What can be done to eliminate white/gray 'hot spots' on aluminum extrusions?--Our Aluminum Expert Answers Your Questions

摘要

Hot spots are usually associated with lower-hardness areas due to coarse precipitates caused by non-uniform cooling after extrusion. These regions appear after anodizing. According to Parson et al., in "The Metallurgical Background to Problems Occurring During the Extrusion of 6xxx Alloys," Proc. of the 5th International Aluminum Extrusion Technology Seminar, Vol. II, The Aluminum Association and The Aluminum Extruders Council, 1992, hot spots are often observed in sections where there is localized contact with a carbon support block on the run-out table. Regions in contact with the carbon cool very rapidly momentarily and then are reheated from the adja-cent mass of metal into a critical range for magnesium silicide precipitation.