Development of light composite materials with low coefficients of thermal expansion

Composite materials based on aluminium are used in different fields where weight, thermal expansion, and thermal stability are key requirements. The aim of the present study was to develop a universal method and scientific approach for evaluating the design of lightweight, Al matrix composites with low coefficients of thermal expansion (CTE) and high dimensional stability, and to produce such composites using the vacuum plasma spray (VPS)process. The methodology is general and could be applied to other composite systems. The VPS-produced Al and Al alloy 6061 based composites were reinforced with a variety of ceramic particles including Si₃N₄, B₄C, TiB₂, and 3Al₂O₃.2SiO₂. These composites have low CTE values ((12–13)×10^-6 K^-1), similar to that of steel, and high dimensional stability (capable of keeping dimensions stable with changes in temperature). They have low porosity (98–99%dense) and a uniform distribution of the strengthening particles. Hot rolling of the VPS-formed composites, followed by heat treatment, resulted in a significant improvement in the mechanical properties. Deformed and heat treated 6061 based composites, containing 20 wt-%TiB₂ and 40 wt-%3Al₂O₃⋅2SiO₂, showed excellent mechanical properties (ultimate tensile strength 210–250 MPa, elongation >4%).