How does one slow down, stop or repair the galvanic corrosion between aluminum panels and steel or stainless steel? Wire bush or sand blast it followed by a coating of something maybe?
Kenny
definitely both clean panels should be coated where they mate, at minimum the correct primer for each - asphaltic or rubberized undercoat sprayed between can work too, but messier - when using dissimilar metal fasteners a spot of never-sieze works wonders
Bill
Where are you having this problem on your bus? My bus has aluminum body panels riveted to 90,000 PSI steel frame members, and there is what appears to be some mastic between each interface. After twenty years, albeit in California's Central Valley, there is absolutely no sign of any galvanic corrosion anywhere, so it seems Crown knew what they were doing - they have used this construction technique since 1951 without problems. I recently made a small storage compartment using a structural framework of painted mild steel and some aluminum panels to enclose it, and between the different metals I used two layers of duct tape as as barrier against GC.
When I worked in the bicycle business I often had to deal with the effects of GC on bicycles. Triathletes' bikes were the worst, because those folk sweat a lot, and they jump on their bikes straight from the swim stage while they are still wet - the worst problem area was always between the aluminum stem and the fork's steel steerer tube. Every time any triathlete's bike came into the shop I would routinely remove the stem and smear more grease inside the steerer tube, and this PM completely prevented the dreaded white fuzzy stuff from taking hold. If GC had happened, I would sand or wire-brush it off both surfaces, then apply a good waterproof grease such as boat trailer grease generously to all affected surfaces. If the aluminum was anodized it would slow down GC, but not completely prevent it. We even had some issues with GC occuring in carbon-fiber frames; only stainless steel and titanium seemed to be impervious to it.
Prevent moisture, especially containing electrolytes such as salt, from getting trapped between dissimilar metals, and you shouldn't have problems with GC. Otherwise the aluminum will act as a sacrificial anode, which is good for boats but not so good on buses.
John
Wire brush the steel and then treat it with OSPHO. The black iron phosphate is really tough and will hold up rust for quite q while. It isn't the final coat.....rust bullet or whatever. Clean the alu with a cleaner wash. You can get it at auto paint supply for many bucks an ounce. The trailer rental outfits and professional auto detailers get it for under $10/gal and that will last a lifetime given the dilution rate is 20 to one. After cleaning the alu can also be painted and should be. That layer of duct tape between metal layers is a great idea. The bolts that go tru both metals must also be isolated....fibre or plastic washers. Paint the fasteners as a last step. This would be mil spec kind of brutal approach.
John
In the trailer business, we use a Mylar tape between aluminum and steel.
First of all the bus is an 83 MCI 9. I've recently been gutting the battery, OTC heat and condenser compartments. Some of the aluminum panels are corroded where they fasten to steel or stainless steel framing. A few are very much eaten away. Don't want to if I don't have remove repair or replace some of the aluminum panels. Any other fixes?
Kenny
Kenny, Are you sure of the cause? Salt will eat away alumium, road salt caught between the metals? Goodluck. Tom Y
There is nothing that I know of that replaces or cures the corrosion that has already taken place. A phosphate wash will remove corrosion and leave the surface of the aluminium naked for a very short period of time, but the surface layer of corrosion actually forms in minutes and is a protective barrier for the rest of the aluminium. Road salt, dampness, and all that acts as an accelerant to the galvanic corrosion that sacrifices the aluminium. The only cure is don't have the two metals touching, have a barrier, hence the coatings, the mylar tape, in the old days rubber tape, primers and such. If you have it in a compartment, to cure it you have to take away the aluminium so that you can re-install it with the barriers. Or simply patch as required, do the best you can to cure, and keep up with it while you own the bus. I figure these buses are like us, they have a life span, and we can keep them going for a long time with vitamins and potions, but at the end of the day they will be old, saggy and crotchety just like I am...
Brian
I have an old DART bus which has never seen road salts, but some high humidity. Many of the 'pop' rivets in the engine compartment have corroded away. I'm sure it's galvanic corrosion (well almost sure) as nothing else seems to fit. These rivets held clamps for wiring and were not insulated with that human fly-paper that MCI uses on the body panels both in and out. It's black rubberized muslin or such that has some mythic sticking power.
Thanks 47FLXclipper for the comment on spraying undercoat as I have been pondering how to replace the pop rivets so they wont just rot out again.