Effect of FSSW parameters on grain size and hardness of 6061-T6 Al indissimilar joining to DP590 dual phase steel

Dissimilar 6061Al alloy/DP590 dual phase steel joints were fabricated using friction stir spot welding (FSSW). Microstructural examinations by optical and scanning electron microscopy exhibited the occurrence of dynamic recrystallization in the stir zone of aluminum and steel sides that lead to refined grains. Five distinct regions in the stir zone of aluminum (having different mean grain size from ~ 1.5 to 12 μm) were found as a function of process parameters. The grain size of these distinct regions was found to increase with increasing of tool rotation speed. Inaddition, the grain size of these distinct regions decreased with increasing plunge and retraction rates. However, with increasing dwell time, the mean grain size showed increasing; this was associated with near homogenous grain size distribution. The process parameters were found to have relatively less effect on variation in hardness values of the aluminum side.

Keywords:

Friction stir spot welding , Dissimilar joint , Aluminum alloy , Grain size , Micro-indentation hardness