4XXX:Aluminum Silicon Filler Alloys
Keganhirl > 07-10-2019, 08:32 AM
Featuring silicon (Si) as the primary alloying element, the most common 4XXX fillers, 4043 and 4047, are simple binary AlSi alloys. Some of the 4XXX fillers, such as 4643 and 4010, have a small amount of Mg, which helps to make the weld heat-treatable to more closely match the base metal properties. This is especially important in applications where the welded assembly will be completely reheat-treated—solution heat-treated, quenched, and aged—after welding.
Some 4XXX filler alloys also are made to match various casting alloys, such as R-A356.0 and R-A357.0. These fillers are used in foundries to repair 3XX castings before they are heat-treated so that the chemistry of the weld matches that of the casting.
The AlSi filler metals are characterized by excellent fluidity and very good resistance to weld cracking. In addition, they are less prone to develop porosity in the weld than the 5XXX fillers.
The 4XXX fillers are widely used to weld 6XXX extrusions and sheet or plate. They are also used to weld castings to 6XXX alloys and to themselves. In fact, during welding of 6XXX alloys, which are prone to cracking, the AlSi chemistry of the 4XXX filler, when diluted with the 6XXX base alloy, provides a weld chemistry that is highly crack-resistant.
It is not recommended that welders use 4XXX fillers to weld AlMg 5XXX alloys, such as 5083. The high Si content of the 4XXX alloys, when combined with the high Mg of the 5XXX base material, produces the intermetallic compound magnesium silicide, which is an exceptionally brittle substance. Consequently, the weld tends to have poor ductility and toughness. The one exception is welding 5052 using 4043. This works because 5052 has a low Mg content. Base material 5052 also can be welded using 5XXX fillers.
While 4XXX fillers are stronger than 1XXX fillers, they are soft enough that feeding difficulties sometimes occur in gas metal arc welding (GMAW). For this reason, push/pull guns and feeders are recommended but not always necessary with larger diameters.