Introduction: A trivalent chromium passivator for high-silicon die cast aluminum must be chosen around the cast surface, pretreatment, and film targets—not just the bath chemistry.
A die caster running A380, ADC12, or another high-silicon alloy sees a very different surface after demolding than an extrusion plant sees after drawing. The as-cast skin, silicon-rich surface layer, and loose material from the die all affect how a conversion coating forms. A passivation line tuned for extruded profiles will not deliver the same result on a casting without adjustment. The practical decision is to choose a passivator that covers wrought and cast substrates, set pretreatment so the cast surface is ready, and define salt spray, heat exposure, and powder coating targets before running a trial. AL-100 is suitable for wrought aluminum and for high- and low-silicon die castings, so it can serve as the starting point for that work.
Die cast aluminum is a different material family from wrought aluminum, and The Aluminum Association separates cast and wrought alloys into distinct categories for that reason. Die castings solidify quickly against a steel die, so the surface that comes out is not a clean aluminum skin. It carries as-cast material, die lubricant residue, and, in high-silicon alloys, a network of silicon particles in the aluminum matrix. That silicon-rich layer affects every pretreatment step and determines how evenly the conversion coating grows once the part enters the bath. In this context, high-silicon die castings are those above 1% silicon, while low-silicon castings are at or below 1%. High-silicon alloys can leave silicon-rich smut after etching or desmutting, and if that smut remains on the surface, the passivation bath can be blocked from the aluminum underneath. The result is a film that looks patchy, sits thin at edges, or fails early in salt spray. AL-100 is suitable for both low-silicon (≤1%) and high-silicon (>1%) die castings, so the same bath chemistry can be trialed on both. What changes is how much pretreatment work the surface needs before it is ready for the tank. The passivator does not dissolve silicon; the surface must be prepared so the bath can reach the aluminum. For high-silicon castings, that means removing as-cast skin and silicon-rich smut before passivation. AL-100 leaves a transparent, light colored film, which helps inspection: patches, streaks, and missed areas are easier to see before powder coating rather than after.
Wrought aluminum arrives at the passivation line with a relatively uniform surface. Extruded profiles, rolled sheet, and drawn tube all have a thin, consistent oxide layer and predictable grain structure, so a standard degrease-clean-etch-desmut sequence usually produces a surface that takes a conversion coating evenly. Powder coating specifications such as QUALICOAT treat that pretreatment stage as part of the coating system itself, because the conversion film is what the powder anchors to. For a wrought profile, the film target is usually thin, uniform, and judged for adhesion as part of the powder coating system. A die casting offers a different starting point. The as-cast skin holds die lubricant, oxide inclusions, and, in high-silicon alloys, that silicon-rich layer. Machined die castings expose another surface again, sometimes with porosity opened at the cut. Pretreatment therefore has to work harder: remove lubricant and loose material, strip back the as-cast skin, and leave a chemically active surface without over-etching the part or leaving smut behind. If the casting reaches the passivation bath before that surface is ready, the film forms unevenly and the defect only appears later, after salt spray or after the coating line. The film target shifts too. A wrought extrusion for architectural powder coating is judged mainly on appearance and adhesion. A die cast automotive or industrial part is usually judged on three things at once: neutral salt spray hours, adhesion of the paint or powder applied on top, and behavior under heat. European Aluminium's automotive work points to the same pressure from the vehicle side—more aluminum parts, more exposure to road salt and moisture, and a coating system that must keep bonding through service exposure. That is why AL-100 is intended for use as a coating base as well as a corrosion layer. The transparent, light colored film it leaves on cast and wrought parts is designed to be coated over, not stripped off.
AL-100 runs at 100–500 ml/L in deionized water, at pH 3.7–3.95 and 30–40 °C, and it works in immersion, spray, and hand wipe lines. The tank must be stainless steel or steel lined for acid and fluoride resistance, so tank material belongs in the trial setup. Once the line and the substrate are sorted, the trial plan comes down to four decisions.
Die casting material decides pretreatment, and the film target decides your acceptance criteria. High-silicon castings need more surface preparation than wrought profiles before the passivation bath can do its job, but both substrates are covered by the same bath chemistry when the line is set up correctly. The neutral salt spray result of more than 336 hours under ASTM B-117 and DIN 50021 SS NSS, the 100 °C heat resistance, and the transparent film that doubles as a coating base give you concrete targets to trial against. Whether you are sourcing from electroplating chemicals manufacturers or aluminum anodizing chemicals manufacturers for a die casting line, the useful next step is the same: send your alloy, silicon content, surface condition, treatment method, tank materials, and target salt spray hours so trial parameters can be prepared for your line.
A: Yes. AL-100 is rated for wrought aluminum and for both high-silicon (>1%) and low-silicon (≤1%) aluminum die castings, and it leaves a transparent light colored film on either substrate. High-silicon castings need their as-cast skin and silicon-rich smut removed before passivation, so the exact behavior of a specific alloy is worth checking with a sample trial on your parts.
A: Gather the alloy designation and silicon content, whether parts are as-cast or machined, current pretreatment steps, intended application method (immersion, spray, or hand wipe), available tank and heating materials, target salt spray hours, and downstream coating system. Also confirm deionized water supply, pH adjustment chemicals, and wastewater handling. These details let the trial match the line and the parts being processed.
A: Yes. The AL-100 film is designed to act as a primer for paint, powder coating, and sizing, not as a final cosmetic layer. Keep the film uniform and parts clean between the passivation tank and the coating line, and confirm adhesion with the standard tests your powder coater already uses; coating specifications such as QUALICOAT treat pretreatment and adhesion as one system.
Standards | The Aluminum Association
Automotive Life-Cycle Assessment Model - European Aluminium
