Bonding Aluminum Strips After Rolling

I have heard of a process in which components made of aluminum or an alloy thereof can be diffusion bonded together; the process involves chemically treating the components to remove aluminum oxide on the surface of the components, subjecting them to grit blasting and to a second chemical oxide removal step and finally pressing the components together under heat until they form diffusion bonds. I think Boeing was using heat and pressure to bond Aluminum parts together back in the 60s.

Totally out of my field, but from your description of the process see below:-

1) Surface contamination stopping intermetalic fusion

2) Insufficient pressure to cause the surface molecules to be caused to "mix" and bond.

3) Irregular surface meaning pockets of air/gas trapped between the laminates.

4) Incompatible alloys.

5) Insufficient heat to enable bonding (either rushed through pre-heating or temperatures too low)

6) Grain direction of material versus rolling direction.

As I said, way out of my field, but some guesses by someone not prejudiced by "knowing" what should be happening.

Hope this helps

Some things to be aware of include:

1,Make sure the surfaces to be bonded are clean and free of any organic soil.

2. Assuming that the two pieces of "Al' are annealed pure Al, cold-roll in such a fashion to reduce the thickness of each piece by 10-20%. This is necessary to break up the tenacious surface-oxide that exists on the strips' surfaces and promote contact between the un-oxidized metal. It is necessary for atoms to be transferred between the two pieces for bonding to occur.

3. Try cold-rolling, as the lower temperature will aid in preventing re-oxidation of the two surfaces that are being brought in contact .

Thank you, Everyone, for your comments.

We normally scratch brush the surface only and then remove any loose particles and grease with an organic solvent and, normally, get good bonding. We do not normally remove the oxide layer chemically. it might be that the scratch brushing was just not done sufficiently. Maybe we should make the scratch brushing machine operator independent.

First you must remove the native oxide and contamination that forms on contact with air. Plasma cleaning can be effective for this. Then you must keep the cleaned surfaces free of contamination between the cleaning process and the bonding process. Nitrogen, Argon, or vacuum can be used for this. Third, you must apply enough pressure to cause plastic deformation or yielding at the surface of the aluminum. This helps to promote large area surface contact. Ultrasonic agitation also helps promote bonding.

Contamination-Contamination and contamination major one

Oterhs

1. Lower pressure

2. Wrong alingment of grains

3. Rougness uncontrol

Poor alloy quality

This is out of my field but I can add some pertinent points on aluminum and aluminum oxide. Unlike aluminum, aluminum oxide is a very hard non-conductive non-reactive layer found on any sheet of aluminum. The mineral example of aluminum oxide is called sapphire, Moh's hardness 9.0. Bare aluminum reacts quickly (on the order of a second) with air to form a one or two atom thick layer of aluminum oxide. So if your mechanical abrasion is not done in a non-oxidizing atmosphere (pure nitrogen, argon, vacuum etc.) or very quickly before your pressure bonding attempt, you will be trying to pressure weld sapphire and not aluminum.