Thermal and mechanical properties of Al/Al2O3 composites at elevated temperatures

The objective of this study is to determine the effects of phase volume content, processing conditions, the size of aluminum particles, and porosity, on the physical and thermo-mechanical properties of an alumina reinforced aluminum composite in 25–450 °C temperature range. Composites with 0%, 5%, 10%, 20% and 25% volume contents of alumina are manufactured using powder metallurgy technique. Two types of composites with different aluminum powders were manufactured: composite A – 99.97% pure Al with 7–15 μm particles, and composite B – 97.5% pure Al powder with 3–4.5 μm particles. For both composites A and B, alumina powder with <10 μm particle size was used. The composite samples were characterized for their porosity, relative density and distribution of the alumina phase. The elastic properties (Youngʹs modulus and shear modulus) of the composites were determined using resonant ultrasound spectroscopy (RUS) as a function of temperature while the coefficient of thermal expansion (CTE) was determined at various temperatures using thermo mechanical analyzer (TMA). It was found that the composite with smaller aluminum (composites B) particles had higher values of the relative density and thus higher elastic moduli, and lower values of the CTE than the composites with larger aluminum particles (composites A). In all cases, increasing the volume contents of the alumina increases the elastic moduli and reduces the CTE of the composites. Increasing the testing temperature from 25 to 450 °C, significantly reduces the elastic moduli of the composites, while the CTE the composites only slightly changes with temperatures.