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Originally Posted by SidewaysFeltham
I would never ever weld for structural modifications.
The core problem with welding is that since the bead has to achieve full penetration, you are in fact re-smelting the added part and the original structure. Which causes crystalline metal either side of the bead.
Always use brazing: for difficult and heavily loaded items (wishbones; locating arms/rods) we always used Manganese Bronze, since its melting point was very low and its tensile strength very high.
For everything else such as seaming saloons body shells, we used a special Eutectic Silicon bronze rod which was used by Fords at Boreham and Avely to build their rally car shells.
Can't remember the spec but it was tested to warranted to circa 42 tonnes tensile strength.
Of course, if you have the skill and the kit, then you can nowadays use TIG; however bad TIG welds would be inferior to good bronze.
MIG will still create weak points of crystalline structures either side of the weld.
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The worlds moved on a bit from Boreham in 1971 though I still have my copy of their rally preparation guide.
I have been MIG (and TIG) welding brackets, gussets, doublers and roll cages into cars for 25 years and never had a crystalline weld failure. I know what they are but assume that since MIG is the manufacturers preferred weld type it will be OK for us. The material the makers use has bugger all carbon or anything else expensive in it and MIGs beautifully. If there is gal. grind/sand it off and make sure your gussets are clean and bright and off you go.
With regards to bronzing, especially on dirty material or where there are laps and gaps the chances of getting a good join are not that high and the possibility of stewing the metal and 'crystallising' it are considerable.
Cheers