Microstructure and wear properties of surface composite layer produced by friction stir processing (FSP) in AA2024-T351 aluminum alloy

Abstract

Friction stir processing (FSP) is applied to create surface metal–matrix composites (SMMCs). This study aims to develop defect-free surface composites on AA2024 aluminum alloy with structural hardening (T351). It focuses on the effect of the number and direction of FSP passes on the particle distribution and microstructural modifications of the processed region, and their relationship with wear behavior of the composite layers. Results confirm that FSP can fabricate an SMMC with an acceptable homogeneous dispersion of particles. An electron backscatter diffraction (EBSD) technique is used to investigate the evolution of the grain size through the different regions of the friction stir-processed (FSPed) samples, indicating a significant grain size reduction in the nugget zone because of dynamic recrystallization. The surface properties are studied by measuring hardness and resistance to sliding wear. Although SMMC hardness at the nugget is similar to the base material, it demonstrates improved wear resistance. Under the sliding conditions of this study, specific wear rate is reduced significantly (between 24 and 40 pct) with respect to the as-received aluminum alloy. Moreover, the worn tracks indicate the same wear mechanisms operating simultaneously in both materials.