# Aluminium 6061 or 7005



## a1rports (May 17, 2009)

Can anyone tell me the difference between numbers associated with alloy frames, thanks for any info, J


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## brant (Jan 6, 2004)

944.


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## RoyDean (Jul 2, 2007)

Strength. Heat treat requirements.

Those are the two big ones. 6061 is stronger, but has a more involved heat treat process.


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## shovelon (Mar 16, 2006)

RoyDean said:


> Strength. Heat treat requirements.
> 
> Those are the two big ones. 6061 is stronger, but has a more involved heat treat process.


True. 7005 has much more zinc in the material. Takes longer to heat treat, but also takes longer to anneal. Long enough to not lose much strength during the weld process. In fact 7005 was developed by Easton specifically for welding without requiring a full heat treat.


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## scottzg (Sep 27, 2006)

brant said:


> 944.


this alloy will make your bike handle like a porsche.


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## michigan_maniac (Dec 30, 2009)

Hi There!

6xxx, 7xxx, and 2xxx series aluminums are precipitation hardened alloys. They DO, in fact, require post-weld heat-treat that is specific to each alloy. (something to keep in mind). Precipitation hardened alloys need to be "re-solutionized".

((Resolutionizing: The alloying element in the materials crystal structure, gain electrons, called inter-metallic precipitates, durring the resolutioning process of your heat treatment; this is literally called "aging", (however most ppl use the steel terminology of tempering.) This is what gives the alloy it's increased strength. However, over-aging will cause these atoms in the crystal structures to gain too-many electrons, which will cause intermetallic stress-concentrators. Each preciptation hardened alloy has a specific temperature per time that needs to be aged at.)

6061 does have a higher Ultimate Tensile Strength than 7075, just as "shovelon" stated.

For typical heat treatment "designations" check out the following website:
http://www.engineershandbook.com/Tables/alumtemper.htm
T6 is very common in engineering grade aluminum alloys. Read what that process typically entails.

(Sorry for the length.)

-MB


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## shovelon (Mar 16, 2006)

Just to clarify, 6061 T-6 will lose most of tensile value when welded. In fact, the pool zone will go to T-0 during the weld cycle, and strain harden to approximately T-2 immediately upon cooling. Then over time naturally age to T-4. If you want the original T-6, solution heat treat and artifical aging is the only answer.

7005 will not lose much strength, and because the heat affected zone will not lose any strength due the very long anneal time 7000 series has. Then the pool area will restrain to its original temper. 

The only step if desired is a slight stress relief, which is a whole different Oprah compared to a solution heat treat. This is done in the Powder coat oven at 400 degrees. F. while baking the powder.

A full solution heat treated 6061 T-6 weldment is costly, but stronger than a stress relieved 7005 weldment. Both alloys must be joined with high strength filler with when solidified starts the immediate strain hardening.

There are some cases when welding alum that "Over Aging" will occur. Thus, an over hardening due to incomplete preheating, incomplete penetration, or wrong filler. Typically you see this on very thick sections where the base metal acts as a heat sink and simulates a cold quench.

Brain is tired, that's all.:thumbsup:


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## RoyDean (Jul 2, 2007)

I liked my answer the best.


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## michigan_maniac (Dec 30, 2009)

If I recall correctly ... (it has been a while). I am pretty sure that if you want the original T-6 on a 6061, I believe that aging is done at a Max 150 degrees F, for 23 hrs max to achieve highest UTS. 

I sure could not afford to do this for a bicycle frame (I wouldn't want to....). Shovelon is right anyway, it's going to naturally age overtime. 

On a different note: I am the worst aluminum welder in the entire world or at least feel like. I am just intimidated by it. (bad experience in the past). Does anyone know of a Frame building school that does offer an aluminum class? Or are there any small-shop builders who offer Aluminum frame building on the side?

Any help would be great!


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## glitz (Jan 27, 2010)

I prefer 6013 and 6069.


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## zonian1903 (Jun 19, 2007)

Deleted reply and starting a new topic so as to not hijack the thread.

Frank


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## rideonjon (May 27, 2009)

glitz said:


> I prefer 6013 and 6069.


want to fill us as to why?


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## nim-rod (Apr 21, 2010)

"Aging" occures when the carbides precipitate to the outter boundaries of the slip plane of the grain structure. Take a ball peen hammer to a brass rod and you will see what I mean by slip plane when the rod actually splits. The carbides will align with that area keeping aluminum from splitting and creating hardness. T-4 and T-6 are not designating a hardness value they only designate the method of "aging".T-4 being naturally aged and T-6 being artificially aged. T-0 is basically straight from the foundary from molten metal to a solid with no aging done to it other than the time from the solid state to the time you work it. 6061 and 7075 take too long to naturally age (several years at room temp) to max hardness to be effective so they are artificially aged with 7075 needing dual temps first high (900 deg) then lower (450 deg) for a total of 16 hours. 2024 ages to it's max in 24 hours and we used to refer to it as "age on the plane" while I was in the Air Force. 7075 is actually considered a non weldable aluminum alloy where as 6061 is weldable. I have welded it myself and as long as its not a stressed member thats fine to do but it will crack eventually under stress same goes for 1100 series aluminum. Most aluminum is welded with high silicone 4043 filler material and it bonds best with most weldable aluminums.
Welding heat treated aluminum makes the aluminum return to the "T-O" state in the area melted during welding so it must be done again to get back to the strength needed.


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## michigan_maniac (Dec 30, 2009)

Thank you "nim-rod"

Most people have not been educated as to how intermetallic precipitates form, as well as, each precipitation hardened alloy has a specific aging process (Hold-temperature for a specific amount of time). AND, that if over aged, these "precipitates" become too large (as the atom gains too many electrons) WILL cause stress-concentrators at the m oilecular level.  ((Many of the Cafe-racers (motorcycles) today that run aluminum chasis use 2024 b/c full aging occurs NATURALLY (without heat) in such a short period of time.))


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## shovelon (Mar 16, 2006)

Nimrod and Michigan Maniac, really good stuff. You explained it so easy right down to "Molecular Level". 

A question. I am familiar with participate migrations during age hardening, so does overaging and fatigueing begin with participate enlarging? I am gathering that fatigueing occurs after participate migration has reached it's limits.


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## michigan_maniac (Dec 30, 2009)

Shovelon,

Overaging and fatiguing are two completely different "failure modes".

(However, overagging can contribute to a rapid fatiguing failure)

Overaging occurs from poor knowledge of the aluminum being heat treated. Or a "Oh ****, I forgot I had something in the oven!"

Fatiguing occurs from excess stress through Cyclical Loading (repitition). This can happen from High stress at very few cycles or small stress at SEVERAL cycles. The cause is: Work hardening! Just like bending that metal shirt hanger back-and-forth over and over and over again, the material gets brittle and breaks. That hanger (or whatever) is in a constant compression-tension cycle. The lattices (the molecular bonds) in the crystall structure can only take so much pulling and bending before they break. It is a mechanical failure through dislocation motion.

You can easily tell if your structure failured do to fatigue: Where the failure ended you will notice a "clam shelling appearance" which physically grew larger and larger. Look up ASTM definitions "Fatigue". A quick look-up http://en.wikipedia.org/wiki/Fatigue_(material)

You can graphically represent fatiguing by plotting: Stress over Number of Cycles. (Stress on Y-axis and # of cycles on X-axis). Basically all materials can sustain a High stress under low cycles but siginificantly fall. Metals fatigue-curve do not fall linearly though. There is a drastic decline before Steel and Ti reach a somewhat asymptotic line. However, Aluminum gradually drops to zero Stress at Approximately 5 X 10^8 cycles. Aluminum WILL eventually fail from fatigue. This is where it is your and my job to OVER-design our aluminum structures (frames) to accept higher loads.

-MB


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