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Surface finishing plays a critical role in the performance, durability, and appearance of metal and plastic parts, regardless of the manufacturing process used. While processes such as CNC machining, die casting, casting, sheet metal fabrication, and additive manufacturing define the geometry of a part, surface treatment ultimately determines how the part performs in its actual application environment.
Proper surface finishing can significantly improve corrosion resistance, wear resistance, mechanical performance, and service life, while also enhancing visual quality and functional reliability. This guide introduces commonly used surface treatment technologies applicable across different manufacturing processes and provides practical guidance for selecting the most suitable surface treatment based on material type, application requirements, and cost considerations.
II. Common Surface Treatment Technologies
Applicable materials: Aluminum alloys, titanium alloys
Anodizing is an electrochemical process that forms a dense oxide layer on the surface of the base material. This layer improves corrosion resistance, increases surface hardness, and enhances appearance without significantly affecting dimensional accuracy.
Typical applications:
Aerospace components, automotive parts, electronic housings, and lightweight structural components.
Applicable materials: Metals, plastics
Bead blasting uses abrasive media to clean surfaces, remove minor defects, and create a uniform matte texture. It also improves surface roughness and enhances adhesion for subsequent coatings or painting.
Typical applications:
Decorative components, electronic enclosures, die-cast parts, and pre-treatment for coating processes.
Applicable materials: Steel, aluminum, zinc alloys, copper alloys
Nickel and chrome plating provide a protective metallic coating that improves wear resistance, corrosion protection, and surface appearance. These coatings also enhance oxidation resistance and extend component service life.
Typical applications:
Automotive components, hardware, mechanical parts, die-cast zinc components, and decorative or functional parts requiring a durable and glossy surface.
Applicable materials: Stainless steel, aluminum, copper alloys
Electrolytic polishing removes microscopic surface irregularities through electrochemical reactions, producing a smooth, clean, and reflective surface. It also improves corrosion resistance by reducing surface defects.
Typical applications:
Medical devices, food processing equipment, fluid-handling components, and precision copper or stainless steel parts.
Applicable materials: Carbon steel, alloy steel, tool steel
Black oxide is a chemical conversion coating that forms a thin black layer on the metal surface. It provides mild corrosion resistance, reduces light reflection, and maintains tight dimensional tolerances due to its minimal thickness.
Typical applications:
Fasteners, tooling components, mechanical assemblies, and precision parts where dimensional stability is critical.
Applicable materials: Carbon steel, alloy steel, tool steel
Hardening and heat treatment processes modify the internal microstructure of the material to increase hardness, strength, and wear resistance. These processes are often combined with machining, forging, or forming operations to achieve final mechanical performance.
Typical applications:
Gears, shafts, molds, wear-resistant parts, and load-bearing mechanical components.
Applicable materials: Metals, plastics
Coating treatments involve applying functional or protective layers to enhance corrosion resistance, wear resistance, thermal stability, or chemical resistance. Coatings may be applied as standalone treatments or combined with other surface processes.
Typical applications:
Aerospace components, automotive parts, industrial equipment, and electronic products operating in harsh environments.
Steel:
Steel components commonly require plating, black oxide treatment, or heat treatment to improve corrosion resistance, wear resistance, and mechanical strength. Stainless steel may additionally benefit from electrolytic polishing for enhanced surface quality.
Aluminum Alloys:
Anodizing is the most widely used surface treatment, providing excellent oxidation resistance, surface hardness, and improved appearance.
Zinc Alloys (Die Casting):
Zinc alloy parts are commonly treated with nickel plating, chrome plating, or coating to improve corrosion resistance and appearance. Bead blasting is often used as a pre-treatment to achieve a uniform surface finish before plating or painting.
Copper and Copper Alloys (Brass, Bronze):
Copper and its alloys typically require plating, polishing, or coating to prevent oxidation and improve wear resistance. Electrolytic polishing and nickel plating are commonly applied to enhance surface quality and durability.
Titanium Alloys:
Titanium alloys are typically anodized to enhance corrosion resistance and surface hardness, making them suitable for aerospace and other high-performance applications.
Nylon:
Bead blasting or coating treatments improve abrasion resistance and surface durability.
Polycarbonate (PC):
Protective coatings enhance UV resistance, heat resistance, and impact strength, especially for outdoor or high-stress environments.
PVC:
Spraying and thermal treatments improve chemical resistance and anti-aging performance.
For parts exposed to corrosive environments, anodizing, plating, or protective coatings are recommended. For components subjected to high wear or mechanical stress, hardening or heat treatment should be considered. For parts requiring minimal dimensional change and controlled appearance, black oxide treatment is an effective solution.
In high-performance industries such as aerospace, automotive, and medical manufacturing, surface treatments must balance corrosion resistance, mechanical performance, dimensional stability, and visual quality.
Surface treatments must be compatible with the base material and the manufacturing process. Zinc alloys and copper alloys, commonly used in die casting and precision components, require surface treatments specifically designed to prevent oxidation and maintain surface integrity.
Surface treatment costs vary depending on complexity and performance requirements. Advanced plating, heat treatment, and functional coatings provide superior durability but involve higher costs, while bead blasting and black oxide offer cost-effective solutions with functional benefits. The optimal choice balances performance requirements with project budget.
Surface finishing is a critical stage in manufacturing that defines the final performance, durability, and reliability of metal and plastic parts across all production methods, including CNC machining, die casting, forging, and sheet metal fabrication. By selecting appropriate surface treatments based on material properties, application requirements, and cost considerations, manufacturers can achieve optimal performance and long-term value.