Powder coating on aluminium casting

[dogbural]

Hi,

We have encountered an issue that the powder coated aluminium casting could not pass salt spray testing, while aluminium sheet sample passed 2000 hours testing.

With aluminium casting,
1 x sample (with E prime and top coat)- failed at 1000 hours with scribe undercut by 5mm
2 x samples (with top coat only) - failed at 250 hours, being seen blistering from scribe lines.

All of them are pre-treated as below
5 tank process:
1. PRELUDE AC50
2. RINSE
3. RINSE
4. SURTEC 609GV
5. RINSE

Obviously E-prime is necessary and gave better resistance but still failed at 1000 hours.

Is failure related to gas emission from cast aluminium?
Is there any process to follow to have better coating?

Regards,
MK

 

[TugboatEng]

What alloy of aluminum? Also consider using a chromate conversion coating prior to powder coat.

Aluminium, like stainless steel should be left bare if possible due to crevice corrosion issues.