Evaluation of Corrosion Resistance Properties of Aluminium 7075-Beryl Composite Materials in Acid Chloride Medium

Abstract

Metal matrix composites are popular now a day due to the fact that their properties can be tailored by the addition of reinforcements like particulates, fibres and whiskers. Metal matrix composites show improved mechanical propertieswhen compared with those of matrix alloy. Improved ultimate tensile strength, hardness, percentage elongation, young’s modulus, impact strength and compression strength are shown by metal matrix composites. In the same way the corrosion resistance properties of composites are also improved over the same property of matrix alloy. Composites show improved weight loss corrosion resistance, stress corrosion resistance and polarisation studies. Hence the composites are important in the fields of aircraft, automobile and marine industries due to their increased life, improved mechanical and corrosion properties. In the present research work, aluminium 7075 alloy is selected as matrix and beryl or beryllium aluminium silicate is selected as reinforcement. Both are commercially available. Metal matrix composites containing different volume fraction of beryl particulates were successfully manufactured through liquid melt metallurgy technique using vortex method. Pre heated but uncoated beryl particulates of 50-80 micro meters are used in the manufacture of composites. Characterization studies were conducted on the aluminium 7075 alloy and its composites samples to evaluate the microstructural properties and corrosion properties. Microstructures were taken by using scanning electron microscope. Microstructural characterizations of composite samples reveal the presence and homogeneous distribution of beryl particulates. The corrosion tests conducted were static weight loss corrosion and potentiodynamic polarisation test using Elico make Potentiostat / galvanostat model CL95. Hydrochloric acid with different concentrated solutions usedas corrosion medium.Hydrochloric acid with three different concentrations of are used for the study. Corrosion current and corrosion rates were determined for matrix and composites in the above mentioned tests. In all the tests the composites decreased corrosion rate and decreased corrosion current when compared to those of matrix alloy. Hence composite materials are more suitable for the different applications than the matrix.