮、滑块等耐磨件 / Gears, sliders, wear parts | Zamak 5 | 硬度更高 / Higher hardness |
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07Common mistakes
Choosing Zamak 5 only because it has a higher tensile number. If the real failure mode is impact, snap breakage, or assembly cracking, the lower ductility may make Zamak 5 the wrong choice. Treating Zamak 3 as “soft” and unsuitable for functional parts. It still provides useful strength, hardness, impact performance, and excellent castability. Ignoring creep and sustained load. A part that passes a short tensile test can still move under constant load at temperature. Gearbox covers, levers, clips, and threaded bosses need a creep review. Assuming the trade name is a complete specification. State No. 3 or No. 5, the governing standard, chemistry limits, as-cast or aged condition, and any RoHS or customer restrictions. Reusing the same dimensional tolerance without validation. Die temperature, cooling, ejection, section thickness, aging, and inspection timing can affect the result. A table value is a starting point, not a capability guarantee. Approving a surface finish from a flat test coupon only. The real casting may have gate scars, parting lines, ejector marks, polishing direction, and local porosity. Approve a representative production sample.
08Our typical approach
An experienced supplier does not begin with “Zamak 3 is cheaper” or “Zamak 5 is stronger.” The supplier maps failure modes, load duration, cosmetic requirements, wall thickness, tooling plan, and volume first. Zamak 3 is the default for balanced cost and castability; Zamak 5 is selected when copper's measurable benefit is worth the reduced ductility and stability margin. First, define the load case. We identify impact, static or repeated load, wear, temperature, vibration, and press-fit or thread assembly. Sustained stress receives a creep check, not a tensile-only review. Second, compare the two alloys against the geometry. We review wall thickness, ribs, bosses, draft, slides, gate location, overflow, and ejection. If Zamak 5 enables a thinner section, we confirm that the new geometry does not create a difficult fill or a distortion problem. Third, define condition and inspection timing. We record as-cast or aged status, measurement timing, and whether strength data comes from a coupon, separately cast bar, or the part. Fourth, validate finishing. For polished, plated, painted, or chemically coated parts, we approve a representative sample covering trimming, pretreatment, coating thickness, adhesion, appearance, and corrosion testing where required. Fifth, control material and process changes. Copper level, ingot supplier, remelt practice, metal temperature, shot profile, die temperature, lubricant, aging time, and finishing chemistry are controlled variables. A change that appears small on a certificate can still affect fit, appearance, or long-term movement.
09Questions buyers should ask
1. Is the requested alloy Zamak 3 / No. 3 / AG-40A or Zamak 5 / No. 5 / AG-41A, and which standard governs it? 2. What copper range will be certified, and what are the limits for Al, Mg, Fe, Pb, Cd, Sn, and other restricted elements? 3. Is the part exposed to sustained load, elevated temperature, wear, impact, or vibration? 4. Should the requirement be evaluated in the as-cast condition or after natural/artificial aging? 5. Which dimensions are most sensitive to long-term movement or inspection timing? 6. Does the design depend on pressure tightness, and what leak test and acceptance limit will apply? 7. Which surfaces are cosmetic, polished, plated, painted, or chemically coated? What sample defines acceptance? 8. Where are the gates, overflows, parting lines, and ejector marks relative to functional and cosmetic features? 9. What evidence will be supplied at first article: chemistry, dimensions, hardness, mechanical tests, coating tests, or sectioning? 10. What changes require written approval before production continues? These questions turn “Zamak 3 versus Zamak 5” into a controlled engineering decision. They also let buyers compare quotations on performance and risk, not only on unit price.
SOURCES AND NOTE
- [1]North American Die Casting Association (NADCA). NADCA Product Specification Standards for Die Castings: Aluminum, Aluminum-MMC, Copper, Magnesium, Zinc and ZA Alloys, 12th edition, revised for 2024. Section 3, Zinc and ZA Alloys, pp. 3-12 to 3-15; Tables A-3-13, A-3-14, and A-3-15.
- [2]North American Die Casting Association (NADCA). Product Design for Die Casting: In Recyclable Aluminum, Magnesium, Zinc and ZA Alloys, 7th edition. Guidance used for alloy selection, zinc die-casting design, dimensional control, machining, and finishing.
- [3]North American Die Casting Association (NADCA). Introduction to Die Casting. Background used for zinc die-casting process and production considerations.
This is a technical introduction and design guide, drawing on the sources listed above and on Jinxiong's many years of production practice. It is for reference only and is not a commitment for any specific project. For a specific project, the technical agreement between both parties governs.
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