Zinc casting refers to a precision manufacturing technology where metallic zinc or zinc alloy is heated to a molten state and injected into a mold cavity through specific processes. After cooling and solidification, parts conforming to the designed shape are obtained. As a mature casting technology, the core advantages of zinc casting lie in its low melting point and high fluidity.
The low melting point of zinc reduces melting energy consumption, while high fluidity allows for easy forming of complex structures (such as thin-walled or hollowed parts). These two core advantages give zinc casting strong casting capabilities, which is the key reason for its widespread application in the field of precision manufacturing.
What is Zinc Casting?
Design - Prototype - Molds - Casting
Zinc casting refers to a precision manufacturing technology where metallic zinc or zinc alloy is heated to a molten state and injected into a mold cavity through specific processes. After cooling and solidification, parts conforming to the designed shape are obtained. As a mature casting technology, the core advantages of zinc casting lie in its low melting point and high fluidity.
The low melting point of zinc reduces melting energy consumption, while high fluidity allows for easy forming of complex structures (such as thin-walled or hollowed parts). These two core advantages give zinc casting strong casting capabilities, which is the key reason for its widespread application in the field of precision manufacturing.
Four Core Processes of Zinc Casting
Design - Prototype - Molds - Casting
Zinc casting is divided into four main processes: raw material melting, mold preparation, pouring/forming, and post-processing. Each core process ensures the production and delivery of qualified zinc castings through precise material ratios, strict temperature control, and error control.
Raw Material Melting
The raw material melting process in zinc casting involves feeding high-purity zinc ingots (purity typically ≥99.99%) or zinc alloy raw materials into a furnace, heating them to a liquid state at 419°C - 450°C (the melting point of zinc is 419°C). During this process, refining agents (0.2%-0.5% of the melt mass, furnace temperature control error ≤ ±5°C, lining water content ≤0.5%) are added to remove impurities and ensure the purity of the molten zinc.
Mold Preparation
In the mold preparation stage for zinc casting, metal molds (commonly made from H13 hot-work tool steel) are machined according to the part design and preheated to 150°C - 200°C to prevent cracking when the cold mold contacts the hot molten zinc. The die-casting mold cavity requires a titanium nitride coating (thickness 5-10μm, to improve wear resistance), and the mold clamping gap is strictly required to be ≤0.05mm.
Pouring and Forming
The core of the zinc casting pouring and forming process is controlling the melt filling state. The molten zinc is injected into the mold cavity by gravity, pressure, or other methods. After the zinc completely fills the cavity, a certain pressure is maintained (for die-casting processes) to accelerate cooling. Notably, this process requires ensuring venting; the total length of the die-casting mold venting slots should be ≥1.5 times the part's perimeter to prevent air pocket defects.
Post-Processing
After demolding, parts undergo deburring, polishing, plating (such as zinc plating, chrome plating), or painting. These post-processing steps can enhance the corrosion resistance and aesthetics of zinc casting products to a certain extent. For heat treatment, zinc alloy materials from the Zamak series commonly undergo T5 treatment (aged at 120-150°C for 2-4 hours, cooled with the furnace, increasing hardness by 10%-15%), avoiding temperatures exceeding 200°C to prevent grain coarsening.
For surface treatment, zinc casting parts require pickling before plating (10%-15% hydrochloric acid solution, 20-30°C, 5-10min); after pickling, the plated zinc layer thickness is 5-15μm. Before painting, phosphating is required (phosphating solution concentration 8%-12%, 40-50°C, 10-15min), with a paint film thickness of 20-50μm and adhesion meeting GB/T 9286 Grade 1 standard.
Two Core Types of Zinc Casting
Design - Prototype - Molds - Casting
Among the subdivided processes of zinc casting, zinc die casting and zinc alloy die casting are the two most widely applied types. Although both belong to the die-casting category, they have significant differences in raw materials, performance, application scenarios, and other dimensions.
What is Zinc Die Casting?
Zinc die casting uses pure zinc (Zn content ≥99.95%) as the raw material. Pure zinc has a low melting point (419°C) and excellent fluidity, but it's important to note that pure zinc has lower strength (tensile strength about 100MPa) and is prone to deformation under high pressure and impact. The process characteristic of zinc die casting is the use of high-pressure die-casting machines (clamping force typically 50-2000 tons) to inject molten pure zinc into the mold cavity at high speeds of 5-50 m/s.
This high efficiency results in short forming cycles (10-30 seconds per part), making it very suitable for mass production of low-strength, high-precision small parts (such as connectors for electronic equipment, toy accessories, decorative metal parts, etc.). Because the raw material used in zinc die casting (pure zinc) has a low cost, it has significant advantages in the field of high-volume, low-cost parts.
What is Zinc Alloy Die Casting?
Zinc Alloy Die Casting uses zinc alloy as the raw material. Common material grades are Zamak 3, Zamak 5, Zamak 7, with small amounts of the ZA series used. Differences in alloy composition directly affect the process and product performance.
By adding elements like aluminum and copper, strength (Zamak 5 tensile strength about 280MPa), hardness, and corrosion resistance are significantly improved, while retaining zinc's high fluidity. The working principle of Zinc Alloy Die Casting is consistent with the zinc die casting process principle, but the melting temperature (typically 420°C - 480°C) and die-casting pressure need to be adjusted according to the alloy composition.
Some high-demand parts require vacuum die-casting technology to reduce porosity for better yield rates. Zinc alloy die casting covers medium to high-strength parts, such as automotive door lock housings, engine brackets, mobile phone mid-frames, medical device components, etc., and is currently the fastest-growing subdivision direction within zinc casting technology.
Because the strength-to-weight ratio of zinc alloys is better than cast iron and aluminum alloys, demand continues to rise in the trend towards automotive lightweighting.
Alloy Type | Mass Fraction | Core Properties | Process Adaptation Requirements |
Zamak 3 | Zn: Bal.; Al: 3.9-4.3%; Cu: ≤0.1%; Mg: 0.03-0.06% | Optimal fluidity (relative value 100), best corrosion resistance (salt spray test ≥72h), high toughness (elongation 10-15%) | Suitable for die-casting ultra-thin-walled parts (min. wall thickness 0.15mm), complex cavity parts; no need to adjust high-pressure parameters; lower mold venting requirements |
Zamak 5 | Zn: Bal.; Al: 3.9-4.3%; Cu: 0.7-1.2%; Mg: 0.03-0.06% | Highest strength (tensile strength 280-300MPa), high hardness (HB90-110), but slightly poorer fluidity (relative value 85-90), weaker corrosion resistance | Requires increased die-casting pressure (10-15% higher than Zamak 3), larger gate size; suitable for structural parts (need to bear loads) |
Zamak 7 | Zn: Bal.; Al: 3.0-3.5%; Cu: 0.3-0.6%; Mg: 0.005-0.02% | Balanced comprehensive performance (medium strength, medium toughness, medium corrosion resistance) | Die-casting parameters between Zamak 3 and 5; suitable for parts requiring both “strength + toughness” |
ZA-8 | Zn: Bal.; Al: 8.2-8.8%; Cu: 0.25-0.35% | High-temperature strength (tensile strength at 100°C still ≥250MPa), good wear resistance | Higher melting temperature (460-480°C), requires enhanced mold cooling; suitable for high-temperature environment parts (e.g., heater accessories) |
Why is Zinc Casting the Preferred Choice in Manufacturing?
Design - Prototype - Molds - Casting
Compared to traditional technologies like aluminum alloy casting or cast iron casting, zinc casting (including zinc die casting and zinc alloy die casting) holds irreplaceable advantages in terms of cost, casting precision, complex formability, environmental friendliness, recyclability, and equipment compatibility.
Energy Consumption and Cost Advantages:
Zinc's melting point is only 419°C, far lower than aluminum alloy (660°C) and cast iron (1147°C), reducing melting energy consumption by 30%-50%. Simultaneously, zinc casting molds have a long lifespan (one mold can produce 500,000 - 1,000,000 parts), resulting in significantly lower per-part costs compared to other metal castings after allocation.
Precision and Surface Quality Advantages:
The dimensional accuracy of zinc casting (especially zinc die casting) can reach CT4-CT6 grade (tolerance range ±0.05mm), with surface roughness Ra ≤1.6μm. Most parts can be assembled directly without subsequent machining, reducing processing steps.
Complex Forming Advantages:
Zinc (and zinc alloys) have excellent fluidity, allowing the forming of thin-walled parts with wall thicknesses of 0.5mm-5mm, or parts with complex internal cavities and hollow structures (e.g., automotive transmission housings), which is difficult to achieve with aluminum alloy casting.
Environmental and Recycling Advantages::
Zinc has a high recycling rate of over 95%. Waste generated during zinc casting production (such as gates and flash) can be directly remelted without causing environmental pollution. Moreover, zinc alloys do not contain harmful elements like lead or cadmium, complying with environmental standards such as RoHS and REACH.
Assembly Compatibility Advantages:
Zinc has good ductility, allowing zinc casting parts to undergo subsequent processing like tapping, riveting, and welding directly without additional pre-treatment. Also, zinc's density (7.14 g/cm³) is moderate, balancing part weight and structural stability.
Common Issues in Zinc Casting
Design - Prototype - Molds - Casting
Common issues in zinc casting production include porosity defects, dimensional deviations, and surface oxidation. These three types of problems are core pain points in zinc casting production.
Porosity Defects:
Porosity is one of the most common defects in Zinc Casting, especially in zinc die casting. It manifests as small holes (typically 0.1-1mm in diameter) inside or on the surface of the part. In severe cases, it can lead to a decrease in the part's tensile strength (e.g., zinc alloy die casting part strength may decrease by 15%-20%), and even cause "air leakage" or "chipping" during subsequent processing (like drilling).
To address porosity issues in Zinc casting,mold improvements can be made first, such as adding venting slots and incorporating air pins to enhance venting efficiency. For high-precision zinc alloy die casting parts, vacuum die-casting technology (vacuum level controlled at ≤50 mbar) can be used to reduce air entrapment during zinc filling.
Reducing the die-casting speed for complex parts from 30-50 m/s to 15-25 m/s can lower turbulence.
Dimensional Deviations:
If the actual size of a Zinc Casting part deviates beyond the tolerance range from the design size (e.g., CT4 grade part tolerance ±0.05mm, if the deviation reaches ±0.1mm), it cannot be assembled. Dimensional deviations arise from three different reasons.
- Mold Factors:After long-term use (e.g., over 100,000 parts), the cavity of a Zinc casting mold (commonly H13 steel) wears, causing dimensions to increase; or uneven mold preheating (local temperature difference >50°C) leads to inconsistent shrinkage during cooling.
- Uneven Cooling:Unreasonable design of the mold cooling channels (e.g., no channel in thin-walled areas) causes significant differences in local cooling rates (e.g., cooling time in thick sections is 2-3 times that of thin sections), resulting in different shrinkage amounts.
- Uncontrolled Alloy Shrinkage Rate: For Zinc alloy die casting, failure to adjust the shrinkage rate according to the alloy grade (e.g., Zamak 3 shrinkage rate 1.2%, Zamak 5 shrinkage rate 1.3%) means the mold size does not reserve sufficient shrinkage allowance.
To address dimensional deviation issues, strictly monitor the mold production count and actively maintain Zinc casting molds, paying attention to local part temperatures. For different zinc alloy grades,reserve the corresponding shrinkage allowance during the mold design phase (e.g., the mold size for a Zamak 5 part needs to be 1.3% larger than the design size) to avoid the part being undersized after cooling.
Surface Oxidation:
Surface oxidation manifests as "gray-white powder" or "dark yellow spots" on the surface of Zinc Casting parts. This not only affects appearance (e.g., decorative zinc die casting parts cannot be used directly) but also reduces corrosion resistance (the oxide layer can accelerate further zinc corrosion, potentially reducing salt spray test time from 500 hours to below 200 hours).
The direct cause of this problem is the prolonged residence time of molten zinc in the furnace exceeding 2 hours, or aging of sealing elements, or failure to perform timely surface treatment (passivation, plating) after part demolding. The zinc liquid frequently contacts air, generating zinc oxide (ZnO), leading to corrosion on Zinc casting parts.
To address surface oxidation issues in zinc casting, strictly control the residence time of zinc liquid in the furnace (≤2 hours), and improve or upgrade the sealing system. Immediate mold cleaning can also help resolve the issue.
Conclusion
Design - Prototype - Molds - Casting
In summary, zinc casting, as a manufacturing technology that balances cost, precision, and environmental protection, has become an indispensable part of modern manufacturing. A deep understanding of the principles and applications of zinc casting will give you greater insight into your product manufacturing process.
Supro can provide a complete zinc casting manufacturing process, from raw material selection to process precision. You can obtain the customized zinc casting service you desire from us. Feel free to contact us at Supro anytime.