Effect of ultrasonic vibrations and silicon carbide additions on microstructure, mechanical and tribological behavior of Al7075 alloy

Abstract

Aluminium alloy Al7075 is a novel alloy used in various applications where strength is critical factor compared to its corrosion resistant behaviour. It has been reported in many literatures that fine-grained equiaxed microstructure results in improved quality of the metal in turn reduction in cracking. Many investigators have also found that when mechanical vibrations induced during solidification of metals and alloys, modify its microstructures. During solidification process, when high intensity ultrasonic waves are made to propagate through the molten metals, results in formation of fine-grained equiaxed structure by the suppression of columnar grains. In the present investigation the effect of silicon carbide (SiC) particulate addition and effect of ultrasonic vibration on mechanical properties and tribological behaviour of aluminium metal matrix (Al-MMC) composites has been investigated. A specially fabricated die assisted with ultrasonic vibration module was employed for investigation. The specimens were fabricated as per ASTM standards. Laboratory experiments were conducted on prepared specimens for different frequencies and a constant amplitude. The mechanical properties such as ultimate tensile strength and yield strengths are determined for both alloy and for the alloy with reinforcement. The findings are analysed. Microstructure examination reveals the presence of a aluminium dendrites surrounded by fine secondary phase particles. Hardness measurements have also been carried out. Dry sliding wear studies on composites were carried out using pin-on-disc testing machine for varying speeds and loads. The experiments were conducted for three different loads 1kg, 2kg and 3kg and disc speed of 400, 600 and 800 rpm for a test duration of 5 minutes. Weight loss method has been considered for the analysis. The weight loss of the composites was found to increase with the increase in normal load. With increased speed increase in the weight loss has been observed. Reduction in weight loss were noticed after SiC reinforcement additions and specimens with castings taken at higher ultrasonic frequency. The result indicates that SiC and ultrasonic frequency has an influence on the wear properties of the composite.