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Anodizing discoloration at joins

 

I have recently had 10 aluminium windows made for my sailboat. They are shaped like a rectangle with rounded corners. They were apparently joined ( welded?) at a point where the upper half of the window can be joined to the lower half - in other words, roughly joining 2 'U' shapes together. They were then anodised in a bronze like color. Now they are installed there is a clear discoloration of the anodization at the joins (looks silver against the bronze - visible from the inside as well as the outside of the boat) and I am only now told by the contractor who did the job that this discoloring is normal where aluminium is joined together and later anodized.

I am annoyed because the look of the windows is important on a pleasurecraft and because I was anxious before the job was done to look at both anodizing and powder coating to get the best effect. Unfortunately I was not told of this 'usual' effect of anodising which I am now told was predictable.

Is the problem one which could have/ should have been avoided?

Rodney Lewis
- Sydney, Australia

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Rodney,

What you were told was correct, if the parts were indeed welded. To minimize the discoloration, the parts should have been welded using the same alloy of welding rod as what the frames were made of. However, I would still expect some discoloration due to the heat thats generated (changing the temper) during the welding process. If you want perfect color uniformity, perhaps they should have been painted, or powder coated.

Marc Green
anodizer - Boise, Idaho