The short answer
White rust on aluminium die-castings is aluminium hydroxide formed when moisture stays on the surface after washing. Remove it with an inhibited acidic brightener such as POWER CLEAN ALB at 5–9% in ultrasonic at room temperature, then prevent recurrence with an inhibited cleaner, a clean rinse and thorough drying.
- Alloys
- ADC10, ADC12 (LM6 / LM24), 3000/5000/6000 series
- ALB ultrasonic dose
- 5–9% at 25–35 °C, 3–8 min
- ALB manual soak
- 10–15%, 15–20 min
- Ultrasonic frequency
- 28–40 kHz
- Documented result
- White-rust defects 3.2% → 0.4% in 45 days
White rust is the defect that quietly destroys yield on die-cast lines. Parts leave the washer looking acceptable, and by the time they reach inspection or the customer, a dull white bloom has formed across the surface. It is rejected as cosmetic, but the cause is process, not appearance.
What white rust actually is
Aluminium oxidises the moment it meets air, forming a thin protective oxide layer. That layer is stable when dry. When moisture is trapped against the surface — in a blind hole, under a fixture, between stacked parts, or simply because the part was not dried properly — the reaction continues and produces aluminium hydroxide: a loose, powdery white deposit. Die-castings are especially prone because their porosity holds water.
- Parts stacked or binned while still damp
- Incomplete rinsing, leaving alkaline residue that keeps reacting
- Hard or untreated rinse water leaving mineral deposits that hold moisture
- An uninhibited high-alkaline cleaner attacking the aluminium directly
- Humid storage without any protective film
Removing existing white rust and oxidation
Removal needs controlled acidity. POWER CLEAN ALB is an organic acid-based brightener developed for ADC10 and ADC12 — strong enough to strip oxidation, black marks and grey staining, mild enough that it does not aggressively attack the base metal the way mineral acids do.
| Method | Concentration | Temperature | Time | Best for |
|---|---|---|---|---|
| Ultrasonic (recommended) | 5–9% | Room temp 25–35 °C | 3–8 min | High volume, complex geometry |
| Manual soak | 10–15% | Room temp | 15–20 min | Small batches, delicate parts |
| Air agitation | 10–12% | Room temp | 10–15 min | Medium volume, moderate soiling |
Stopping it coming back
Stripping the bloom is the easy half. If the process that created it is unchanged, it returns within days. Four changes fix it in almost every plant we have worked in.
- 1Switch to an inhibited cleaner formulated for aluminium. POWER CLEAN LF-59 is built for ADC10, ADC12 and 6000-series work, with phosphonate-based corrosion inhibitors and biodegradable surfactants, and runs from ambient temperature with no foam in spray systems.
- 2Rinse thoroughly, preferably with DM water. For critical parts use a two-stage rinse — it removes residue completely and prevents water spotting.
- 3Dry completely and immediately. Filtered hot air or nitrogen; do not bin parts while damp.
- 4Control the bath. Monitor concentration by titration or refractometer, keep filtration running, and hold the working pH in band — LF-59 typically sits at pH 9.3–10.3.
“After switching to POWER CLEAN LF-59 for our ADC12 engine housings, we saw a reduction in white-rust defects from 3.2% to 0.4% within 45 days.”
— Major automotive OEM, Bengaluru
The commercial case
A drop from 3.2% to 0.4% rejection on a die-cast line is not a cosmetic improvement, it is recovered yield on every shift. A second plant running 6000-series extrusions through a spray tunnel reported 20% faster cycle time in low-foam mode, with re-works down.
There is a consolidation benefit too. Because LF-59 is safe across mixed metals, aluminium, brass, copper and steel can run in the same bath — one process instead of separate lines with a change-over between them.
Send us an affected part. We will clean it, return it, and tell you which process change caused the bloom.
Get a free part evaluationFrequently asked questions
What causes white rust on aluminium die castings?
Moisture trapped against the aluminium surface after washing. Aluminium reacts with water to form aluminium hydroxide, a powdery white deposit. Die-castings are especially prone because their porosity retains water, and the problem is worsened by incomplete rinsing, damp stacking or an uninhibited alkaline cleaner.
How do you remove white rust from aluminium?
Use an inhibited acidic brightener. POWER CLEAN ALB at 5–9% in an ultrasonic bath at 25–35 °C for 3–8 minutes removes white rust, oxidation and black marks without aggressively attacking the base metal. Follow with a thorough DM-water rinse and immediate drying.
Can I clean ADC12 and 6000-series aluminium with the same chemical?
Yes. POWER CLEAN LF-59 is formulated for both high-pressure die-cast alloys (ADC10, ADC12) and 6000-series extrusions, and is compatible with ultrasonic, spray-wash, immersion and tunnel systems.
Does the brightening bath need heating?
No. POWER CLEAN ALB is designed to work at room temperature, typically 25–35 °C. Warming to 40 °C can speed up heavily oxidised parts but is not normally required.
How long does an aluminium brightening bath last?
Typically 3–6 months in ultrasonic systems, depending on load and contamination. Regular concentration monitoring and filtration extend it considerably.
Will cleaning cause white patches on aluminium?
Not with an inhibited, aluminium-specific product used at the correct dilution with a proper rinse and dry. White patches almost always trace back to an uninhibited alkaline cleaner, residual cleaner left on the part, or parts stored damp.
