Aluminum Corrosion

[DFreedom]

I am in the process of rebuilding my aluminum I-beam trailer, new hubs, springs, shackles, axle bolts, plates, bunks and bunk supports. It should be like new when I finish. When I removed the galvanized (now rusty) bunk supports, there was what appeared to be crusted on salt deposits between the supports and the square aluminum tubing. Upon cleaning this off with a wire brush, it appears that the aluminum has corroded (it s pitted). Is this normal, is it a reaction between the alum/galv? It is not close to going through the tube but, what should I do to these spots, and is this something I can inhibit when putting new supports on? Last question, this is a flats boat so the boat sits entirely on the bunks, not on keel rollers. Would it make a big difference if I moved the bunks out/in a few inches to avoid these "corroded" areas? Thanks for any/all input.

[kingair]

I am in the process of rebuilding my aluminum I-beam trailer, new hubs, springs, shackles, axle bolts, plates, bunks and bunk supports. It should be like new when I finish. When I removed the galvanized (now rusty) bunk supports, there was what appeared to be crusted on salt deposits between the supports and the square aluminum tubing. Upon cleaning this off with a wire brush, it appears that the aluminum has corroded (it s pitted). Is this normal, is it a reaction between the alum/galv? It is not close to going through the tube but, what should I do to these spots, and is this something I can inhibit when putting new supports on? Last question, this is a flats boat so the boat sits entirely on the bunks, not on keel rollers. Would it make a big difference if I moved the bunks out/in a few inches to avoid these "corroded" areas? Thanks for any/all input.

Salt water is nasty. When they were powder coating my t-top, salt water was leaching and caused a sandy texture. They fixed most of it, but there are a few spots that feel sandy to the touch. They baked it for 2 more cycles and sandy what came out, but the top is 12 years old.

[north coast]

Any, other metal that comes in contact with aluminum will eventually cause corrosion.I don't know if there is a solution,but an Idea that came to mind,for your situation is, why not add a thin aluminum plate between the support and the actual trailer?like a sacrificial zinc,only aluminum.

[vanc]

I am in the process of rebuilding my aluminum I-beam trailer, new hubs, springs, shackles, axle bolts, plates, bunks and bunk supports. It should be like new when I finish. When I removed the galvanized (now rusty) bunk supports, there was what appeared to be crusted on salt deposits between the supports and the square aluminum tubing. Upon cleaning this off with a wire brush, it appears that the aluminum has corroded (it s pitted). Is this normal, is it a reaction between the alum/galv? It is not close to going through the tube but, what should I do to these spots, and is this something I can inhibit when putting new supports on? Last question, this is a flats boat so the boat sits entirely on the bunks, not on keel rollers. Would it make a big difference if I moved the bunks out/in a few inches to avoid these "corroded" areas? Thanks for any/all input.

What happened is the galvy did its job. It corroded sacrificially to the aluminum, but eventually it was spent. Then you corroded the steel under the galvy (your red rust) and the aluminum. You might try to slip a thin sheet of tough plastic between the galvy and alumuinum, you want to isolate them eletrically if possible, but the bolt may may complete the circuit. So you are probably fine with new galvy plates and isolating may lengthen the replacement time, how long did it take to get to this condition?

[DFreedom]

What happened is the galvy did its job. It corroded sacrificially to the aluminum, but eventually it was spent. Then you corroded the steel under the galvy (your red rust) and the aluminum. You might try to slip a thin sheet of tough plastic between the galvy and alumuinum, you want to isolate them eletrically if possible, but the bolt may may complete the circuit. So you are probably fine with new galvy plates and isolating may lengthen the replacement time, how long did it take to get to this condition?

It is a 2003 trailer so you have a point. With any luck and a little extra cash, I'll be getting something a tad bigger within the next year or so.

[nitz]

It is a 2003 trailer so you have a point. With any luck and a little extra cash, I'll be getting something a tad bigger within the next year or so.

You can isolate the aluminum from the other metal using shower pan liner (vinyl). We use it all the time to isolate aluminum boat lifts from the pressure treated poles (which contain copper). They sell it by the foot at home depot, lowes, etc... Anywhere you are reinstalling a bolt through the aluminum you should coat it with some tef-gel http://www.tefgel.com/contain.php?param=tefgel_infor. Otherwise you will continue to get the galvanic corrosion.

[DFreedom]

Thanks for the tip, good idea!