I seem to be spending a lot of time making little brackets for various bits and bobs. Some times I use Ali and some times I use mild steel strips. When bending the metals (both Ali and Mild steel) I have had much better results with heating the metals up with a propane torch and then bending, hitting with hammer etc. I have then either let these cool naturally or cooled them in water. Does this process weaken the metals at all?? If so what is the best way the bend both Ali and Steel bar to form such things as 90 degree bends etc.

heating and repeated super cooling of metals causes micro cracks which weaken them. the thickness and quality of the metal changes the effect so its not really an exact science.

Im with my steel fabricator sorting my roll cage out at the moment so i thought id ask the question for you.

Hows your stuff coming along. we should meet up for a beer soon with me being 20 mins up the road....

We should meet up at some point - my build is coming along slowly but surely. Sometimes more slowly than surely. When I said heating the metal I mean to glowing orange hot. Does this still cause these microcracks?

I've made brackets from ali in the past and had the ones I cold formed snapped. Now I always heat metal before bending as there is less stress on it when forming and the only times I've seen cracks appear when bending is when it’s not been heated.

[Edited on 11/4/11 by Mr Whippy]

With Aluminium of any thickness I would anneal before bending. The technique I was taught was to rub a bar of soap on the metal then heat from the other side with the torch some distance from the metal, when the soap turns brown then that's near enough the temperature for annealing. Leave the metal to cool naturally, quenching is not a good idea.
To get a tight bend in mild steel heat to cherry red along the line of the bend before hitting it, quenching low carbon steel is not so bad but almost always better to allow things to cool without quenching.
Copper on the other hand should be heated to a dull red heat and then quenched.