CoataBond AL-650

1. Product Characteristics

● Non-hexavalent chromium passivation for aluminum materials.

● Can be used as a post-treatment solution for anodic oxide layers.

● Capable of forming conversion coatings on magnesium.

● A concentrated liquid based on trivalent chromium.

● Corrosion resistance superior to hexavalent chromium passivation processes.

● Suitable for aluminum alloys and aluminum die castings.

● Can be used as a pre-treatment for painting, powder coating, and adhesive bonding.

● Complies with all ELV, RoHS, and WEEE requirements.

● Easy to operate via immersion, spray, or manual wiping to form a transparent, lightly iridescent coating.

● Corrosion resistance standards exceed MIL-DTL-81706 and MIL-DTL-5541; initial white rust appears after more than 336 hours of neutral salt spray (NSS) testing.

● Low contact resistance.

● High heat-resistant inorganic passivation film.

2. Preparation Method

CoataBond AL-650 can be applied via immersion, spray, or wiping processes. Use deionized (DI) water for dilution during bath setup.

Process Parameters

Bath Setup & Equipment

Bath Setup: Dilute CoataBond AL-650 with deionized water to the required volume and stir thoroughly. Monitor the pH level and, if necessary, adjust using 5% sulfuric acid or 1% sodium hydroxide.

Tank Material: Stainless steel or steel with acid-resistant and fluoride-resistant lining.

Hanger/Rack Material: Titanium, stainless steel (V4A), aluminum, or plastic.

Filtration: Required (minimum of 2 cycles per hour). For coating applications, solution particles must be filtered to less than 25 microns.

Heating: Required; heating equipment must be resistant to acid and fluoride.

Exhaust System: Recommended for worker health and safety.

General Immersion Pre-treatment Process

Aluminum Alloy (Silicon content < 1%)

● Weak Alkaline Degreasing

● Alkaline Etching

● Deoxidizing (Desmutting)

● CoataBond AL-650 Trivalent Chromium Passivator

Aluminum Alloy (Silicon content > 1%)

● Weak Alkaline Degreasing

● Deoxidizing (Desmutting)

● CoataBond AL-650 Trivalent Chromium Passivator

General Spray Pre-treatment Process

Acidic Degreasing:

● Acidic Degreasing

● CoataBond AL-650 Trivalent Chromium Passivator

Note: Water rinsing must be performed between every step. The rinsing method should be appropriate for the specific production line. These steps are general guidelines; parameters should be adjusted based on site conditions to achieve optimal results.

Technical Guidance & Tips

Handling: Metal barrels or goods intended for passivation must be handled individually.

Storage: Some sediment may form during storage, but this does not affect the quality or performance of the product.

Process Flow: Surfaces must be thoroughly degreased and deoxidized (water-break-free) before using CoataBond AL-650. If the degreaser contains silicates, it is best to follow up with a fluoride-containing acid etch. It is recommended to adjust the pH of the final rinse before passivation to 3.5–4.0 to prevent significant pH fluctuations in the passivation bath.

Post-Treatment: The film must be rinsed with pure water after treatment to ensure superior corrosion resistance. If painting follows passivation, the conductivity of the final rinse must be maintained at < 30 µS/cm.

Testing: A "spot test" can be performed to confirm the presence of the trivalent chromium film. (Test kits and instructions are available separately). Before conducting Neutral Salt Spray (NSS) testing, parts must be aged at room temperature for 24 hours.

Corrosion Resistance & Coating Tips

Process Parameters:

Temperature and immersion time are inversely related. Higher temperatures require shorter immersion times, while lower temperatures require longer times.

Coating Weight

Coating weight is closely linked to the surface roughness of the aluminum.

● Best Corrosion Resistance: ~0.25 g/m² (Range: 0.11–0.5 g/m²)

● Colorless Film: ~0.08 g/m² (Range: 0.05–0.20 g/m²)

● Powder Coating Pre-treatment: 0.05–0.12 g/m² (for extruded profiles).

Tempering/Thermal Stability

During drying, the surface temperature should not exceed 65°C. Freshly formed films contain hydrated molecules; drying too quickly at high temperatures can cause micro-cracks, reducing corrosion resistance. However, once the film is properly dried (aged), it can withstand high-temperature processes like paint baking without significant performance loss.

Note: Stability varies by aluminum grade. For example, copper-free aluminum can often be dried at temperatures above 100°C without negative effects.

pH Control

For pure corrosion protection, the pH range must be strictly maintained at 3.9 (3.7–3.95). Deviations outside this range will lead to a decrease in corrosion resistance.

Storage After Treatment

Workpieces can be painted immediately after treatment or stored. The film protects against contamination and extreme temperature fluctuations. For best results, coat within 7 days (ideally within 12 hours).

Drying Temperature

Recommended at 65°C (Range: Room Temperature to 100°C).

3. Technical Data

The following values are measured at 20°C:

4. Maintenance and Analysis

Regularly monitor the pH value and adjust the concentration of the CoataBond AL-650 solution at scheduled intervals.

4.1 Sample Preparation

Extract a sample from a well-mixed bath. Allow it to cool to room temperature. If the sample is turbid, let the sediment settle and filter it using high-quality filter paper.

4.2 Analysis of CoataBond AL-650 Concentration — Titration Method

Reagents:

● 10% Sodium Hydroxide

● 30% Hydrogen Peroxide

● 17% Hydrochloric Acid

● Potassium Iodide

● 0.1N Sodium Thiosulfate solution

● 1% Starch solution

Procedure:

1. Pipette 100 ml of the passivation bath solution into a 250 ml Erlenmeyer flask; add 20 ml of 10% sodium hydroxide solution.

2. Add 5 ml of hydrogen peroxide and stir for 5 minutes.

3. Boil the solution for 20–30 minutes to remove excess hydrogen peroxide. (The volume should not drop below 50 ml; if it approaches 50 ml, stop heating. Cover the flask with a watch glass during boiling).

4. Cool the solution to room temperature and filter with precision filter paper.

5. Wash the filter with 10 ml of deionized water. The filtered solution must be clear and free of sediment.

6. Dilute the filtrate to approximately 100 ml with deionized water.

7. Acidify the filtrate by adding 40 ml of 17% hydrochloric acid (the solution color will change from yellow to orange).

8. Add 1 g of potassium iodide.

9. Titrate with 0.1N sodium thiosulfate until the solution turns pale yellow.

10. Add a few drops of starch solution and continue titrating until the blue color disappears.

Calculation:

ml consumed x 1.613 = % Vol CoataBond AL-650

4.3 Analysis of CoataBond AL-650 Concentration — AAS Method

Atomic Absorption Spectroscopy (AAS)

Procedure:

1. Place 5 ml of 1:1 analytical grade nitric acid solution into a 100 ml volumetric flask.

2. Pipette 5 ml of CoataBond AL-650 bath solution into the flask and mix thoroughly.

3. Let stand for 5 minutes, then fill to the mark with pure water; invert 10 times to mix.

4. Calibrate the AAS with a chromium standard solution, then measure the prepared sample.

Parameters:

Wavelength: 357.9 nm

Slit Width: 0.7

Calculation:

Value (PPM) x 0.0974 = % Vol CoataBond AL-650

Note: Dilute the sample as necessary to ensure it falls within the range of the AAS standard curve.

4.4 Coating Weight Test Method

Equipment: Analytical balance (+/- 0.1 mg)

Reagents: 50% vol Nitric Acid (65%)

Procedure:

1. Passivate a sample piece of known surface area (m2), typically larger than 2 dm2, using CoataBond AL-650.

2. Rinse with pure water and blow dry with compressed air at room temperature.

3. Weigh the sample (M1) using the analytical balance within 3 hours of passivation.

4. Strip the passivation film using nitric acid (at 20–25°C for 4 minutes).

5. Rinse with pure water and blow dry with compressed air at room temperature.

6. Weigh the dried workpiece again (M2).

7. Perform degreasing and deoxidizing on a blank sample piece (without passivation), then repeat the above steps to obtain M3 and M4.

Calculation:

1. (M1 - M2) / Surface Area = A

2. (M3 - M4) / Surface Area = B

3. Coating Weight (g/m2) = A - B

5. Composition

Trivalent Chromium Salts (Cr3+)

6. Inventory

Consumption is primarily determined by the "drag-out" rate. Below is an average assessment of consumption:

Every 1 m2 of treated surface area requires approximately 45–55 ml of CoataBond AL-650 solution (based on a bath concentration of 20% vol and an average drag-out of approximately 200 ml/m2).

Surface Roughness: Drag-out may increase when processing rougher workpieces. On rough surfaces, the actual reactive surface area is greater than the physical dimensions of the part, leading to higher chemical consumption.

Contamination: Carrying alkaline solutions into the CoataBond AL-650 bath will cause additional chemical consumption.

To prevent supply issues, a certain level of inventory should be maintained. We recommend keeping a stock of 500 kg of CoataBond AL-650 for every 1,000 L of bath volume.

7. Product Safety and Environmental Protection

To avoid harm to personnel and the environment, it is essential to obtain the safety and environmental protection instructions for this product. The Material Safety Data Sheet (MSDS) provided by our company contains these comprehensive instructions.

8. Troubleshooting

‍‍‍9. Disclaimer‍‍‍

All recommendations and suggestions regarding our company's products in this manual are based on experiments and data we deem reliable. Since we cannot control the actual operations of other practitioners, our company cannot guarantee or be held responsible for any adverse consequences.