A hardness–microstructure correlation study of anodised powder-metallurgical Al–Cu alloy composites

• Microstructure of anodic alumina on Al–Cu composites with ceramic particles
• Microstructure of particles, partially converted and embedded in the oxide layer
• Indentation hardness profile of anodic alumina on Al–Cu composite with SiC
• Hardness improvement by an adjusted anodised alumina coating using an Al 99.5 shell

Powder-metallurgical Al–Cu alloy composites with Al2O3 and SiC particles have been anodised. The microstructure of the resulting oxide layers with respect to the composition of the matrix and the reinforcing particles has been correlated to nanoindentation results. The reinforcing particles are well-bonded in the conversion layer regardless of remaining stable (Al2O3) or being converted to mixed oxides (SiC → AlxSiyOz). The distinctive pore structure of the matrix conversion layer is known from anodising of bulk Al–Cu alloys and impedes the formation protective coatings on the studied composites. A shell of partly or completely converted aluminium on the Al–Cu composite shows options to improve the hardness of anodised aluminium oxide coatings on Al–Cu alloy composites.