Investigation of the causes of failure of a welded joint performed with continuous wire mag technology
The object
Welded joint that from visual inspection shows a break in the center of the weld seam of the two welded joints with an extension equal to its length
The analyses
Visual Examination
Preliminary visual examination of the subject part found that one of the two welded joints has a break in the center of the weld seam with an extension equal to its length.
To investigate the possible causes of welded joint failure, the two welded joints identified as “SX” and “DX” were compared.
On both joints, transverse to the weld seam, two macro sections were taken and then subjected to observation under a stereomicroscope.
SX welding
In the two macrographs, which refer to different positions of the same weld, no defects or macroscopic abnormalities are detected. In macrograph SX2, weld seam shape defects are evident: excessive light between the two base materials and unproportional weld seam width…
DX Welding
Looking at the macrograph, it will be seen that the weld rupture originates from the apex of the weld and propagates throughout the entire resist section. On the second macro (see figure), a ponding was detected at the apex of the weld and a crack originates at the apex of the weld and is oriented to the center of the fused zone.
Conclusions
The failure of the welded joint is attributable tothe bonding of the weld seam.
Bonding is a two-dimensional defect and results in a concentration of stresses that, especially in the component subjected to stresses during operation, can lead to the generation and subsequent propagation of a crack, resulting in the catastrophic effect of part failure.
Possible causes of weld bead sticking should be eliminated.
It is also advisable to take the best care of the assembly of various components at the pre-welding stage so as to obtain proportional weld beads and reduction of the gap between base materials.
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