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PostPosted: Tue Feb 13, 2007 11:57 am 
BoTM Winner
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not so obvios jez

fatigue is there because of the constant bending/movement of the metal

but if its brittle , wont it snap at the first movement ?


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PostPosted: Tue Feb 13, 2007 12:02 pm 
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or am i making things more confusing :D

anyway where`s rody when you need him





ps , nothing lasts forever :P


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PostPosted: Tue Feb 13, 2007 12:10 pm 
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SLIM wrote:
or am i making things more confusing :D


Yes! :)

IF aluminium did degrade over time, then the one that'd been ridden would be suffering from that as well as any potential fatigue issues...

I'm just not aware of anything that would cause brittleness over time.


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PostPosted: Tue Feb 13, 2007 12:10 pm 
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Age hardening
After solution treatment and quenching hardening is achieved either at room temperature (natural aging) or with a precipitation heat treatment (artificial aging). In some alloys, sufficient precipitation occurs in a few days at room temperature to yield stable products with properties that are adequate for many applications. These alloys sometimes are precipitation heat treated to provide increased strength and hardness in wrought or cast products. Other alloys with slow precipitations reactions at room temperature are always precipitation heat treated before being used.

In some alloys, notably those of the 2xxx series, cold working or freshly quenched material greatly increases its response to later precipitation heat treatment.

Natural Aging. The more highly alloyed members of the 6xxx wrought series, the copper-containing alloys of the 7xxx group, and all of the 2xxx alloys are almost always solution heat treated and quenched. For some of these alloys, particularly the 2xxx alloys, the precipitation hardening that results from natural aging alone produces useful tempers (T3 and T4 types) that are characterized by high ratios of tensile to yield strength and high fracture toughness and resistance to fatigue. For the alloys that are used in these tempers, the relatively high supersaturation of atoms and vacancies retained by rapid quenching causes rapid formation of GP zones, and strength increases rapidly, attaining nearly maximum stable values in four or five days. Tensile-property specifications for products in T3- and T4-type tempers are based on a nominal natural aging time of four days. In alloys for which T3- or T4-type tempers are standard, the changes that occur in further natural aging are of relatively minor magnitude, and products of these combinations of alloy and temper are regarded as essentially stable after about one week.

In contrast to the relatively stable condition reached in a few days by 2xxx alloys that are used in T3- or T4-type tempers, the 6xxx alloys and to an even greater degree the 7xxx alloys are considerably less stable at room temperature and continue to exhibit significant changes in mechanical properties for many years.


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 Post subject:
PostPosted: Tue Feb 13, 2007 12:12 pm 
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Still confused though


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PostPosted: Tue Feb 13, 2007 12:13 pm 
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Mark_h4dng wrote:
high supersaturation of atoms and vacancies retained by rapid quenching causes rapid formation of GP zones


there you go,clear as mud :lol:


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PostPosted: Tue Feb 13, 2007 12:13 pm 
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Erm.


So does that mean alloy does experience material changes as it ages?


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PostPosted: Tue Feb 13, 2007 12:14 pm 
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Mark - that's talking about the first hours / days after solidifying from molten, not long term.


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PostPosted: Tue Feb 13, 2007 12:15 pm 
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Mark_h4dng wrote:
7xxx alloys are considerably less stable at room temperature and continue to exhibit significant changes in mechanical properties for many years.


That bit's interesting though!

I wasn't aware of anything that would cause change other than things like excessive heat, fatigue, corrosion, but that seems to suggest otherwise... 7xxx (zinc?) series are pretty common for bike frames aren't they?


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 Post subject:
PostPosted: Tue Feb 13, 2007 12:21 pm 
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think i will stick to building and riding , and leave the metallurgy to you lot :lol: :lol: :lol:


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