There is no Aluminium in stainless steel. Wonder where that "white powder" came from, but it wasn't from the stainless steel bolts.
The Chromium % in with Iron provides the 'stainless' effect. Stainless steel IS steel: iron and carbon, alloyed with other metals typically chromium and other metals eg nickel and molybdenum.
This brings back happy 'MPM' engineering degree study memories.
Aluminium "in" stainless steel?
If I interprete that as a mechanical contact, it's ofcourse the opposite, stainless steel "in" aluminium, and there are plenty examples of that: a stainless steel valve through an aluminium rim, a ss bolt in an alu frame, and so on.
One of my cases, as example given, was the mount of the bike stand, on a frame tube (the one that goes from bottom bracket to rear wheel dropout position, with a shaped block inbetween. Two stainless steel (304 aka A2) bolts went through holes in that block. At some point the stand showed play and I had to retension the bolts to solve it. Some months later, repeat story. Some weeks later, repeat story. Some days later. Repeat story. Some hours later. Repeat story. Really haha, I was on a flea market, lotsa stand up/downs, and it took like 15 min to notice again play.
Back home I decided this is not normal, time to find out what is going on. Took out the bolts, took the interface block, and its holes sat full of white powder, which was of course aluminium, from both block and frame thread. Then I realized the cause galvanic corrosion. I solved it by replacing the A2-70 bolts with non stainless bolts, and washers and nuts on the other side. Problem never reappeared since.
So it's not the stainless steel that "loses" material, as said, it's the aluminium that does, the chemical reaction dissolves it to white powder, causing the mounts to weaken, and loose.
Same for those Magura brake mount pens.
So yes, I started to refrain from using stainless steel bolts.
I reported the bike stand case to the bikes production company (Santos) and they acknowledged the problem and said they would consider using galvanized (zinc on surface) bolts in the future but listed a few drawbacks as:
- for them harder to acquire (not explained why, rather expect the opposite)
- once the zinc layer completely gone, rust on that place, ex given as head of allen bolt.
They asked me if I thought these would serve better and I answered that I replaced them with common steel bolts (nearly all sold are galvanized), greased, and put silicone in their heads.
Didn't have to touch the heads later on anyway since the bolts kept their tension - the problem was solved.
