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Problem passing guided bend test on 5083 base alloy

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Q – I have a customer who is having problems passing guided bend tests on 5083 base material.  What filler alloy should he be using and why are the bend tests failing.

A – Base material 5083 can be welded successfully with 5356, 5183, and/or 5556. All three of these filler alloys may be suitable for welding this base material, however, choosing one of these filler alloys is dependent upon the application and service requirements of the component being welded.  The 5083 base material can be used in a number of applications including shipbuilding, cryogenic tanks, military vehicles and structural fabrications.  From a design standpoint, considering fillet welds, the typical transverse shear strength values of these three filler alloys are 26Ksi, 28Ksi and 30Ksi for 5356, 5183 and 5556, respectively.   Considering groove weld transverse tensile strength, the 5356 filler alloy is normally only used on 5083 base material when there is no requirement for groove weld welding procedure qualifications. The 5356 filler alloy may not consistently achieve the minimum tensile strength requirements of the code (40ksi – 275MPa) for groove weld transverse tensile testing of 5083 base material.  The 5183 filler, developed specifically for welding the 5083 base material, will meet the mechanical property requirements for groove weld procedure qualification.  The 5556 base alloy has slightly higher mechanical properties over the 5183 and can be used to weld the slightly higher strength 5456 base material, but will also meet the minimum tensile requirements for the 5083 base material.  The 5083 base material should not be welded with a 4043 or a 4047 filler alloy.  It not recommended that any 5xxx series base material with more than 2.5% magnesium be welded with a 4xxx series filler alloy.

Failing a guided bend test can be due to a number of reasons:

  1. The most obvious reason is that there is some form of discontinuity in the weld, which has caused the break, usually lack of fusion.  To determine the presence of any significant discontinuities that may have caused the failure, the failed sample needs to be inspected.
  2. Was the test conducted correctly?  The samples may not have been prepared correctly prior to bending, or maybe they were bent over the incorrect radius.  Examination of the failed samples is necessary to verify that they were prepared in accordance with the relevant specification.  The test procedure should be evaluated to determine its correctness. 
  3. Which testing method was used?  The wraparound guided bend test method is the preferred method of testing aluminum weldments because of the significant variations in the as welded mechanical properties of some aluminum alloys.  The plunger test method is not recommended for higher strength aluminum alloys like those that you are testing. 
  4. 4.   The use of an inappropriate filler alloy such as a 4xxx series used on this base material, could result in a weld with low ductility and therefore susceptibility to failure.