Effects of quenching media on the mechanical properties of Al-Al2O3 metal matrix composite

Abstract

In the present investigation, Al–Al2O3 nano- and microcomposites with different volume fractions of alumina was fabricated using powder metallurgy route and then characterized using X-ray diffraction and scanning electron microscope succeeded by density and Vickers microhardness measurements. The heat treatment of the samples was done by first heating the composite specimens to conditioning temperatures of 150°, 200°, 250° and 300°C separately in furnace, then holding the samples at that temperature for 1 hour and finally quenching them in different media such as air, brine solution (7 wt. %), engine oil, liquid nitrogen and polymer (poly ethylene glycol-5 wt. %) solution. After quenching the microhardness values were again measured. 3-point flexural test was conducted on the quenched samples at a loading rate of 0.5 mm/min. Some of the selected fractured samples were then taken for fractography analysis using field emission scanning electron microscope (FESEM). The results revealed that the strength and hardness of the composites were significantly enhanced as a result of quenching heat treatment. Higher strength and hardness was observed for brine quenching followed by liquid nitrogen, oil, polymer and finally air cooling. The betterment of mechanical properties of AMCs after quenching can be accredited to the intensified dislocation density produced due to coefficient of thermal expansion mismatch between the particles and the matrix and also due to the back stress developed due to particles blocking the plastic flow of the Al matrix phase. The significance of study of quenching of AMCs is realized in applications such as cooling of cylinder liners and pistons in automobiles and aerospace structures which are suddenly subjected to very low temperatures at high altitudes due to presence of strong winds.