[TowerTalk] welding aluminum

[Jim Thomson]

Date: Fri, 30 Jan 2015 10:02:06 -0700
From: Bob Tabke <bob at onehorsecreek.com>
To: towertalk at contesting.com
Subject: [TowerTalk] welding aluminum

I am building a 6m H-frame (33'x40') and need to connect two 4.5 inch 
pieces of T6 aluminum pipe as well as two sections of 3" al tube. I have 
an al welder. But I am wondering if anyone has experience with welding 
T6 aluminum causing a loss in strength due to lessening the temper? The 
joints will have cradles on either side to reinforce the joint...

Thanks,

Bob, N7IP

## N6bt told me years ago, the welded joint will drop down to T0.... then
work harden back to T1.   I find that hard to believe, since  welded AL
joints are very strong, same deal on welded AL boats, ferries etc. 

##  A local PE  buddy of mine sez you will lose 40% , strength wise,
with any welded AL joint. 

##  I talked to a business here in town that does Al welding, and also mobile,on site
al welding.   I believe  Al can be heliarc welded and also tig welded.   Same  local
business told me that an even stronger method is to just GLUE the pieces together. 
He said the glue was far stronger than any weld.... BUT it cant be used for any type
of electrical connection.   Say you were joining 2 x 2 inch od pieces of al tubing...
and had a 3 inch overlap..via swedge, or outer or inner sleeve,  etc .   Say the
overlap was aprx 3 inchs.   2 inch OD = 6 inch circumference..... X  3 inch overlap
.... =   18  square inchs of glue.  He said this glue is beyond super strong....and only god can get it
apart.  BUT, you wont have electrical continuity.  You could get that with a short AL strap across
each glued connection.   Bikes using AL frames are glued and not welded.   Apparently you can
also do a tiny weld on the circumference of the glued joint, to retain the electrical continuity. 

##  Its just another option.  Bolted joints  will also work.  Short inner and outer sleeves can also be used
to re-enforce the bolted connections.   IE:  increase wall thickness where the bolts pass through.  If bolts
are too tight, u just end up crushing the tubing.   .25 inch  rivets will also work..provided u use enough of them,
like a row of 5 of em...... every 90-120 degrees. 

Jim   VE7RF