Three zinc alloys dominate small precision die casting: Carichi 3, Carichi 5, e Zamak 7. They share roughly 96% zinco e 4% alluminio, yet the copper and magnesium adjustments between them create meaningful differences in strength, formabilità, and creep resistance. Specify the wrong one and the field failure follows a predictable path. A bent latch snaps during assembly. A bracket deforms under sustained load near a heat source. A part pays for strength the design did not require. The right alloy choice is a materials engineering decision, not a purchasing afterthought.
Choosing among these three alloys is often the cheapest material decision in a zinc program, yet it is frequently left to habit rather than analysis. This guide puts the real differences on the table with published composition bands and die-cast properties. It then walks through the selection rules that separate a textbook Zamak 3 part from a copper-strengthened or creep-resistant specification. IL Carichi 5 property comparison on this site covers the aluminum alloy side if the metal family itself is still open.
The Composition Bands That Separate Them
All three belong to the Zamak family, standardized for die casting under ASTM B86 for castings and B240 for ingots, with EN 1999 covering European specifications. The aluminum band from roughly 3.8 A 4.3% is shared across all three, the 4Al baseline the ScienceDirect zinc-castings alloy table records for each Zamak grade. What changes is the second alloying lever. Magnesium stays near 0.04% in the general-purpose alloys, while copper steps up in the strengthened grades or magnesium rises in the creep-resistant specialist.
| Lega | Rame (%) | Magnesio (%) | Trazione, pressofuso (MPa) | One-line role |
|---|---|---|---|---|
| Carichi 3 | ≤0.1 | 0.035-0.06 | ~280-285 | General-purpose default |
| Carichi 5 | 0.75-1.25 | 0.03-0.06 | ~330 | Strength and hardness step-up |
| Carichi 7 | ≤0.05 | 0.5-0.8 | ~295 | Creep and toughness specialist |
Read the yield columns of the same data sets and the pattern sharpens. Published values for the copper-strengthened grade place the 0.2% yield strength near 260 MPa, mentre Zamak 3 yield sits in the 180 A 220 MPa range depending on the source. That is a genuine gain in strength, with tensile roughly 10 A 15% above Zamak 3 and hardness climbing from about 80 A 91 Hb. This alloy achieves its behavior through copper addition, all'incirca 1% versus the minimal copper in Zamak 3. The creep-resistant specialist buys its performance a different way. Elevated magnesium around 0.55% rather than 0.04% improves hot-tearing resistance, creep strength, and impact toughness without adding copper at all.
Carichi 3 as the General-Purpose Default
Carichi 3 is the most widely cast zinc alloy globally for a set of unglamorous reasons. It offers the best fluidity in the family, predictable dimensional behavior, easy plating acceptance, and the largest ingot availability across supply chains. If a part is a knob, a toy component, a decorative fitting, an electrical housing, or general hardware, Carichi 3 is the alloy the cost model assumes. The part sees no sustained load and no elevated temperature. Its tensile band covers the majority of small hardware ever designed, and its ductility measured as elongation is the family benchmark that the strengthened alloys trade away.
The failure mode to watch is not Zamak 3 breaking in service. The risk is engineers reflexively stepping up to the copper-strengthened grade because higher strength sounds safer. Strength the design does not load is cost the program does not need, and the step-up carries a forming penalty the next section addresses.
Strength and Forming Behavior in the Copper-Strengthened Alloy
Carichi 5 is Zamak 3 plus approximately 1% rame. In European sourcing it has historically been the preferred general alloy. The copper lifts tensile strength toward 330 MPa, pushes yield to roughly 260 MPa, and adds hardness for wear resistance. That is why latches, levers, parentesi, hinge bodies, and automotive interior hardware get specified as Zamak 5 when a part feels flexed or scraped in service.
The trade-off is ductility and forming behavior. Copper-strengthened Zamak accepts less bending, staking, and riveting than Zamak 3 without cracking. Parts designed for aggressive secondary forming either return to Zamak 3 with thicker sections or get the geometry changed to avoid the bend entirely. Designers in the habit of solving every strength question by changing the alloy should first try wall thickness and ribbing adjustments. Those are free on a hot-chamber shot, while the material premium is not. IL precision complex components page on this site covers the geometry envelope where thin-wall zinc casting works.
Carichi 7 the Creep-Resistant Specialist
Carichi 7 trades the copper route for magnesium, all'incirca 0.55% instead of a tenth, and lands between its siblings with a distinct role. It offers better creep resistance than Zamak 3 at elevated temperature. It delivers higher impact energy and improved as-cast ductility because the elevated magnesium refines the grain and resists hot tearing during fill. Screw bosses that carry sustained load, latch strikers, and thin complex fills near warm environments are where this alloy earns its specification. The availability constraint is real but manageable with early supplier engagement.
The honest caveat is supply. This alloy moves in far smaller volumes than Zamak 3 e Zamak 5. Most jobbing foundries stock the first two as standard ingot, so a Zamak 7 request becomes a stock check and a minimum-heat conversation before it becomes a quote. If a drawing specifies this grade without a tested reason, the design for manufacturing call is to challenge it. Usually the challenge pushes toward Zamak 3 for economics or Zamak 5 for strength. Keep the specialist only when creep or impact genuinely rules the part out.
The Service Limits All Three Share
Family loyalty ends where the physics begins, and three constraints bind every Zamak alloy equally. First is heat. Sustained service beyond roughly 100 °C drives creep and microstructural change across the whole family. If the part lives against an engine or a heat sink, this is the wrong alloy shelf entirely, and the answer is aluminum or a ZA-series high-alloy zinc. IL leghe di alluminio ad alta conducibilità termica l'articolo su questo sito riguarda la selezione delle leghe per il funzionamento dei dissipatori di calore.
Second is purity. Long-term dimensional stability depends on holding lead, cadmio, and tin impurities to the tens-of-parts-per-million ceilings the specifications impose. Those elements migrate to grain boundaries and cause intergranular corrosion, the classic old zinc part crumbles failure. This is why incoming chemistry verification on a direct-reading spectrometer matters more for zinc than the alloy name on the drawing.
Third is geometry honesty. All Zamak alloys cast beautifully thin, but every design that must flex, peel, or survive a crash should not be zinc at all, regardless of grade. IL frequently asked questions page on this site addresses common material selection questions buyers raise.
Selection Rules Applied In Order
Does the part carry a sustained or impact load? If no, specify Zamak 3 and stop. If yes but mostly static, the copper-strengthened grade is the common step-up. If the load is constant at elevated temperature, the creep-resistant specialist or leave the family entirely.
Does manufacturing bend, stake, or rivet the part? Secondary forming pushes the choice back toward Zamak 3 geometry with thickness where the bend lives. Copper-strengthened alloys resist being deformed after they cool.
Will the supplier stock the alloy without a special melt? Carichi 3 e Zamak 5 are widely available. Carichi 7 is a scheduled purchase at most foundries. Ask before the drawing locks the specification.
Run those three questions against the published capability profiles and the answer arrives with a quote attached. When the drawing is ready but the alloy decision is not, invialo tramite il pagina dei contatti. The team returns a quote and a free DFM analysis report that makes the recommendation in writing.
Cost and Availability Across the Family
Pricing follows availability. Carichi 3 e Zamak 5 move in high volume through most zinc ingot suppliers, so the material cost difference between them is small relative to the total piece price. The premium for the copper-strengthened grade shows up as a percentage addition on the ingot cost. That addition is typically single-digit. It matters most when the part weight is high and the annual volume justifies close examination of the material line item. For a small bracket at fifty thousand pieces per year, the alloy choice matters less than the tooling amortization, the cycle time, and the secondary operations that follow the casting.
Carichi 7 sits in a different category. The lower volume means fewer suppliers keep it in stock, and a purchase may require a minimum melt quantity that exceeds the program need. That constraint drives the design for manufacturing challenge mentioned earlier. If the part can perform adequately on Zamak 3 o Zama 5, the supply chain simplicity and cost transparency favor the more common grades. The specialist earns its place only when the application data show creep or impact requirements the other two cannot meet at the design temperature.
Scrap and regrind behavior is consistent across the family. All three alloys accept clean internal regrind at controlled percentages, and the incoming spectrometer verification catches contamination before it reaches the melt. The cost of getting the alloy wrong shows up later, in field returns or assembly failures, not in the ingot invoice. A program that specifies the right alloy from the start avoids multiple downstream costs. It avoids the cost of late-stage material changes. It avoids the cost of retooling for different flow characteristics. It avoids the cost of field failures that trace back to a material selection made by habit rather than analysis.
Considerazioni finali
The three alloys sit close enough in composition that the differences look small on a spectrometer readout. Yet those small differences drive field performance in opposite directions. Carichi 3 wins on economics and formability for parts that see no sustained load. The copper-strengthened grade wins on strength and hardness for parts that flex or wear in service. This specialist grade wins on creep resistance and impact toughness for parts that carry load near heat.
The wrong choice compounds over thousands of pieces, and the right choice is usually the cheapest one that meets the actual load path. A decorative knob needs no copper premium. A latch that gets bent during assembly needs the ductility that copper takes away. A screw boss near a motor needs the creep resistance that only elevated magnesium provides. The numbers are published, the trade-offs are clear, and the DFM pass should make the call explicit before the tool is cut.
Questions About Zamak Alloy Selection
Is the copper-strengthened grade stronger than Zamak 3?
SÌ, this alloy delivers roughly 330 MPa tensile and 260 MPa yield versus Zamak 3 near 280 MPa tensile and 180 A 220 MPa yield. The strength gain comes from approximately 1% aggiunta di rame. The trade-off is reduced ductility and less tolerance for secondary forming operations like bending or staking.
What makes the creep-resistant grade different?
The strengthening route differs. The copper-strengthened grade adds copper for tensile and hardness. The creep-resistant grade adds elevated magnesium around 0.55% for creep resistance, impact toughness, and hot-tearing behavior at moderate strength. The first is the common step-up from Zamak 3. The second is the specialist that also requires a stock check since it moves in smaller volumes.
How hot can Zamak die castings run in service?
Hold steady below roughly 100 °C for sustained loads. Above that threshold the whole Zamak family creeps and its microstructure coarsens. Carichi 7 postpones the problem with elevated magnesium but does not solve it. Parts that bake continuously belong to aluminum die casting or the high-aluminum ZA series, not to any Zamak 3, 5, O 7 decision.
Why do old zinc castings crumble over time?
Intergranular corrosion driven by lead, cadmio, and tin impurities at parts-per-million levels. Those elements segregate to grain boundaries and, with humidity, age the casting from inside. The specifications cap these impurities near 50 ppm each, which is why alloy choice is only half the question. The other half is incoming ingot chemistry verification lot by lot rather than trusting the ingot sticker.
