Microstructural evolution of a eutectic Al–Si engine subjected to severe running conditions

The sliding wear behavior and microstructural evolution of a linerless eutectic aluminum–silicon combustion engine has been thoroughly investigated. The engine was subjected to nearly 300 h of high load, high speed, and high temperature dynamometer testing. The as-prepared cylinder surface, which consisted of silicon particles protruding ∼0.2 μm from the matrix, evolved to a microstructure that provides sufficient wear resistance and prevents scuffing and excessive wear. Antiwear films on the worn surface were less than 10 nm thick. The evolution of the bore microstructure is explained in terms of fragmentation of silicon particles and subsequent “polishing” of the entire worn surface caused by sliding contact with the rings. The evolved microstructure consisted of exposed silicon particles with smooth surfaces and rounded edges and a tribofilm on the aluminum matrix. The microstructural evolution prevented excessive wear and limited the macroscopic wear to 4 μm pertaining to the ultra-mild wear regime.