Mad,
I believe the process is called 'MagnaFlux' for checking out aluminum for cracks. I will also have balance, etc.. checked out.
The process of MagnaFluxing is used to detect cracks in ferrous (or iron) based materials. Like crankshafts and connecting rods.
The process of detecting surface cracks in non-metallic alloys like aluminium or titanium (wheels, FGT engine block, pistons, etc.) is FPI (fluorescent penetrant indicator).