Introduction: Choosing a trivalent chromium passivator for an aluminum line starts with the substrate, line mode, and a bath window the plant can hold every shift.
A concentrated liquid passivator lets a finishing plant run one chemistry across extruded profiles and cast aluminum parts, then adjust concentration, pH, and temperature for immersion, spray, or hand-wipe work. Separate substrate decisions from line-mode decisions before setting a trial bath; that sequence keeps the first trial small and makes results easier to read.
Start with the metal. The Aluminum Association separates aluminum products into wrought and cast categories, and that split matters for passivation planning. Wrought aluminum covers extruded profiles and rolled sheet. Cast aluminum covers cast parts, which vary in surface condition and silicon content. Fengfan AL-100 is a concentrated liquid trivalent chromium passivator for aluminum. It is used on wrought aluminum and on cast aluminum with low or high silicon content. One passivator can serve an extrusion line and a cast aluminum line, but the two lines need separate trial plans. Extruded profiles usually have a more uniform surface, so passivation focuses on film consistency and adhesion before paint or powder coating. Cast parts often need more cleaning and surface preparation because porosity, release agent residue, and silicon-rich phases can change how the bath wets the surface. Line mode determines how the chemistry contacts the surface. Immersion, spray, and hand-wipe stations expose aluminum to chemistry in different ways. Immersion gives longer contact time and more uniform wetting around complex shapes. Spray lines move fast, so the bath must react quickly and drain cleanly. Hand-wipe work suits large parts or repair spots, but the operator controls contact time and coverage. AL-100 works in all three modes. The mode changes the starting concentration: immersion typically runs at 200–300 ml/L, spray at 250–300 ml/L, and both sit inside the wider 100–500 ml/L dilution range. If a line handles extrusions and cast parts, choose one primary mode for the first trial, then confirm the second mode on a small set of panels before committing the full tank.
Once substrate and line mode are clear, set the bath. AL-100 has a working window of 100–500 ml/L, pH 3.7–3.95, and 30–40 °C. Within that range, it forms a transparent, light-colored conversion coating. Pick a starting point inside the range, hold it steady, and adjust from panel results. Concentration controls how much active chemistry reaches the surface. pH controls the balance between film formation and bath stability. Temperature controls reaction speed and how evenly the film builds. When one parameter drifts, the coating may look thin, cloudy, or uneven, and downstream salt spray or contact resistance can shift with it.
Deionized water is the right starting point because tap water brings unknown hardness, chloride, and metal ions into a bath designed for controlled chemistry. Those ions can interfere with film formation and make it harder to hold pH 3.7–3.95. Mix AL-100 with deionized water and add the concentrate under steady agitation. Set initial pH with 5% sulfuric acid to lower it or 1% sodium hydroxide to raise it, then target about 3.9. That middle value leaves room to correct in either direction without leaving the working window. Check pH before each shift and after heavy drag-out; a titration routine and a calibrated meter help keep the film consistent from the first rack to the last.
Temperature and line mode work together. At 30 °C, the bath reacts more slowly, which can suit hand-wipe work or parts with complex geometry. At 40 °C, the reaction is faster and more complete, which is why immersion and spray lines commonly target 40 °C. A spray line often needs the higher end because contact time is short, so spray concentration is typically 250–300 ml/L while immersion is typically 200–300 ml/L. The spray bath has less time to react, so higher concentration supports film formation during brief exposure. Immersion can use a slightly lower concentration because the part stays in the bath longer. For immersion, a practical starting point is 250 ml/L at 40 °C and pH 3.9. For spray, start at 275 ml/L at 40 °C and pH 3.9. Adjust in small steps and record film appearance, coating weight if measured, and downstream test results.
A trial bath should answer three questions: Does the coating protect the part, does it support the electrical or coating requirement, and can the line hold the parameters in daily production? AL-100 gives performance targets to design around. In neutral salt spray testing per ASTM B-117 and DIN 50021 SS, the coating resists white rust for more than 336 hours. Contact resistance is below 0.8 mΩ/cm² on the tested film. The coating also withstands 100 °C, which matters for parts exposed to heat during assembly, powder curing, or service. Performance meets or exceeds MIL-DTL-81706 and MIL-C-5541 criteria; QPL listing is a separate qualification. If the finish specification requires powder coating adhesion, the transparent conversion coating acts as a pretreatment base. QUALICOAT specifications are a useful reference for architectural aluminum powder coating pretreatment, and the line still needs its own trial because alloy, cleaning, and rinse quality influence adhesion. If electrical grounding or shielding is required, test the low contact resistance target. If the part sees outdoor exposure, use the neutral salt spray result as the durability benchmark. Run the trial on small panels or scrap parts from both the extrusion line and the cast aluminum line. Use the current cleaning and rinsing sequence first, then passivate at the starting concentration, pH, and temperature for the chosen mode. Change one variable at a time. Hold pH near 3.9 and temperature near 40 °C while comparing two or three concentrations inside the working range. For immersion, compare 200, 250, and 300 ml/L. For spray, compare 250, 275, and 300 ml/L. After passivation, evaluate film appearance, neutral salt spray performance, contact resistance, and coating adhesion if paint or powder is applied. Exact pretreatment steps for a specific alloy are trial-dependent, so keep the first trial small and document every step. Confirm local wastewater rules for rinse water and spent bath. Before mixing the first bath, confirm that the tank and heating equipment are stainless steel or lined for acid and fluoride resistance.
Choosing a trivalent chromium passivator for an aluminum line is a parameter decision. Start with substrate: wrought aluminum profiles and cast aluminum parts can share one passivator family, but they deserve separate trial plans. Choose the line mode before setting concentration. Immersion typically runs at 200–300 ml/L, spray at 250–300 ml/L, with pH 3.7–3.95 and temperature 30–40 °C. Use deionized water, hold pH near 3.9, and keep the bath at 40 °C for immersion and spray trials. Design the trial around acceptance tests: neutral salt spray per ASTM B-117 and DIN 50021 SS, contact resistance below 0.8 mΩ/cm², 100 °C resistance, and paint or powder adhesion. AL-100 offers a defined operating window, a transparent, light-colored coating, and a consumption rate of about 15–25 ml of concentrate per m² including drag-out. Share the alloy type, line mode, tank size, and target finish with Fengfan to request technical details and a quote for a trial range that fits the plant.
A: Start with the working range of 100–500 ml/L, then use the mode-specific range. Immersion usually runs at 200–300 ml/L because the part stays in the bath longer. Spray usually runs at 250–300 ml/L because contact time is shorter and the bath must form the film quickly. Mix with deionized water, choose a mid-range starting point such as 250 ml/L for immersion or 275 ml/L for spray, and adjust in small steps based on film appearance, salt spray, and contact resistance.
A: Maintain pH between 3.7 and 3.95, with about 3.9 as the practical target. Use 5% sulfuric acid to lower pH and 1% sodium hydroxide to raise it. Keep temperature between 30 °C and 40 °C; immersion and spray lines commonly run at 40 °C for faster, more complete film formation. Check pH and temperature before each shift and after heavy drag-out so the bath stays inside the working window.
A: Yes. AL-100 is used on wrought aluminum, including extruded profiles, and on cast aluminum with low or high silicon content. The working ranges are the same, but the trial plan should be separate. Extruded parts often need a focus on film consistency and coating adhesion, while cast parts may need more attention to cleaning and surface prep. Run panels from both lines before converting a full tank.
Standards | The Aluminum Association
