aluminum oxidation

[piers]

I have a twin engine gil bracket that is made from cast aluminum with a very hard baked on porcelin like paint finish.Near where the engines mount to the bracket, above the waterline, the paint is starting to bubble up.It seems to be mostly concentrated around where the engines are mounted.The paint bubbles have not broken through to the air yet.I wanted to know if anyone has had this problem and what they did to fix it.I wanted to fix it before it spread much further.<br /><br /> Thanks ...2600

 

[Solittle]

Re: aluminum oxidation

What you see is normal corrosion. You can scrape it off, coat with a good alumnium primer and top coat. Make sure that you have good zinks as alumnium attracts galvanic corrosion - and that may be the cause of what you have now.

 

[18rabbit]

Re: aluminum oxidation

Sound like you have powered coated aluminum. Like stainless steel, aluminum doesn’t really oxidize past the first few molecules in contact with the air. If other minerals come in contact with it there is a problem with galvanic corrosion. I suspect what has happened is the powder coat got a hole in it and water with dissolved minerals was trapped next to the aluminum, the galvanic corrosion just creeps along under the powder coat. Could also be epoxy coated aluminum, you’d get the same result.<br /><br />Obviously, clean up the mess. You’ll probably find white powder under the bubbles. If you want to paint the bracket, you should clean the aluminum, wash it with a mild acid like vinegar, and apply a zinc chromate primer. The best you can do is remove the bracket, take it to be bead blasted (like sand blasting, but with glass beads), then have the bracket re-baked with a new powder coating. Probably cost you in the neighborhood of $100USD for blasting and coating.<br /><br />If you opt for powder coating, look in the yellow pages under ‘powder coating’, call and ask what colors they are running. Companies that do powder coating often have large production runs for other manfing companies. If they are running a color you can live with you can often slip in your piece for next to nothing.<br /><br />Oh, and welcome to iboats!<br />

 

[EZLoader]

Re: aluminum oxidation

Read these links to understand what's going on...<br /><br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=26;t=004086

 

[piers]

Re: aluminum oxidation

thanks everyone for the replys...18rabbit,I think you hit the nail on the head.I am kinda hoping to fix it without removing the bracket.I will try the first fix,clean it up,etch and prime.To remove the engines and bracket is a big job.....but I have a feeling it may come to that.I have a zinc anode located on each engine bracket where it is connected to the gil bracket.Beacause the engine is connected to the gil bracket I figured this should protect the gil bracket from corosion.<br /><br /> Thanks.....2600

 

[Dunaruna]

Re: aluminum oxidation

What condition are the anodes in?<br /><br />The problem with NOT removing the bracket is that you won't be able to coat the bolt holes etc. One tiny exposed area and the galvanic process will get a foothold.<br /><br />I agree with 18R, but before painting, I would use an etch primer.

 

[piers]

Re: aluminum oxidation

Zincs are in good shape and all the bubbles are above the waterline.I check the etch primer...<br /><br /> thanks 2600