Metal working aluminum tailgate.

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farmerfred

Member
I need to do some repairs on the aluminum tailgate on my 2019 GMC Sierra 1500. I had i minor incident that placed a number of small dents in the one side of it. They are shallow and also caused the typical raised area around them. I have never tried metalworking aluminum and need some advice on how to proceed. I do not want to stretch the metal any more than it already is. I can get to the back side fairly easy. Can aluminum be shrunk if needed? Thanks.
 
i am far from a pro at any kind of metal working. as a matter of fact i kinda suck at it. i can tell you by buddy who is a super skilled metal shaper, he does aluminum using most of the same tools he does with steel. he shrinks, stretches and hand forms all kinds of crazy organic shapes. wait for one of the pros to chime in concerning the dents before you jump in and do it.
 
I've never had a problem with aluminum, as long as if you work the metal a lot you will want to heat it up enough to resoften the metal (anneal). That will lessen the chance of oil caning or cracking the aluminum.
 
Problem you will find with the stuff they use now, it's heat treated and doesn't work like 3003 or 5052. It some sort of hardened alloy.
 
Best thing I can tell you is if you work the dents out some, first clean your hammer and dolly well. You don't want to embed steel particles in the AL because it will cause the paint to fail. If you do stretch too much, be very cautious using heat as it will often crack due to the alloy used (some form of 6000 series). A shrinking disc would be the safest way to shrink. Use a phenolic backing pad or the backside of a (flexible) type grinding disc if you don't have a shrinking disc. You will find that it is very tough, doesn't want to move very easily. It's very bouncy. Acts like it's work hardened because it is already hardened. Realisticly try to simply work them some getting the highs around the dents down and the dent out some. Then fill it.
 
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Annealing hardened alloys does not produce the same results as the non heat treatable alloys like 3003 and 5052. Why I say be careful using heat.
 
I worked on a 2020 Silverado tailgate, and it seemed to hammer and dolly easily, It must not have been the hardened aluminum or was just in a good area not to give me problems.
 
RenewAP said:
I worked on a 2020 Silverado tailgate, and it seemed to hammer and dolly easily, It must not have been the hardened aluminum or was just in a good area not to give me problems.
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It's been a while and most of my experience is on F150's so maybe some/all of what I wrote doesn't apply to those GM gates.
 
Thanks all for the helpful replies. I have never tried to metal work aluminum so this will be a learning experience for me, I can do pretty well with steel body parts So I will proceed with caution. I spoke to a friend who has a body shop and he said it might be best to replace it with new, but I cannot see spending that much money because of how small the area is that is dented. He did not seem too interested in repairing it. I think I will use the hammer off dolly method to try to work down the raised areas and bring up the lows and finish with filler.
 
I don't know what alloy the manufacturers use to do body sheet parts. I do know that 6000 series in sheet thickness is not good for bending - forming. Example 60?? aluminum sheet brake bend and will snap off at the bend. 6061 aluminum tubing will crack in the tubing dies unless you anneal the bend area prior to bending. The tube work hardens in the bend after bending.
 
I should not comment, but 6061 is very workable which depends on the condition.
T6 is a common heat treated condition and is annealed by bringing it to temperature and quenched….then held in a walk-in freezer until dimensionally corrected. Then back to an aging oven to bring them to the desired hardness.
I know it sounds odd, but I worked hundreds of welded assemblies that were heat treated in this manner.
I have no experience with this unknown aluminum used in automotive body panels.
 
Worn Out Welder said:
I should not comment, but 6061 is very workable which depends on the condition.
T6 is a common heat treated condition and is annealed by bringing it to temperature and quenched….then held in a walk-in freezer until dimensionally corrected. Then back to an aging oven to bring them to the desired hardness.
I know it sounds odd, but I worked hundreds of welded assemblies that were heat treated in this manner.
I have no experience with this unknown aluminum used in automotive body panels.
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Every OEM aluminum hood is heat treated as is the entire aluminum F150 exterior. Not having done an Al GM tailgate I was assuming it was heat treated as well. What they use IDK. It's most definitely a heat treatable alloy. Nothing like working 3003 or even 5052. I have seen it crack when heated then attempted to work something out. It behaves nothing like steel. Or how annealing works with 3003 and 5052. I hate the stuff and working on those vehicles. IMO none of it is designed to be repaired, just replaced.
 
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farmerfred said:
Thanks all for the helpful replies. I have never tried to metal work aluminum so this will be a learning experience for me, I can do pretty well with steel body parts So I will proceed with caution. I spoke to a friend who has a body shop and he said it might be best to replace it with new, but I cannot see spending that much money because of how small the area is that is dented. He did not seem too interested in repairing it. I think I will use the hammer off dolly method to try to work down the raised areas and bring up the lows and finish with filler.
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Go easy with it. Don't get crazy with hammer blows and trying to move it if it doesn't want to move. And you are right, most Shops have no interest in repairing the stuff, just replacing it. You should see the amount of what would be easily repaired F150's (if still steel) that are totalled now. I spent a year doing almost nothing but rebuilding totaled al F150's for one customer who was a dealer. Nine of them in total. Learned quite a bit doing them but gawd it sucked working on them.
 
Worn Out Welder said:
I should not comment, but 6061 is very workable which depends on the condition.
T6 is a common heat treated condition and is annealed by bringing it to temperature and quenched….then held in a walk-in freezer until dimensionally corrected. Then back to an aging oven to bring them to the desired hardness.
I know it sounds odd, but I worked hundreds of welded assemblies that were heat treated in this manner.
I have no experience with this unknown aluminum used in automotive body panels.
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Yes, you should comment! A lot of weird techniques are used in all metal manufacturing. All the alloys and heat treats are different, and I only know some of the general guide lines. Whatever I had here was not the right condition and it was in worse condition after I bent it o_O.
 
IIRC correctly from the I-Car class I took like 8 years ago now, looking at my notes I took, the alloy in F150's is 7000 series. Which is aerospace grade stuff. I think 5000 series is used in some places. I would be willing to bet that the GM is using 5000 series for the tailgates which while it is harder to work than 3003 is still workable till it completely work hardens. Then it needs to be annealed. If it is then it will be workable and you should be able to get the dents out relatively easy like Renew said. If you overstretch it, the shrinking disc would be a good tool to shrink it with.
 
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7000 series is great for strength, but limited weld ability.
The crude method I was taught to anneal 6061 was to use a ox/acetylene torch….light the torch with no oxygen, which we know leaves a sooty carbon that you cover the desired annealing area with.
Then use a neutral flame to heat the area.
When all the carbon soot has burned off, quench with water…..Is it zero condition? I highly doubt it, but it will be more workable.
It does age harden, but not back to the previous state without adding the correct amount of heat over time.
It looks like you would have to hold it at 775F for about an hour to effectively anneal it.
I didn’t look at the aging temperature since it seems impractical for this type of work.

IMG_8619.pngI like Chris’s idea, take down the highs, and fill the lows.
Far less stress
 
Chris_Hamilton said:
Go easy with it. Don't get crazy with hammer blows and trying to move it if it doesn't want to move. And you are right, most Shops have no interest in repairing the stuff, just replacing it. You should see the amount of what would be easily repaired F150's (if still steel) that are totalled now. I spent a year doing almost nothing but rebuilding totaled al F150's for one customer who was a dealer. Nine of them in total. Learned quite a bit doing them but gawd it sucked working on them.
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If you think vast amount of aluminum trucks are totalled now just wait till there is more battery operated cars are wrecked. From what I've read they just about have to total most of them because the structure that encases the battery is usually damaged.
 
elwood said:
If you think vast amount of aluminum trucks are totalled now just wait till there is more battery operated cars are wrecked. From what I've read they just about have to total most of them because the structure that encases the battery is usually damaged.
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Check out the giga casting Tesla started and everyone is going to copy. Will be like the video of the 41k rivian box side but on mass scale. Aluminum just cannot be sectioned like steel.
 
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