i agree with the above you need clean shiny metal to weld to both axle and the new brackets
try a good flap wheel if the axle is pitted it needs to be cleaned up shot blasting comes to mind
you don't want a link coming off at high speed do we now
Might not look it in the pictures but I have cleaned the area with a grinder prior to welding. If you look you can see grinder marks, I have just cleaned where I was welding.
I have been messing about with scrap. Most of it is welding fine, but yesterday I welded two pieces at 90 degress and one piece just pulled away with no effort.
Again the weld looked like it was just spat against the surface.
The metal was clean. i have tried removing the extension cable with no changes in results.
Only other thing it my eath connection to the welder is loose, but making contact. Could this be doing anything?
if you don't have a good earth then you are flogging a dead horse, earth needs to be onto metal as clean and shiny as you are welding and secure, I use a pair of mole grips for my welding clamp, works really well.
you might have cleaned up the axle with a grinder but it still looks rusty and pitted i would try cleaning it up with a coarse flap disc seems to work better for me than a grinder also you might try upping the amps a bit more as well
have fun