Influence of tool rotation speed on grain refinement,precipitation behavior,and corrosion behavior of friction stir processed AA6063-Cu composites

Abstract

This current investigation studies the influence of different tool rotation speeds (700, 800, 900, and 1000 rpm) on the microstructure, precipitation, and corrosion behavior of AA6063-Cu composites fabricated via friction stir processing (FSP). Microstructural analysis using optical microscopy, Scanning Electron Microscopy (SEM)-Energy Dispersive Spectroscopy (EDS), and XRD revealed significant grain refinement, improved copper distribution, and improved phase transformation at 900rpm. The finer grain size of 4.9 ± 3.0 µm and the most homogenous reinforcement dispersion were achieved at this speed owing to optimized dynamic recrystallization. SEM-EDS confirmed enhanced precipitate fragmentation and uniformity, minimizing microstructural defects. XRD analysis exhibited increased Al₂Cu and Al₂CuMg phase formation at 900 rpm, promoting strengthening mechanisms. Corrosion resistance, investigated through weight loss, open circuit potential, and Tafel polarization tests, indicated the highest corrosion resistance at 900 rpm, with the lowest weight loss (0.241 ± 0.119 mg), highest pitting potential (0.253 ± 0.104 V) and most positive corrosion potential (0.313 ± 0.179 V). The refined microstructure improved passivation, reducing localized galvanic interactions. Lower speeds (700 rpm) led to poor Cu distribution and increased corrosion rate, while excessive heat at higher speeds (1000 rpm) caused grain coarsening and localized Cu segregation, negatively impacting corrosion resistance.