[Henry Schmidt]

I think we're seeing a lightly confusing description of the difference between Nikasil and Alusil cylinders.
The aluminum alloy used to produce Alusil is actually a very high silicon alloy and is very hard. .
Much higher than the silicon content in Nikasil cylinders.
Imagine if you can a cylinder wall that is lined with little beads of glass. Than is in essence how Alusil works. The silicon beads (glass) in the alloy are isolated via an etching process that removes aluminum from around the beads and then the beads are honed to produce a relatively smooth surface.
The Nikasil cylinder is actually a lower silicon content alloy (softer) that has a plating of high nickel chrome.
When parts of similar material operate in a friction environment the materials tend to stick (gall) together.
With Nikasil you have chrome in contact with aluminum where with Alusil you have aluminum in contact be it slight with aluminum so to prevent galling the piston in the Alusil cylinder is plated with iron thus producing dissimilar material.