Portal de Periódicos da CAPES

Effect of Annealing Temperature on Anodic Activation of Rolled AA8006 Aluminum Alloy by Trace Element Lead

2005; Institute of Physics; Volume: 152; Issue: 9 Linguagem: Inglês

10.1149/1.1972728

1945-7111

Yingda Yu, Øystein Sævik, Jan Halvor Nordlien, Kemal Nisancioḡl̄ū,

Aluminum Alloys Composites Properties

Certain aluminum alloys exhibit electrochemical activation in chloride media as a result of annealing at temperatures above , attributed to the enrichment of trace element Pb at the oxide-metal interface. Activation is manifested by a significant negative shift in the corrosion potential and a significant increase in the anodic current when polarized above the corrosion potential in aqueous chloride solution. The degree of activation normally increases with increasing annealing temperature and time. This work presents electrochemical and surface analytical characterization of alloy AA8006 (nominal composition in wt % 1.5 Fe, 0.4 Mn, 0.2 Si, 0.02 Mg) as a function of annealing temperature in the range . For fixed annealing time, maximum activation and Pb enrichment were obtained at an annealing temperature of independent of the original surface condition. This was attributed to an enhancement of Pb enrichment related to the presence of Mg in the alloy. Reduced activation with further increase in the heat treatment temperature was attributed to the formation of a dense thermal oxide consisting of the crystalline spinel embedded in amorphous aluminum oxide. The results furthermore show that the nanocrystalline grain refined surface layer (GRSL) on this alloy, originally formed by the hot-rolling process, oxidizes probably before becoming recrystallized during heat treatment. Stable nanocrystals remain after heat treatment at temperatures as high as .