Etching Aluminium

Neil

As Rod says Cupric Chloride might be worth a try. I switched to using it for etching circuit boards many years ago as it has many advantages over Ferric Chloride (lasts forever as it is easily regenerated after use,amongst others) , and I can testify that it does etch aluminum as I have a heater mounted on an old ali electronic chassis that I use to heat the etchant and it has numerous well etched spots on it from spills.

It can be easily made by dissolving 200gms CuCl2 in100gms conc. HCl (37.5 %) and diluting to 1 litre. The Cupric Chloride is readily available from pottery suppliers as a glaze material, and I use Muriatic acid (readily available at a builders supply) adjusting the quantity as it is normally only supplied as 20 baume which has a density of 1.16 as apposed to the conc. which is 1.18. If maintained at a density of 1.17 g/mL and a acid concentration of 3.5 to 4.0 % or 1.1 to 1.3 Molar it lasts for ever and just keeps increasing in volume.

John

Not sure if you ever solved this, but I've been etching Aluminium with electro-etching. There are plenty of videos on youtube. It really seems to be the only way to do it at home with decent results. It also gives whatever you're using as a mask a better chance of not being removed by extreme reactions of heat and corrosion.

I’ve had stuff Anodised professionally on a few occasions and as I didn’t want a shiny finish they said they’d etch it with Sodium Hydroxide. I’ve always thought sand blasting was a good start for painting aluminium and this was confirmed in a YouTube video I watched some time ago.

Could you put an extra, caustic proof layer below the etch resist and develop that in a second tank?

I have used hydrofluoric acid to etch aluminium at work, but only because it was a process requirement. I would avoid it if there were alternatives as it's one of the worst chemicals one can handle, so much so that apart from al the necessary ppe we also have a specific first aid kit with antidote for paramedics in case of an accident. Exposure effects of HF can be delayed, leading to severe injuries.

I would suggest electo-etching. Chromic acid might work, but it's an anodizing process rather than a etching one, so you will get a golden brown contrast without taking away any of the parent metal, but I believe it works only on alloys of aluminium.

I know this is an old thread and Neil has probably sorted his etchings out years ago, but since it has come back to life, I can confirm that ferric chloride works well. My stuff has also been used to etch a small amount of copper which may/may not matter.

Edited By Andy_G on 13/06/2021 11:04:57

In the days before H&S schoolchildren were invited to etch glass at home using HF extracted from teeth

For what it is worth, most etch primers for aluminium contain phosphoric acid as the active ingredient. Being a cheapskate I usually prime aluminium with phosphoric acid and then just paint with any old paint. It seems to work well as the oldest aluminium to have had this treatment is 30 years old now, with no sign of peeling.

Andrew.

In a previous life I was Managing Director of Turco Products Ltd. manufacturers of etchants and maskants for the aerospace industry. A process we called 'chemical milling'.

Googling Turco and Chemical Milling will bring up a fair bit of information for you Neil.

The etchants had a basic ingredient of caustic soda with a number of additives. (In a similar way a plating bath has additives to modify the basic chemistry for a better finish). The maskants were made from a mixture of toluene, rubber and chalk.

Can I second the warning to keep well clear of hydrofluoric acid. The pills referred to are to replace the calcium that this leached from your bones and we instructed staff to start taking them straight away if they came into contact with the acid. Nasty stuff. The rare times we used this in our manufacturing process the operatives had to wear full haz mat protection.

Hi, hydrofluoric acid is indeed nasty stuff, it will dissolve glass, burn through your skin and attack your bone before you feel it and the vapours will damage your lungs in a relatively short period of time. Don't use it unless you understand how to use it and dispose it safely and using proper full PPE which you can shower/wash off before removing.

Regards Nick.

Beautifully done Andy. A compressor I see

Neil

Thank you very much! (Well spotted! )

Edited By Andy_G on 15/06/2021 13:12:28