A short but detailed summary of the Nikasil/Galnickel and Alusil block metallurgy.
"I think by "Galnickel" you mean "Nikasil," which is what BMW called the OEM M60 engines. I do not know what the bulk alloy composition is, but the cylinder bores are cross-hatched by a mechanical process and then plated with a thin layer of nickel, which is a refractory (hard, heat-resistant) metal. If it weren't for the high sulfur content in our gasoline, this would've been the end of it and everyone would be thrilled with Nikasil.
Alusil isn't a new technology at all, being used originally in the M70 V-12-engined BMW's since 1987. The process in this case is entirely different. The aluminum used in Alusil blocks is a high-silicon-content alloy. After casting, the cylinder bores are chemically etched to remove aluminum and expose the silicon crystals in the matrix. Silicon is also a very hard, refractory material.
In either case--Nikasil or Alusil--one of the keys to longevity is having a slightly-rough surface to hold the lubricating oil film. In the case of Nikasil it's in the cross-hatching; in the case of Alusil, it's from the etching process which exposes the silicon. I looked at a new Alusil block this morning and there's no detectable cross-hatching; the surface appears to have a matte finish. On an old Nikasil block the cross-hatching is easily visible. The only things I haven't seen are a new Nikasil block (and no one will, since they're no longer made) or an old Alusil block, since they don't fail often! All BMW V-8 engines starting with 1996 production are Alusil composition and 4.4 liter displacement (or maybe 3.5 if you live outside the U.S.)." Dave Walker