Breathe easy! No registration or passwords; no maddening pop-up or floating ads :-)

Home /
Search 🔍
the Site
pub Where the world gathers for
plating, anodizing, & finishing Q&As since 1989


How to remove the surface oxide of aluminum diecastings ?

August 16, 2010

I have a problem in removing the surface oxide skin from the aluminum die castings. The castings are intended to be used as the LED light seat so that the heat dissipating coating that we have developed can be applied on effectively. We have tried the normal alkaline dipping,however, the surface will be left with gray smut and thus shall influence the adhesion of the coating.

I-lin Cheng
product designer - Kaohsiung, Taiwan, ROC

simultaneous August 17, 2010

No No. do not alkaline etch die castings. Alkali etching removes aluminum and increases the area of silicon - exactly opposite of what you want to do - stay out of the alkali etch.

Clean in a non-etch or silicated cleaner, rinse, dip in 50% nitric acid plus one pound per gallon ammonium bifluoride until the surface turns frothy white all over, about 20 to 30 seconds, remove, do not stop to look, rinse two times, anodize.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina

August 17, 2010

Hi l-lin cheng,

It seems that you have a smut residue on the surface, probably from the non-dissolvable alloying elements in your Aluminium alloy. If you have e.g. a Si-rich alloy, you should try to remove this smut in a (1) HNO3/HF acid dip (e.g. 3 vol. parts of 1,42 D HNO3 and 1 vol. part 48% HF) or in (2) 50 g/l. Chromic acid/100 ml/l. D=1.82 sulfuric acid dip. Some people even recommend dipping in (2) first, followed by (1) and again followed by dipping in (2). Another possibility is: seek assistance from the big supply houses and ask if they have a reliable process. The solutions I mention are unpleasant to maintain and to handle both from safety and environmental point of view.

Best regards,

Harry van der Zanden
Harry van der Zanden
- Budapest, Hungary

(No "dead threads" here! If this page isn't currently on the Hotline your Q, A, or Comment will restore it)

Q, A, or Comment on THIS thread -or- Start a NEW Thread

Disclaimer: It's not possible to fully diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations might be harmful.

If you are seeking a product or service related to metal finishing, please check these Directories:

Chemicals &
Consult'g, Train'g
& Software

About/Contact    -    Privacy Policy    -    ©1995-2023, Pine Beach, New Jersey, USA