To metallurgist out there: difference between receivers made of 6061, 7075 and 7029

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    Ultimate Member
    Jul 31, 2008
    1,194
    Westminster
    Just bought a DPMS LR-308 and the receiver material is called 7029 aluminum. I also know receivers are made of 6061 and 7075 aluminum. I believe 7075 is the mil-spec material but what are the practical differences between the three?
     

    Ranchero50

    Ultimate Member
    Dec 15, 2012
    5,411
    Hagerstown MD
    You can Google the traits of each material but in layman's terms it durability for the most part and even that is more dependant on the quality and depth of the anodizing. My son recently bought a Bravo Company upper and the charging handle has already worn through the anodizing from him hand cycling it a couple dozen times. Not a round down range yet. Some flavors machine better, some have tighter quality standards. Forged versus cast effects the grain structures. Again for our intended the use and duty there's not a huge difference. I think the most loaded part on an AR receiver is the bend between the pistol grip where the buffer screw in. That's where the 3d printed ones failed.
     

    ToolAA

    Ultimate Member
    MDS Supporter
    Jun 17, 2016
    10,499
    God's Country
    Not a metallurgist.

    DPMS machines the upper from an extruded bar stock instead of a forging. Sort of hybrid manufacturing process similar to machining a solid billet but the shape of the extrusion will mean that they have less material removal. The 7029 Aluminum alloy is more suited to extrusion.

    Differences in manufacturing are really cost based not strength based. Making parts from billets are more expensive but have less tooling and setup cost, so more suited for smaller runs or custom parts. Having a custom extrusion made has some more up front cost, but not much. Forging would have the most up front cost but once the tooling cost is amortized over the entire run they usually yield the lowest unit cost.

    I doubt there would be any noticeable difference in part strength or wear resistance once anodized.
     

    gwchem

    Ultimate Member
    MDS Supporter
    Dec 18, 2014
    3,434
    SoMD
    Both 6061 and 7075 are used on airframes of different planes, but you're right that 7000 series is more often. Generally, 7075 would be a little stronger. Depends on temper as well.

    Neither is inherently prone to bad corrosion, but 7075 should be a little better.
     

    dmable44

    Active Member
    Jul 4, 2018
    117
    Not a metallurgist but a welder. For 9/10 people here that aren’t dragging there ARs up and down Everest or through the Sahara, it doesn’t make a damn bit of difference. All this “aircraft grade” and “T6/T5” is just used as a marketing term to fool people into spending more money.
     

    Pinecone

    Ultimate Member
    MDS Supporter
    Feb 4, 2013
    28,175
    T5/T6 DOES have meaning.

    It has to do with the heat treating levels and has to do with ductility and brittleness.

    Aircraft grade is a marketing term.

    Aircraft use a number of alloys for different use. There is no real "aircraft grade." 2024T6 is 2024T6

    There are some specific forms of shapes that are made for aircraft use. Most aircraft skins are 2014 Alclad. Alclad is a like a modern US coin. A sandwich. the bulk of the sheet is 2014, but each side has a thin layer of pure aluminum for corrosion resistance.
     

    dmable44

    Active Member
    Jul 4, 2018
    117
    T5/T6 DOES have meaning.

    It has to do with the heat treating levels and has to do with ductility and brittleness.

    Aircraft grade is a marketing term.

    Aircraft use a number of alloys for different use. There is no real "aircraft grade." 2024T6 is 2024T6

    There are some specific forms of shapes that are made for aircraft use. Most aircraft skins are 2014 Alclad. Alclad is a like a modern US coin. A sandwich. the bulk of the sheet is 2014, but each side has a thin layer of pure aluminum for corrosion resistance.


    Well yes, everything has a meaning. However to 9/10 people it won’t make any difference for what they are using the firearm for.
     

    Boxcab

    MSI EM
    MDS Supporter
    Feb 22, 2007
    7,865
    AA County
    Some basics...

    Heat-Treatable Alloys


    Some alloys are strengthened by solution heat-treating and then quenching, or rapid cooling. Heat treating takes the solid, alloyed metal and heats it to a specific point. The alloy elements, called solute, are homogeneously distributed with the aluminum putting them in a solid solution. The metal is subsequently quenched, or rapidly cooled, which freezes the solute atoms in place. The solute atoms consequently combine into a finely distributed precipitate. This occurs at room temperature which is called natural aging or in a low temperature furnace operation which is called artificial aging.

    2xxx Series

    In the 2xxx series, copper is used as the principle alloying element and can be strengthened significantly through solution heat-treating. These alloys possess a good combination of high strength and toughness, but do not have the levels of atmospheric corrosion resistance as many other aluminum alloys. Therefore, these alloys are usually painted or clad for such exposures. They’re generally clad with a high-purity alloy or a 6xxx series alloy to greatly resist corrosion. Alloy 2024 perhaps the most widely known aircraft alloy.

    6xxx Series

    The 6xxx series are versatile, heat treatable, highly formable, weldable and have moderately high strength coupled with excellent corrosion resistance. Alloys in this series contain silicon and magnesium in order to form magnesium silicide within the alloy. Extrusion products from the 6xxx series are the first choice for architectural and structural applications. Alloy 6061 is the most widely used alloy in this series and is often used in truck and marine frames. Additionally, the iPhone 6 extrusion was made from 6xxx series alloy.

    7xxx Series

    Zinc is the primary alloying agent for this series, and when magnesium is added in a smaller amount, the result is a heat-treatable, very high strength alloy. Other elements such as copper and chromium may also be added in small quantities. The most commonly known alloys are 7050 and 7075, which are widely used in the aircraft industry. Apple®’s aluminum Watch, released in 2015, was made from a custom 7xxx series alloy.

    Non Heat-Treatable Alloys

    Non-heat treated alloys are strengthened through cold-working. Cold working occurs during rolling or forging methods and is the action of “working” the metal to make it stronger. For example, when rolling aluminum down to thinner gauges, it gets stronger. This is because cold working builds up dislocations and vacancies in the structure, which then inhibits the movement of atoms relative to each other. This increases the strength of the metal. Alloying elements like magnesium intensify this effect, resulting in even higher strength.

    3xxx Series

    Manganese is the major alloying element in this series, often with smaller amounts of magnesium added. However, only a limited percentage of manganese can be effectively added to aluminum. 3003 is a popular alloy for general purpose because it has moderate strength and good workability and may be used in applications such as heat exchangers and cooking utensils. Alloy 3004 and its modifications are used in the bodies of aluminum beverage cans.

    4xxx Series

    4xxx series alloys are combined with silicon, which can be added in sufficient quantities to lower the melting point of aluminum, without producing brittleness. Because of this, the 4xxx series produces excellent welding wire and brazing alloys where a lower melting point is required. Alloy 4043 is one of the most widely used filler alloys for welding 6xxx series alloys for structural and automotive applications.

    5xxx Series

    Magnesium is the primary alloying agent in the 5xxx series and is one of the most effective and widely used alloying elements for aluminum. Alloys in this series possess moderate to high strength characteristics, as well as good weldablility and resistance to corrosion in the marine environment. Because of this, aluminum-magnesium alloys are widely used in building and construction, storage tanks, pressure vessels and marine applications. Examples of common alloy applications include: 5052 in electronics, 5083 in marine applications, anodized 5005 sheet for architectural applications and 5182 makes the aluminum beverage can lid. The U.S. military’s Bradley Fighting Vehicle is made with 5083 and the 7xxx series aluminum.

    https://www.aluminum.org/resources/industry-standards/aluminum-alloys-101



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    Boxcab

    MSI EM
    MDS Supporter
    Feb 22, 2007
    7,865
    AA County
    As for Aircraft use, just one page from my DAC Structures Design Manual...
    It has lots of pages dealing with different kinds and forms of ALUM.

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    jrumann59

    DILLIGAF
    MDS Supporter
    Feb 17, 2011
    14,024
    Not a metallurgist but a welder. For 9/10 people here that aren’t dragging there ARs up and down Everest or through the Sahara, it doesn’t make a damn bit of difference. All this “aircraft grade” and “T6/T5” is just used as a marketing term to fool people into spending more money.

    Basically you are saying most ARs are safe queens....:innocent0
     

    dmable44

    Active Member
    Jul 4, 2018
    117
    Basically you are saying most ARs are safe queens....:innocent0

    Yupp. The average person isn’t taking theirs out on a 2 week field ruck or “insert any other actual hard use scenario that these firearms were designed for”. Yes, I’m sure a few use and abuse but most are just taken to the range and back.
     

    Z_Man

    Ultimate Member
    May 23, 2014
    2,698
    Harford County
    well you can have drastic strength differences of 7075 depending on the Temper. the yield strength for 7075 without heat treat is ~21,000 psi while T6 is ~65,000 psi. for 6061 with no heat treat the yield strength is ~8000 psi, and 6061 with T6 heat treatment is roughly 35,000 psi of yield strength. yield strength is that point at which plastic deformation (permanent) begins. also, 6061 has MUCH better corrosion resistance to 7075, but its also cheaper which is why some discount rifles will use it over the 7075. yield strength isn't everything as far as wear reduction, surface prep, coatings, and anodizing will have a big impact on longevity of an individual rifle part. i would be more critical of a lower receiver being manufactured out of a sub mil-std part than an upper receiver, due to the function and stresses on each part. if the part is properly surface finished, and the rifle is lubricated correctly i don't see the upper receiver being the point of failure. but i am not an expert, and the threaded area the barrel is torqued to would be the area of concern.

    the 7029 is going to be similar to 7075, but i cannot comment on its strength based on heat treatment. the material matters, but to most people it really won't. it all depends on cost savings and what you'll use the rifle for. an upper reciever is a relatively inexpensive piece of the rifle. last i checked retail price on a stripped mil-spec forged upper reciever is ~50 bucks. if you shop for sales $35. i don't know how much cheaper a 6061 or a 70xx material upper would be, as i don't know if I've ever seen them for sale retail.
     

    Eddie Van

    Dude
    Feb 4, 2011
    647
    Hollywood Star Lanes
    Aircraft parts manufacturer and Materials Engineer here and can confirm Boxcab, Pinecone and Zman covered the subject well.

    Will only add that 7029 is a high strength alloy approaching the properties of 7075 provided both are tempered (T5/T6/T7) to spec.

    Cost-wise for raw material, 6061-T6 is cheaper than 7075-T7 and 7029-T5 is in the middle (if it can be sourced, which is difficult as it's not too popular compared to 7075 )
     

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