Which Materials Are Not Suitable for Wet Polishing? Material Restrictions and Process Analysis of Wet Polishing

1. Core Principle of Wet Polishing Limitations

Wet polishing uses water as the medium to assist grinding. By process nature, it is only suitable for water‑resistant, oxidation‑resistant and structurally stable metals. For workpieces with high chemical activity, porous water‑absorbing structure, poor waterproof performance or water‑sensitive downstream processes, water environment accelerates material corrosion, impurity precipitation and surface texture deterioration. Besides, residual water stains and water films from wet grinding may trigger bubbling, delamination and color difference in subsequent electroplating, spraying and PVD coating. This is the primary reason why wet polishing is prohibited for many high‑end precision components.

2. Materials Absolutely Unsuitable for Wet Polishing 

1. Magnesium Alloy & Magnesium‑Aluminum Alloy (Highly active oxidation‑prone materials) Magnesium alloy features extremely high chemical activity. Grinding with water triggers rapid oxidation, resulting in widespread whitening, hazing and oxidation spots on workpiece surfaces. Continuous rusting and darkening will occur during storage. Trapped water inside gaps after wet grinding can hardly be fully dried, creating hidden corrosion points that cause defective electroplating and anodizing. It is the top forbidden material for wet polishing. Dry drag finishing is mandatory for mass production.
2. Zinc‑Alloy Die‑castings (High‑end appearance parts) General zinc‑alloy parts can undergo short‑term wet rough grinding. However, wet polishing is strictly forbidden for high‑end cosmetic, mirror‑finish and matte precision zinc‑alloy components. Zinc alloy has loose density and tends to absorb liquid. Wet processing leads to white haze, watermarks and uneven color shades. Dried water stains cannot be eliminated, ruining uniform surface texture and bringing about show‑through effect, mottling and poor coating adhesion after electroplating.
3. Powder Metallurgy & Porous Sintered Materials These workpieces are characterized by dense internal pores and loose structure. Water and polishing fluid penetrate into micro‑pores during wet polishing and cannot be thoroughly cleaned or dried. Liquid trapped inside pores will later cause moisture resurgence, mildew, whitening and rusting, damaging structural stability and service performance. Only dry polishing is applicable.
4. Precision Electronic Conductive Components 3C conductive terminals, micro‑contacts and precision electronic connectors demand ultra‑high cleanliness and stable conductivity. Wet polishing leaves residual water and chemical contaminants, giving rise to contact oxidation, poor conductivity and micro‑short‑circuit risks. Water trapped in crevices is difficult to remove, failing to meet high‑cleanliness mass‑production requirements for electronic parts.
5. Hygroscopic Non‑metallic Materials Deteriorated by Water Resin, certain soft plastics and special‑coated parts will swell, suffer surface whitening, coating peeling and soft deformation upon water exposure. Wet polishing destroys original structure and cosmetic precision. Dry flexible polishing shall be adopted.

3. Materials for Cautious Wet Polishing 

Aluminum alloy and copper alloy can be wet‑ground for short‑time rough deburring, yet not suitable for wet fine polishing and brightening. Wet grinding easily causes hazing & whitening on aluminum parts and discoloration on copper parts. Fine and uniform premium matte finish cannot be achieved. Dry drag finishing is recommended for all high‑end appearance parts to guarantee consistent texture.

4. Industry‑Standard Material‑Process Matching 

• Ordinary stainless steel, iron parts, large castings, sanitary rough castings → Prioritize wet polishing for efficient deburring and scale removal
• Magnesium alloy, premium zinc‑aluminum parts, powder metallurgy, precision electronic parts, porous materials → Adopt dry drag finishing / dry precision polishing uniformly

5. Key Summary for Process Selection

Wet Polishing Prohibited: Magnesium alloy, high‑grade zinc alloy, powder metallurgy, porous sintered parts, precision conductive electronic components, water‑sensitive non‑metallic parts