2.2. Mechanical test and metallographic evaluation
In order to determine the tensile shear load bearing capacity of spot
welded dissimilar materials, one set of three test samples were prepared
according to standards (Fig. 1). The tensile shear load bearing capacity
of welded materials was determined by using microprocessor controlled
SHIMADZU UH type servo hydraulic universal testing machine. The
yield load at 0.2% offset strain under tensile shear test was determined with
the help of load vs. extension diagram plotted during the test.
The vickers microhardness measurement across the weld nugget and
HAZ (heat affected zone) and of the base metal was carried out on the
metallographic specimens with a load of 50 g.
The transverse sections of the weld passing through the weld nugget as
well as the similar section of the base plate were prepared by standard
metallographic procedure. Due to nature of dissimilar materials weld,
two stages etchant was used for etching. In the first stage of etching in
which 3% alcoholic nitric acid solution revealed microstructure of IF steel
side of welded materials. The microstructure of weld nugget, HAZ, and
austenitic stainless steel base metal side of welded materials was revealed
by using 10 ml nitric acids, 15 ml hydrochloric acid, 10 ml acetic acid
and two drops glycerin solution.
In the present work, optical examination of samples was carried out
using a Nikon DIC microscope. Photoshop computer program was used
to obtain microstructure profile of welded materials.