Effect of nanoparticles and multipass friction stir processing on microstructure and mechanical properties of AA7475

Abstract

The base metal, AA7475, initially contained nanoparticles of SiC within a coarse dendritic structure. The multipass FSP (MPFSP) process successfully broke these coarse and dendritic clusters, resulting in a homogenous microstructure in the stir zone. This inhibition led to a continual reduction in grain size. The presence of SiC reinforcement particles also played a role in imbvproving the microstructure and tensile properties of the MPFSP/SiC composite. The optimal process parameters for MPFSP/SiC on AA7475 were identified as a rotational tool speed of 1500 rpm, welding speed of 40 mm/min, and a tilt angle of 2°. As the number of FSP passes increased, the agglomeration of SiC particles reduced, further enhancing the dispersion. Before MPFSP/SiC, the base metal AA7475 exhibited a tensile strength of 410±5 MPa and a % strain of 10.83±0.3. However, after MPFSP/SiC, the tensile strength increased with the number of FSP passes. The highest tensile strength of 521±8 MPa was observed after the 5 th pass of FSP. This increase in tensile strength was attributed to the presence of fine grains formed through the DRX mechanism during the MPFSP process.