Removing fillet welds is not a problem as long as you have easy access to the weld and if you can gain access with an angle grinder then that is good news. The only question then is, 'Which products do I need?'
Several years ago now Cibo developed flap discs with a flexible edge. The flexible edge gives better access and allows the flaps to follow the curve of the corner as you begin to remove the weld. Given the ease of grinding the aluminium and the need for control we recommend 80 grit for this operation.
Below you have the option for 4 1/2" or 5" grinders.