Qualified to AWS A5. 10 R4043, ABS, ISO Designation AISi5. 4043 is a 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 ^xxx series than other welding alloys. Common applications are automotive parts, truck trailers, bicycles. Also ideally suited for brazing thin aluminum sheet and tubing.