Development of Metal Matrix Nanocomposites of AA6061 – SiCp Using Ultrasonic Cavitations in Squeeze Casting Process
Authors: Bangaru Mohan , Azhagan Murugan Thirumal , Arunachalam Rajadurai 
Published: March 2016

In the recent days, aerospace, automotive and defense sectors have been the main driving force behind the search of lighter and stronger materials in order to use in the production of vehicles. The growing demand for the production of light weight structural components and systems is fulfilled by the development of innovative metallic materials such as composites and alloys particularly based on aluminium because of their desirable properties such as low density, good castability, excellent strength and excellent corrosion resistance. Widely employed processes such as gravity and pressure die casting are used for processing aluminium alloys but the components exhibit several casting defects such as porosity, cracks, segregation and hot tears etc. This drives the industries to develop new processes which produce defect free components in shorter time as they have been under competitive pressure. Of the many such processes, squeeze casting has good capacity to produce less defective components. Squeeze casting is the process in which the molten metal solidifies under the application of pressure. The development of Aluminium Matrix Composites (AMCs) through squeeze casting has been one of the major areas of research in recent times. Research works on AMCs reinforced with micrometric particles have shown that the ability to strengthen the matrix alloy by them is lesser than nanometric particles. Metal matrices reinforced with nanoparticles are characterized by significant improvement in strength and wear resistance, improved ductility and improved dimensional stability at elevated temperatures. But, nanosized ceramic particles constitute problems during fabrication as it is extremely difficult to obtain uniform dispersion of nanoparticles in liquid metals owing to their high viscosity, poor wettability in the metal matrix, and a large surface-to-volume ratio. These problems induce agglomeration and clustering of nanoparticles. The nanoparticles can be dispersed uniformly in the metal matrix by means of employing ultrasonic cavitations. Ultrasonic cavitations include the formation, growth and collapse of micro-bubbles in liquids, under cyclic high intensity ultrasonic waves. The cavitation bubbles collapse and generate a huge amount of energy, which could be used in dispersion of the nanoparticles more uniformly in the melt. In this study, squeeze casting is combined with ultrasonic cavitations to develop Metal Matrix Nanocomposites (MMNCs) of AA6061 – SiCp as a maiden attempt. The impact of varying volume percentage of SiCp nanoparticles (average size of 45 nm – 65 nm) by ultrasonic cavitations on mechanical properties such as ultimate tensile strength and hardness exhibited by MMNCs were analyzed. In this research, volume percentage of SiCp nanoparticles was varied at 0.4%, 0.8% and 1.2% respectively by employing ultrasonic vibrations at the amplitude of 70 μm to the melt of AA6061. The melt of AA6061-SiCp was poured into the pre heated die cavity and squeeze pressure of 105 Mpa was applied over it for a certain period while developing MMNCs. Scanning Electron Microscope (SEM) images showed the uniform distribution of SiCp nanoparticles in AA6061 matrix. Energy Dispersive Spectroscopy (EDS) in SEM confirmed the incorporation of SiCp in AA6061 matrix. The obtained results confirmed the effectiveness of ultrasonic cavitations in squeeze casting process to disperse the nanoparticles of SiCp uniformly in AA6061 matrix. The mechanical properties of MMNCs such as ultimate tensile strength and hardness exhibited an increasing trend with respect to the increase in volume percentage of SiCp nanoparticles. Thus there prevails a great scope to develop MMNCs of aluminium using ultrasonic cavitations in squeeze casting process.