Aluminum stays -6061 vs. 7071?
Urban Sherpa
I believe my TNF Prism has the same 2x 6061. (I'm quite happy with
both)
I saw that Dan McHale raves about 7071 stays as being better.
These two grades of aluminum are also used in tent poles with 7071
getting top billing.
Could someone (who really knows) please enlighten me on the
difference(s) between the two grades?
How is 7 series 'better' than 6 series?
Thanks,
Karl Roberts
Ilja Friedel
> Could someone (who really knows) please enlighten me on the
> difference(s) between the two grades?
> How is 7 series 'better' than 6 series?
Here is what www.mcmaster.com tells us:
Alloy 6061 Aluminum: Extremely versatile, this heat-treadable alloy
combines good weldability and formability, high corrosion resistance, and
medium strength. Use it for chemical equipment, vehicle parts,
scaffolding, and pipe fittings. Yield strength is 40 ksi. Hardness is 95
Brinell. Melting range is 1080' to 1205'F.
Alloy 6013 Aluminum: This heat-treatable alloy offers the corrosion
resistance of Alloy 6061 with improved machinability and greater hardness.
It also has the strength of Alloy 2024. When machining, this alloy breaks
into small chips, reducing the downtime caused by metal buildup on cutting
tools. Yield strength is 62 ksi. Hardness is 130 Brinell. Melting range is
1052' to 1195'F.
Alloy 6063 Aluminum: Superb corrosion resistance and ready weldability
make this heat-treatable alloy great for outdoor applications such as
architectural trim, railing, and piping. Yield strength is 21 ksi.
Hardness is 60 Brinell. Melting range is 1140' to 1210'F.
Alloy 7075 Aluminum: One of the hardest aluminum alloys, this
exceptionally strong, heat-treatable alloy has good machinability and fair
corrosion resistance. An "aircraft alloy", it is ideal for aviation parts,
keys, gears, and other high-stress parts. Yield strength is 73 ksi.
Hardness is 150 Brinell. Melting range is 890' to 1175'F.
For hiking applications the cold weather behavior of the 7075 would be
interesting to know. I suspect it might be more prone to damage because it
is harder.
I'm not an expert of Aluminum. I was just looking into it for a project
during the past few days. The numbering refers to international standards
on what was mixed into the Aluminum and how it was treated later. Higher
numbers are not automatically better for hiking applications than lower
numbers.
Ilja.
Jim Morris
degree. I think that I might be able to help.
"Better" is far to general a term and will just lead to flame wars
because better to you is not better to me. You just need to understand
the characteristics of the materials in question an pick the material
with the best performance and price for the application. Reading the
definitions doesn't help much, that is why I have a job.
Both 6061 and 7075 are heat treatable and must be heat treatable to be
useful. At peak strength, 7075 is roughly twice the strength of 6061.
For comparison 6061-T6 is similar in strength to mild steel. While that
makes 7075 sound wonderful, we need to consider the application and
other material characteristics.
* Weldability - not important
* Corrosion resistance - for this application, the differences are not
important.
* Hardness - Most people equate hardness with strength and brittleness.
It doesn't work except for low alloy steel.
* Low temp brittleness - Nope. Airplanes use these alloys to at least
-75 degF and the charts show no problems down to -400 degF.
* Formability - Ah ha. This is important. Most people bend the stays to
improve the fit. With 7075 this would be nearly impossible due to the
extreme strength. Forming in 7075 is best done prior to heat treatment.
Poor formability in the T6 condition but "higher tech" for marketing.
6061 on the otherhand will form in the final heat treat condition pretty
well; especially in the T4 temper. Easier to customize the fit but "old
news" for marketing. Especially since no one mentioned the temper, I bet
that the marketing wins the day.
The best combination would be 6061-T4 from the manufacturer. Then tweak
the fit by bending; then age the stays to the T62 condition. The yield
strength less than 7075-T6 but will tripple the yield strength of
6061-T4. It could also be done in a normal home oven, but you must start
in the T4 condition.
Jim
Bob Gross
---Bob Gross---
"Jim Morris" <jim.m...@nospam.boeing.com> wrote in message
news:3C028EAB...@nospam.boeing.com...
Ilja Friedel
> Jim, this says something, but nothing about the -7071 in the subject.
I brought the 7075 up, because he asked if the 7xxx is better than the
6xxx and I had no data on 7071. I checked Google, but he could try it too.
Ilja.
Urban Sherpa
Thanks for all input. (rec.hiking, and rec.backcountry)
My question was meant to be broad, and my references to 6061, and 7071
should really have been 6-Series, and 7-Series. (encompassing 7075,
and all the T-4, and T-whatever treatments)
I can gleen from the excellent responses that the 6-Series Aluminum
grade put in my Dana pack (and my other packs) is probably the best
metal for the applications at hand.
From what I gather - If I had 7075 it would be the 'cats ass' of
aluminum, but I really can't hand-shape it to my personal contour like
the versatile 6061.
Thanks again
Karl Roberts
Jim Morris
Jim Morris
no references that I would trust. I assumed that the poster meant 7075
but didn't know or care about the differences.
It doesn't really matter. 7000 series alloys do not have the equivalent
of a -T3xxx or -T4xxx type (naturally aged tempers). The -T6xxx and
-T7xxx tempers are the norm. In the -T6xxx tempers, 7000 series alloys
are quite strong and relatively brittle. This would be fine for usage
but not for custom hand forming. Since heat treatment by the user or
retailer is not practical, then you would have to live with the
manufactured shape.
OTOH - If 6061-T4 were used then hand forming is very practical but the
strength would be significantly less. It would probably be good enough
but still much less than 7075-T6. The ideal for me would be to buy the
6061-T4 stays, custom fit them and then age harden them in my own home
oven to the -T6 condition. Triple the yield strength and still
customized. The key is to be certain that you are starting with the -T4
temper.
BTW: To age 6061-T4 to 6061-T6 requires 350 degF for 8-10 hours. That is
well within the capability of a home oven.
Cheers.