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Thread: Crack and small hole repair to alum casting

  1. #1
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    Crack and small hole repair to alum casting

    I was cutting a small steel angle (2"x2") in my FEIN cold metal chop saw and it slipped from the vise jaw, rotated, then cracked and fractured (made a small hole) to the alum cast base. Grrrr!

    Is it possible to use an alum spool MIG gun (with argon) and repair this alum casting?

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    Re: Crack and small hole repair to alum casting

    Maybe but Tig would be better because if it was dirty Tig would burn the impurities out easier. Cleaning it really good a series of Mig tacks may work. May have to grind out dirty welds till it's clean.

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    Re: Crack and small hole repair to alum casting

    It can be done with a spool gun if you are careful . Use a piece of copper for a backer when welding up the hole. It will help a lot. If you can't find some copper get a piece of copper plumbing pipe. Cut a short piece off, Heat it to about 800 degrees and quench it in water to anneal it. Then take a hammer to flatten it. It will work for what you need to do.

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    Re: Crack and small hole repair to alum casting

    In addition to copper, steel also works as a backer for aluminum.

    Good luck on the repair.
    Dave J.

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    Re: Crack and small hole repair to alum casting

    Any possibility it could be magnesium?

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    Re: Crack and small hole repair to alum casting

    Welder Dave, thegary and MinnesotaDave - thanks for your insight. I was intending on using copper backing - I purchased some recently for some carbon steel backing to groove welds.

    tapwelder - you may be right. My only experience with magnesium has been with concrete screeds/floats - and they tend to weather/discolor to a dark grey color. How would I 'litmus test' the saw base to check if magnesium or aluminum?
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    Re: Crack and small hole repair to alum casting

    Be careful because magnesium will burn and you can't use water to put it out. It will explode. I read where you can put some vinegar on it and if it reacts it's magnesium and if it doesn't do anything it's aluminum. You can also file some shavings and see they burn like a sparkler. If I had to guess I'd say it's probably aluminum.
    Last edited by Welder Dave; 4 Weeks Ago at 02:28 AM.

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    Re: Crack and small hole repair to alum casting

    Thanks Welder Dave.

    I shall try the 'burn-the-filings' trick. Thanks.
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    Re: Crack and small hole repair to alum casting

    Your chance of igniting solid magnesium, even under welding conditions is super low. It burns like the devil once ignited, but lighting it is not easy. Anytime someone wants to show mag burning it is with filings/dust to get enough surface area to ignite easily.

    But if you try to use alum weld on a mag part, that ain't gonna work.... so.... look up the saw on Fein's website and see if it is mag. Since that is a feature (lighter, costlier) if it is mag they will say it for sure.
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    Re: Crack and small hole repair to alum casting

    Quote Originally Posted by davec View Post
    Your chance of igniting solid magnesium, even under welding conditions is super low. It burns like the devil once ignited, but lighting it is not easy. Anytime someone wants to show mag burning it is with filings/dust to get enough surface area to ignite easily.

    But if you try to use alum weld on a mag part, that ain't gonna work.... so.... look up the saw on Fein's website and see if it is mag. Since that is a feature (lighter, costlier) if it is mag they will say it for sure.
    davec:

    Great idea. I looked it up, and it is alum cast base.

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    Thanks.
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    Re: Crack and small hole repair to alum casting

    I think I would drop by HF, pick up some low temperature aluminum welding rods to use with propane, and give it a try with some type of backing.

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    Re: Crack and small hole repair to alum casting

    I've used Alumiweld. It's great for some things but I don't think it's right for this repair. It doesn't flow and wet out like solder. It only wets well where you can scratch the base metal with a sharp tool while the puddle is molten. It's going to be hard to scratch the surface down into that crack.

    I give a plus one to using a backer with TIG.

    And I'd add preheat to of the part to about 400-500 F so the part is up to temp for at least 5 minutes. It helps empty the air pockets in the aluminum porosity. My experience is if you don't preheat it will feel like trying to weld styrofoam. I think a 4043 rod will work but I've also used 4943 rod that's supposed to be better for cast aluminum.

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    Re: Crack and small hole repair to alum casting

    Quote Originally Posted by sand_man_red View Post
    I've used Alumiweld. It's great for some things but I don't think it's right for this repair. It doesn't flow and wet out like solder. It only wets well where you can scratch the base metal with a sharp tool while the puddle is molten. It's going to be hard to scratch the surface down into that crack.

    I give a plus one to using a backer with TIG.

    And I'd add preheat to of the part to about 400-500 F so the part is up to temp for at least 5 minutes. It helps empty the air pockets in the aluminum porosity. My experience is if you don't preheat it will feel like trying to weld styrofoam. I think a 4043 rod will work but I've also used 4943 rod that's supposed to be better for cast aluminum.
    4943 would definitely be the better of the two for a better strength match to the cast. 5356 would even be better. Too bad we don't know where your location as it would be a very simple tig repair. And I agree with clamping a steel backer to hold flat.
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  20. #14
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    Re: Crack and small hole repair to alum casting

    400-500 deg. preheat seems high for aluminum and this isn't a very thick casting.

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