Solid-state joining of powder metallurgy Al-Al2O3 nanocomposites via friction-stir welding: Effects of powder particle size on the weldability, microstructure, and mechanical property

Abstract

Solid-state butt-joining of powder metallurgy (PM) fabricated Al-Al2O3 nanocomposites was assessed using friction-stir welding (FSW), in which the PM materials were prepared from aluminum powder with different particle size distributions of <9 μm, <63 μm, and <250 μm. After establishing a suitable working window in terms of rotational speed (w) and traverse velocity (v), the effects of initial powder particle size on weldability, microstructure and mechanical properties joints were studied. The joint quality was assessed by macro cross-sectional examinations, where deterioration occurs due to defects at the weld root with increasing traversal speed. A defect-free friction stir weld with a more homogenous cross-section is produced for all powder sizes using FSW parameters of w = 1200 rpm and v = 300 mm/min. The native amorphous aluminium oxide (am-Al2O3) layer on the powder is redistributed and partially transformed to crystalline γ-Al2O3 nanoparticles depending on FSW parameters which is revealed by transmission electron microscopy (TEM). Detailed electron back-scattered diffraction (EBSD) analysis indicates the formation of a fine equiaxed grain structure in the range of 1.5–3.7 μm as a function of initial aluminum particle sizes and FSW parameters with a mixture of ideal random and shear components as the dominant texture. Transverse tensile and indentation hardness testing revealed no significant changes in mechanical properties for the composite weld, with ductile fracture occurring in the base metal with hardening only occurring in the stir zone for the powder particle size.