Friction stir welding of 6061 aluminum alloy: Process design strategies for joint microstructure and mechanical performance enhancement

Friction stir welding (FSW) has emerged as a pivotal solid-state joining technology for the 6061 aluminum alloy in aerospace, automotive, and rail transportation applications, offering superior joint quality while avoiding fusion welding defects like solidification cracking and alloying element vaporization. Despite these advantages, FSW joints still exhibit performance limitations, including suboptimal strength, heat-affected zone softening, and brittle intermetallic formation, especially in dissimilar material combinations. Recent research has focused on developing comprehensive process design strategies to enhance both microstructural characteristics and mechanical properties of FSW joints in 6061 aluminum alloy. These strategies span the entire welding process chain, from pre-weld material treatments and surface modifications to in-process auxiliary strengthening involving external field assistance and advanced cooling techniques, as well as post-weld thermal treatments. This review systematically categorizes recent advances in these strategies, highlighting the integration of emerging materials, technologies, and methodologies into FSW practice. Furthermore, it critically evaluates unresolved scientific and technical barriers while projecting future research directions. By establishing a comprehensive process-microstructure-property framework, this work aims to promote the development of high-performance 6061 aluminum alloy FSW joints for industrial applications.