how did bodyshops fix aluminium parts?

Depends on the era of the car. Alloys used prior to 360 were pretty malleable and straightened easily. The newer cars are using different, harder alloys and many don't try repairs.

 

We used this stuff to fix fighter jets, they are aluminum. It is really good stuff.
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The big problem with Al alloys used for car body panels is that they plasticly strain easily, so when an area is dented substantially, the material in the local area gets stretched out quite a bit, and permanently. The result then, is that when you try to form it back to the original shape, there is basically too much material (dimensionally too long) to fit precisely back into the original space. So, you end up with a wave / wrinkle / distortion in the area of repair.

The only way really to determine if it's gone too far (stretched too much) is to go ahead and straighten it back, and then observe the result ---- if it waves too much...... the panel should really be replaced. Sometimes it is not very noticeable and therefore acceptable, other times it is not.

Frankly, if you can justify the expense, I would recommend to just replace the panel without trying to repair it ---- but, of course, that can easily double, triple, or more the cost of simply bending it back ---- so, a trade needs to made with overall quality against the higher cost.

And, yes, if the material has been strained too much, then it will be structurally compromised if bent back --- only a shop that has had a lot of experience with repairing aluminum body panels will have the proper judgment to make that call (most body shops do not have that level of expertise). Definitely go to a place that specializes in aluminum repair for an opinion.

FTR, when the Audi A8 first came out (the first, large scale production car with aluminum body panels), insurance premium costs for damage / collision were extremely high because Audi had recommend that panels ALWAYS be replaced rather than attempted to repair --- in fact, they forbid all their dealership network to do anything but replace --- they were not allowed to even attempt to straighten dents and buckled panels.

 

There are so many Aluminum chassis cars today and in the past that just about every shop claims to be able to repair aluminum. The problem with AL vs. Steel is that the window for error with AL is smaller thus needing someone who knows what they are doing is higher just like it is a lot easier to find someone to competently rebuild your modern corvette motor than your Ferrari motor even though the principals are all the same.

Here is a great pdf on aluminum chassis.
www.alueurope.eu/wp-content/uploads/.../1_AAM_Body-structures.pdf

 

My guess is that Ford will do the same with their new, all-aluminum pickup. However, it'll be interesting to follow this for the long-term.
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In this case you may have to saw cut for "relief" and then re-join the parts. You can use the correct welding equipment to fix and file it smooth. If the part sees a lot of loads or is weakened by the repairs you can add an extra layer of aluminum material behind the seam (doubler) and fill with the putty I am showing. Either way you will be filing/sanding smooth after but filing aluminum is so much easier than steel IMO.

Lets see some pictures of this repair area!

 

Is it epoxy based and how does it sand relative to aluminum alloy of jets? Shrinkage over time? How flexible is it compared to the workable vintage aluminum bodies and newer alloys? Sounds like you have used it quite a bit and are the one to ask. Thanks for the tip.

 

In my experience it files and sands like you would expect of an unhardened cast part or a fresh aluminum weld. You can put a near mirror finish on it with the right grit paper or a smooth mill file. I have used it on broken cast and billet, and torn sheet metal. It could be useful in the right hands, when access to the correct welding equipment is not available or when heat may deform the part. YMMV

I am by no means an expert with the stuff but it has amazed me many times. it is a two part system where one of the components looks like aluminum dust soaked in a solution and the other a grayish IIRC catalyst I presume. I have not used it on a highly contoured surface but I'll bet the answers to your wise questions are out there.

 

There are techniques for shrinking aluminum (or steel) body panels that are a little more old-world. Example:

https://www.youtube.com/watch?v=b4K0b6k5Qco

 

I should probably clarify my statement about obtaining a mirror finish. Perhaps silver shiny surface is more appropriate a description. I never tried to go for a mirror finish.

 

Whenever I had a Cobra for example repaired, more often than not, we formed a new piece and welded to the existing good parts. A good metal worker can do this, unfortunately, it is becoming a dying art. we are very lucky to still have some of the best performing in Indiana.

 

I've had to weld aluminum. The tolerances are extremely low and you need to have the temperatures perfect for it to stick, which includes preheating it with a torch. It's quite a pain.

 

Same deal here, our normal procedure also.

 

I have an old set of gas torches that was used to fab old figher planes alum panels from a local guy here in SoCal, he told me how to do it but NOPE, maybe in a few years I will try again LOL

 

Thank you never seen it, any downsides?

 

It has a short-ish shelf life IIRC.
Is not cheap.
You need to know how to prep aluminum.
MEK is the best general cleaner FWIW.
Prep surface as per directions
I have not used it as a finish surface ready for show paint so I am not sure how that might work out.
I am sure there are a lot of others.
My experience was not that of a body shop more of light structural repairs on hidden components. Although I have used it on cast aluminum motorcycle parts to repair cracked cases and fix sealing surfaces that were broken away and would see a gasket.
I would choose a real weld over this stuff in most instances but I don't trust many people to weld aluminum well. YMMV

Lets see some examples of what you interested folks are thinking about repairing and I might be able to suggest a course of action that would be good enough for government work...or at the very least open up some dialog of some options!

 

Scrap aluminum is expensive so practicing isn't easy!

 

Then when you get it dialed in you wont see aluminum for a year then you have top dial it in again LOL

 

I'm used to finding beer can and soda can patches on my old helicopters so we just patched and riveted.

 

They were treating them special! Mach 2 tape is the quick and dirty method!

**3M? Aluminum Foil Tape 425
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I am not sure what your picture is showing.
Are you talking about the area in the circle or what appears to be a missing chunk of material "Area B"?

Check these out.

AW Collision Aluminum Repair -    "Where Quality and Service are Never a Compromise!"
Working with Aluminum | Dent Fix Equipment

..."Aluminum behaves differently than steel. Change the shape of a steel part; it remembers the form it used to be in. The opposite is true when working with aluminum. Once it is reshaped it forgets its original form and will take on a new shape.

It is a work hardened material. When aluminum is stamped into shape it becomes stronger. After the panel is bent in a collision it becomes stronger still. Flex it too much and it breaks or cracks like a bent spoon. In order to repair and pull the damaged area, the panel must be heated to 400°F to allow the metal to soften. Aluminum dissipates heat very quickly but can become permanently changed if heated past a certain point, approximately 750°F. The heated panel can now be pulled and while pulling the material it is being work hardened to set the new memory."...
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Maybe with some fiberglass on top haha