Here is a photo meant to depict a before and after example of lapping the aluminum engine block cylinder walls. The aluminum actually has 30% silicon content and a process using felt pads on a hone coated with alusil honing paste(the cylinder walls also get coated with the paste and regular engine oil in the process) brings forth the silicon for the piston rings to slide on. The silicon is much more durable than the aluminum alone which is part of the reason m113’s typically last a long time