Anelastic and Elastic Measurements in Aluminum Metal Matrix Composites

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Abstract
The piezoelectric ultrasonic composite oscillator technique (PUCOT) has been used at temperatures up to 638 K and at 80 kHz to measure dynamic Young's modulus E, mechanical damping or internal friction Q−1 and strain amplitude ϵ in Al/SiCw and Al/Sicp. For four adjacent specimens from one sheet of 6061 Al/SiCp E-values varied in the range 114–119 GPa at room temperature. The composition dependence of the modulus followed E = 68.6 + 2.2X with R = 0.95 (E is in GPa and X in volume percent SiC). The temperature dependence of the dynamic modulus followed E = 138.7 − 0.11T with R = 0.98 (E is in GPa and T in Kelvin). The amplitude dependence of Q−1 for 6061 Al/SiCw revealed a damping peak at ϵ = 10−6. An analysis of the internal friction data in terms of a damping theory yielded values for the minor pinning length of dislocation lines and the density of mobile dislocations. The results are discussed in terms of the microstructure.