ASM Online Member Community

  • 1.  staining/discoloration of aluminum ingots

    Posted 20 days ago
    We produce alloyed aluminum ingots for foundries to re-melt and make functional castings.  To make the ingot shape the molten metal comes out of the furnace tap hole into the mechanism that distributes it to each ingot mold as they come by on a continuous conveyor.  The mold conveyor takes the filled ingot molds to a water spray area to quickly cool down the molten metal and to solidify the ingots.

    Some times the ingots get a stain or discoloration instead of the usual bright shiny silver color.  The color is usually a dull yellow to brown.  Sometimes an iridescent pink/blue, like oil on water.  This colorizing has been described as an oxide layer just a few atoms thick that reflects the light like a diffraction grating, thus the colors.  This is harmless and usually goes away upon re-melting at our customer's foundry.  However, some customers don't like this.  They question the quality of the ingots.

    Is there some way we can prevent this from happening, or stop it once we see it starting to discolor our ingots?

    Ron Zakrzewski, Laboratory Manager
    Custom Alloy Sales

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    Ron Zakrzewski
    Laboratory Manager
    Custom Alloy Sales
    CITY OF INDUSTRY CA
    16263693641
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    Data Ecosystem - Global Materials Platform


  • 2.  RE: staining/discoloration of aluminum ingots

    Posted 19 days ago
    You can scarf the billet  with Al shot media just enough to get dull finish off the surface. Doesn't have to be high hardness.


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    Sanjay Kulkarni
    Materials Engineer
    MSSC
    Troy, MI
    248-840-1056
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    Data Ecosystem - Global Materials Platform


  • 3.  RE: staining/discoloration of aluminum ingots

    Posted 19 days ago

    Thank you, Sanjay.  But that's simply not practical.  I forgot to mention that we're a pretty big operation.  If we had one heat (batch) go off color, that would be 3000 ingots. 

     

    As to the cause, I'm placing my bet on the cooling water hardness and/or pH.

     

    Ron

     

    Ron Zakrzewski

    Laboratory Manager

    Custom Alloy Sales Inc.

     

    Contact: (626) 369-3641 ext. 2800

    Email:   Ron.Zakrzewski@customalloysales.com

     

    https://customalloysales.com

     

    All price quotes are subject to confirmation

     

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    Data Ecosystem - Global Materials Platform


  • 4.  RE: staining/discoloration of aluminum ingots

    India Chapter Admin
    Posted 18 days ago
    You hunch is right, the discoloration is primarily due to some minerals present in the water. The normal way to get rid of this problem is to have a slightly acidic water if that is possible for you. Also corrosion inhibitors are available in the market that make the cooling water acidic and probably won't have any environmental impact. Since it is not always happening, you may check the water on days that does happen.

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    Vivek Singal
    Mumbai
    919769208775
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    Data Ecosystem - Global Materials Platform