Any real risks corrosion etc combining aluminium and steel

[Chris TickTockParticipant @christicktock]

Hi, I believe putting stainless steel with aluminium can lead to corrosion but is mild steel / silver steel OK/ The reason for asking is aluminium is hopefully easier to machine. Have to say I haven't yet machined any on lathe but hopefully will be easier?

Chris

[Chris TickTockParticipant @christicktock]

[Paul KempParticipant @paulkemp46892]

Depends on actual material grades, how combined, environment in which they will reside, design stresses and corrosion allowance and your perception of risk.

Paul.

[Phil PParticipant @philp]

Early Land Rover bodies were a mixture of steel and aluminium, if they ever got road salt on them they corroded really badly. I know this from experience of restoring a 1950 series 1 model years ago.

I suppose it depends on the surrounding environment as to whether you will encounter any problems, if it is parts for a clock, I would say you should be OK. I quite often mix aluminium and steel for making fixtures etc, and have not had any noticeable corrosion problems in the workshop.

Phil

[VidarParticipant @vidar]

Relative surface areas are important: A little bit of stainless steel (fasteners etc) in larger parts of aluminium is usually fine and quite common in marine settings. The other way around though, a little aluminium in large stainless parts, would not work.

Edited By Vidar on 28/12/2019 14:42:02

[pgk pgkParticipant @pgkpgk17461]

Depedning on application is it possible to put a barrier between them?

[Ian PParticipant @ianp]

Paul Kemp's reply says it all!

Until Chris TT addresses Paul's points I think its pointless offering advice and prolonging the agony as it were.

There are reason and places where two particular materials are best not combined so there is nothing wrong with Chris asking the question so we can offer advice in the right context.

Ian P

[Phil WhitleyParticipant @philwhitley94135]

Astom Martin used to use aluminium skins rolled and folded onto a steel tub chassis, wherever steel and aluminium touch, they use a cotton cloth soaked in what appears to be something like Waxoyl or Anchor wax, wrapped around the edge, and then the aluminium is clenched onto the steel like the edges of a door skin. Something like Sylglass tape would also work, if you can still get it. Steel bolts into aluminium can be treated with waxoyl, Densogrease or the silver version of Coppaslip grease, which is not, as far as I can remember called Allyslip! The whole purpose of seperating dissimilar metals in this way is to stop the ingress of water, which becomes an electrolyte between the dissimilar metals, and thus creates a battery, with the resultant electrolytic corrosion. Regardless of the materials, if they are dissimilar, a moisture resistant barrier will minimise the problem. It is like putting vaseline on battery terminals!

Phil

[Chris TickTockParticipant @christicktock]

Thanks Guys, my post was intended only as a general question arising from my need to make a small tool rest for my 50mm slow speed sharper and looking at what materials I have in stock i just started thinking.

I note having done more research that 2 dissimilar metals where moisture is present can be an issue in terms of electrolytic corrosion but not in this case. The tool rest will only be for very light use so aluminium angle at the sides possibly with a steel table. It would be easier to mill a slot in the aluminium on my Sherline mill than steel…that is the entirety of my thinking to date.

Chris

[Phil WhitleyParticipant @philwhitley94135]

clean and oil the table before you fit it= no problem!

Edited By Phil Whitley on 28/12/2019 18:52:43

[not done it yetParticipant @notdoneityet]

Distance apart in the Electrochemical Series is a good guide to the risks of electrochemical reactions altering levels of precautions necessary, where dissimilar metals contact.

Sacrificial blocks are often used where corrosion is to be avoided – moving the metal loss to an easily monitored position and making replacement an easy or routine operation.

[Clive FosterParticipant @clivefoster55965]

Where significant areas of both materials are concerned, shucha s car bodies on steel frames, proper practice its to electrically insulate any areas of contact.

Realistically mutual corrosion only occurs when things get damp or wet to provide an electrolyte.

Clive

[HopperParticipant @hopper]

"Any real risks?" No. Not in your application.

Almost every motorcycle engine ever made is a combination of aluminium casings and steel (mild and stainless) fittings, crankshafts, cams, pumps, bearings etc etc. Screws threaded dry into aluminium and left untouched for 20 years or more sometimes tend to need an impact driver to shock them loose due to the fine layer of corrosion holding them in place. Other than that, I have never seen evidence of any actual damaging corrosion of components, even on bikes 80 years old.

Just put a bit of anti-seize grease on any screw threads going into ally and carry on.

[Ron LadenParticipant @ronladen17547]

A company I worked for built high tech transit containers for space and military hardware. The container build was all aluminium with steel/stl stl fittings and fasteners all of which were coated with Duralac on assembly.

Duralac prevents corrosion between dissimilar metals and is impressive stuff I have seen steel parts removed from aluminium ones where the item has lived out in all weather's for 20 years and the mating surfaces looked like new.

I don't think it needed in your case though Chris.

[Chris TickTockParticipant @christicktock]

Thanks Guys , useful posts. i may end up using all steel anyway but at least i now mixing metals is OK for many applications but keep an eye out for those jobs where moisture is prevalent.

Chris

[VidarParticipant @vidar]

Even moisture and salt is fine if there is lot of surface of the anode (aluminium) and little surface of the cathode (stainless). Some tiny damage distributed over a large surface has no practical impact.

[vintage engineerParticipant @vintageengineer]

The tape Aston Martin used was a disaster as the cotton tape would dry out in the summer and absorb water in the winter which would cause the aluminium to rot like hell!

Posted by Phil Whitley on 28/12/2019 16:28:52:

Astom Martin used to use aluminium skins rolled and folded onto a steel tub chassis, wherever steel and aluminium touch, they use a cotton cloth soaked in what appears to be something like Waxoyl or Anchor wax, wrapped around the edge, and then the aluminium is clenched onto the steel like the edges of a door skin. Something like Sylglass tape would also work, if you can still get it. Steel bolts into aluminium can be treated with waxoyl, Densogrease or the silver version of Coppaslip grease, which is not, as far as I can remember called Allyslip! The whole purpose of seperating dissimilar metals in this way is to stop the ingress of water, which becomes an electrolyte between the dissimilar metals, and thus creates a battery, with the resultant electrolytic corrosion. Regardless of the materials, if they are dissimilar, a moisture resistant barrier will minimise the problem. It is like putting vaseline on battery terminals!

Phil

[SillyOldDufferModerator @sillyoldduffer]

Posted by Chris TickTock on 29/12/2019 09:24:39:

Thanks Guys , useful posts. i may end up using all steel anyway but at least i now mixing metals is OK for many applications but keep an eye out for those jobs where moisture is prevalent.

Chris

More to it than 'jobs were moisture is prevalent' I'm afraid. On an oily lathe, I wouldn't worry about mixing stainless steels and Aluminium because it's not a critical application. But the same combination is absolutely unacceptable on an aircraft exposed to weather and salt because the risk and impact of a failure are far higher.

Whilst breakage of safety critical parts due to corrosion is a risk most Model Engineers don't need to fret about, clock-makers and builders of fine models have another worry. A display item like a clock will be exposed to decades of air pollution, temperature swings and humidity. Careless mixing of materials is best avoided in these circumstances because small-scale corrosion is disfiguring. We don't want some as yet unborn expert tut-tutting over a beautifully made Chris TickTock Clock spoiled because a poor combination of materials reacted chemically over the previous century. Even though we'll all be dead.

Happy New Year everyone!

Dave

[Phil PParticipant @philp]

Just to put Dave's clock comments above into context.

I have a 1920's Art Deco wall clock that is made predominantly from aluminium rather than brass.

Almost 100 years on, there is no sign of corrosion between the aluminium and steel parts. I have no idea why they used aluminium, probably just to be different and more modern looking in the period it was made.

Phil

Edited By Phil P on 29/12/2019 11:55:52

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