Cast aluminum cookware is widely favored in household and commercial kitchens due to its excellent thermal conductivity (120–150 W/(m·K)), lightweight properties (density 2.7 g/cm³), and good formability for complex shapes.

However, pure cast aluminum has inherent drawbacks: poor corrosion resistance (prone to oxidation and pitting in acidic/alkaline environments), low surface hardness (HV 30–40), and lack of non-stick performance.

Surface treatments and non-stick systems are therefore critical to enhancing the durability, safety, and usability of cast aluminum cookware.

1. Fundamental Characteristics of Cast Aluminum Cookware Substrate

The surface treatment effect is directly determined by the substrate properties of cast aluminum cookware, which are closely related to the casting process:

Casting Processes and Surface Morphology

• Sand Casting: Low-cost, suitable for large cookware (e.g., stock pots). The surface is rough (Ra 3.2–6.3 μm) with inherent defects such as porosity (diameter 50–200 μm) and sand inclusions, requiring intensive grinding and polishing before surface treatment.
• Die Casting: High precision, smooth surface (Ra 1.6–3.2 μm), and dense structure, widely used for frying pans and saucepans. However, the rapid cooling process may cause surface segregation and oxide films, affecting coating adhesion.
• Gravity Die Casting: Balances precision and cost, with surface roughness (Ra 2.0–4.0 μm) and mechanical properties superior to sand casting, suitable for mid-to-high-end cookware.

Substrate Pretreatment: The Foundation of High-Quality Surface Treatment

Pretreatment aims to remove surface contaminants, adjust roughness, and form a transition layer to improve the adhesion of subsequent coatings. The standard process includes:

1. Degreasing: Uses alkaline degreasers (5–8% NaOH solution, 50–60℃, 10–15 minutes) to remove machining oil, mold release agents, and organic residues.
   For die-cast aluminum, ultrasonic degreasing (frequency 40 kHz) is recommended to eliminate contaminants in micro-pores.
2. Pickling/Etching: Uses dilute phosphoric acid (8–12%, 25–35℃, 3–5 minutes) to etch the surface, remove the natural oxide film (Al₂O₃), and form a micro-rough structure (Ra 0.8–1.2 μm) to enhance mechanical interlocking with coatings.
   Avoid hydrofluoric acid-based etchants due to environmental and safety risks.
3. Chemical Conversion Coating: Forms a thin (0.5–2 μm) protective film on the aluminum surface, commonly using chromate-free systems (e.g., zirconium-titanium-based, 2–3 μm) to replace traditional hexavalent chromate (banned by EU REACH regulations).
   This layer improves corrosion resistance and coating adhesion, with a corrosion current density reduced to <1×10⁻⁶ A/cm².
4. Drying and Activation: Dries at 80–100℃ for 20–30 minutes to remove residual moisture, then activates at 150–180℃ to enhance the reactivity of the conversion film.

2. Mainstream Surface Treatments for Cast Aluminum Cookware

Anodic Oxidation (AO)

Anodic oxidation is a mature surface treatment technology that forms a dense aluminum oxide (Al₂O₃) film on the cast aluminum surface through electrolysis, significantly improving corrosion resistance and hardness.

• Technical Principle: Uses cast aluminum as the anode in an electrolyte (sulfuric acid 15–20%, 18–22℃), applies a DC voltage of 12–18 V, and controls the current density at 1–2 A/dm².
  The aluminum surface undergoes electrolytic oxidation: 2Al + 3H₂O → Al₂O₃ + 6H⁺ + 6e⁻.
  The resulting anodic oxide film is porous (porosity 10–15%) with a double-layer structure (barrier layer 0.1–0.3 μm, porous layer 10–20 μm).
• Performance Characteristics: Hardness reaches HV 300–400 (5–10 times that of the substrate), corrosion resistance is Class 9 (per ASTM B117 salt spray test, no corrosion after 1000 hours), and the film is non-toxic and heat-resistant (up to 500℃).
  However, the porous structure is not inherently non-stick and requires sealing or coating.
• Modified Processes:

• Hard Anodic Oxidation (HAO): Uses low-temperature electrolytes (-5–0℃) and high current density (2–3 A/dm²) to form a thicker film (20–50 μm) with hardness HV 400–500, suitable for high-wear cookware (e.g., grill pans).
• Colored Anodic Oxidation: Dyes the porous layer with organic/inorganic dyes (e.g., black nickel sulfate, red acid dyes) to improve aesthetics, with color fastness meeting ISO 105-A02 standards.

Chemical Conversion Coating (CCC)

As a pretreatment or standalone surface treatment, chemical conversion coatings are widely used in mid-range cookware due to their low cost and environmental friendliness.

• Zirconium-Titanium-Based Conversion Coating: The most common chromate-free system, forming a composite film of zirconium oxide, titanium oxide, and aluminum oxide.
  It has good compatibility with non-stick coatings, with a pull-off adhesion strength of ≥3 MPa (per ASTM D4541).
• Phosphate Conversion Coating: Uses phosphoric acid and zinc phosphate to form a crystalline phosphate film (1–3 μm), which enhances wear resistance but has lower corrosion resistance than zirconium-titanium-based films, suitable for indoor-use cookware.

Ceramic Coating

Ceramic coatings (inorganic non-stick coatings) are gaining popularity due to their high temperature resistance and environmental friendliness, composed of alumina, silica, and titanium dioxide.

• Preparation Process: Sprays ceramic slurry (solid content 40–50%) onto the pretreated cast aluminum surface, followed by drying (120–150℃, 30 minutes) and sintering (450–500℃, 60 minutes).
  The slurry contains inorganic binders (e.g., sodium silicate) and dispersants to ensure film uniformity.
• Performance Advantages: Heat resistance up to 600℃ (no decomposition or toxic gas emission), hardness HV 500–600 (excellent scratch resistance), and compatibility with metal utensils.
  However, brittleness is a drawback—impact resistance is poor (per ASTM D2794, flexural strength <5 MPa), and cracks may occur under severe temperature changes.

Electroless Nickel Plating (ENP)

Electroless nickel plating forms a uniform nickel-phosphorus (Ni-P) alloy film on cast aluminum, suitable for specialized cookware (e.g., commercial woks) requiring high wear resistance.

• Technical Parameters: Uses nickel sulfate (20–30 g/L) as the main salt, sodium hypophosphite (25–35 g/L) as the reducing agent, pH 4.5–5.5, temperature 85–90℃, and plating time 60–90 minutes. The film thickness is 10–20 μm, with a phosphorus content of 8–12%.
• Performance: Hardness HV 500–600 (after heat treatment at 400℃), corrosion resistance (salt spray test >2000 hours), and good non-stick properties after polishing.
  However, the high cost and potential nickel ion migration (regulated by FDA 21 CFR 175.300) limit its household application.

3. Non-Stick Systems for Cast Aluminum Cookware

Non-stick systems are divided into organic (polymer-based) and inorganic (ceramic-based) categories, with polymer-based systems dominating the market due to superior non-stick performance.

Polytetrafluoroethylene (PTFE) Non-Stick System

PTFE (Teflon) is the most mature non-stick material, with a low surface energy (18–20 mN/m) that prevents food adhesion.

The non-stick system typically uses a multi-layer structure:

• Structure Design:

• Bottom Coat (Primer): 15–20 μm thick, composed of PTFE and phenolic resin (adhesive), with aluminum oxide particles (5–10 μm) added to enhance adhesion and wear resistance.
• Top Coat (Finish): 10–20 μm thick, high-purity PTFE (95%+), ensuring non-stick performance.
  For high-wear applications, a middle coat (10–15 μm) with glass fiber reinforcement is added.

• Preparation Process: Sprays the primer first, dries at 120–150℃ for 15 minutes, then sprays the top coat, and cures at 380–420℃ for 30–40 minutes.
  Curing temperature must exceed PTFE’s melting point (327℃) to form a continuous film.
• Performance Evaluation:

• Non-stickiness: Passes the "fried egg test" (no oil, egg slides off easily) and "tomato sauce test" (no adhesion after 24 hours).
• Wear Resistance: Meets ASTM D4060 (Taber abrasion test, weight loss <5 mg after 1000 cycles with 500 g load).
• Safety: PTFE is inert at temperatures <260℃; decomposition occurs above 350℃, releasing toxic perfluoroisobutylene (PFIB). Thus, cookware with PTFE coatings is labeled "max temperature 260℃".

Perfluoroalkoxy Alkane (PFA) Non-Stick System

PFA is a modified PTFE with better melt flowability and adhesion, suitable for complex-shaped cast aluminum cookware (e.g., curved frying pans).

• Key Advantages: Higher temperature resistance (continuous use up to 260℃, short-term up to 290℃), better flexibility (elongation at break >300%), and easier repair of coating defects.
  The film is transparent, maintaining the aluminum’s metallic luster.
• Limitations: Higher cost than PTFE (1.5–2 times) and slightly lower scratch resistance (Taber abrasion weight loss <8 mg after 1000 cycles).

Ceramic-Based Non-Stick System

Ceramic non-stick systems use inorganic materials (alumina, silica, titanium dioxide) with added organic modifiers (e.g., silicone resin) to balance non-stickiness and hardness.

• Performance Characteristics:

• Heat resistance up to 450–500℃ (safe for oven use), no toxic gas emission, and compatibility with metal utensils.
• Non-stickiness is achieved by the smooth ceramic surface (Ra <0.2 μm), but it is inferior to PTFE—food may adhere slightly after repeated use.

• Failure Mechanism: The organic modifier decomposes at high temperatures, leading to reduced non-stickiness; the ceramic film is brittle and prone to cracking under thermal shock (e.g., sudden cooling from 300℃ to room temperature).

Emerging Non-Stick Technologies

• Diamond-Like Carbon (DLC) Coating: Forms an amorphous carbon film (sp³ hybridized) with surface energy <25 mN/m, hardness HV 1500–2000, and heat resistance up to 400℃.
  It combines excellent non-stickiness and wear resistance but is limited by high deposition cost (CVD process).
• Fluorine-Free Polymer Coatings: Uses polyetheretherketone (PEEK) or polyphenylene sulfide (PPS) as the base material, with surface energy modified by silicone additives.
  PEEK coatings have high temperature resistance (260℃) and biocompatibility but poor non-stickiness compared to PTFE.
• Composite Non-Stick Systems: Combines anodic oxidation with PTFE/ceramic coatings—anodic oxide film as the base layer (corrosion resistance), PTFE/ceramic as the top layer (non-stickiness).
  This system has a service life 2–3 times longer than single-layer coatings, suitable for high-end cookware.

4. Conclusion

Surface treatments and non-stick systems are core technologies determining the quality, safety, and service life of cast aluminum cookware.

Anodic oxidation, chemical conversion coatings, and ceramic coatings address the substrate’s corrosion and hardness issues, while PTFE/PFA-based non-stick systems ensure usability.

The performance of these technologies depends on substrate pretreatment, process parameter control, and compliance with safety standards.

Reference article: https://langhe-industry.com/custom-cast-aluminum-cookware-supplier/