Introduction
In the manufacturing industry, lightening parts, reducing costs, and improving functionality are constant challenges. Die casting (die casting: a casting technology that involves injecting molten metal into a mold at high pressure to form a shape in a short time) is an essential solution. In particular, aluminum die casting and zinc die casting are two major materials that are frequently compared and considered in manufacturing plants. While they may appear similar at first glance, their properties are significantly different.
This article provides valuable information for Japanese manufacturing executives and procurement managers to help them make optimal material choices. We will explain the clear differences between aluminum and zinc die-cast parts from three perspectives: cost, performance, and applications. By utilizing this information, you can gain important insights for achieving both product requirements and cost performance, thereby enhancing your competitiveness.
Aluminum and Zinc: Fundamental Differences Based on Physical and Chemical Properties
Specific Gravity and Weight: Lightness or Heaviness?
The most notable difference between aluminum and zinc is their specific gravity. The specific gravity of aluminum is about 2.7 g/cm³, while that of zinc is about 6.6 g/cm³, making it approximately 2.4 times heavier than aluminum. This physical difference is a crucial factor in determining the applications for each die-cast part.
Aluminum die casting, leveraging its lightweight properties, is widely used in fields where lightness is a priority, such as automobile engine parts, structural materials for aircraft and railway vehicles, and electronic device housings. The demand for aluminum die casting is increasing year by year, especially in the automotive industry, as lighter vehicles directly lead to better fuel efficiency.
On the other hand, zinc die casting, utilizing its moderate weight and high rigidity, is used for mechanical parts, precision equipment housings, and building materials. It is suitable for products that require a sense of substantial weight and a stable center of gravity (e.g., camera bodies, handles for high-end furniture).
Melting Point and Casting Method: Production Efficiency and Mold Life
The difference in melting points significantly affects the die-casting process. The melting point of aluminum is high, around 660°C, whereas zinc’s is relatively low, at about 420°C. This difference has a major impact on the casting machines used and production efficiency.
In aluminum die casting, a heat-resistant “cold chamber die casting machine” is used to inject high-pressure molten aluminum due to its high melting point. Because of aluminum’s hardness, this process causes significant mold wear, and the mold life is generally said to be around 70,000 to 100,000 shots.
In contrast, since zinc die casting has a low melting point, a “hot chamber die casting machine” where the cylinder is submerged in the molten metal is used. This method has a shorter cycle time and higher productivity compared to aluminum. Furthermore, the low thermal load on the mold means that the mold life can often be more than double that of aluminum. This significantly impacts manufacturing costs, especially for mass production.
Comparison of Cost, Performance, and Recyclability
Manufacturing Costs: Initial Investment and Running Costs
The cost of a die-cast part is determined by a combination of material costs, mold costs, and the running costs of the manufacturing process.
Initial costs tend to be higher for aluminum die casting. This is due to the need for heat-resistant mold materials and the higher frequency of mold replacement because of faster wear. Zinc, on the other hand, has a longer mold life, resulting in a lower cost per mold shot, making it suitable for projects that need to keep initial costs down or for mass production.
In terms of running costs, aluminum die casting requires more energy to maintain the furnace at a high temperature due to its high melting point. In contrast, zinc die casting requires less energy because of its lower melting point, contributing to lower manufacturing costs.
Mechanical Performance: Strength or Precision?
Strength Aluminum has a high strength-to-weight ratio and is suitable for structural parts that require high strength despite being lightweight. While zinc’s overall tensile strength may be higher due to its heavier specific gravity, aluminum’s strength-to-weight ratio is advantageous for products that require weight reduction.
Impact Resistance Zinc is characterized by its high hardness and excellent impact resistance. This property is a major advantage for parts that are expected to be subjected to external impact, such as automotive crash safety components and industrial machine housings that require durability.
Dimensional Accuracy and Fluidity Zinc alloy has extremely high fluidity, allowing for the high-precision molding of complex parts with thin walls. Additionally, its low solidification shrinkage rate ensures excellent dimensional stability, enabling the precise reproduction of fine details like screw holes. For this reason, it is highly effective for products that require high precision, such as connectors, small electronic components, and decorative items.
Recyclability: Contribution to Sustainable Manufacturing
Both aluminum and zinc are metals with excellent recyclability.
Aluminum requires only 3% of the energy needed to produce new aluminum from bauxite. Flawed die-cast products and scrap can be re-melted and reused, which significantly contributes to reducing environmental impact.
Zinc is also a nearly 100% recyclable metal. Its low melting point means less energy is required for re-melting, making the recycling process efficient.
Application Examples: Choosing the Right Material Determines a Product’s Success
Main Applications of Aluminum Die Casting
- Automotive Parts: Engine blocks, transmission cases, wheels, suspension parts, and other components where weight reduction is crucial for improving fuel efficiency.
- Electronic Devices: Housings for smartphones and PCs, and heat sinks for LED lighting. Their excellent thermal conductivity allows for efficient heat dissipation.
- Building Materials: Window frames, handrails, and other outdoor parts that require corrosion resistance and strength.
Main Applications of Zinc Die Casting
- Small Electronic Components: Connectors, switches, USB ports, and other parts that require high dimensional accuracy.
- Furniture and Decorative Items: Doorknobs, handles, hinges, and other parts that require a sense of weight and intricate design.
- Precision Machine Parts: Bearing housings, gears, tool parts, and other components that require high hardness and wear resistance.
Conclusion
Aluminum and zinc die casting each have their unique strengths and weaknesses, and the optimal choice depends on the part’s required specifications, production volume, and cost targets.
Aluminum die casting is the best choice when you need to achieve both lightweight and high strength, require excellent corrosion resistance for outdoor use, or need to efficiently dissipate heat. The aluminum die-casting market is expected to continue to expand, driven by the growing demand for weight reduction in the automotive and aerospace industries.
On the other hand, zinc die casting is an excellent option when you need to manufacture complex, precise parts, require high hardness or impact resistance, or want to keep initial mold costs down for mass production. Thanks to its superior castability, it continues to prove its value in a wide range of fields, including home appliances, small electronic devices, and decorative items.
Choosing the right die-casting material significantly impacts a product’s performance, cost, and market competitiveness. Understanding these properties and selecting the right partner for your product development is the first step toward success.