Bill Tindall, E.Tn.
It would seem that the only purpose of the iron or chromium is to be a pigment to color the aluminum oxide abrasive stick. It sure as hell is not doing any significant abrading at those concentrations.

Alpha aluminum can be made in about any particle size one desires. With some looking about any micron size is out there to be found.

We used to do a teamwork exercise for new employees that thought they knew it all. The result was that several people working on a task was shown to generated more and better information than a one . Investigating the creation and attributes of the Unicorn Profile reaffirms this generally valid point.

(there were amusing exceptions. In one exercise the team had to survive in the desert until searchers found us and a rescue was made. One dominating team member whose military experience consisted of driving a submarine insisted he would walk the 30 miles to the nearest road in the cool of the night. Another, with cross country land experience, convinced the rest of the folly of this plan. )

OK on lookers. Get out there, do something, and make discoveries.