The Effect of the Percentage of Reinforcing Basalt Fibers on the Microstructure and Mechanical Properties of the Al-7Si-0.3Mg Matrix Composite Fabricated by the Thixomixing

Abstract

Semi-solid casting is an advanced technique for fabricating aluminum components with enhanced mechanical properties. In this study, basalt fibers at volume fractions of 0, 2, 4, and 6% were uniformly dispersed within semi-solid A356 aluminum alloy to produce metal matrix composites. The fabrication was performed using an improved thixomixing method, a novel semi-solid processing technique that effectively overcomes poor fiber-matrix adhesion without relying on conventional fiber coatings or in-situ chemical treatments. This method employs shear forces to achieve uniform dispersion of basalt fibers within the semi-solid aluminum, facilitating the formation of intermetallic compounds at the fiber/matrix interface and thereby enhancing interfacial bonding. Semi-solid temperatures of 575 and 585 °C were selected for comparative analysis. The resulting composites were evaluated through shear punch tests, hardness measurements, compression testing, and microstructural characterization. The composite containing 6 vol.% basalt fibers cast at 575 °C exhibited the highest performance, with shear strength, hardness, and compression strength reaching 132 MPa, 71.3 Hb, and 458 MPa, respectively. Microstructural investigations revealed that the formation of intermetallic phases on the basalt fiber surfaces, along with the development of globular α-Al and non-dendritic Si-Al phases within the matrix, played a pivotal role in improving mechanical properties. This semi-solid continuous casting approach presents a promising route to fabricate high-performance composites with superior strength-to-weight ratios, offering a viable alternative to conventional metal components.