Peças de alumínio fundido são amplamente utilizadas na indústria automotiva, eletrônica, e indústrias de hardware, mas a sua superfície crua muitas vezes carece de proteção, decoração, ou funções específicas. Die casting aluminum surface treatment solves this problem through systematic processes—yet many engineers struggle with choosing the right method. Este artigo detalha os processos principais, comparações, e estratégias de seleção para ajudá-lo a tomar decisões informadas.
1. Why Is Pretreatment the Foundation of All Surface Treatments?
Pretreatment eliminates surface defects and contaminants, directly determining the quality of subsequent treatments. Skipping or rushing this step leads to coating peeling, uneven coloring, or poor corrosion resistance. Below is a detailed breakdown of key pretreatment steps:
| Pretreatment Step | Core Purpose | Common Methods | Key Notes |
| Degreasing | Remove grease, release agent residue | Solvent cleaning, alkaline degreasing, limpeza ultrassônica | Choose methods based on contamination level (por exemplo, ultrasonic for heavy grease) |
| Oxide Film Removal | Eliminate natural thin oxide layer and slight surface metamorphism | Weak alkaline solution soaking | Avoid strong alkalis—they may etch the aluminum surface |
| Sanding/Descaling | Clear embedded mold sand or dirt from die casting | Manual sanding, mechanical sanding | Focus on areas with dense sand (por exemplo, gate or overflow grooves) |
| Deburring/Polishing | Remove burrs (at parting lines) and smooth surfaces | Manual polishing, mechanical grinding | Over-polishing closes pores (hurts coating adhesion); under-polishing leaves burr defects |
| Sandblasting/Shot Blasting | Improve surface roughness (boost coating adhesion) | Abrasive particle spraying (alumina, contas de vidro) | Uniform spraying is critical—avoid uneven roughness |
Special Note for Porosity: Usar impregnation (fill tiny pores with resin or wax) to improve air tightness—this is a must for subsequent dense treatments like electroplating.
2. Protective Treatments: Which One Fits Your Corrosion Resistance Needs?
Protective treatments extend the service life of die casting aluminum parts. Below is a comparison of the most common methods to help you choose:
| Tipo de tratamento | Working Principle | Vantagens | Limitações | Ideal Application Scenarios |
| Chemical Conversion Film | Chemical reaction forms a thin protective film (por exemplo, cromato, phosphate) | Baixo custo, simple process; good pre-coating base | Poor long-term corrosion resistance | Short-term protection (por exemplo, temporary storage) or pre-coating for spraying |
| Anodização | Electrochemical reaction generates a thick alumina film (duro, poroso) | Alta dureza (resistente ao desgaste); excelente resistência à corrosão | Die castings’ high porosity causes film blistering; poor dyeing effect | Parts needing high corrosion resistance (por exemplo, ferragens marítimas, luminárias ao ar livre) |
| Galvanoplastia | Electrolysis deposits metal layers (cromo, níquel) on the surface | Dual benefits: resistência à corrosão + decoração; high hardness (cromagem) | Complex pretreatment; strict control of chemical solutions (to avoid pore defects) | Decorative-cum-protective parts (por exemplo, acabamento automotivo, bathroom fixtures) |
| Pulverização | Apply coatings (pó, liquid, electrophoretic) on the surface | Rich colors; good coverage (fits complex shapes); powder coating is eco-friendly | High-temperature curing (needs temperature control to prevent deformation) | Parts with complex shapes (por exemplo, gabinetes eletrônicos, utensílios de cozinha) |
3. Decorative & Functional Treatments: Meet Special Requirements
Beyond protection, decorative treatments boost product value, enquanto functional treatments enable specific performance.
3.1 Decorative Treatments: From Matte to Metallic Shine
| Tratamento | Effect Description | Key Process | Limitações | Target Products |
| Polished/Brushed | Brilhante (polido) or textured (escovado: straight grain, studded grain) superfície | Mechanical grinding + polimento | Requires high initial surface quality | High-grade hardware (por exemplo, faucet handles, luxury electronic casings) |
| Sandblasting Effect | Uniform matte surface | Fine abrasive spraying | Cannot hide major surface defects | Parts needing low-gloss appearance (por exemplo, industrial control panels) |
| Anodização + Coloração | Dyeing (organic dyes) or electrolytic coloring (bronze, preto) after sulfuric acid anodizing | Anodizing → coloring → sealing | Die castings’ porosity limits dyeing uniformity | Semi-decorative parts (por exemplo, medium-grade furniture hardware) |
| Vacuum Coating (PVD) | Deposits metal/ceramic films (ouro, rose gold, titânio) via physical vapor deposition | High-vacuum environment + ion sputtering | Requires highly smooth substrate surface | High-end decorative parts (por exemplo, molduras para smartphones, casos de relógios de luxo) |
3.2 Functional Treatments: Tailored to Performance Needs
| Functional Requirement | Treatment Method | Exemplos de aplicação |
| Condutividade | Electroplating copper/silver; conductive oxidation | Conectores eletrônicos, electromagnetic shielding parts |
| Isolamento | Anodização (thick film); polyurethane insulating paint coating | Componentes do motor, electronic insulation brackets |
| Resistência à abrasão | Hard anodizing (film thickness: 20-50μm); PVD durable film; wear-resistant spray coating | Moving parts (por exemplo, engrenagens), cilindros, pneumatic components |
4. 4 Key Factors to Choose the Right Surface Treatment Process
Choosing a process is not about “the best” but “the most suitable.” Consider these four factors:
- Final Requirements: Clarify priorities—Is it corrosion resistance (por exemplo, outdoor parts need anodizing), decoração (por exemplo, luxury parts need PVD), ou funcionalidade (por exemplo, connectors need conductive plating)?
- Propriedades dos materiais: Alloy composition and surface quality matter. Por exemplo, ADC12 aluminum alloy (high silicon content) may affect electroplating uniformity; porous surfaces require impregnation first.
- Custo & Environmental Friendliness: Balance budget and regulations. Cromagem (alto custo, toxic) is being replaced by eco-friendly options like powder coating or PVD.
- Production Scale: Processos automatizados (por exemplo, electrophoresis, revestimento em pó) suit mass production; manual polishing/PVD fits small-batch high-end products.
Yigu Technology’s Perspective on Die Casting Aluminum Surface Treatment
Na tecnologia Yigu, we believe pretreatment precision and process matching are the keys to successful die casting aluminum surface treatment. Over the years, we’ve seen many projects fail due to neglected porosity (no impregnation) or mismatched treatments (por exemplo, using anodizing for highly porous ADC12 parts). We advocate a “test-first” approach: conduct small-batch trials to verify pretreatment effectiveness and coating adhesion before mass production. Adicionalmente, as environmental regulations tighten, we prioritize eco-friendly processes like powder coating and chrome-free conversion films—helping clients meet both performance and sustainability goals.
Perguntas frequentes (Frequently Asked Questions)
- P: Why do die casting aluminum parts often have blistering during anodizing?
UM: The main cause is high surface porosity of die castings. During anodizing, air or moisture in pores expands under electrolysis, leading to blistering. Solve this by adding an impregnation step before anodizing to seal pores.
- P: Which is more cost-effective for mass-produced outdoor aluminum parts—anodizing or powder coating?
UM: Powder coating is more cost-effective. It has lower equipment investment than anodizing, faster curing speed (suitable for mass production), and excellent outdoor weather resistance. Anodizing is better only if ultra-high hardness is required.
- P: Can vacuum coating (PVD) be applied to die casting aluminum parts with rough surfaces?
UM: Não. PVD requires a highly smooth substrate (Ra ≤ 0.2μm). Rough surfaces will cause uneven film deposition, affecting both appearance and wear resistance. Pre-treat rough parts with fine polishing or sandblasting to smooth the surface first.