[shovelon]

Why not build the post and yoke from alum, and bolt a base made from steel to keep bottom heavy? I see they are bolted in your image.

Alum is not really more expensive than steel, because you get 3 times the amount per pound. Alum could be potentially cheaper in the long run. Get alum extruded tube and weld threaded plated inside.

 

[AluminumWelder]

Thats what im doing now all aluminum with steel base
Steel is about half the price per equivalent need
However by the time i factor in cleaning by hand and prime and paint the labor makes it more expensive

 

[shovelon]

Thats what im doing now all aluminum with steel base
Steel is about half the price per equivalent need
However by the time i factor in cleaning by hand and prime and paint the labor makes it more expensive

Good point. The weight of the steel base does help keep it from tipping over. I have parking signs that I put out every day that are light alum tube with steel rods in the legs. I can tip them to 45 degrees and they still right themselves.

 

[A_DAB_will_do]

i guess what I dont' understand is how can the 2000 and 7000 series aluminum be considered stronger alloys, but have the same youngs modulous?
doesn't a stronger metal bend less?
...

This graph might make things more clear:

This illustrates how various materials compare in stiffness(young's modulus) vs density. Aluminum alloys fall at about 100 on the modulus vertical axis and 3 in the horizontal density axis. What you're asking for is a material that is stiffer, and/or lighter(lower density) than Aluminum. So look at the chart left and/or up from where aluminum sits. The only materials in that area of the chart are some fiber reinforced laminates(glass, carbon, or kevlar reinforced polymers) and some engineering ceramics. All those materials are much, much more expensive than aluminum.

 

[ManoKai]

^ Ashby Plot. Perfect context! :cool

 

[AluminumWelder]

so these high strength aluminum allows will bend just as easy as the cheap alloys
The only benefit is if you are building somethign that will have pull streteching forces on it and then it won't break as easily?

Kind of useless to me, most things I build dont' get pulled apart, they have side loads that cause bending. and if they do get pulled apart it is typically at a joint that is riveted or bolted together since these high stregth alloys can't be welded. , even if you could weld them the temper is near zero at a welding joint.

Love to know what applicaitons this aluminum is needed in? I know in aerospace, but where? on a plane wing? ON a rudder?

my guess is they are nich product and therefore expensive due to low manufacturing volumes.

 

[AluminumWelder]

tha'ts a cool graph, gotta look for a higher resolution link, becuase it's hard to read.

 

[ManoKai]

IF you needed exceptional strength-to-weight & high cyclic fatigue resistance, THEN 2024 would be ideal. Main alloying element is Cu.

IF you desired excellent strength, stress/strain resistance, and anti-corrosion properties, THEN 7075 would be a solid candidate. Main alloying ingredient is Zn.

Your application/design needs none of those properties.

Aerospace Aluminum Alloy Development

 

[bent]

so these high strength aluminum allows will bend just as easy as the cheap alloys

The high strength alloys will bend further and return to the original configuration than a low strength alloy. They may have other desirable properties as well, such as corrosion resistance and fatigue resistance, among others.

 

[ManoKai]

Commercially available, Kiosk Stands. Note the dimensions and tare WEIGHT of these stands. The carrying handle is convenient.

 

[AluminumWelder]

"IF you needed exceptional strength-to-weight & high cyclic fatigue resistance, THEN 2024 would be ideal. Main alloying element is Cu.
IF you desired excellent strength, stress/strain resistance,................. then 7075....."

When I read this those two sentences mean the EXACT same thing to me.
looked up fatigue is the weakening of a material caused by repeatedly applied loads
stress strain is applying a load and measuring the deformation.

Not trying to be dense, but obviously there are reasons to choose one over the other that can be explained more simply? 7075 springs back to it's orginal shape better? is that the main difference you are trying to convey?

 

[NinjaRay]

I got a headache from this thread :laugh: here you go !

http://www.ebay.com/itm/New-PSPADLK...splay-Case-Tamper-Proof-/350914164288?pt=LH_DefaultDomain_0&hash=item51b41d3640

 

[Kelvin]

Unless the aluminum is tempered (and if you weld it, that usually requires heat-treating it after you weld it), in general, pound-for-pound, steel is slightly stiffer and stronger than aluminum.

 

[A_DAB_will_do]

tha'ts a cool graph, gotta look for a higher resolution link, because it's hard to read.

https://en.wikipedia.org/wiki/Material_selection

Looks like the paper charts I'm familiar with have been digitized and built into a computer software package

http://www.grantadesign.com/products/ces/

Look up materials information by a British guy named Ashby. About 30 years ago he compiled a whole textbook of these type of plots or graphs. strength vs density, strength vs modulus(stiffness), melting temp vs density, etc. They are used to help with materials selection when designing or re-designing something to strict engineering requirements. E.g. a company needs their widget to be 10% stronger but no heavier.

 

[A_DAB_will_do]

^ Ashby Plot. Perfect context! :cool

I took a training class many many years ago on how to use these plots. They are very cool. I have books with plots in small print at home somewhere. But the computer software version that's available now looks even more useful.

 

[ManoKai]

@ A_DAB_will do - check out the high-rez Dick Ashby plots in the Metallurgy sticky (post #22).

 

[Oscar]

"IF you needed exceptional strength-to-weight & high cyclic fatigue resistance, THEN 2024 would be ideal. Main alloying element is Cu.
IF you desired excellent strength, stress/strain resistance,................. then 7075....."

When I read this those two sentences mean the EXACT same thing to me.
looked up fatigue is the weakening of a material caused by repeatedly applied loads
stress strain is applying a load and measuring the deformation.

Not trying to be dense, but obviously there are reasons to choose one over the other that can be explained more simply? 7075 springs back to it's orginal shape better? is that the main difference you are trying to convey?

The difference lies in how the loads are applied. That is how the fatigue resistance differs from stress/strain loading. you even said it yourself: repeatedly applied loads. But then what does "repeatedly" mean in the time domain? Everything has an exact definition that sometimes differ from our natural intuitive definition. keep looking up information and you will eventually be able to internalize the differences.