Alloy Vs Steel

Discussion in 'Architecture & Engineering' started by Harry2, Oct 23, 2014.

  1. Harry2 Registered Member

    Messages:
    5
    I wonder if there is a specialist out there that could answer this question please?

    I work in the motor trade and the manufacturers use engine parts made of alloy and install mild steel bolts/studs when assembling parts. After years of use and weathering the mild steel stud or bolt when trying to loosen it can without warning shear off, hence having to drill out the remaining part before re-threading the component part.

    I sometimes apply heat to the alloy housing to help loosen the stud/bolt when my experience at the time tells me that the stud/bolt may shear off, but sometimes the stud is only very thin and may shear without warning, so my question becomes;

    Which is the correct way to heat up the assembly, is it;

    1 / heat the alloy, or

    2 / heat the mild steel stud/bolt

    Thank you for any replies
     
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  3. Dr_Toad It's green! Valued Senior Member

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    Are you talking about Aluminum alloys? This is an old problem, and the main reason for Helicoil replacements. Aluminum and steel bond better than red Loctite given enough time.
     
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  5. Facial Valued Senior Member

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    2,217
    Sounds like #1 is the better option if you cannot detach the part. However heat decreases the strength of metals and it may be not the best option in that circumstance.

    Sounds to me like there is some galvanic corrosion, or stress concentration, or both (stress-corrosion) present. This causes interference stress upon formation and an incredibly high friction to overcome. In this case it would be aluminum oxide (white powder) or if it's a real corrosion resistant alloy (like 6061) you can have rust present.

    I would actually need to look at a schematic of this to do a proper stress analysis. But that's my guess for now.
     
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  7. Harry2 Registered Member

    Messages:
    5
    Yes I am
     

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