bond AL

Application? How big? What about aluminum solder, or aluminum braze??

Surface prep is nearly everything, using the right adhesive is the rest. Hardware store epoxy ain't it. What were you using?

I have tensile tested bonded metal strips that tested a better strength than the parent metal, but it was using a heat cured adhesive with a acid etch for prep.

One trick that works is to scrub the aluminum surface while wet with epoxy, using a sandpaper or abrasive pad. Object being, to get the epoxy in contact with the base metal, rather than the oxide layer that forms on alum. almost instantly on exposure to air.

Scrub the aluminum into each surface, squeeze then together, and clean off the excess.

I use a fair bit of EA 956 and a bit of 2216. The EA 956, IIRC has an aluminum powder in the mix, while the 2216 is a little bit flexible, and is a plain epoxy.

Cheers Trevor Jones

Hardware Hank's

Ah, this makes sense. Do you just use the part A to wet the surface and scrub, or already mixed adhesive?

Thanks,

Karl

Epoxy is very sensitive to surface cleanliness, especially to oil or grease films, and it takes *very* good cleaning and degreasing to achieve a good bond. Even a fingerprint will prevent bonding.

1. I would start with wet-sanding the surfaces using windex (or equivalent) to wet the sandpaper, rinse well, and towel dry. Make sure that the entire bond area has been abraded. Wash your hands with soap and warm water just before beginning (to cut down on the inventory of people grease), and do not touch anywhere near the bond surfaces to be.
2. If you will use the "scrub the surface under a layer of wet epoxy" approach, you still must clean the surfaces as described above, before applying the epoxy. One can use a new piece of sandpaper liberally smeared with the mixed epoxy (not just part A or part B) to perform the scrubbing. Wear disposable gloves while doing this, to keep you out of the epoxy and the epoxy off you. This process is very messy.
3. After hardening overnight at room temperature, one can increase the bond strength by baking at 200 F for an hour or two.

Step 1 is essential. Steps 2 and 3 are optional, to be done only if needed. One can do 1 alone, 1 and 3 alone, or 1, 2, and 3, always in that order.

Joe (who once worked in a potting and gluing lab) Gwinn

After cleaning you can test for how well it is cleaned by putting it under the tap and then seeing if the water wets the entire surface.

In aerospace before painting or bonding, one cleans, water flow tests, then applies a surface prep ( alodyne ), pat dry, let air dry a short while ( long air drying let the surface get contaiminated ) and then paint or bond.

Dan

Phosphoric acid, sold as a prep for alodyne, will take off the oxide, if it isn't too bad...

Jerry