Surface morphological changes of aluminium alloys in alkaline solution: effect of second phase material

The dissolution of 1050, 1602 and 3103 series alloys in alkaline solution has been studied, with particular emphasis on the roles of the various second phase material on the corrosion rate of the alloy and resultant surface morphology. Iron and iron plus manganese containing phases, with and without silicon, have been identified in 1050, 1602 and 3103 alloys respectively. The population densities of silicon and silicon-free second phases, which show lower and higher rates of dissolution respectively than the alloy matrix, dictate the dissolution rate of alloy in sodium hydroxide solution. Continued development of silicon-containing phases on the surfaces of 3103-1 and 3103-2 alloys enhances the rate of hydrogen evolution, leading to increases in alloy dissolution rate during prolonged etching. High rates of dissolution of silicon-free particles result in the limited presence of second phase material on the surfaces of 3103-3 and 3103-4 alloys (low silicon content alloys); consequently, such particles have less effect on the rate of matrix dissolution than silicon-containing particles. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.