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Thread: Can I heat and straighten this cast aluminum?

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    Mud's Avatar
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    Default Can I heat and straighten this cast aluminum?

    A customer brought me this antique bumper car grill to repair.





    I plan to mill a new center bar and weld it in place. I also want to repair the other bars which appear to be bent in use. I've always considered cast aluminum to be not bendable, but if I warm it up a bit, could I push them back into their original position or close to it? The alternative would be to just weld beads of aluminum on the edges and fill the rest with body filler, which I consider a kludge. Has anyone here done this successfully?

    I guess the age to be 1940s, no idea on alloy of course.

    I'm open to any and all knowledgeable suggestions, including barroom BS.
    Attached Thumbnails Attached Thumbnails dscn0628b.jpg   dscn0629b.jpg  
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    HuFlungDung is offline Diamond
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    Not an expert opinion here but I would try a very careful approach using a couple of steel flats, one on each side of each web, and clamp with C clamps through the broken out space. Heat the steel bars to 5 or 600 hundred degrees and keep bringing the tension up on the clamps as you feel them relaxing when the material gives a little bit. I suspect that the aluminum will not spring back significantly afterwards.
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    Limy Sami is offline Diamond
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    My thoughts - don't know if they're any help, - apologies for the bleeding obvious.

    It doesn't look like zinc alu diecast so I'd say you're in with a good chance.

    IME gentle heat on cast alu works wonders,....... the old trick of using ordinary bar soap as a guide for annealing -(when it turns black it's hot enough) is a good guide.

    How it behaves when heated will give you a guide on it's malleability and weldability, alu brazing might be the route to go - alu braze rod melts at a lower temp - needs flux when used with OA,... don't know about TIG never tried it.

    ''Nurse'' it back in to shape rather than a big ''gesture''................. if it starts to go back and stops...... re- anneal.
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    If it has a high silicon content then it can suffer from age hardening to the point of becoming brittle after > 20 years of age to the point where it will just shatter from an impact. Limy's idea of annealing it would be a really good idea if it's age hardened.

    My only experience with heating aluminium is that there's a sudden transition from not hot enough to too hot where it just melts and lets go, there are aluminium solders out there which would allow fairly low temp repairs to be done.
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    Hdpg is offline Stainless
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    When you are heating aluminum, cast or extruded, up to the annealing temperature a couple of ways to tell you are there are:

    Paint regular motor oil onto the backside of where you are heating and when it starts smokiny you are hot enough.

    Get a small length of soft pine wood and periodically pull the torch away and rub the wood against the are you are heating, if it smokes and chars you are hot enough.

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    Mike C. is offline Diamond
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    DON'T TRY TO BEND IT HOT. Aluminum is hot short and it is a sure fire way to crack it. You can anneal it, let it cool and then work it, but don't work it hot. Put it on a wood block and work from the back side GENTLY with a big rubber or rawhide mallet. You may want to go a bit past level, then flip it over and come back down. If all the bars are not bent, it's proabably stretched the bent ones a little. Going both ways will help to shrink it back.

    Should be no trouble to TIG. Try to make your replacement out of soft conditon O material.

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    Is there a transitional temperature where it starts to get hot short, or does any heat at all cause that?

    What is the correct temp for annealing? I have an IR temp gun, I can measure it directly.

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    Mr. O is offline Cast Iron
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    We used to take an O/A torch and soot the area, then heat it just enough to burn the soot away.
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    Limy Sami is offline Diamond
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    Quote Originally Posted by Mud View Post
    Is there a transitional temperature where it starts to get hot short, or does any heat at all cause that?

    What is the correct temp for annealing? I have an IR temp gun, I can measure it directly.
    There ya go getting all technical on me Mud ........... any help?

    http://www.metalshapers.org/tips/covell/annealing.shtml

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    tdmidget is offline Titanium
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    Mike, what do you mean by "hot short"? That is a term used in steel rolling mills to describe the condition where the strip splits at the edges like a pie crust being rolled too thin. It is commonly caused in steel by a high sulfur or phosphorus content.
    It is also used to describe a brittleness from excess copper.
    I have never heard it applied to aluminum though.

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    Quote Originally Posted by Limy Sami View Post
    There ya go getting all technical on me Mud ........... any help?

    http://www.metalshapers.org/tips/covell/annealing.shtml
    Yep, he says 800 for annealing.

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    Limy Sami is offline Diamond
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    Quote Originally Posted by tdmidget View Post
    Mike, what do you mean by "hot short"? That is a term used in steel rolling mills to describe the condition where the strip splits at the edges like a pie crust being rolled too thin. It is commonly caused in steel by a high sulfur or phosphorus content.
    It is also used to describe a brittleness from excess copper.
    I have never heard it applied to aluminum though.
    The hot short mentioned is when metals become more brittle (fragile?) rather than malleable at elevated temperatures, cast iron for example, ....... a lot depends on the alloy but brass can be made too hot and never recover.

    It also applys to aluminium, and IME especially cast.

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    mobile_bob is offline Stainless
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    get a 550 degree temp stick, your gonna need it later when you start
    to weld on it.

    don't even think about welding cast aluminum unless it is fully up to 550 degrees F and stable there, no drafts, weld and reheat to 550, and let cool in the oven

    if you don't i guarantee you will have a bigger mess than when you started

    bob g

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    ray french is offline Titanium
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    If this is a restoration project I recommend leaving it as it is.Otherwise it will lose value as an antique,which it appears to be.

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    Mud's Avatar
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    Quote Originally Posted by ray french View Post
    If this is a restoration project I recommend leaving it as it is.Otherwise it will lose value as an antique,which it appears to be.
    Do you mean with the center bar missing? Or one straight bar and the rest bent? Or bend the new center bar to match the rest?
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    Mike C. is offline Diamond
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    Limy Sami has it on the "hot short" explanation. It's something that seems counter intuitive if you have only worked with steels. Heat it up to bend it and it breaks? no way... WAY.

    One of the FIRST things I learned in the aviation restoration field. As Sami explains, instead of becoming malleable, aluminum at elevated temps loses both strength AND ductility, meaning it bends real easy, but it doesn't stretch, so it breaks... about the consistency of a warm chocolate chip cookie. I was told anything above 375F was playing with fire (I'll take the pun), as far as aluminum strength.

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    So, Mud, how'd this turn out? Got any pics of the result?

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    I laid a heavy steel bar across the nose and gradually pulled the bent bars into position with a big clamp while cold, sort of like straightening a bar in a press. Haven't finished the job, it's still around here somewhere, and I haven't heard from the customer in a long time. It's only been 4 years, you don't want to rush these things, y'know.
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    Aptplas is offline Plastic
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    Guys, There are good reference sources that will explain how the various approaches outlined in this thread may get you into trouble - if you want to maintain material properties and/or achieve best results.

    The mentioned approaches are all fairly inaccurate methods of achieving "W" temper - which relieves from the effect of "cold work" but doesn't technically "anneal". W temper is specifically for alloys that spontaneously age harden. Temps are around 500-650 deg F) I understand repeated trips through "W" temper degrades material property.

    First you need to know whether the particular alloy is considered "Non-heat-treatable or Heat-treatable" as the latter alloys (All 2000,6000&7000 series) get very technical. For example, the 2000 & 3000 alloy series want to see 775 deg F for an extended time, then accurately ramped cooling at a rate of 1 deg/min down to 500 deg F, after which uncontrolled cooling is allowed.

    For when I'm not sure, I made "friends" with a local recycler. He's got one of those $28000.00 hand-held spectrometer that not only tells you the alloy # but will give you the various % of alloy elements.

    Better to be "informed" than sorry!

    mjb
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    opscimc is online now Hot Rolled
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    Quote Originally Posted by tdmidget View Post
    what do you mean by "hot short"?
    I've long known what this term means in practice, but the words don't make sense in the context of what they are describing. So, I finally took the time to find the origin of the term. In case anyone besides me is interested, it comes from the Swedish 'rodskor' which is a combination of red (rod, with a line over the 'o') and brittle (skor, again with a line over the 'o'). That word subsequently evolved in English from meaning something that was brittle when red-hot to the more general brittle when hot. I can even imagine how a mispronunciation of 'rodskor' in a noisy steel mill could sound like 'hotshort'.
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