Mechanical and metallurgical characterization of SiC-reinforced friction stir welded joints of dissimilar AZ91D and AA6061-T6 metals Mechanische und metallurgische Charakterisierung von SiC-verstärkten rührreibgeschweißten Schweißverbindungen aus AZ91D und AA6061-T6

Abstract

The friction stir welding (FSW) of dissimilar metals, such as aluminum AA6061-T6 and magnesium AZ91D, presents challenges due to their limited metallurgical compatibility and the tendency to form brittle intermetallic compounds (IMCs), limiting the mechanical performance of the joints. These challenges limit their wider application in weight-sensitive industries such as the aerospace and automotive sectors. To overcome this, the present work investigates the influence of process parameters on the mechanical and microstructural characteristics of dissimilar friction stir welding joints reinforced with silicon carbide (SiC) nanoparticles, using a groove arrangement in the contact surfaces to minimize nanoparticle dissipation. A process insight was established to identify the optimal parameters for friction stir welding. Silicon carbide nanoparticles were incorporated into the weld samples to refine the microstructures of welded joints. The mixing behaviour, formation of intermetallic compounds, microstructures of the weld, and mechanical properties of the weldments corresponding to various welding process parameters, such as tool rotation speed (TRS) and traverse speed (TS) at constant tool tilt angle (TTA) of 2°, were investigated. Results revealed that SiC reinforcement effectively refined the microstructure through a pinning mechanism and promoted challenging intermetallic phase formation. Among the tested parametric combinations, the joint fabricated at 700 min⁻¹ tool rotational speed and 25 mm/min traverse speed exhibited the highest tensile strength of 115 MPa, with a strain of 6.6 % and joint efficiency of 52.51 %, and a microhardness of 88.9 HV 0.1, representing a significant improvement over the unreinforced joint. These findings demonstrate the potential of SiC nanoparticle reinforcement and provide practical insights for achieving enhanced-strength, defect-free dissimilar aluminum/magnesium welds.