grade 9 titanium vs 7075 aluminum
grade 9 titanium vs 7075 aluminum
(OP)
which metal has the better strength to weight ratio, i have heard many conflicting ideas. i am trying to build staffs for circus/juggling use. i want the lightest and strongest metal tube possible, so far i am looking at grade 9 titanium and 7075 aluminum, any thoughts?





RE: grade 9 titanium vs 7075 aluminum
RE: grade 9 titanium vs 7075 aluminum
RE: grade 9 titanium vs 7075 aluminum
Typical properties for Grade 9 (Ti-3Al-2.5V)
Annealed: YS = 485 MPa, UTS = 621 MPa, Elongation = 15%
Cold Worked, Stress Relieved: YS = 724 MPa, UTS = 862 MPa, Elongation = 10%
Density: 4.51 g/cm3
So, YS/density = 107 for annealed or 160 for CWSR
Typical properties for 7075 (ASTM B221)
T6: YS = 503 MPa, UTS = 572 MPa, Elongation = 11%
T73: YS = 434 MPa, UTS = 503 MPa, Elongation = 13%
Density: 2.80 g/cm3
So, YS/density = 179 for T6 or 155 for T73
Since Al has a modulus (stiffness) of 71 GPa, and Ti has modulus of 100 GPa, the Al will deflect more than Ti for a given mass. A Google search of "bending stiffness stress tube" will give you some additional information on the subject.
RE: grade 9 titanium vs 7075 aluminum
RE: grade 9 titanium vs 7075 aluminum
Since your OD and length are fixed it makes it a little easier.
The higher the Yield strength the less likely it will be to dent or bend, so advantage Ti.
The overall weight though is a separate issue. Since the Ti3-2.5 is so much stronger it will have a thinner wall than the 7075 for the same overall strength level. In fact for the same strength tube the Ti would have 2/3 of the all of the Al. This brings their overall weight very close to each other.
The Al tube (even with thicker wall) will flex more than the Ti, this may or may not be good for you.
You do need to decide how much overall strength (wall thickness) you want.
Not to make this more confusing but there are other choices also. You could use a high strength stainless steel (Custom 465) with a Yield strength of >1700MPa and a density of 7.83 g/cc.
This YS/d = 217, so per pound this material is stronger than either Ti9 or Al7075.
And Reynolds Technology in UK does make ultra high performance bicycle frame tubing from this alloy that they call 953.
But this tubing, even with a wall that is 1/3 of the Al will be much stiffer (less flex).
Reynolds also makes frame tubes in Ti6-4, a slightly higher strength alloy than the gr9. They might be able to make these for you in either Ti6-4 or 953. Give them a call.
If you made them:
953 23*0.5mm wall
Ti 6-4 23 x 1.0mm wall
Al7075 23 x 1.5mm wall
They would all weigh between 450 and 500g, and the strengths would be within a 5% range.
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Plymouth Tube
RE: grade 9 titanium vs 7075 aluminum
RE: grade 9 titanium vs 7075 aluminum