Why do weld areas on some parts look different than the rest of the part? How can such anomalies be minimized?
Welds can discolor for a couple of different reasons. First, the metallurgy of the welding wire is different than that of the alloy being welded. Since the finish produced in the anodizing process is somewhat dependent on the metallurgy, the metallurgical difference will show up as a shade difference. Secondly, during the welding process a significant amount of heat is built up around the weld. This heat buildup actually changes the temper of the aluminum immediately surrounding the weld bead. Since a temper change is really a metallurgical change, again this shows up after anodizing as a color difference. These areas are commonly called halos or ghosts. There are a few things that can be done to minimize the color differences. First, excellent results may be produced by using welding wire alloy 5356. This alloy reportedly produces the best color or shade match when used to weld 6xxx series alloys. The second problem, concerning halos or ghosts, is a little more difficult to solve. Try
