Cause of streak that occurred after surface treatment in 6063 aluminum alloy extruded section

摘要

Surface defects that appear as configurations of white dots (hereafter: streak) often occur after surface treatment in 6063 aluminum alloy extruded section. The cause of streak occurrence is thought to be in the welding seam of billet-to-billet extrusion since streak occurrence is concentrated in the beginning part of extrusion. This study surveyed the streak occurrence in detail and examined the influence of the welding conditions of billet-to-billet extrusion upon streak occurrence. In conclusion, this study showed that defective welding occurs partially at seam of billet-to-billet extrusion due to oxide and air enclosure, and that the welding seam remains in extrusion section. Then it was inferred, in the case where the welding seam is near the surface of the extruded section, that pits are formed during pretreatment, and that streak occurs in those locations after pigmentation.