Effects of aluminium and sulphur on resistance spot weldability of steels

Spot weldability, as measured by the peel test, has been studied for galvanized sheet steels with variations in: (i) aluminium content in the zinc coating and (ii) sulphur content within the sheet steel. A response surface statistical analysis was employed, using a range of welding currents and times. The results indicate that the aluminium content, over the range 0.14 to 0.32 wt% may increase weldability by increasing the range of currents which will produce acceptable button sizes. However, very slight increases in sulphur level can reduce weldability, due to a combination of small spacing of sulphide inclusions and high hardness causing poor fracture resistance within the weld metal.