Bicycle Mechanics - Any metalurgists out there? (hammering aluminum)

I am making some reinforcement rods for my rear rack. I bought some 3/8th Al rod at the hardware store. When I tried to hammer the ends flat, it was tough to do. So I fired up the propane torch and heated the ends (short of melting) and it was easier. The rods are for for/aft stabilization, not main load bearing. I pounded the ends to about 3/16th inch and drilled for a 5mm screw. When I drilled, the material was harder to drill through that I expected. Any ideas about how strong these ends are, or are they going to dissolve in the rain?

By hammering any metal, you are strain hardening it. This will make the metal harder, more brittle, and more reactive. By using a torch to heat the metal to nearly red-hot, then allowing it to cool slowly, you will end up annealing it, which will negate some of the alteration to the metal which was caused when you plastically deformed it with the hammer. Effective annealing, however, requires that you bring the object up to about 1/2 way to the melting temperature of the metal, and leave it at that temperature for several hours.

As far as corrosion is concerned, you better make sure those bolts are stainless steel, or it will dissolve your frame (or, at least the bolts). In an aluminum-steel galvanic cell, it is the steel which acts as the anode.

Aluminium does not work harden, only steel.

The hardness of alumium generally depends on the alloy you use.

If the screw doesn't move, then it will corrode first, since the alloy will form an aluminium oxide coating, which has a lower reaction series than steel.

D*alex and John999,

Thanks for the info. I am using SS screws. The rack is also made of Al rod that has been powdercoated. I plan to paint my rods. I don't think corrosion will be any more of a problem that with the other mounts, but I am concerned that I might have created rod ends that are nothing more that loose bits of metal hovering around a hole just for entertainment value.