Increase of Si content increases wear resistant properties of hypereutectic Al-Si alloys. However, large primary Si phase is inevitable in Al-Si alloy when the alloy is produced by conventional casting processes, which deteriorate its machinability as well as its mechanical properties. The objective of this study is to produce graded Al/Al-Si nanocomposite coating onto an A1050 Al alloy substrate by mixing Al and Si nanoparticles with Supersonic Free-Jet PVD (SFJ-PVD). The SFJ-PVD has been developed as a new coating method in which a coating film is formed by depositing nanoparticles with very high velocity onto a substrate. This SFJ-PVD provides a high deposition rate and produces a mixture of different kinds of nanoparticles formed in different evaporation chambers on the substrate. The graded Al/Al-Si coating film is produced by depositing Al and Si nanoparticles formed in different evaporation chambers with the controlled evaporation rates of Al and Si respectively. A smooth, compact and defect-free microstructure is formed both at the interface between the substrate and the coating film and inside the coating film. The graded Al-Si coating film has very fine, varying from 10 to 20 nm in diameter, Si phases in Al matrix. It is confirmed with nano-indentation hardness tester that the graded Al/Al-Si coating film on A1050 substrate has graded hardness from 0.65 to 5.9 GPa corresponding to the gradual compositional change of Si up to Al-57.8 at%Si.
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