Can someone elaborate on Yield and tensile strength of metals and how
they are measured? For instance, I'm searching McMaster Carr for various
ideas and types of metals and question the strength ratings.

When the stats indicate 35,000 yield strength, is that per inch, per
foot, per yard, etc? What happens when I cut it down? I'm also comparing
a flat stock aluminum at 1/4" thick x 2" wide to a 2" wide(base) x 1"
high(leg) x 1/4" thick and a 1/8" thick aluminum channel. The 1/8" thick
channel has the same yield strength as the flat stock. Is it due to the
1/8" difference in thickness? Would a 1/4" thick channel have a greater
yield? Does that have anything to do with flexibility?

My objective is to weld pieces of aluminum into this shape
........https://www.flickr.com/photos/18223943@N06/14816003838/ which I
already did with the 2" x 1/4" aluminum I mentioned. Through trial and
error, I learned it flexes too much for my need. Therefore, I need
stronger and less flexing(preferably none). I choose aluminum due to
it's lightweight, but if necessary, then I will use steel or something
else anyone may want to suggest. Overall, I assume channel or even
rectangular tube would be more ideal to eliminate flex and provide more
strength but I need to stay at 1/4" thickness and 2" width.

All help appreciated.

Thank you