I'm working on a new polespear, and using some different materials along the way. We'll see how it goes.
First, I ran some calculations, and decided to use a thin wall tube (5/8" OD x 0.049" wall) of normalized 4130 steel. That is a chrome-molybdenum steel, which is about twice as strong as plain vanilla carbon steel, but still relatively inexpensive. It's the stuff often used in race car roll cages and some home built aircraft.
As it turns out, this 5/8" tube is a fair bit stiffer than a piece of solid 5/8" aluminum, because steel is about three times as stiff as aluminum (other things being equal). At the same time, this hollow tube weighs about 1.5 lbs, vs. about 1.8 for a solid aluminum rod.
The only problem, of course, is rust. I turned a piece of G10 epoxy-glass rod that inserts about 1-1/2" into each end. I plan to put a carbon fiber sleeve over the whole thing, hopefully providing a tough outer skin to prevent rust. It should bond very well to the G10 at each end, and prevent any water from leaking in. At least, that's the plan . . .