Corrosion Behavior of As-Cast and Heat-Treated Al–Co Alloys in 3.5 wt% NaCl

Abstract

The present work evaluates the effect of Co content on the microstructure and corrosion performance of Al–Co alloys of various compositions (2–32 wt% Co), fabricated by flux-assisted stir casting. A preliminary investigation on the effect of heat treatment (600 °C, up to 72 h) on the microstructure and corrosion behavior of Al–20 wt% Co and Al–32 wt% Co was also conducted. The Al– (2–10) wt% Co alloys were composed of acicular Al9Co2 particles uniformly dispersed in an Al matrix. The Al–20 wt% Co and Al–32 wt% Co alloys additionally contained Al13Co4 blades enveloped in Al9Co2 wedges. Heat treatment of Al–20 wt% Co and Al–32 wt% Co led to a significant reduction in the volume fraction of Al13Co4 and a decrease in hardness. Al–Co alloys with high Co content (10–32 wt% Co) exhibited greater resistance to localized corrosion in 3.5 wt% NaCl, but lower resistance to general corrosion compared to the (0–5 wt% Co) alloys. Heat treatment led to a slight increase in the corrosion resistance of the Al–Co alloys. The microstructure of the produced alloys was analyzed and correlated with the corrosion performance. Finally, corrosion mechanisms were formulated.

Keywords

• Al–Co alloys
• Al₉Co₂
• Al₁₃Co₄
• stir casting
• heat treatment
• X-ray diffraction