Abstract
Frictional heat generation, in Friction Stir Spot Welding of steels, was assessed by producing welds with pinless tools. In order to analyse the influence of base material characteristics on heat generation, spot welds were produced, using varied process parameters, in DC01, DX51D and HC420 LA steel sheets (1 mm thick). Uncoated and coated sheets, with galvanised films of different thicknesses, were tested in order to assess the influence of surface properties on heat generation. The welding thermal cycles were measured using thermography and hardness measurements were done to evaluate the influence of the maximum temperature, maintenance time and cooling rates on welds properties. It was found that the main factors influencing the frictional heat generation are, by order of importance, the tool diameter, the tool rotation speed and the presence of low melting point coatings. Differences in frictional heat generation, for the different base materials, were only registered when welding with a 10 mm diameter tool. The analysis of the average welds hardness enabled to conclude that the hardness increase in the weld region, relative to the base material, is determined by the maximum temperature reached during welding and by the grain size of the base material.
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