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Aluminum: When, or is, stress relief needed?

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  • #16
    Unless you are machining Invar that is a problem that affects nearly all materials. Plastics are far worse as they often have coefficients of linear expansion ten times greater than metals.
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    • #17
      Hi Folks,
      When i was serving my apprenticeship in the late 1950/s, We were making aluminium castings in various specifications, I remember one particular component, where the customer specified that the castings be put in water & brought up to boiling temperature, and boiled for a specific period, Then allowed to cool down,
      does anyone have any ideas, what this "heat treatment" was supposed to achieve for this particular component? sorry i cant remember the metal spec, Was it some form of stress relieving? Wish i could recall the details of the casting etc.

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      • #18
        A lifetime of work.

        I once met and did a little work for a University Professor who spent literally a lifetime investigating how to improve the strength of aluminium castings. Apparently early helicopters had many unexpected failures of aluminium castings, despite great care having been taken in their manufacture, and this got the fellow interested. The "secret" to make better castings apparently was in keeping temperatures of the melting and pouring cycles very tightly controlled. There was no mention of later heat treatments of the castings. Hope this is of interest. Regards David Powell.

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        • #19
          Casting alloys are an entirely different category of aluminum alloys compared to the heat treatable and fabrication alloys. I am not as familiar with the casting alloys since they are not much used in aircraft construction. It's a lot harder to inspect and qualify a casting for soundness than it is a sheet or plate product and the alloys are very different with most commonly much larger percentages of silicon to enhance the pourability and liquidity of the molten metal. The silicon content of the fabrication alloys may be as high as a couple of percent but the casting alloys may go as high as 15 percent. That makes a big difference to the properties including especially the response to temperature variations.
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          • #20
            http://www.eurospares.com/graphics/m...IL-H-6088G.pdf

            is a milspec doc on the heat treatment of aluminum alloys that may be of interest to some.

            cheers,
            Michael

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