The dissimilar welding of steel and aluminium alloys has attracted widespread attention in the
automobile industry to make lighter automobile parts for better fuel efficiency and reduced
emissions. The fusion welding processes are not suitable for dissimilar welding for various
reasons, such as formation of aluminium oxide, wider heat-affected zone (HAZ), hot cracking,
and formation of intermetallic compounds (IMCs). Friction stir welding (FSW) is a solid-state
welding process that can overcome these issues and is also known for forming fine and
equiaxed recrystallized microstructure. The current research focuses on the dissimilar FSW of
aluminium alloy (AA6082-T6) and dual-phase steel (DP780) of different thicknesses in lap
configuration for minimizing tool wear and IMCs formation. Different process parameters,
such as tool rotation speed, transverse speed, plunging depth, and tool tilt angle, were
considered to establish the process parameter window based on microstructural analysis and
mechanical property evaluation. The thickness and types of intermetallic compounds formed
at the interface play a significant role in achieving a joint with optimum performance. Higher
rotational speed promoted the formation of thicker IMCs layer at the lap joint interface that
appeared to have a negative effect on lap shear strength. Tensile shear fracture took place at
hook on retreating and this supported the effects of IMCs layer on shear strength. FSW refined
the grain size. The average grain size in the stir zone was 2.53μm and 3.78μm in the hook zone
compared to 25μm for the base metal of AA6082. For the DP steel side these were 1μm , 1.7μm
and 2.9μm respectively.