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Strengthening Aluminum

  1. Jun 22, 2007 #1

    Astronuc

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    Periodically, I receive useful information on materials. This short note was sent from ASM.

    Two most common methods to increase the strength of aluminum alloys are to:
    • Disperse second-phase constituents or elements in solid solution and cold work the alloy (non heat treatable alloys)
    • Dissolve alloying elements into solid solution and precipitate them as coherent submicroscopic particles (heat treatable or precipitation-hardening alloys)

    Elements most commonly present in commercial aluminum alloys to provide increased strength, particularly when coupled with strain hardening by cold working or with heat treatment (or both) are copper, magnesium, manganese, silicon, and zinc. These elements all have significant solid solubility in aluminum, and in all cases, the solubility increases with increasing temperature. Of all the elements, zinc has the highest solid solubility in aluminum (a maximum of 66.4 at.%). The maximum solid solubility in aluminum alloys occurs at the eutectic, peritectic, or monotectic temperature.
     
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  3. Jul 2, 2007 #2

    Astronuc

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    One-Minute Mentor
     
  4. Jul 6, 2007 #3

    Astronuc

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    Second-Phase Strengthening of Aluminum Alloys

    http://asm.asminternational.org/ht-echarts/3046_OMM070607_figure.pdf
     
  5. Jul 13, 2007 #4

    Astronuc

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    Strain Hardening of Aluminum Alloys

    http://asm.asminternational.org/ht-echarts/3046_OMM071307_figure.pdf
     
  6. Jul 20, 2007 #5

    Astronuc

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    Heat-Treatable Aluminum Alloys

    Examples of heat treatment time and effect on strength - http://asm.asminternational.org/ht-echarts/3046_OMM072007_figure.pdf

    It's really important to pay attention to the chemistry specifications and ranges of particular elements in the alloy. Chemistry specs are written to allow some flexibility in manufacturing and avoid costly rejection. However, the effectiveness and effect of heat treatment, material properties and corrosion behavior can vary widely over the range of allowable composition. This matter is particularly critical when extending the performance range of a material.
     
    Last edited: Jul 20, 2007
  7. Jul 28, 2007 #6

    Astronuc

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    Natural Aging in Aluminum Alloys

    http://asm.asminternational.org/ht-echarts/3046_OMM072707_figure.pdf


    Here is a more general article on strengthening of metals, which features prominently a section on "Precipitation in Al-Cu Alloys".
    http://www.key-to-metals.com/Article128.htm
     
  8. Aug 5, 2007 #7

    Astronuc

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    Artificial Aging in Aluminum Alloys

    http://asm.asminternational.org/ht-echarts/3046_OMM080307_figure.pdf
     
  9. Aug 10, 2007 #8

    Astronuc

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    Artificial (Over)Aging Aluminum Alloys

    This can affect corrosion behavior as well as mechanical performance.

    http://asm.asminternational.org/ht-echarts/3046_OMM081007_figure.pdf


    When one is selecting an alloy one must also consider service conditions such as temperature, not only from consideration of corrosion and strength, but also the aging affects, which also change the corrosion and mechcanical performance.
     
  10. Aug 19, 2007 #9

    Astronuc

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    Effect of Precipitation on Aluminum Alloy Properties

    http://asm.asminternational.org/ht-echarts/3046_OMM081707_figure.pdf
     
  11. Aug 31, 2007 #10

    Astronuc

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    GP Zones in Precipitation Hardening Aluminum Alloys

    http://asm.asminternational.org/ht-echarts/3046_OMM083107_figure.pdf
     
  12. Sep 7, 2007 #11

    Astronuc

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    Solution Treating Time for Aluminum Alloys

    http://asm.asminternational.org/ht-echarts/3046_OMM090707_figure.pdf


    Students should consider membership in ASM International and TMS. They provide excellent resources and an opportunity to network with colleagues and potential employers.
     
  13. Sep 14, 2007 #12

    Astronuc

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    Quenching Solution Treated Aluminum Alloys

    http://asm.asminternational.org/ht-echarts/3046_OMM091407_figure.pdf

    See how the strength is affected by temper as well as quench rate, which is also affected by alloy composition.
     
  14. Sep 23, 2007 #13

    Astronuc

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    Quench Rate vs. Properties of Solution Treated Aluminum Alloys

    http://asm.asminternational.org/ht-echarts/3046_OMM092107_figure.pdf

    The optimal quench rate will depend on composition because different intermetallics have different precipitation/solubility temperatures. Knowing the solubility temperatures of different phases, and in fact, knowing the phases which are present, is critical with respect to having a controlled and reproducable process.

    Strength, toughness and corrosion resistance are all dependent on microstructure as well as composition, and in fact composition and microstructure go hand in hand. The other key factor is the thermo-mechanical process.
     
    Last edited: Sep 23, 2007
  15. Sep 30, 2007 #14

    Astronuc

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    Effects of Quench Delay of Solution Treated Aluminum Alloys

    http://asm.asminternational.org/ht-echarts/3046_OMM092807_figure.pdf

    When developing a process and transferring from laboratory to production, things like transfer time (and interruptions) must be carefully considered and then monitored, especially where the process is not fully automated.
     
  16. Sep 30, 2007 #15

    FredGarvin

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    I am loving this weekly Aluminum factoid you're doing for us Astro. As someone who uses only a couple grades, I find it really interesting. Thanks!
     
  17. Oct 5, 2007 #16

    Astronuc

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    Water-Immersion Quenching of Aluminum Alloys

    Thanks for the compliment Fred. I get this about every Friday, and I try to add something of value from my experience with different materials.

    http://asm.asminternational.org/ht-echarts/3046_OMM100507_figure.pdf


    The key is understanding the solution treatment temperature with respect to the temperature at beginning of quench and then the quench rate. Nucleation and precipitation of secondary phases are a function of temperature, and as second phases precipitate, the solid solution will be depleted of alloying elements. The longer the cooling time, the larger the second phase particles will become, so secondary phase particle size and distribution will be affected, which may have a dramatic impact on corrosion and mechanical performance.


    The pdf file in the above link is a Time-Temperature curve. In general, I would caution any user not to necessarily take any T-T or phase diagrams as gospel. In my experience, somewhat inaccurate T-T curves and phase diagrams have made their way into the literature, e.g. one for Inconel-718 and one for Zr-Nb, so I would be suspect of any curve unless I have independent data. Inaccuracies arise from specs that may be too broad or which do not consider some subtle behavior or sensitivities which can be easily overlooked or unanticipated. Such sensitivities can be initial fine precipitates (nm scale), e.g. intermetallics such as silicides, which have very high dissolution temperatures and which may still be present if the solution temperature is not sufficiently high. Very fine precipitates then serve as nucleation sites for subsequent precipitation, and even for entirely different compositional phases. It is best (practice) to obtain independent and current data for verification of any T-T curve for one's particular alloy system.


    Another aspect with respect to each of the processes mentioned in this thread is the separate and integrative qualification. Each step must be controlled within some range, but then the sequence of steps (integrated process) must be optimized and then controlled. Previous steps DO have an impact on subsequent steps, so the process/materials engineer must be cognizant of these matters. And this does not simply apply up to the point where product leaves the shop, but it applies to subsequent application (performance) in the field. On-going performance monitoring and feedback to the responsible engineering organization is crucial to safety and reliable (economical) use of materials and engineered products.
     
  18. Oct 12, 2007 #17

    Astronuc

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    Spray Quenching of Aluminum Alloys

    Sometimes one cannot quench a part/peice in a tank due to geometry or design consideration, or the heating is limited to the surface and the quenching must be done locally. So spray quenching is the answer.

    http://asm.asminternational.org/ht-echarts/3046_OMM101207_figure.pdf

    In addition to velocity and volume - the quenchant temperature is important.

    This is an area where use of a good multiphysics (particularly heat transfer) is important, and becoming moreso.
     
  19. Oct 20, 2007 #18

    Astronuc

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    Quench Severity for Aluminum Alloys

    http://asm.asminternational.org/ht-echarts/3046_OMM101907_figure.pdf
     
  20. Jul 27, 2011 #19
    I'm new to this forum and see a great amount of information.
    We are aluminum forgers. One customer has required an upper and lower limit on hardness (90 to 110 BHN). We have only been required to hold a minimum limit by all other customers.
    In doing my FMEA what in the heat treat process will impact hardness so that it would be greater than110?

    Also, we have been doing an eddy current conductivity test in heat treat for years before me. What is the purpose of this and what in the heat treat process impacts conductivity?

    Thank you for your time.

    Regards
     
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