Microstructural evaluation of monolithic and continuous fibre reinforced Al-12wt.%Si produced by low pressure plasma spraying

The spray/wind process is a concurrent fibre winding and plasma spraying technique and may be used for the manufacture of continuous fibre reinforced composites in a single spraying operation. The microstructure of low pressure plasma sprayed (LPPS) Al-12wt.%Si coatings and spray/wind Al-12Si composites reinforced with continuous fibres has been investigated. The LPPS monolithic Al-12Si deposit sprayed in a single-pass was characterised by splat-quenched microstructure and Si solubility extension in α-Al, whereas multi-pass spraying of thicker deposits promoted precipitation and growth of Si particles because of a corresponding increase of substrate–deposit temperature during LPPS. Four-layer Al-12Si composites reinforced with stainless steel wire and Sigma 1140+SiC fibre have been successfully manufactured by the spray/wind process. Both composites exhibited low porosity and well-controlled fibre spacing. Surface roughness of the sprayed Al-12Si matrix was the key factor in controlling composite porosity and fibre distribution. During subsequent vacuum hot pressing (VHP) consolidation, there were minimal fibre movement and no fibre breakage. Limited fibre/matrix interfacial reactions occurred because the relatively low spray/wind porosity of spray/wind composite reduced thermal exposure during VHP consolidation. However, some surface damage of the Sigma 1140+SiC fibres occurred during both spray/wind and subsequent VHP consolidation.