Effect of nanoparticles adhesion and multipass friction stir processing on metallurgical properties of AZ91D magnesium alloy

Abstract

In this work, the effect of SiC and Al₂O₃ nanoparticles and multipass friction stir processing (MPFSP) on the metallurgical properties of AZ91D was carefully investigated and observed a homogenous dispersion of nanoparticles and refined grain size in the processed zone. The presence of the Mg₁₇A_l12 intermetallic compound in the MPFSP of AZ91D with SiC and Al₂O₃ nanoparticles has significant implications for the material’s properties. Mg₁₇Al₁₂ is a typical intermetallic phase formed in magnesium alloys and can profoundly affect thermal, microstructural, and mechanical properties. The intermetallic phase can improve the processed region’s strength due to its inherent hardness and solid solution strengthening effect, resulting in enhanced tensile properties and hardness. As the FSP passes increased, the tendency for reinforcement agglomeration diminished. Before undergoing MPFSP/(SiC + Al₂O₃), the base metal AZ91D exhibited an ultimate tensile strength (UTS) of 208.36 MPa and a strain percentage 15.72. After implementing MPFSP/(SiC and Al₂O₃) on AZ91D, the UTS consistently increased with each FSP pass. This effect was evident at the fourth FSP pass, yielding a higher UTS of 284.35 MPa. In essence, this process facilitated a marked enhancement in the metallurgical properties of AZ91D, signifying the efficacy of the MPFSP approach when combined with reinforcement particles. The hardness value was higher when the indenter engaged with Mg₁₇Al₁₂ than α-Mg. The SZ of 4-pass FSP (Al₂O₃+SiC)/AZ91D reached a maximum hardness value of 69.37 HV, while single-pass FSP (Al₂O₃)/AZ91D exhibited a minimum value of 64.89 HV.

Keywords:

• nanoparticles
• microstructure
• multipass FSP
• tensile properties
• microhardness

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