Synthesis and optimization of mechanical properties of aluminium composite reinforced with high entropy alloy

Abstract

Aluminium Matrix Composites (AMCs) are finding a wide range of applications in automobile, aerospace, defense, and general engineering sectors, because of their higher specific strength and stiffness, good wear and seizure resistance, and improved high temperature properties as compared to the base alloy. Potential uses of these materials in automobile sectors are found in making the components like brake drums, pistons, cylinder heads, drive shafts, etc. Most of these components are subjected to abrasive and sliding types of wear during operations and are presently either made of cast iron and steels or aluminum alloys. AMCs are lighter than cast iron or steel and the former has a better specific strength and wear resistance as compared to the latter one. Thus, considerable efforts are being made to replace these components with AMCs. It will not only improve the life of components but also reduce the weight and improve fuel efficiency. An Mg-Si-based Aluminium 6082 alloy with varying concentrations of CoCrFeMnNi high entropy alloy (HEA) reinforced composites were fabricated through stir squeeze casting assisted with an ultrasonic transducer probe. The composites were heat treated to examine the age-hardening effect (T6) on microstructural changes, fracture mechanism, and an interface between HEA particles and aluminium matrix. The evolution of microstructure and topography of HEA particles, alloy, and composite at as cast and heat treated conditions, was investigated through field emission scanning electron microscope (FESEM) with energy dispersive X-Ray Spectroscopy (EDS) and transmission electron microscope (TEM). X-ray diffraction (XRD) is used to characterize the phase evolution of HEA particles, alloys, and composites at the as-cast condition, and heat-treated condition. In this study, the mechanical behavior of alloy and composite was investigated and the cause of failure was studied through tensile fractured surface. Under the T6 condition, composites exhibit superior mechanical properties such as improved hardness, yield strength, and ultimate tensile strength, however, the ductility of composites is less as compared to the as-cast condition which might be due to the formation of precipitates. The performance of industrial tribo-systems depends on advanced composites with superior tribological characteristics. The effect of HEA particles on the dry sliding wear performance of HEA reinforced Aluminium metal matrix composites was examined in as-cast conditions using a pin-on-disc wear tester at varying pressure and constant sliding I speed, special emphasis is centered on response factors such as wear rate, and seizure resistance. The composite showed an ability to withstand higher temperatures and better seizure and wear resistance over the alloy. The topography of the worn-out surface was examined through an optical profilometer and FESEM. In all the wear conditions, the wear rate of 8 wt.% HEA/AA (T6) composite shows maximum resilience against wear, the inclusion of HEA particles also influences the extent of the subsurface at the seizure condition. Whereas, at higher applied pressures, the wear surface was depicted as a series of parallel transverse as well as longitudinal cracks and damaged portions. The propagation of longitudinal and transverse cracks resulted in the formation of flaky shape debris. Furthermore, FESEM of the subsurface of alloy shows a mechanically mixed layer (MML), a thin plastically deformed and bulk undeformed zones. With increased applied pressure, the extent of subsurface deformation was increased. The flow of Al dendrite was noted in a less deformed region. It depicted a highly plastically deformed region, which was formed due to void formation and shear deformation of the alloy. During the sliding action, this void joined together and formed subsurface cracks, which were in due course joined together forming wear debris.