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Composition, properties, processing, and commonly used material grades of zinc alloys
I. Chemical Composition: Element Functions and Synergistic Effects
Aluminum (Al): The core alloying element. Its primary function is solid solution strengthening, which enhances strength and hardness. It also significantly improves the fluidity of the alloy melt, reducing casting defects. The aluminum content in conventional die-casting alloys (Zamak series) is approximately 4%, while high-aluminum zinc alloys (ZA series) can contain 8%–27% aluminum, resulting in significantly improved strength and heat resistance. Copper (Cu): A secondary strengthening element. Its main role is to increase hardness and creep resistance (i.e., resistance to slow deformation under stress). Its content is typically below 2%. Excessive copper reduces corrosion resistance and increases brittleness. Magnesium (Mg): A trace but critical element. Its primary function is to inhibit intergranular corrosion by fixing impurities such as iron and preventing their harmful effects. Its content must be precisely controlled (usually 0.02%–0.05%). Excessive magnesium can impair fluidity and toughness. Impurity Control: Impurities such as iron, lead, and cadmium must be strictly limited to ensure material ductility, stability, and environmental compliance (e.g., meeting RoHS standards).
II. Performance Mechanism: From Structure to Performance
III. Material Modification: Enhancing Performance
Composition Optimization Eco-Friendly: Development of low-lead (content < 0.003%) and cadmium-free alloys to meet stringent environmental regulations. High-Performance: By adjusting aluminum and copper content and adding trace elements such as nickel and titanium, special alloys with higher strength, better heat resistance, or improved thermal conductivity are developed. Process Optimization Melting Control: Use of protective gas melting and vacuum degassing to reduce oxidation and porosity, improving material purity and density. Semi-Solid Forming: An advanced forming technique that achieves finer microstructures, significantly enhancing mechanical properties and dimensional accuracy. Heat Treatment: Aging treatment for ZA series alloys promotes the precipitation of strengthening phases, further improving strength and hardness. Surface Treatment Chemical Conversion Coatings: Such as chromium-free passivation, which generates a corrosion-resistant protective layer, is an environmentally friendly and effective anti-rust method. Plating: Such as nickel plating, which greatly improves surface hardness, wear resistance, and corrosion resistance, as well as appearance. Coating: Use of powder coating or electrophoresis to provide long-lasting corrosion protection and color options.
IV. Selection Strategy: Based on Requirements
High-Wear and High-Hardness Components (e.g., core parts of locks, wear-resistant bushings, high-end zipper sliders) Preferred: Zamak 2 Reason: Among the Zamak series, it has the highest hardness and wear resistance, capable of withstanding intense friction and wear, with a long service life. General Structural and Appearance Parts (e.g., electronic components, casings, hardware parts) Preferred: Zamak 3 or Zamak 7 Reason: Balanced comprehensive performance, excellent casting fluidity, easy to achieve high surface quality, suitable for subsequent processes like electroplating, and cost-effective. Load-Bearing and Wear-Resistant Components (e.g., car seatbelt buckles, small gears, locks) Preferred: Zamak 5 or ZA-8 Reason: Higher hardness, strength, and creep resistance, meeting higher mechanical requirements. High-Temperature or High-Strength Lightweight Components (e.g., aerospace engine components, high-load bearing seats) Preferred: ZA-27 Reason: Possesses the highest strength, hardness, and heat resistance among all zinc alloys, with low density. Note: It has poorer plasticity and is unsuitable for high-impact loads. Components with Strict Environmental and Safety Requirements (e.g., medical devices, food machinery) Preferred: Environmentally Compliant Zamak 3 Reason: Ensures compliance with harmful substance limits and combines appropriate surface treatments to meet hygiene and corrosion resistance requirements. High-Toughness and Impact-Resistant Components (e.g., tool housings, safety parts, high-performance automotive components) Preferred: ACuZinc 5 Reason: Its high copper content provides strength close to the ZA series while maintaining excellent elongation and impact toughness, making it an ideal alternative to brass for complex loading conditions.
Performance Requirements: Clearly define specific requirements for strength, hardness, toughness, heat resistance, and corrosion resistance. Manufacturing Process: Evaluate part complexity, wall thickness, and production volume, selecting alloys with the best compatibility with die-casting processes. Cost Control: Prioritize more economical grades (e.g., Zamak 3) while meeting performance requirements. Regulatory Compliance: Ensure materials meet environmental directives such as RoHS and REACH for target markets.
V. Comparison of Common Zinc Alloy Grades
Mechanical Property Comparison Feature Comparison Alloy Grade Naming
ASTM B240-2022 Standard Specification for Zinc and Zinc-Aluminum (ZA) Alloys in Ingot Form for Foundry and Die Castings ASTM B86-2018 Standard Specification for Zinc and Zinc-Aluminum (ZA) Alloy Foundry and Die Castings EN 1774-1997 Zinc and Zinc Alloys - Ingots and Liquid Zinc Alloys for Casting