Corrosion behaviour of heat treated Aluminium Metal Matrix composites reinforced with Fused Zirconia Alumina 40

Abstract

The hardness and corrosion behaviour of aluminium composites reinforced with Fused Zirconia Alumina 40 (FZA40) subjected to heat treatment was investigated. Aluminium composites reinforced with FZA in volume % of 0, 5, 10 and 15%, respectively, were manufactured using stir-casting techniques. Eight different cast specimens were prepared in various proportions for testing, and their hardness and corrosion properties were compared with those of the casted Al6061. Among them, four casted pieces were heat-treated to a temperature of 250 °C for one hour and air cooled. To find the elemental composition and to determine the crystallographic properties of the prepared Al6061 and its composites, Energy-Dispersive X-ray Spectroscopy (EDS) and X-ray Diffraction Spectroscopy (XRD) analyses were performed. Scanning Electron Microscopy (SEM) analyses were also performed on the specimens to study the bonding and distribution of reinforcements in the matrix. Microhardness evaluation was done on the base metal and the composites to compare the strength of the base metal and the composites. An intermetallic layer formed on the surface of the composites improved the hardness of the composites to a great extent. To analyse the corrosion behaviour of the composites, chemical and electrochemical measurements techniques were adopted. The polarization curves and the passivity characteristics of the composites were similar; irrespective of the volume % of the composites and heat treatment process when immersed in 0.3 M H2SO4 solutions. From the results obtained, it was found that the corrosion current density of the composites decreased with an increase in volume % of the heat-treated composite, comparatively more than the specimens that were not heat-treated. The composite with 15 vol % FZA reinforced Al6061 displayed less corrosion effects than the other composites. The microstructural images taken before corrosion showed uniform distribution of the reinforcement throughout the matrix. Deep pits were observed in the SEM images of the base metal taken after corrosion. The pits were getting shallower as the reinforcements increased. It can been concluded that the composites were stable in their structure as they maintained their corrosion resistance levels after heat treatment process.