Formation and characterisation of Ti–Zr based conversion layers on AA6060 aluminium

Formation of a Ti–Zr based conversion layer on AA6060 aluminium has been studied electrochemically and by use of various surface analytical methods. Measurements show that the α-Al(Fe,Mn)Si particles present in AA6060 are cathodic to the aluminium matrix in a fluorotitanate–zirconate (H2TiF6–H2ZrF6) based solution, and reduction reactions occur predominantly on the particles. The alkaline diffusion layer thus formed causes preferential deposition of a hydrated Ti and Zr oxide covering the particles and surrounding areas, eventually leading to a conversion layer with significant variations in thickness. In addition to substrate metallurgy, agitation and pH of the conversion bath are factors that significantly control the conversion layer deposition. The conversion layers formed cause only a small reduction in the cathodic activity of the α-Al(Fe,Mn)Si particles and do not impart improved corrosion resistance of the AA6060 alloy in chloride solution.