Qualified to AWS A5.10, ABS / CWB / Designation AlSi5, Alloy 4043 is an all-position 5% silicon alloy used to weld heat-treatable base alloys. It is most often used to weld the 6XXX series of alloys. The silicon addition improves puddle fluidity, producing an appealing bead profile. It is less crack sensitive on the 6XXX series than other welding alloys.