Microstructural, Tribological, and Corrosion Behavior of Alumix® 123 PM Alloys: Effects of Sizing Mechanical Surface Treatment

Abstract

This thesis investigates the effects of sizing mechanical surface treatment on the microstructure, wear behavior, and corrosion performance of AA2014 aluminum powder metallurgy (PM) alloys. Although sizing is a widely adopted post-sintering operation in the aluminum PM industry to improve dimensional tolerance and densification, its broader implications on functional properties remain underexplored in the existing literature. Through a comprehensive experimental approach, this work provides new insights into how varying sizing pressures influence the performance and long-term reliability of AA2014 PM alloys. Industrially sintered Alumix 123 premix powders, which are chemically equivalent to AA2014, were used in this study. A range of sizing pressures from 200 MPa to 400 MPa was applied to evaluate the effects of this surface treatment on surface morphology and height reduction. A series of characterization techniques including scanning electron microscopy (SEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and confocal laser scanning microscopy was employed to assess microstructural evolution and pore morphology. Tribological performance was evaluated using a ball-on-disk reciprocating wear test against a steel counterface. While sizing generally improved surface hardness, the wear response exhibited a complex dependence on applied sizing pressure. Lower-pressure sizing led to localized stress concentrations around pores, promoting crack propagation and delamination. In contrast, higher-pressure sizing (400 MPa) produced a more uniform misorientation distribution and enhanced resistance to wear. Electrochemical characterization was conducted to study corrosion behavior in chloride-containing environments. Open-circuit potential monitoring, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) revealed that high-pressure sizing improved corrosion resistance, mainly through effective pore closure. However, the presence of intermetallic phases introduced by plastic deformation increased susceptibility to localized corrosion. Long-term impedance monitoring over 144 hours revealed a transition from capacitive to diffusion-controlled behavior, with the appearance of inductive loops at higher sizing pressures, indicative of elevated localized attack risk. Overall, the results demonstrate that while sizing can enhance certain performance aspects of AA2014 PM alloys such as hardness, wear resistance, and corrosion resistance, the choice of sizing pressure must be carefully optimized based on specific application requirements. This work contributes to a deeper understanding of the interplay between mechanical surface treatment, microstructural evolution, tribological response, and electrochemical behavior in aluminum PM alloys, offering valuable guidance for the optimization of post-sintering processing strategies in powder metallurgy industry.