[TowerTalk] Grading of Aluminum

[TexasRF@aol.com]

Here is what my aluminum manufacturing company tells me about 6061-T6 vs. 
6063-T832:
6063-T832 material was developed initially for the furniture manufacturing 
industry. They needed a strong alloy with a very smooth and shiny finish to 
make their products hold up well and look good with a minimum of added 
processing steps.

The product starts as a normal 6063 alloy ingot which has a typical yield 
strength of about 28,000 psi. The process involves drawing and redrawing the 
tubing to achieve the desire bright and smooth finish. This drawing process 
work hardens the material to a final yield strength of typically 40,000 psi. 
Incidentally, there is another little known material called 6063-T834 with a 
final yield strength of about 44,000 psi. I assume this involves an added 
drawing step but this is a total guess on my part. It adds about 5% to the 
total cost for this material.

6061-T6 is a totally different process that uses a higher yeld strength base 
material to begin with and less work hardening steps in production. The 
finish is often quite ugly especially when "oil quenching" (whatever that is) 
is used in the production process. The 6061-T6 is all marked as to alloy, lot 
numbers, etc for tracking purposes. The cost of 6061-T6 drawn tubing is 
significantly higher than 6063-T832.

Extruded tubing is a whole different process yet. We can get 6061-T6 
extrusions for only pennies per pound more than 6063 extrusions. There is no 
6063-T832 process for extruded products that I am aware of, only 6063 which 
has a typical yield of 28,000 psi as mentioned above. This is not what we 
want to use for antenna construction, and incidentally is what you are 
getting at Home Depot, Lowes and other places that sell tubing in 8 ft 
lengths.

Almost all commercial amateur antenna manufacturers are using 6063-T832 
because it is less expensive, looks good and has excellent strength. Force12 
and Tenadyne are the holdouts using 6061-T6 for reasons unknown to me. In the 
case of Force12 some of their parts use wall thicknesses less than .058 inch 
and this probably is available only in a 6061-T6 alloy. Higher wind speed 
ratings can take full advantage of the .058 wall thickness and the sizes all 
telescope nicely with a good fit and little "slop" between pieces.  This is 
important in the case .058 is too thin and 2 or more sizes are pushed 
together for extra strength. Designs for nearly any wind speed can be 
accomodated by using this technique.

The ARRL Antenna and Big Handbook both need updating to reflect the currently 
available and commonly used tubing materials. Perhaps someone in the ARRL 
loop will see this note and look into the matter.

Hope this info is helpful. Please call us if you need aluminum tubing or have 
questions about the sizes we carry at 1 800 272 3467.

Thanks/73 de Gerald Williamson, K5GW/Texas Towers

--
FAQ on WWW:               http://www.contesting.com/towertalkfaq.html
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm