Different materials are spot welded together?

The immediate reply is yes, but it may be neither easy nor advisable in certain cases if brittle structures are produced by the different metals mixing in the molten nugget.

In exacting austenitic stainless steel and carbon steel is not generally spot welded jointly since the resulting nugget arrangement risks being hard and brittle, though it can be studied and modified using the Schaeffer diagram and particularly conceived warmth treating cycles.

Materials having widely dissimilar properties need that a warmth balance be achieved by compensation. The additional conductive material, electrically and thermally, have to be heated extra as it provides fewer resistive warmth, and the warmth is lost more easily by conduction.

An ordinary method uses an electrode of smaller face diameter and superior resistivity facing the additional conductive material, or by inserting a foil of poorly conductive material among them.

Concerning the number of sheets weldable with a single nugget, usual practice advices not more than three layers, although four sheets are infrequently spot welded jointly. In any case the ratio of the thickest to the thinnest sheet should not go beyond three.