1970 Volume 39 Issue 2 Pages 124-137
In this report, the breakdown of oxide layer between the sheets and the subsequent temperature rise will be discussed in detail.
Firstly, it is observed that there is a clear difference in the mode of temperature rise between mild steel and Al alloys under degreasing treatment. In the surface preparation for spot welding of Al alloys, degreasing and pickling treatment as well as degreasing was occasionally used. We compare the temperature pattern of degreased specimens with that of degreased and pickled specimens, and see how changes in surface preparation influence on the initial temperature rise. The temperature patterns of the degreased and pickled specimens have good reproducibility and symmetry. Scattering of weld strength is small, if degreasing and pickling treatment is applied to Al alloys.
An interesting fact is that the temperature rising region increases its area remarkably within one or two cycles at 60 Hz, which is a general character of spot welding of Al alloys.
Furthermore, it is found that a specimen of Al alloys (degreasing treatment) which is scratched with a scriber the checker on the contact surface between the specimens shows the tendency of temperature rise which closely resembles that of mild steel.
Lastly, from the result of many observations, contribution of a contact surface between the specimens to temperature rise is examined, and it becomes evident that this contribution is mainly caused by the plastic deformation on the contact surface, i.e., sheet separation. Meaning of contact resistance in spot welding is also discussed.