Chemically removing aluminum from steel

will remove aluminum galling from the sides of steel punch press punches without damaging the steel?

Caustic Soda will disolve the aluminum without affecting the steel.

Best Regards Tom.

IIRC, the bluing tanks used in gunsmithing are famous for dissolving aluminum parts. I think it is lye based.

Strong acid (e.g. hydrochloric) will also work, although it'll let the steel rust up pretty quick afterwards...

Just don't get this option mixed (literally) with the other (lye)! ;-)

Tim

Definitely use Caustic soda (Sodium Hydroxide) to kill the aluminum. Hydrochloric acid can pit the steel and if the immersion time is but a few seconds to run the risk of hydrogen embrittelment of the base metal.

While HCL would attack the aluminum violently, it will also effect the steel to some degree. Sodium hydroxide would be the best choice.

Harold

Use a heated solution of the soda. The old cleaning tanks in rebuilding shops of years ago used a temp of about 180 degrees F. They'd remove just about anything from steel or iron, and woe to the new guy who tried to clean aluminum or zinc in it.

Dan

That reminds me... does anyone know exactly what chemical reaction takes place on zinc? I've never heard of a zincate solution..

Tim

-- "That's for the courts to decide." - Homer Simpson Website @

Zinc reacts with weak NaOH solutions by forming zinc hydroxide, which is insoluble in weak NaOH, and forms a white precipitate. In higher concentrations of NaOH, it forms a soluble complex called sodium zincate.

Most metals form hydroxides when exposed to weak lye solutions. Only Al, Pb, and Zn redissolve and form complexes at higher concentrations. Of those, only zinc hydroxide is soluble in ammonia. So that's a definite qualitative analysis method of determining if zinc is present, ie form the precipitate with a weak lye solution, and see if the precipitate will dissolve in ammonia. If it does, you've got zinc.

Gary