Bond to Anodising or Raw Alu?

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#1

I need to bond a one off part to an anodised (black) aluminium part for a bike frame Im making. (Its the rear dropout that holds the axle). Im not sure what type of anodising/sealing process was used as its an off the shelf part.
What would you do in this situation for surface preparation? My thinking would always be to abrade relatively vigorously with say 80 grit or something (no blasting facilities available) but this will almost certainly go through the anodising and surely that would defeat the point of anodising would it? Bear in mind this is standard anodising and not pre-bond anodising: Im not sure if theres a difference in the two
Have you found stronger bonds by fully going through the anodised surface or barely scuffing it or doing nothing at all?
The plan afterwards is to bond to film adhesive and glass carrier with epoxy.

Thanks

#2

On a lot of marine components are hard anodized to prevent corrosion and to improve bonding. The anodizing has micro pores that the resin gets into, improving bonding.

#3

Thanks - yeah that’s what I always thought but I have read it massively depends on the type of anodising and not being too well up on it, I cant tell the difference!

#4

Use specific instructions from your adhesive supplier (Hysol, etc) and if you can’t find their literature call them. Don’t second guess surface prep for a critical joint like this.

#5

I was looking at 3M instructions but couldn’t find any and was under time pressure so couldn’t reach them in time. I just took a chance and abraded off the anodising as this has worked with the resin well in the past but I was curious as to what could be optimised. Ill contact 3M anyway, hopefully it was the right decision :slight_smile:

#6

I’d be interested to hear what 3m say

#7

Bare aluminium oxidizes very quickly (aluminum oxide is very plentiful on earth for a reason). So your joint will be strong at first but then quickly deteriorate as the oxidation starts along the edges and works its way in.

That’s why you bond to a surface that has a chemical conversion that stops the oxidation. Anodizing, etch/alodine, etc. depending on mfg recommendations.