This book provides a practical understanding about the friction stir welding (FSW) of dissimilar alumiunium alloys. It considers about the effect of friction stir welding process parameters on the output responses tensile strength and hardness. Friction stir welding of aluminium alloys are playing a vital role in aerospace, automotive and marine applications. The objective of this investigation is to explore the effect of friction stir welding process parameters. The authors aim of this book is to provide extensive introduction regarding friction stir welding (FSW) of dissimilar alumiunium alloys on their mechanical properties and microstructure.