optimum extruded aluminum alloy for lightweigt construction

huangyhg

optimum extruded aluminum alloy for lightweigt construction
we are constructing a superstructure matrix dish for solar collection and have found the 3/8" od drawn t6-6061, .035 wall, more than sufficiently strong, however after bending and drilling it is too brittle and cracks. major concern is for availability of tubing in developing countries, so we can't get too exotic as we prefer off-the-shelf materials , and cost, as well as better machineability. we are wondering if 1/2" extruded even if still t6-6061, would be better, more machineable. appreciate any help.
tadb,
   a long time ago before i knew what i was doing, i designed a sheet metal box out of 6061-t6.  it did not work very well.  the material is not suitable for bending because it is too brittle.  i am not aware of problems drilling it, unless you are drilling through the area you weakened by bending.
suggestions:
   do not bend the 6061-t6 extrusions.  purchase, or design and fabricate corner brackets, and assemble the your structure with nuts and bolts.
   if you need rigidity rather than strength, consider 6061 without the heat treatment.  this should be bendable.  the t6 in the specification indicates heat treatment.  do not bother trying to tap holes in the stuff, as it is very soft.
   the bendable aluminium is the 3000/5000 series, which is used for sheet metal.  i do not think extrusions are available.  could you design your structure as an enclosed box?  
   consider the fact that the mass, and the elastic modulus of steel are three times that of aluminium.  if you are building a truss structure loaded entirely in tension and compression, the steel structure  will have the same weight and rigidity as the aluminium one.  due to the smaller cross sections, it will buckle at a lower load.  due to the fact that it is steel, everybody and his dog will know how to fabricate it.
                          jhg
i suggest switching to al 3003.  it is more bendable & readily available in both rigid and coiled tubing.
pretty corrosion resistant, too; as good or better than al 6061.
bendable alloys include 5052-h32
consider using the alloy in anealed condition "o" then heat treating after machining.  
we recently studied using glass composite in some structures.
for a quick comparison of properties of a few common al alloys, see
kenvlach,
great. but finding al 3003 or 5052 has not been easy. what industries might use this or where might i look to find a manufacturer or supplier? appreciate the help.
you must not be in the usa.  3003 and 5052 are extremely common alloys, unless you are looking for extrusions (which your initial post stated).  in that case, try a 6063-t52 for a bendable extrudable alloy.  not as bendable as some, but much better than 6061-t6.
for the al alloys try taber metals, gulfport ms or alcola