Thermally Sprayed Prepregs for Advanced Metal Matrix Composites

Abstract

Advanced continuous fiber reinforced metal matrix composites (MMC) are manufactured using thermally sprayed prepregs and subsequent semi solid forming. The prepregs consist of fiber woven fabrics, which will serve as reinforcement and a thick metal alloy coating on top of the fabrics, which will serve as matrix material. The coated fabrics are trimmed to the shape of the component and laminated in packages of 40 to 80 prepregs to form a component. The prepregs are reheated into the semi- solid state of the alloy and can be solidified to a dense MMC with no residual porosity by semi- solid forging (thixoforging). The deposited alloy infiltrates the fabrics with 40% to 60% vol. liquid fraction. The fine- grained structure of the thermally sprayed metal coatings allows the required formation of globular grains during remelting and improves the impregnation behavior. Conventional thixoforming alloys achieve this structure by continuous casting with electromagnetic stirring or spray forming under inert gas atmosphere to form a massive billet rod, not suitable for infiltration of fiber structures. The thermal spray coating process is carried out under atmospheric conditions and allows the manufacturing of continuous reinforced MMC due to significant reduction of fiber damage. Chemical interaction and mechanical load on the fibers are minimized during processing due to a globular grain structure of the solid phase dispersed in the metal matrix melt, short flow paths during thixoforging, short cycle times and only a liquid fraction of 40% to 60% vol.. A production line to coat fiber fabric coils in a single continuous procedure is introduced to provide the MMC production with prepregs consisting of various reinforcement fiber materials and a wide range of metal matrix alloys capable for thixoforging densification.