An investigation on wear and machinability characteristics of al7068 si3n4 bn hybrid metal matrix composites

Abstract

In the recent decades, Aluminium based composites have become better substitutes for the conventional aluminium alloys in many advanced applications such as aerospace and automotive owing to their outstanding properties such as improved strength to weight ratio, low thermal expansion and good wear resistance. Many researchers have developed Aluminium Metal Matrix Composites (AMMCs) by adding different ceramic reinforcing materials to aluminium alloys. The addition of ceramic reinforcing materials improves strength, hardness and wear resistance. However, adding the ceramic reinforcing materials results in poor machinability and frictional characteristics, thereby giving way to the use of multiple reinforcements in the aluminium alloy. Aluminium matrix composites with multiple reinforcing materials (Hybrid AMMCs) are the second generation of composites that include combined properties of their reinforcing materials, and, therefore, exhibit improved mechanical and tribological properties. Due to this, hybrid AMMCs have the potential to replace single reinforced composites for a wide range of components, especially, in aerospace and automobile applications. Various research studies have been directed towards the development of hybrid AMMCs wherein hard ceramic material such as SiC, B4C and Al2O3 is added to improve mechanical properties, and solid lubricant such as Graphite and Molybdenum disulfide is added to improve machinability and tribological characteristics. The aluminium alloy Al7068, one of the strongest commercial aluminium alloys, was used as the base matrix alloy for the development of composites. Silicon Nitride (Si3N4), a hard-ceramic material, was used as the primary reinforcing material to improve the mechanical and wear characteristics of the composite material. Whereas, in order to enhance tribological and machining behaviour of the composites, Boron nitride (BN), a solid lubricant material, was used as the secondary reinforcing material. The composition of Al7068 alloy was identified using EDS. The morphology of reinforcing materials (Si3N4, BN) was obtained with the help of SEM analysis. The aluminium metal matrix composites have been developed through stir casting process by reinforcing different weight fractions (0%, 5% and 10%) of Si3N4 and BN. To study the basic mechanical characteristics of the developed composites tensile and hardness tests were carried out. The tensile test was conducted on the developed composite specimens by employing computerised universal testing machine. Brinell hardness test was carried out to determine the hardness of the composite samples. newline