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Can someone help me finding information about the typical strength for bolts threaded into Al?

  1. Feb 23, 2016 #1
    I'm looking for any information about the typical strength for bolts that are threaded into aluminium. I've tried googling them but I'm having hard time finding information; I've tried looking through machinery's handbook and it doesn't seem to be showing the information for this specifically.

    Can someone help?
  2. jcsd
  3. Feb 23, 2016 #2


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    It's not clear what you mean by 'bolts threaded into aluminum'. Bolts are used in many different applications, and it is the analysis of the application which determines the strength of the bolt or bolts to be used. It's just about impossible to say what the typical strength value is for a bolt without knowing details of the particular application.
  4. Feb 23, 2016 #3
    http://www.faztek.net/img/mless_app.jpg [Broken]
    well the bolt will be used to join 2 aluminum extrusions similar to the picture above I guess to analyze the shear and deformation. But don't bolts have strength properties like ultimate shear strength and possible for aluminum threaded ones of their own?
    Last edited by a moderator: May 7, 2017
  5. Feb 23, 2016 #4


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    What is the material and grade of the bolts? Are the bolts in shear or in tension?

    If a steel bolt is screwed into threaded aluminium, then when excessive tension is applied, I would expect the aluminium thread to shear and be pulled from the hole. That often happens when a bolt is over-tighten in threaded aluminium. If you calculate the section of aluminium being sheared and the number of turns engaged, you can calculate the tension needed to pull out the aluminium thread.

    There is a device called a “Screw Thread Insert”, STI, sold under names such as “Recoil” or “Helicoil” that are used to repair stripped threads in anything from plastic to steel. It is often the case when aluminium needs to be threaded that STIs are installed during manufacture. While that slightly increases the area of the shear plane, it also avoids galling, wear and corrosion damage to the aluminium thread material by the steel bolt that might weaken it over time. Stainless steel STIs are often used in aluminium.

    Another solution to threading aluminium is to use a captive nut such as a “Nutsert”. That is a more bulky solution and so is usually only used when working with thin aluminium sheet that may need to be disassembled later and cannot include many turns of thread.
  6. Feb 23, 2016 #5
    1. So we can't just get information for strength properties of aluminum threaded bolt just in general overall? or possibly list of these based on various grades and sizes? we didn't specifically choose a model yet and would like to obtain some information.

    2. I just would like to make sure I understand this part. What do you mean by a steel bolt screwed into threaded aluminium or bolt threaded into aluminum? Doesn't it just mean the thread part of bolt is made of aluminum material?

    sorry for asking such trivial questions.
  7. Feb 23, 2016 #6


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    Here is a catalog from a US supplier of aluminum bolts.


    The strength properties of the various grades of aluminum bolt material can be found on p. 4.

    Google "aluminum bolts" or "aluminum fasteners" for more information about these bolts and their suppliers.
    Automobile engines are often made with a mix of iron and aluminum parts. Typically, the cylinder block is cast iron while the cylinder head(s) is cast aluminum. Generally, steel bolts are used to assemble all the engine parts together, because of steel's higher strength and better resistance to temperature fluctuations.
  8. Feb 24, 2016 #7
    thank you for the file and responses. But I checked pg. 4 and they only seem to be giving out dimensions with no strength properties.
  9. Feb 24, 2016 #8


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    The p.4 I was referring to is the fourth page in the Acrobat document. There is a table at the bottom on that page entitled "Minimum Mechanical Properties for Threaded Fasteners". The catalog is small so don't be afraid to thumb thru it.
  10. Feb 24, 2016 #9
    wait is this aluminum bolt threaded into aluminum or steel bolt threaded into aluminum? I'm actually looking for steel bolt threaded into aluminum.
  11. Feb 24, 2016 #10


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    That appears to show a standard section that has captive steel nuts in the slots, now typically used to build 3D printer frameworks. If that is the case the aluminium material is irrelevant.

    The assembly of aluminium extrusions with steel bolts almost never uses standard profile screw threads tapped into the aluminium. It is almost always the case that the aluminium is locally deformed as the steel thread is first screwed in. The steel thread is only part engaged radially, but over a greater length of the thread.

    The bolt failure mode expected will be typical for the steel bolts used, in shear or tension. That is independent of the aluminium material.

    The aluminium material may fail if there is insufficient area in compressive contact with the steel thread or if the bearing area of the bolt head is insufficient.

    What type and size of bolts are you considering ? What is the thread profile ?
  12. Feb 24, 2016 #11
    1. Wait I don't understand. So you're saying the standard steel bolt with steel thread will cause deformation for aluminum extrusion and steel bolts with aluminum threads are almost never used for aluminum extrusion? Then what type of bolt really works?

    2. We didn't really determine the any size or thread profile. We're just looking for strength properties of steel bolt threaded in aluminum like SteamKing provided; except the one he provides is for complete aluminum bolt with aluminum thread.
  13. Feb 24, 2016 #12


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    Steel bolts with the standard 60° metal thread profile will first need a thread cut in the aluminium. That may use a STI, but extrusions are not designed to take STIs. Extrusions are usually designed with “C” shaped channels to take “self tapping” screws.

    Where “self tapping” screws are used in aluminium extrusion, local deformation by the cutting process will occur. That determines the contact area of the steel thread with the aluminium. The area of that aluminium contact determines the strength of the contact between the steel and aluminium.

    Then consider two independent failure modes separately.
    1. The strength of the steel bolt in shear or tension. That is standard data and does not involve aluminium.
    2. Failure of the aluminium material that is in contact with the thread of the steel bolt.
  14. Feb 25, 2016 #13
    Thanks for the response, I hope I'm not taking too much of your time as I'm really new at these stuff.

    I have few more questions.

    1. So if I just find the strength of steel bolt, it'll show the strength not involving aluminum. What kind of difference is there going to be when involving threading into aluminum?

    2. So when you mean by failure of the aluminum, I guess you're talking about ultimate shear/tension strength of aluminum. But does it matter whether it's in contact with the tread of the steel bolt or not in terms of value for the failure of the aluminum? (I guess it's kinda similar to number one).

    thank you
  15. Feb 25, 2016 #14


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    If the steel screw has a long section engaged with the aluminium then failure of the steel bolt will occur before stripping of the aluminium thread.

    If only a few turns of a steel bolt are engaged then it will be the aluminium thread that will fail by shear first. In that case the steel bolt will be pulled out with a helix of aluminium filling it's thread. The hole in the aluminium will be a candidate for a STI as it has lost it's thread. The area of aluminium sheared is slightly less than; the bolt diameter * Pi * length of thread engagement. Accurately cut threads will carry greater loads than sloppy threads.
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