A shear test was used to investigate the effect of shielding gas (Argon, Nitrogen and none) on the properties of laser spotwelds in Fe-28Ni-17Co alloy (Kovar).  The load vs. displacement curves obtained, while superficially resembling those of a standard tensile test, were quite non-reproducible, and obscured the differences due to process conditions.  Fractographic examination of the samples and analysis of the testing conditions led to significant conclusions about how to correctly interpret the  shear test results, which in turn enabled a determination of the real effects of the change in shielding gas.  Several different types of fracture morphology were noted, depending upon where the fracture surface propagated relative to the weld faying surface.  This resulted in the disparate nature of the load-displacement curves.  The results of the shear testing, fractography, supporting finite element analysis  and metallography will be used to interpret the differences found with respect to porosity formation, strength and work hardening behavior.
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.