Aluminum Backplate/Galvanic corrosion

[vel525]

I went on a week long trip this summer and left my backplate attached the entire week. I did rinse the entire rig with freshwater at the end of each day, but I didn't not take everything apart. I have an AL BP and SS STA and bolts. At the end of the week I noticed the AL plate had some white substance around the hole. This is galvanic corrosion right? Well, I just wiped it off and rinse it and although it doesn't look at pretty as I first bought it was not significantly damaged. Actually, this fall I went on a liveaboard for a week and again rinsed my gear everyday, but did not take everything apart and my gear is fine.

I think it will take a long time and a lot of exposure for the AL BP to get functionally damaged.

 

[vshearer]

Oh well, I suppose I could always bolt a couple of these Clamshell zincs on for trim weights.

 

[Rudebob]

Like others said, the potential for any form of galvanic corrosion between the dissimiliar metals will be minimal based on exposure limits alone. There are ten of thousands of similar material combinations, such as aluminum boat outdrives/lower units held by stainless steel hardware, that hold up for years under constant exposure to saltwaters. A magesium anode might help but IMO be a waste of time.


The bigger possible problem for corrosion would be in the form of crevice corrosion where minute quantities of moisutre perentrate tight gap interfaces which limit drying times and excellerate corrosion rates. Even still, with the possibility crevice corrosion cracking, normal maintenance should limit the extent of possible damage well beyond the typical life of the system.

'bob

 

[vshearer]

Like others said, the potential for any form of galvanic corrosion between the dissimiliar metals will be minimal based on exposure limits alone. There are ten of thousands of similar material combinations, such as aluminum boat outdrives/lower units held by stainless steel hardware, that hold up for years under constant exposure to saltwaters. A magesium anode might help but IMO be a waste of time.


The bigger possible problem for corrosion would be in the form of crevice corrosion where minute quantities of moisutre perentrate tight gap interfaces which limit drying times and excellerate corrosion rates. Even still, with the possibility crevice corrosion cracking, normal maintenance should limit the extent of possible damage well beyond the typical life of the system.

'bob

Thanks, actually the more I think about this the more I agree. Just making a habit of a really good rinse each time should avoid any problems for quite some time. I may still put the clamshells on though, just for the cool factor. :14:

Oh, and you are right, magnesium is a better choice, and I could always use it for a backup flare?

 

[Rudebob]

Well I don't have magesium washers but if you need a few small pieces for an anode I can probably help you. I manage a metallurgical testing laboratory and I am sure we have some scrap around I could send to you. The only problem is I can't completely promise we have some without looking first as my employees often take it home to make their own "flares".

'bob