Thermo-mechanical characterization of 2080 Al/SiCp composites by mechanical spectroscopy technique

Abstract

The thermo-mechanical behavior of a 2080 Al alloy (Al-3.6Cu-1.9Mg-0.2Zr) reinforced with 20% SiC particles was investigated by mechanical spectroscopy [1]. This technique consists in measuring mechanical loss and dynamic shear modulus spectra as a function of temperature, frequency, strain or stress amplitude, and can be used to provide information relating to microstructural evolution in the material, e.g., dislocation dynamics. The metal matrix composites (MMCs) used in this study were consolidated via powder metallurgy processing and extruded (Aluminum Company of America, Alcoa Center, PA). Three different composites, with varying SiC particle size, were investigated: 23 μm (F-280), 7 μm (F-600) and 5 μm (F-1000). The matrix microstructure was also varied by using two thermo-mechanical treatments: T6 (solutionizing at 493 ◦C for 2 h, water quenching and aging at 175 ◦C for 24 h) and T8 (solutionizing at 493 ◦C for 2 h, water quenching, cold rolling to induce 5% reduction in thickness, and aging at 175 ◦C for 24 h). A comparison of the precipitate morphology and distribution revealed a finer and more homogeneous precipitate distribution in T8 specimens (Fig. 1a and b). The quenching step promotes the formation of a high dislocation density near the interfaces to accommodate the thermal mismatch between matrix and reinforcement. Because dislocations are nucleation sites for precipitation, the final T6 microstructure shows an inhomogeneous precipitate distribution. On the other hand, as a result of the rolling step in the T8 process, a uniform dislocation distribution is obtained in the matrix that results in a homogeneous distribution of precipitates after aging. A detailed study of the tensile and fatigue properties of 2080/SiCp composites can be obtained elsewhere [2, 3]. In these studies [2–4], it was found that rolling of composites reinforced with the largest particle size (F-280 SiC) produced particle cracking and, thus, strength values below that of the base alloy. In composites reinforced with smaller particles, T8 thermomechanical treatment resulted in somewhat higher