Microstructure Investigations of Streak Formation in 6063 Aluminum Extrusions by Optical Metallographic Techniques

• Published in: Microscopy and microanalysis Vol. 19; no. 2; pp. 276 - 284
• Main Authors: Vander Voort, George, Suárez-Peña, Beatriz, Asensio-Lozano, Juan
• Format: Journal Article
• Language: English
• Published: New York, USA Cambridge University Press 01.04.2013; Oxford University Press
• Subjects: Alloys; Aluminum; Aluminum alloys; Aqueous solutions; Ductility; Etching; Extrusion dies; Grain boundaries; Homogenization; Light microscopy; Magnesium; Materials Applications; Microscopy; Particle size; Solidification; Temperature; scanning electron microscopy; quantitative metallographic characterization; streak formation; precipitation; 6063 aluminum alloys; light optical microscopy
• ISSN: 1431-9276; 1435-8115; 1435-8115
• DOI: 10.1017/S143192761300010X

The present study investigates the effect of the solidification strategy for AA 6063 alloy on the surface appearance of anodized extrusions. The microstructure of the samples was analyzed using both light optical microscopy and scanning electron microscopy. Results show that if heavy segregation occurs from rapid solidification, coarse Mg2Si particles form, thus reducing the potential for precipitation strengthening by the finer β-Mg2Si developed in the solid state. Differentially-strained regions formed during hot extrusion induce differences in particle size for magnesium silicide (Mg2Si) precipitates. Anodizing generates surface roughness due to Mg2Si particle dissolution and AlFeSi decohesion, which is related to both particle size and deformation. During anodizing, an oxide layer forms on the surface of the extruded products, which can lead to streak formation, usually a subject of rejection due to unacceptable heterogeneous reflectivity.