Having earned my living in the collision repair industry since 1963, I can’t help but be somewhat amused by the conceptions and misconceptions in the repair industry about aluminum repair. It’s almost like no one ever repaired an aluminum part or vehicle until recently.
Aluminum has been employed since the early days of the automobile. And I’m not talking about some obscure gadget on an unheard-of car that history forgot, either. We’ve all heard of the Model T Ford – and most of us even know what one looks like. We’re car people, aren’t we? But did you know that the hood on a Model T Ford was made of aluminum?
This is a car that Ford literally produced millions of – and its last year of production was 1927. Many luxury automobiles of limited production also used aluminum because of its easy-to-form characteristics, and many pre-1930s vehicles were completely made from aluminum. Pierce-Arrow automobiles had models that employed aluminum castings to make up the body structure, as well as aluminum engines.
My point here is, the American automobile industry used aluminum extensively, especially in the early years, and we know that aluminum has been repaired at least as long as it’s been used in the automobile. And that’s a long time.
This is why I’m a little amused by all the hub-bub about the “dawning of the new age of collision repair.”
Don’t get me wrong. I’m not trying to minimize the difference in repairing steel and aluminum. There are differences, just like repairing plastic composites is different from repairing steel. (In fact, those differences are greater than aluminum and steel because plastic composites aren’t metals.) But as they say in the aluminum industry, “Repairing aluminum isn’t difficult … just different.”
So Where’s Aluminum Been All These Years?
If aluminum was so great in the first place, why did the auto manufacturers shift more and more to steel? You know the answer to that … come on, think … could the answer be … could it possibly be … economics? Yeah … right on!
As auto manufacturers became bigger and bigger, steel became a more efficient and cheaper metal to make automobiles out of. Sheet steel stamping was a major advance in production over hand forming because stamping produced a consistency that went hand-in-hand with the assembly line. And obviously, weight wasn’t a big factor when gasoline was 25 cents a gallon – or even 50 or 75 cents a gallon. It wasn’t unusual for automobiles to tip the scales at 3 tons or more.
But things today are just a little bit different. A couple of months ago, I was pumping gas into my red Dodge pickup for $2.09 cents a gallon. Nasty! Those $40 fillups tend to cause the mind to consider more fuel-efficient technology.
It also seems that there are more of us on the roads these days, which means we’re consuming more fossil fuels (gas). This, in turn, prompts us to explore further afield for ever-more-expensive petroleum in nice places like Iraq.
Of course, all this burning gasoline produces something called emissions (air pollution) that comes out of the tailpipe and makes the air a little hard to breathe in our now heavily populated metropolitan areas like L.A. (and I’m not talking about Lower Alabama)!
So now the government gets all mad and comes to the defense of the “gasping for air” voters who, lost in the smog, are showing up in declining numbers at our polling places. The government sets up some new regulations regarding pollution and fuel efficiency for automobiles, and they tell the auto manufacturers to meet the standards by such-and-such a date. They say they don’t care how the OEMs do it, as long as they just do it. (This flexibility is actually good because the free enterprise system is much better at figuring out how to do something than the government has ever been.)
The auto industry has known for a long time that the lighter a car is, the more fuel efficient it is. And the more fuel efficient it is, the less pollution it produces. Yeah … they’ve known this. But I was around when the first Chevy Citation showed up, and we were told that this unibody was the wave of the future. Hmmm … So how come the shop is full of Suburbans, Durangos, Expeditions and Siennas?
Well, yeah, I guess we don’t really like those econoboxes – at least not enough to buy them. Consider the 1975 VW Golf S, which weighed 780 kg. Then there’s the 1998 Golf, which weighed 1,090 kg. We’re not getting lighter. We’re cramming more electronics and other systems into these vehicles because the car-buying public loves it.
We’ve proven to ourselves that getting smaller isn’t going to do it. Americans don’t seem to want to buy such small cars. So can we stay at a reasonable size (by American standards) and still be fuel efficient?
If we build lighter, we probably can. And it’s easier to achieve fuel efficiency through “lightweighting” than it is through rolling resistance or aerodynamics.
OK, re-enter aluminum. It’s four times lighter and six times stronger than steel. What!! Six times stronger than steel? Yep. Aluminum in its alloyed forms and tempers is up to six times stronger than steel.
Not only that, but consider that aluminum is one of the most plentiful elements on earth. It’s everywhere, and when it’s scrapped and recycled, it takes only 5 percent of the original energy it took to initially form it the first time – and with no loss of quality. This is a huge consideration because aluminum can be recycled at low energy consumption and be extremely environmentally friendly.
Take plastic composites for example: Look in your dumpster. What do you see? Yeah … a bunch of plastic that doesn’t decompose, that’s got a petroleum base, that’s being landfilled and that no good recycling scheme has been engineered for. Wow, sounds kind of shortsighted to me.
The current model-year average American car uses 274 pounds of aluminum. By the year 2015, we should be at 441 pounds per car, according to industry experts. Currently, 80 percent of our automotive use is in castings, with 6 percent in extrusions. That leaves 14 percent for other uses, such as body parts.
Compare the annual U.S. automotive aluminum usage of 3.2 billion pounds to Europe’s 5.5 billion pounds. The Europeans are clearly ahead of us in aluminum consumption – for several reasons: Gas is much more expensive in Europe, pollution is a bigger problem with large tracts of forests dying from acid rain and European governments are mandating recyclability for the automakers prior to production.
We may be behind, but we’re not out of the running. In my practical opinion, we’re going to work with aluminum more and more in the future. It makes sense.
It also makes sense that if aluminum really is the “metal of the future,” then we need to learn to work with it and repair it. First,
let me say this: I enjoy working with aluminum. I like it. And if you start out with a positive attitude and a good outlook, success will be yours.
Galvanic corrosion is an 800-pound gorilla when you’re working with aluminum. You must pay careful attention to avoid cross-pollution of steel and aluminum in the repair process.
“What in the *#%@ is he talking about now?” you ask.
Look, I know most of you aren’t chemists or metallurgists. Neither am I. So let’s approach it in layman’s terms: Don’t allow any steel dust, grindings, sparks, residue or anything like sanding disks or paper that have been used on steel to come in contact with aluminum. If you do and you paint over it, you’ll be redoing it because corrosion will occur.
This is so serious that Audi recommends a separate repair facility with its own tools specifically for their aluminum-bodied vehicles. Think they’d do that if there weren’t potential for corrosion?
Many – or most – of you aren’t going to set up a separate repair facility to repair a vehicle with some aluminum parts or even an aluminum-intensive vehicle like the Audi A8 or Jaguar XJ. You do, however, need to give every consideration to each possibility of potential cross-pollution and make every effort to prevent it from happening.
1. Place your aluminum vehicle away from steel vehicles where grinding, sanding, welding or other intensive repairs are taking place.
2. Clean the jaws of your clamps thoroughly before and after use on aluminum. Upon removal of the clamp, wire brush (using a stainless steel wire brush dedicated to aluminum) in the area that was clamped. This is done because there could be some steel deposits imbedded in the aluminum from the clamp.
3. Clean all your hammers, dollies, files, pry bars and etc., before using on aluminum. You may want to consider a separate set of commonly used hand tools, kept in a small box, to be dedicated to aluminum only.
4. Clean all sanding and grinding tools thoroughly (wipe down and vacuum or air blow) prior to use on aluminum.
5. Always use new sanding discs and sandpaper to avoid cross pollution.
Oxidation is a 750-pound gorilla in aluminum repair. It’s a tiny bit smaller than galvanic corrosion, but it’s still way too big to ignore. (If you do ignore it, you’re going to get hurt … financially.)
Aluminum oxidation is both a good thing and a bad thing. It’s good because when the oxidation layer forms on aluminum, it produces a protective coating that prevents the base metal from corroding. It’s bad because paint, fillers and the welding process are seriously compromised unless this oxidation layer is removed first.
Thing is, it’s invisible to the naked eye in its initial stages, which makes removal all the more important. Coatings don’t stick to oxidation!
How quickly will aluminum oxidation begin to form? The atmospheric climate is a big determiner, but I wouldn’t prime over sanded and treated aluminum after two hours without repeating the process again. Follow your paint manufacturer’s recommendations for your local area.
Immediately prior to welding aluminum, you should always wire brush all your weld areas with a clean, stainless steel wire brush dedicated to aluminum only.
Heating Aluminum to Work or Repair It
Most body panels are tempered or work hardened to add dent resistance or strength to the part. Depending on the size of the dent, it may be necessary to heat the repair area to bring the damage out to its original contour. Because aluminum readily work hardens when deformed, it’ll want to stay in its deformed shape. This is true of both heat-treatable and non-heat-treatable aluminum. They both can be heated to aid in reformation.
Much care should be taken to determine the temperature of the aluminum, to allow forming. Between 400 degrees F and 570 degrees F is the workability range of aluminum. You’ll anneal aluminum in the 700+ degrees F range and lose the strength that was engineered into it. (It’ll become very soft and remain that way when it cools.) This is why you need to be careful not to exceed the 570 degrees F range. Aluminum melts at 1,200 degrees F, but oxide doesn’t burn off until 2,300 degrees F, which is why you need to remove the oxide prior to welding.
All of this occurs with no perceptible change in color of the base metal!
Oh yeah … and it’s pretty easy to melt a hole in aluminum if you’re not using a heat indicator of some kind.
Some heat indicator methods to consider:
1. Heat indicator crayons (available from your welding supplier).
2. Digital thermometer (racers use these for tire temp readings).
3. Laser thermometer gun (point shoot-digital reading appears).
4. Carbon burn-off applied with straight acetylene.
All of these are pretty self-explanatory, except for the old carbon burn-off method. This is a method I’ve used for many years with great success. Turn only the acetylene side of your oxy-acetylene torch on and light it. Turn your gas down at the torch until you have black carbon smoke tailing off the flame. Black off your repair area, and then add oxygen until you have a long feathered heating flame. Warm the panel until the carbon begins to disappear. I checked this with a laser gun thermometer that had been calibrated, and it was 429 degrees F – just right for working.
Methods of heating will vary with accessibility. Heat induction has been used, but you really should use a machine that’s intended to heat aluminum since some heat inductors don’t work well on aluminum. Test before purchasing.
Oxy-acetylene works well with careful attention to heat. Areas that are adhesive bonded to the inner structure for strength, require care and attention. You can also use propane.
Keep in mind that aluminum rapidly dissipates heat, so it’ll cool very rapidly and transfer heat to the surrounding area with great speed. Monitor your heat!
A Step-By-Step for Aluminum Dent Repair
1. Clean your entire panel with soap and water and dry. Wipe the entire panel down with wax and grease remover, and dry wipe off contaminants with a clean rag prior to evaporation of solvent.
2. Develop your repair plan and bring the clean tools and supplies needed to the work area. Be aware of cross pollution and galvanic corrosion sources. Avoid and prevent them.
3. Remove the paint finish from the repair area. Do not use more aggressive grit than 80 grit. Clean the paint from the repair site to allow for proper heating and heat monitoring.
4. Depending on the size of the repair and the stiffness of the repair area, determine if heat is needed. Be aware that straightening a highly tempered or hardened surface without heat can cause cracks.
5. If heat is needed, warm repair area to between 400 to 570 degrees F. Use heat indicator methods to monitor and manage heat. Use caution to avoid annealing damage and losing designed-in strength. It’s not that hard. Just be careful.
6. Work the metal using conventional straightening methods, with care being given to allow for panel softness. Don’t use sharp pick hammers or picks. Instead, use wooden bossing hammers, a ball peen to bring up a low spot instead of a pick hammer and pry bars with rounded tips covered with plastic cups.
Re-heat as necessary. Special stud welders for aluminum are available. The studs should be welded on prior to heating, if heat is to be used.
7. Blocking with 80 grit on a board or block will indicate high and low spots. Bring lows up and massage highs down. You can use a guide coat if necessary. If you’re going to metal finish, use a dull file to avoid excessive metal removal.
8. Finish sand the repair area with a new 80-grit disk. If filler is to be used, prepare repair area for epoxy primer according to paint manufacturer’s recommendations for epoxy primer on aluminum. Apply epoxy primer to prepared repair area.
9. If necessary, apply a thin coat of plastic filler to epoxy primer in the repair area. Finish sand plastic filler to acceptable finish and re-apply epoxy primer to sandwich repair in between the coats of primer.
10. When dry, apply appropriate primer surfacer and then block sand to paintable surface.
Writer Mike West, a contributing editor to BodyShop Business, has been a shop owner for almost 30 years and a technician for almost 40 years. His shop in Seattle, Wash., has attained the I-CAR Gold Class distinction and the ASE Blue Seal of Excellence.