Dislocation Mechanics and Interfacial Grain Refinement in Dissimilar Metal–Ceramic Friction Welds: A Case Study on AA6061/Alumina-25 wt.% YSZ

Abstract

This study explores the fundamental mechanisms governing dislocation behavior and interfacial grain refinement in dissimilar metal–ceramic friction welds, using AA6061 aluminum alloy and an alumina–25 wt.% yttria-stabilized zirconia (YSZ) composite as a representative system. Joints were fabricated via rotary friction welding across a range of rotational speeds (630-2500 rpm) under constant axial force and friction time. Quantitative microstructural analysis was conducted using X-ray diffraction (XRD) peak profile broadening, supported by field emission scanning electron microscopy (FESEM), Vickers microhardness testing, and four-point bending strength measurements for evaluating the flexural performance of the joint. Results revealed that increasing interfacial heat flux led to elevated dislocation densities, intensified strain anisotropy, and refined grain structures due to dynamic recrystallization. Dislocation densities ranged from 8.6 × 1015 to 12.7 × 1015 m−2, while crystallite size decreased inversely with increasing thermal input. The addition of bending strength data allowed the establishment of a clear processing–microstructure–property relationship, demonstrating that joints welded at 630 rpm exhibited improved flexural strength and bonding integrity despite lower hardness values. This was attributed to optimized thermo-mechanical conditions, even though higher rotational speeds produced greater hardness. Modified Williamson–Hall and Hall–Petch analyses confirmed that dislocation-mediated strengthening mechanisms dominated interfacial microstructure evolution. These findings offer transferable insights into the role of thermomechanical energy in tailoring dislocation structures and grain morphology in metal–ceramic joining applications.