Effect of alkaline etching on surface properties of aluminum alloy
[Introduction]The alkaline etching with sodium hydroxide has a great effect on the appearance and surface properties of aluminum alloy.[Method]The removal of natural oxide film from an aluminum alloy surface was inspected by copper ion replacement method.The micromorphology and surface roughness of the specimens were examined by using a 3D profilometer,and their glossiness was measured with glossmeter.[Result]The natural oxide film on the surface of 6061 aluminum alloy could be completely removed after 2 minutes of immersion in a 50 g/L NaOH solution at temperature above 10 ℃ or in a NaOH solution of more than 20 g/L at 20 ℃.However,the scratches caused by lathe polishing could not be eliminated.The hydrogen evolution reaction of aluminum alloy became more and more intense during alkaline etching with the increasing of temperature.The glossiness of the alkali-etched aluminum alloy was increased significantly after desmutting,but lower than the degreased specimen prior to alkaline etching.Alkaline etching above 30 ℃ greatly reduced the glossiness of aluminum alloy surface.The specimens etched in 10-30 g/L NaOH solution after desmutting had higher glossiness than that etched with higher NaOH concentration.The surface roughness of aluminum alloy was increased after alkaline etching with sodium hydroxide.The surface smoothness was relatively high after alkaline etching at 20 ℃ or 30 ℃.The surface roughness Ra was increased with the increasing of alkaline etching temperature in the range of 30 to 50 ℃.The color of smut on the surface of alkali-etched aluminum alloy became darker with the increasing of etching temperature.Alkaline etching at above 40 ℃ resulted in pitting corrosion of aluminum alloy.[Conclusion]Alkaline etching with sodium hydroxide has great impact on the gloss and roughness of aluminum alloy surface.The temperature and NaOH concentration should be determined reasonably.
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