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Application: Structural component used for material handling manufactured from 6061-T6 in material thicknesses of 1/8 to 1/2 inch.
Joint Design: Fillet welds.
Special Operating Considerations: Welding filler alloy should be suitable for sustained high temperature application (250 deg F), provide good structural integrity and suitable feedability characteristics.
This component is to be used in the as-welded condition and will not undergo any post weld heat treatment.
A - The sustained high temperature application (above 150 deg F) requirement for this component is probably your main consideration and will most definitely influence your filler alloy selection. Also, as this component is intended to be used for handling material and the welds being used are fillet welds, I would most certainly consider the shear strength characteristics of the filler alloy.
The high service temperature requirement eliminates the use of any filler alloy with more than 3% Mg such as the frequently used 5356 and the higher strength filler alloys 5183 and 5556. This provides you with 4643, 4043, 4047, and 5554 as possible filler alloys for your application.Evaluation of most appropriate filler alloy
Let us evaluate each of these four filler alloys based on their features and characteristics.
Considerations relating to four filler alloys that may be used for this application: 4643, 4043, 4047 and 5554.
Filler alloy ER4643 – This filler alloy was developed for welding 6xxx series base alloys and developing high mechanical properties in the post-weld heat-treated condition. This alloy was produced by taking the well-known alloy 4043, reducing the silicon, and adding 0.10 to 0.30 percent magnesium, thus ensuring its ability to respond to post-weld heat-treatment. This is a premium filler alloy that is priced for its specialized characteristics and would not normally be used unless post weld heat treating was being performed. Since you stated that post weld heat treatment is not to be used, I would see no reason to use this alloy.
Filler Alloy ER4043 – While the 4043 filler alloy, a 5% Silicon alloy, is often used to weld 6061 base materials, it is not commonly used when shear strength of the component is a predominant consideration. The 4043 filler alloy is a silicon based filler alloy that is often used to take advantage of the elements capability of promoting fluidity in aluminum. While groove welds can be made using this filler alloy that can characteristically pass minimum transverse tensile test requirements, this filler alloy has considerably lower shear strength when compared to the 5xxx series filler alloys. Filler Alloy ER4047 – Like the 4043 filler alloy, 4047 is a silicon-based alloy, but has a much higher level of silicon, approximately 12%. The extra silicon within the alloy provides exceptional fluidity. This alloy, which is also registered as a brazing alloy, is most often used for leak-tight joints in thin wall applications. The 4047 filler alloy has a very narrow freezing range and consequently is very resistant to solidification cracking. The 4043 and 4047 filler alloys have very similar mechanical characteristics - 4047 having slightly higher tensile strength. Both 4043 and 4047 have lower ductility and lower shear strength properties than the 5xxx series filler alloys. They also possess lower column strength when compared to the 5xxx series filler alloys, and consequently, require extra care during feeding in order to minimize feedability problems.
Filler Alloy ER5554 – The 5554 filler alloy was designed to provide the improved strength and ductility characteristics of a magnesium-based filler alloy that was also suitable for elevated temperature applications. It contains 2.4% to 3.0% magnesium thereby providing an alloy that is not susceptible to stress corrosion cracking, but has improved shear strength and improved ductility when compared to the 4xxx series filler alloys. The typical transverse shear strength of 4043 and 4047 is 15.0 ksi and the typical transverse shear strength of 5554 is 23 ksi, an increase of 65% (see Fig 1). In addition to the improved mechanical properties of 5554 on the completed weld, we see an increase in the column strength of the wire. This characteristic can distinctly improve the wires feedability. The 5554 filler alloy will typically produce a weld which is not quite as cosmetically appealing as the 4xxx series filler alloys and has a slightly greater potential for producing “smut” (a black deposit of metal oxides which is not harmful to the weld).