Die Casting When Should You Choose Zinc Over Aluminum for Production Parts

Content Menu

● Introduction

● Die Casting Process Basics

● Aluminum Die Casting Characteristics

● Zinc Die Casting Characteristics

● Head-to-Head Comparison

● Scenarios Where Zinc Wins Decisively

● Real Production Examples

● When Aluminum Remains the Right Choice

● Conclusion

● Q&A

 

Introduction

Die casting remains one of the most efficient ways to produce complex metal components at scale. Engineers regularly face the same question on new programs: should the part be run in aluminum or zinc? The answer is rarely obvious at the quoting stage. Aluminum gets most of the attention because of its low density and familiarity, yet zinc alloys frequently deliver lower total cost, better surface quality, and longer tool life once the full production picture comes into focus.

The decision usually hinges on part size, required mechanical properties, operating environment, annual volume, and how much secondary finishing the design demands. Over the past thirty years working with both alloy systems, I have seen dozens of programs start with an aluminum assumption, only to switch to zinc after the first tool trials revealed porosity issues, short die life, or excessive machining requirements.

This article examines the practical differences between the two alloy families from a manufacturing engineering perspective. It draws on published research, shop-floor data, and specific component examples to show exactly when zinc becomes the smarter choice.

Die Casting Process Basics

High-pressure die casting forces molten metal into a hardened steel die under pressures of 10–200 MPa. Two machine types dominate commercial production: hot-chamber for zinc, magnesium, and lead alloys, and cold-chamber for aluminum, brass, and higher-melting-point materials.

Hot-chamber machines keep the injection system submerged in the melt, allowing cycle times as low as 8–15 seconds. Cold-chamber machines require ladling or automatic pouring, which adds 5–10 seconds per shot and increases thermal shock on the die steel.

These fundamental process differences drive most of the cost and capability gaps between zinc and aluminum.

Aluminum Die Casting Characteristics

Common aluminum die casting alloys include A360, A380, A383, and A413. They offer:

• Density ≈ 2.7 g/cm³
• Typical as-cast tensile strength 310–340 MPa
• Excellent thermal conductivity (90–120 W/m·K)
• Good corrosion resistance in neutral atmospheres
• Ability to withstand continuous operate above 200 °C

Aluminum excels in weight-critical structural components such as transmission cases, engine brackets, and heat-sink housings. However, the high melting temperature (580–660 °C) and aggressive attack on H13 tool steel limit die life to 80 000–150 000 shots in most production programs. Thin sections below 1.0 mm become risky because of cold shuts and incomplete fill.

Zinc Die Casting Characteristics

Standard zinc alloys are Zamak 2, 3, 5, 7 and the higher-performance ZA-8, ZA-12, ZA-27. Key properties:

• Density ≈ 6.6–7.1 g/cm³
• As-cast tensile strength 280–420 MPa (ZA-27 reaches 420 MPa)
• Superior creep resistance up to 100–120 °C
• Exceptional fluidity allowing 0.3–0.5 mm walls and ±0.025 mm tolerances
• Die life commonly 500 000–1 500 000 shots

Because zinc melts at 385–420 °C and is injected through a hot-chamber gooseneck, energy consumption per part drops roughly 60 % compared with aluminum. The lower thermal load on the die steel dramatically extends tool life and reduces solder-related maintenance.

Head-to-Head Comparison

Scenarios Where Zinc Wins Decisively

1. Small, High-Precision Components (< 500 g)

Connectors, lock cylinders, camera bodies, and handheld power-tool housings routinely move to zinc once engineers realize they can eliminate threaded inserts, reduce machining by 70 %, and hit ±0.03 mm tolerances straight from the die.

2. Parts Requiring Decorative Finishing

Chrome, nickel, or powder-coat adhesion on zinc is far superior. Automotive interior bezels, bathroom faucets, and appliance handles almost always run in Zamak or ZA-8 because the as-cast surface accepts plating with almost zero pitting.

3. High-Volume Programs (> 200 000 units/year)

When tooling cost must be spread over many parts, zinc’s 5–10× longer die life and double throughput create compelling economics. A 300-cavity zipper slider tool running zinc will produce 300 million pieces before major steel replacement—impossible with aluminum.

4. Impact and Vibration Resistance at Room Temperature

Hand-tool bodies, lawn-mower deck components, and window hardware benefit from zinc’s higher damping capacity and resistance to brittle failure. Drop-test survival rates are routinely 30–50 % higher than equivalent aluminum castings.

5. Net-Shape Threads and Undercuts

Internal and external threads cast to Class 2B/2A tolerance in zinc eliminate tapping stations entirely. This single advantage has shifted entire product lines (electrical connectors, fuel-system fittings, pneumatic valves) away from aluminum.

Real Production Examples

A major North American lock manufacturer converted a 180 g deadbolt housing from A380 to ZA-8 in 2019. Die life increased from 120 000 to 1.1 million shots, machining was eliminated on six features, and chrome rejection fell from 8 % to 0.4 %. Total piece-price dropped 28 % despite zinc’s higher raw-material cost.

A cordless drill manufacturer switched gearbox halves to Zamak 5. The parts gained 18 % torsional stiffness, absorbed vibration better (reducing perceived noise by 3 dB), and allowed direct molding of the bearing pockets—no boring required. Tooling payback occurred in nine months instead of twenty-four.

An EV charging-station maker moved from aluminum to ZA-27 for the main connector housing. EMI shielding improved, wall thickness dropped from 2.5 mm to 1.2 mm, and the tool ran 1.4 million shots with only minor cavity polishing.

When Aluminum Remains the Right Choice

Large structural parts, anything operating above 150 °C continuously, and weight-critical transportation components still belong to aluminum. Engine blocks, motor housings, and aircraft fittings would be prohibitively heavy in zinc.

Conclusion

Zinc die casting is not a niche process—it is the optimum solution for a surprisingly large percentage of production parts once all costs are considered. The combination of unmatched fluidity, dramatically longer tool life, faster cycles, superior plating response, and excellent room-temperature mechanical properties makes zinc the default choice for small-to-medium components that demand precision and decorative finish.

Next time a new program lands on your desk, run the numbers both ways. In many cases you will find that zinc does not merely compete with aluminum—it clearly outperforms it on total landed cost, quality, and delivery performance.

Q&A

Q1: Will zinc parts corrode faster than aluminum outdoors?
A: In normal atmospheric conditions zinc forms a stable carbonate layer and performs equal or better. Only in continuous wet/acidic exposure does aluminum have an edge.

Q2: Can zinc replace aluminum in structural automotive parts?
A: Generally no—zinc’s higher density and lower high-temperature strength limit it to non-suspension, non-powertrain components.

Q3: How much longer do zinc dies really last?
A: Production data show 500 000–1 500 000 shots for zinc versus 80 000–180 000 for aluminum under comparable conditions.

Q4: Is secondary machining easier on zinc or aluminum?
A: Zinc machines beautifully with excellent chip formation and surface finish; aluminum can gum up tools if not using the right coolant and speeds.

Q5: Are there any EMI/RFI shielding advantages with zinc?
A: Yes—zinc’s higher electrical conductivity and ability to cast thin uniform walls provide 10–20 dB better shielding than aluminum in many connector housings.