Ok we're weldind 1/2" T6-6061 with no preheat on a structural bracket.  Is there an advantage to useing 4643 over 4043 on this base material.  Processes include GTAW and Aluminum wire feed with .062 wire using pure argon.  Fillet weld sizes include .25" and .31" or 1/4" and 5/16".  I appreciate any info regarding this subject.

           Thanks..