Selecting a Filler Alloy

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The material specication for MIG and TIG ller alloys is AWS A5.10, Spec- ication for Bare Aluminum and Aluminum-Alloy Welding Electrodes andRods (88). The term bare differentiatesthese llers from shielded metal arcweldingllers that come with a crusty ux cover and were used before inertgasshielding methods were developed in the 1940s.

The structural design of welded connections is a function of the ller wireused in the weld. Table 7.2-1 of the Aluminum Specication dictates the lleralloy based on the parent metal alloy(s). In many cases, several ller alloysmay be used. You have many factors to consider in addition to strength,including ductility, color match after anodizing, corrosion resistance,hotcrackingtendency, MIG wire feedability, and elevatedtemperatureperformance.Inspite of this, the vast majority of applications use 4043or5356ller,which costs $2.50 to $3.25/ lb [$5.50 to $7.00/ kg]. (4043 isslightlylessexpensivethan5356, but not enough to override other factors in decidingwhich touse.)Other llers can cost as much as $10 to $12/ lb [$22 to $26/kg] and are not as available, soyou need a good reason before using them.

Filler alloys 5356, 5183, and 5556 were developed to weld the 5xxx seriesalloys, but they have also become useful for welding 6xxx and 7xxx alloys.Alloy 5356 is the most commonly used ller due to its good strength, compatibilitywith many base metals, and good MIG electrode wire feedability.

Alloy 5356 also is used to weld 6xxx series alloys because it provides a bettercolor match with the base metal than 4043 when anodized. (4043 tends toturn black when anodized, a look the architect might not have had in mind.)Alloy 5183 has slightly higher strength than 5356, and 5556 higher still. Themost notable example of where the higher strength of 5556 is needed is forwelding 5083 or 5456. Because 5356, 5183, and 5556 contain more than 3%magnesium and are not heat-treatable, however, they are not suitable for elevatedtemperature service or post weld heat treating. Alloy 5554 was developedto weld alloy 5454; both contain less than 3% magnesium so as to besuitable for service more than 150F [66C].

Alloy 5654 was developed as a high-purity, corrosion-resistant alloy forwelding 5652, 5154, and 5254 components used for hydrogen peroxideservice. Its magnesium content exceeds 3% so it is not used at elevatedtemperatures.

Alloy 4043 was developed for welding the heat-treatable alloys, especiallythose of the 6xxx series. Its has a lower melting point than the 5xxx llers,so it ows better and is less sensitive to cracking. Alloy 4643 is for welding6xxx base-metal parts more than 0.375 in. [10 mm] to 0.5 in. [13 mm] thickthat will be heat-treated after welding. Although ller alloys 4047 and 4145are listed for some parent metal combinations in Specication Table 7.2-1,they are primarily used for brazing. Brazing is the process of joining metalsby fusion using ller metals with a melting point above 840F [450C], butlower than the melting point of the base metals being joined.

Brazing is notthe same process as welding, and we won't be discuss it here. Filler 4047has more silicon than 4043, so it ows better, making it better suited toproducing seal welds. 4145 is used for welding 2xxx alloys, and 4047 is usedinstead of 4043 in some instances to minimize hot cracking and increaselletweld strengths.

Alloy 2319 is used for welding 2219; it's heat treatable and has higherstrength and ductility than 4043 when used to weld 2xxx alloys that are postweld heat treated.Pure aluminum alloy llers are often needed in electrical or chemical industryapplications for conductivity or corrosion resistance. Alloy 1100 isusually satisfactory, but for even better corrosion resistance (due to its lowercopper level) 1188 may be used. These alloys are soft and sometimes havedifculty feeding through MIG conduit.The ller alloys used to weld castings are castings themselves (C355.0,A356.0, 357.0, and A357.0), usually in. [6 mm] rod used for TIG welding.

They are mainly used to repair casting defects. More recently, wrought versionsof C355.0 (4009), A356.0 (4010), and A357.0 (4011) have been produced,so that they can be produced as MIG electrode wire. (Alloy 4011 isavailable only as rod for GTAW, however, since its beryllium content producesfumes too dangerous for MIG welding.) Like 4643, 4010 can be used .

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Selecting a Filler Alloy

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This article was published on 2011/08/04