Corrosion Behaviour of High-Strength Al 7005 Alloy and Its Composites Reinforced with Industrial Waste-Based Fly Ash and Glass Fibre: Comparison of Stir Cast and Extrusion Conditions

Abstract

The stringent demand to develop lightweight materials with enhanced properties suitable for various engineering applications is the focus of this research work. Industrial wastes such as fly ash (FA) and S-glass-fibres (GF) were used as reinforcement materials for high-strength alloy, i.e., Al 7005. Stir casting routes were employed for fabricating the four samples, Al 7005, Al 7005 + 5% GF, Al 7005 + 6% FA and Al 7005 + 5% GF + 6% FA. The extrusion process with different extrusion ratios (ER: 5.32:1, and 2.66:1) was used to examine the properties of all four samples. Extruded samples with ER: 5.32: 1 resulted in equiaxed grains with refined structure compared to stir casting parts. The effect of the extrusion process and the addition of reinforcements (GF and FA) on the gravimetric, electrochemical, and electrochemical impedance corrosion behaviour of Al 7005 composites in 1M HCl (Hydrochloric acid) solution were investigated. The results of all three corrosion methods showed that Al 7005 + 6% FA exhibited higher corrosion resistance. Corrosion rate of Al 7005, Al 7005 + 5% GF, Al 7005 + 6% FA and Al 7005 + 5% GF + 6% FA is found equal to 3.25, 2.41, 0.34, and 0.76 mpy, respectively. The FA particles remain inert and act as a physical barrier with corrosive media during the corrosion test. GF undergoes fibre degradation or disrupts the continuity of the glass network as a result of fibre leaching, which increases the corrosion rate in the sample. The gravimetric study showed that the corrosion rates decreased with an increase in extrusion ratio, which might be due to corrosion passivation increases and improved properties. The scanning electron microscopy reveals that corrosion fits, flakes and micro-cracks were observed more in the as-cast composites than that of extrusion composites, promoting the corrosion rate.