Comparison of reinforcing a natural mineral versus a synthetic ceramic on the thermal expansion behavior of LM13 alloy based composites

LM13 alloy is extensively used in automotive industry to make pistons. The high operating temperatures of pistons led to dimensional instability due to high coefficient of thermal expansion (CTE). This problem can be overcome by incorporating ceramic particles with lower CTE values, which also helps tailor the properties of aluminum matrix composite (AMCs) according to other applications (i.e. brake rotor). Hence, the present research investigated the effect of two different types of reinforcements (a natural mineral “ilmenite” compared to a pure synthetic ceramic “boron carbide”) separately on thermal expansion behavior of LM13 alloy-based composites. Stir casting was used to incorporate 5, 10, and 15 weight percent (wt.%) of reinforced particles in the LM13 alloy matrix. Thermal strain and CTE values were determined in the 50°C–300°C range. Thermal strain and CTE values reduced significantly with increased reinforced particle types. A maximum reduction of 45% over the base alloy in thermal strain and CTE value was obtained for IDP-15 composites (IDP-15: ilmenite reinforced composites with 15 wt.% reinforcement) in the operating temperature range of 50°C–250°C. Beyond 250°C, the maximum thermal strain and CTE value reduction was 52% for BDP-15 composites (BDP-15: boron carbide reinforced composites with 15 wt.% reinforcement) at an operating temperature of 300°C. The results signified that for low-to-moderately high-temperature applications like brake rotors, etc., IDPs are a suitable material, whereas, for high-temperature applications like pistons etc., BDPs are more appropriate. The changes in thermal characteristics of AMCs with operating temperature-reinforcement levels were due to variations in the strength of interfacial bonding and changes in the solubility of silicon in aluminum. Experimental values of CTE obtained in the present research were compared to several theoretical models. There was a close agreement in the experimental values and the predictions made by the “Reuss bound” model.