Subject: Re: 7075 Aluminum

From: [email-masked] (Edk4)
Date: 11 May 1996 00:01:21 -0400

Steve Wellcome <[email-masked]> writes:

>ultimate and yield strengths are greatly dependent
>on temperature. 

Okay, but does yield strength correlate with/to stiffness?

For instance, for a given piece of Aluminum angle of the same size, 
thickness and profile, which of the 3 alloys, 2024, 6061 or 7075, would 
have the greater stiffness, in the sense of rigidity, at room temperature?

------------------
Ed Kingsley

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From: Steve Wellcome <[email-masked]>
Date: 13 May 1996 14:06:35 GMT

It's been almost 30 years...but I think for "stiffness" you'd
be primarily interested in the modulus of elasticity, not the
yield point.  I don't think there is a noticable difference
among various aluminum alloys in that respect, they all have
a modulus of elasticity of somewhere around 10 x 10^6.  (Steel,
on the other hand, is about 3 times that at 30 x 10^6, more
or less.)  If stiffness is an important consideration, you'll
do about 3 times better with steel than with aluminum.

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From: Michael Latcha <[email-masked]>
Date: Mon, 13 May 1996 08:47:16 -0400

While the yield strength (the stress at which a material plastically, or
permanently, deforms) and the ultimate strength (the stress at which a
piece of material fractures into two or more pieces) vary dramatically
with alloy content and heat treatment, the stiffness (amount of elastic
deformation given a certain load) of a metal is most dependent on the base
metal of the alloy - in this case aluminum.  The stiffnesses of 2024, 6061
and 7075 aluminum, characterized by the elastic modulus (or Young's
modulus), are essentially the same: 10 million pounds per square 
inch (Mpsi) (about 1/3 that of steel). 

Since you are only interested in elastic properties at room temperature,
you would see no difference in these three alloys.  Your choice then is
driven by other considerations like machinability, cost, availability,
what do you have in your scrap bin, etc. 

--------------------------------------------------------------------
Michael A. Latcha, PhD                     VOICE: (810) 370-2203
Associate Professor                        FAX:   (810) 370-4261
Department of Mechanical Engineering       Email: [email-masked]
Oakland University
Rochester MI 48309-4401

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From: "John R. Johnson" <[email-masked]>
Date: Mon, 13 May 1996 15:42:11 -0500

All aluminum alloys will have approximately the same stiffness.  That
would be the Youngs modulus, which for all aluminum alloys is about
10,000,000.   The Youngs modulus for virtually all steels is about
three times that, or 30,000,000.  Tensile strength, and yield point
may vary between alloys but the stiffness, which is essentially the
slope of the stress/strain curve is, below yield, pretty linear and
is determined by the base metal which is the primary component in the
alloy.
John

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From: [email-masked] (Ron Ginger)
Date: Mon, 13 May 1996 19:44:20 LOCAL

In article <[email-masked]> Steve Wellcome <[email-masked]> writes:
>From: Steve Wellcome <[email-masked]>
>Subject: Re: 7075 Aluminum
>Date: 13 May 1996 14:06:35 GMT

>do about 3 times better with steel than with aluminum.

A BIG caution on 7075-T6. although it has some nice numbers at ROOM 
TEMPERATURE its propertiees fall off at an amazing rate at only warm temp- for 
example its ultimate Tensile at room temp is 83,000psi, but at only 300 
degrees FARENHEIT it has fallen to 25,000.

under the same temps, 2024-T3 goes 70k to 55k and 6061-T6 goes 45k to 34k.

Henry Szostek wrote on this, with a detailed chart, in SIC Vol8, No45. 
June/July 95.

Ron Ginger
my signature is http://www.ultranet.com/~ginger

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From: [email-masked](James I. Lewis)
Date: 15 May 1996 05:30:29 GMT

In <[email-masked]>
>what do you have in your scrap bin, etc. 
    Just to add to this 7075 thing. I've heard but have never tested
the probability that 7075 is notch senitive, more so than the other
structural aluminum alloys. ie I wouldn't use it in a rotor head
because of that caracteristic. However should work fine in landing
gear.

Jim

Just an opinion.

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From: [email-masked] (Bill Webster)
Date: Wed, 15 May 1996 09:16:52 -0400

In article <[email-masked]>,
[email-masked](James I. Lewis) wrote:

> the probability that 7075 is notch senitive,

For those who don't know (like me), what is notch sensitive?

Interesting following this thread.

For model airplane engines, we find that 7075 is used for connecting rods
and for the cylinder head which holds the glow plug.  I would expect the
rod stays at a resonable temperature since it is always getting a spray of
fuel on it.  The cyclinder head is definitely HOT!  Seems we measured this
once, and it was around 290-300F.

regards.

-- 
Bill Webster   [email-masked]

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From: [email-masked](James I. Lewis)
Date: 17 May 1996 04:25:49 GMT

In <[email-masked]> [email-masked] (Bill
>once, and it was around 290-300F.

By notch sensitive I mean if you scratch it it will be stressed in that
scratch and will likely propagate and seperate at the scratch.

Jim

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From: Steve Wellcome <[email-masked]>
Date: 17 May 1996 12:59:28 GMT

Re: notch sensitive:

I don't have the details at hand and my memory may be faulty
on this one, but I think the standard way of measuring this
is called the "Iznod Notch Test" or something like that.  (I"m
not sure at all about that spelling!)

A notch of specified shape and size is cut in the side of a test 
sample of some standard dimensions.  One end of the sample is
clamped in a testing machine, then a swinging weight on an arm is 
raised up and released so it whallops the top of the sample.  The
resistance of the sample to fracture at the notch determines its
"notch sensitivity."  (I'm not sure that's the official term for
it, but basically it's measuring the resistance to crack 
propagation and fracture.)

Maybe somebody who's taken Strengh of Materials more recently
than 30 years ago can provide more accurate detail.

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From: [email-masked] (Ken Knaell)
Date: 21 May 1996 19:06:15 -0400

>degrees FARENHEIT it has fallen to 25,000.
This is very iinteresting since it was suggested to me that 7075
would be a good choice to make internal combustion engine conn-
ecting rods.  Maybe it would not be for the reason you have mentioned.

Perhaps 6061 would be the best if its chemical inertness transposes
into a higher resistance to stress-corrosion failure which micht be
a factor in repeated loading in the crnkcase environment.

A feature I found about machining 7075 is that the chips come off
hot enough to burn your arms liek steel chips do if you are turning
it.  Sorry for the typos, the editor interferes with going back
to correct them.  It is impressive stuff in the strength dept tho.

ken
bethesda, md

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From: [email-masked] (Brian Fairey)
Date: Sat, 08 Jun 1996 08:59:27 GMT

2024 because it mod of el is 10.6 x10/6
7075 is 10.4 and deflection is a function of the above.
Brian