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Should I use 4043 or 5356 filler alloy?

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As a basic description we can say that 4043 is an aluminum filler alloy with 5% silicon added and that 5356 is an aluminum filler alloy with 5% magnesium added.

There are some misconceptions within the industry that you can successfully weld any aluminum base alloy with either 4043 or 5356 filler alloy.  I must start by saying that this is not the case.  However, there are many common structural aluminum base alloys that can be welded with either 4043 or 5356.  One such alloy is 6061.

The question here is when should we choose one of these filler alloys over the other?

When the filler alloy selection chart allows the use of either 4043 or 5356 as filler for a specific base alloy, as a guide, we may wish to consider the following facts about each of these filler alloys.

  • 4043 should not be used if you are considering the best color match after post weld anodizing, as this filler alloy will typically turn dark gray in color after the anodizing process.  5356 will provide a much closer color match after anodizing.
  • 4043 is suitable for service temperatures above 150 Deg. F, however, 5356, because of its 5% magnesium content is not suitable for these elevated temperature applications.
  • 4043 has lower ductility than that of 5356.  This may be of some consideration if forming, after welding is to be carried out.
  • 4043 has lower shear strength than that of 5356 (see Fig 1). This may be of consideration when calculating the size of fillet welds.
  • 4043 is a softer alloy in the form of spooled wire, when compared to 5356.  Typically when Gas Metal Arc Welding (GMAW), feedability will become a less critical issue when feeding the more rigid 5356 alloy.
  • 4043 will typically provide a higher rating for weldability and provide slightly lower crack sensitivity.  4043 will generally tend to produce welds with improved cosmetic appearance, smoother surfaces, less spatter and less smut.  For this reason, it is sometimes more appealing to the welder.


shear strength chart

Fig 1. Shows the typical shear strengths of various filler alloys, as can be seen 4043 has 15ksi in transverse shear and 5356 has 26ksi when loaded in the same transverse direction.

It is wise to use the filler alloy selection chart to assist with the selection of the most appropriate filler alloy to be used.  It is also wise to conduct procedure qualification testing to evaluate the filler alloy selected to verify it’s performance characteristics.