macro etchant for Ali

Hi all Immediately written it, recalled where had made note. Jody at weldingtipsandtricks recommends "Easy Off" oven cleaner as his favoured method. Rich S

Hi all Could you remind me. Macro etchant for Aluminum... To inspect welds on Ali. I think the suggestion a few months back was spray-on oven cleaner. Brands/types which work? Am in the UK, so would have to look for one available here. If anyone nominates a brand which isn't available here, I could still look up the overall nature of its ingredients and find the most similar here. I tried washing soda, which seemed to clean the Ali, but didn't etch it even steaming hot at high concentration. Thanks in advance, Rich Smith

---- The active ingredient is Sodium or Potassium Hydroxide, AKA lye, alkali, caustic soda, caustic potash. Besides Aluminium they also dissolve Zinc and human flesh. They are sold as oven and drain cleaner, for home made soap, and to put on pretzels before baking them, to create the brown color and glaze. Hopefully they absorb CO2 from the air or oven flame and are neutralized to baking soda.

The fizzing when they react with Aluminium is Hydrogen, in case you want to make UFO balloons which we did as pranks in college. It's nearly impossible to correctly estimate the size of or distance to an unidentified object in the sky, or on a movie screen. I wasn't involved in that one but I've flown less ambitious Hydrogen and hot air balloons in that region. The plans for balloon sections (gores) had been published in a Boy Scout magazine. The reported erratic movements are typical of a marginally buoyant balloon in the turbulence around trees and buildings. The bright red light could have been road flare powder.

Thanks. Will make sure NaOH is high up on the list of ingredients. I like the idea of being able to carry NaOH in a convenient form - as a spray-can.

Hi all Just managed to etch my weld with "Drain cleaner / Drain unblocker". Which is NaOH. Couple of teaspoons of in a thin layer of water at the bottom of a stainless steel pan, hot. There is a fizzing reaction on the surface, and I repeatedly wiped it with a tissue wrapped around a rod. Gave a good etch - cross-sectional structure of weld totally clearly revealed. Objective achieved. This is with 5000-series Al-Mg alloy - very corrosion resistant. Rich Smith

Hi all Just managed to etch my weld with "Drain cleaner / Drain unblocker". Which is NaOH. Couple of teaspoons of in a thin layer of water at the bottom of a stainless steel pan, hot. There is a fizzing reaction on the surface, and I repeatedly wiped it with a tissue wrapped around a rod. Gave a good etch - cross-sectional structure of weld totally clearly revealed. Objective achieved. This is with 5000-series Al-Mg alloy - very corrosion resistant. Rich Smith

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The rule is to always add strong acid or alkali to water instead of the water to them, to avoid instant boiling and spattering. Wear safety glasses and if possible use them within reach of a sink or hose so you can wash off any spills.

NaOH will absorb water and CO2 from the air if not kept sealed.

On my own "weldsmith" website - webpage

"Ali MIG/GMAW 1st-ever macro-etch"

Images of the macro. Quite good I venture to reckon.

That makes me want to go out and weld something so I can cut it up and etch it ...

That makes me want to go out and weld something so I can cut it up and etch it ... Snag

------------------------------- Hardening and tempering steel produce distinctive grain patterns too.

Here is more general info on etching for analysis:

Don't try to buy chromic or hydrofluoric acid which are corrosive poisons, or picric acid which is the WW1 explosive Lyddite. Oxalic acid is in Barkeepers Friend cleaner. Although they are not a strong acids, it and citric acid wrap themselves around iron atoms to make them more soluble in water. That's why Coca Cola (and Army coffee, I found) dissolve rust.

Nital becomes explosive if the HNO3 content exceeds 5%. It's what we used in the Materials Science course to show the grain of polished steel samples. Polishing (buffing) minimized the scratches that interfere with seeing grain boundaries. To make the small and irregular metal sample manageable it was cast into a plastic disk of standard size to fit the polishing machine and microscope.

Quite good, I agree.

A note about drain cleaner: there are other ingredients beside NaOH. I use NaOH as paint stripper & when I tried to substitute drain cleaner, those other ingredients made a proper mess. I can't say that they would affect your etching, but you might try pure NaOH to see. The pure stuff is reasonably available from soap-making supply houses.

Quite good, I agree.

A note about drain cleaner: there are other ingredients beside NaOH. I use NaOH as paint stripper & when I tried to substitute drain cleaner, those other ingredients made a proper mess. I can't say that they would affect your etching, but you might try pure NaOH to see. The pure stuff is reasonably available from soap-making supply houses.

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I haven't seen "Red Devil" for a while, but I recently noticed "Rooto" lye in white plastic 1 Lb bottles at a local True Value hardware store.

Thanks for your treatment of the topic. Fantastic information about what works. Well-judged mention of realistic bounds - what's "no go". I've done this with Ali at home, but from what I know I'd grant the "off-limits" for "kitchen" etching you bring into view.

For any onlooker wondering "why" - why this effort, why this happiness...

As seen Snag Bob Engelhardt

"macro" (macro-etch) is a window into the internal form and structure of your weld. Cut across your weld and expose a cross-section; prepare and etch that cross-section.

Coupled with visual inspection seeing the external surface form, you have a strong diagnostic tool. "nick-break" will inspect consistency along a long length of weld, so that is a valued ready test ("macro" samples one plane at random). "Visual", "macro" and "nick-break" take you a very long way refining a weld.

For any onlooker wondering "why" - why this effort, why this happiness...

As seen Snag Bob Engelhardt

"macro" (macro-etch) is a window into the internal form and structure of your weld. Cut across your weld and expose a cross-section; prepare and etch that cross-section.

Coupled with visual inspection seeing the external surface form, you have a strong diagnostic tool. "nick-break" will inspect consistency along a long length of weld, so that is a valued ready test ("macro" samples one plane at random). "Visual", "macro" and "nick-break" take you a very long way refining a weld.

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There are visible lines both between the parent metal and the rod, which are different alloys, and also at the apparent depth of passes within the rod alloy. Are these are crystal size/structure differences due to different cooling rates?

Simple answer - don't know! You are reading a lot more into this than I presumed to be able to (!).

Simple answer - don't know! You are reading a lot more into this than I presumed to be able to (!).

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You seem very well informed so I guessed you might know.

Funny thing - the "steel" weld looks so incredibly similar to some of my own macros - for laser+MIG/GMAW-hybrid... About 3kW to 4kW of laser additional to MIG/GMAW (can't be bothered to look, but doubt ever laser+FCAW as would have had to deal with the slag when already difficult enough going in and out of a locked & interlocked vault to deal with the test-welds). See

sequential page 25 of 48 (numbered page 17) top right-hand-side two

"Monster" penno. not in general useful as engineering design basis - the strength calculations - would usually be penetration / fusion to fillet corner. The cheapness of fillet welds is not just how readily done and robust of conditions to achieve they are, but also you are very satisfied with visual inspection only. You are not asking anyone to believe there is something complex going on deep inside the weldment which would need and expensive volumetric inspection test to see (typically Ultrasonic Testing). [there's no way to "pocket" money for not doing what you are contracted to do with fillet welds - as the external size you can measure at the surface dictates how much metal you must deposit, which forces a cost, and you cannot "trouser" money in any way (you could vindictively do a "not weld" by doing a machine setting which likely gives only "kissing contact" and weld metal there but no weld but that wouldn't "trouser" you any money - and that would show-up on mag-part, which would have you thrown off the job with no pay having run up expenses)]

Anyway, I'm just looking bemused at the similarity - no suggestion of anything at all...

Rich S

(you could vindictively do a "not weld" by doing a machine setting which likely gives only "kissing contact" and weld metal there but no weld but that wouldn't "trouser" you any money - and that would show-up on mag-part, which would have you thrown off the job with no pay having run up expenses)]

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A sabotage trick by slave labor U-Boot hull welders was to pack most of the joint with loose welding rod and only cover it on the outsides.