Compatibilty of metals

Submitted: Friday, Aug 20, 2004 at 03:01
ThreadID: 121398 Views:2928 Replies:2 FollowUps:0
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I know that certain metals are incompatable and will set up an electrolytic corrosion (?) if used adjacent.

Can someone advise if the following are compatible please:

Steel screws into aluminium
Stainless steel screws into aluminium
Stainless steel screws into mild steel
Steel screws into galvanised steel
Stailess steel screws into galvanised steel

What are the real no-no's to avoid?

Many thanks,

Phil
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Reply By: Deleted User - Friday, Aug 20, 2004 at 05:43

Friday, Aug 20, 2004 at 05:43
G'day Phil, I can offer a little insight ... An easy definition of electrolysis of metals ... Any two dissimilar metals in contact with each other especially in the presence of moisture and/or salt. As to their compatibility rating against each other there is a scale called the Nobility Scale of metals. It is a basic list of metals from high nobility to low nobility. The closer the metals to each other on the nobility scale the less electrolysis between the two and thus more compatible to each other. The LEAST noble of the two will corrode faster. The scale goes sumthin like this ...most noble is Gold, then Platinum, Carbo/Graphite, Titanium, Silver, Chrome, Inconel, Nickel, Monel, Bronze, Copper, Brass, Tin, Lead, Cast iron, Steel, Iron, Cadmium, Aluminium, Zinc, Magnesium. Two metals beside each other in the scale will still corrode (very slowly) but are the most compatible. If you now apply this to your selection ..... Steel screws into aluminium .... not good, not bad.
Stainless steel screws into aluminium ... bad juju here (chromium in SS). Aluminium will be sacrificial here.
Stainless steel screws into mild steel ... reasonably bad here steel will corrode (Chrome again is SS.
Steel screws into galvanised steel ... have to check gal coating composition for this one ... I imagine gal coating would go first here ?
Stainless steel screws into galvanised steel ... same again ..check gal composition. My rule has always been (if you can do it) ....use the same metal to fix the metal ... steel into steel ...gal bolts/screws into gal ... Same grade stainless into stainless. Steel rivets into steel sheet ...ali rivets into ali etc etc .. Some steel fasteners can be aluminium coated and then used to fix aluminium. My preference into aluminium (was Cad plated but its a bit "poison" these days) is Zinc plated ...they are beside each other on the nobility scale. Hope this gives ya food for thought .... (waddya makin mate ???!!!) Regards Anthony Explore this Great Land ...Do it Easy ...Tow a Bushtracker

AnswerID: 564810

Reply By: Deleted User - Friday, Aug 20, 2004 at 06:20

Friday, Aug 20, 2004 at 06:20
I am actually doing pre-planning for the next house that we are going to build (well, the builder will actually build it, but we are predominantly responsible for a lot of the design and specifications), which being near the sea makes all this fairly important.

But it is also very relevent to anybody screwing fittings and stuff into their Bushtracker frame or chassis!

I would have gussed that Anthony would be the one to help out on this question, thanks for the advice,

Phil



AnswerID: 564811

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