Dynamic properties of silicon carbide hollow particle filled magnesium alloy (AZ91D) matrix syntactic foams

Metal matrix syntactic foams of very low density (0.97 g/cc) were prepared using silicon carbide hollow particles dispersed in a magnesium alloy (AZ91D) matrix. The composite was evaluated for quasi-static and high strain rate (1330-2300/s) compression and dynamic mechanical properties. The compression test results show that the peak stress and the elastic energy absorbed were strain rate sensitive and the values at high strain rates were up to 1.5 times higher than the quasi-static values. The failure mechanisms of syntactic foams at high strain rates were observed to be failure of the hollow particles, plastic deformation of the matrix and fracture of precipitates that are oriented along the grain boundaries of the alloy. Extensive dynamic mechanical analysis was conducted under the conditions of (a) temperature variation at a constant frequency and (b) frequency variation over a wide range of temperatures to conduct time-temperature superposition (TTS). The damping parameter of the composites was observed to be higher than those of the matrix alloy at all temperatures. The TTS principle allowed extrapolating the material behavior over a wide frequency range from a limited frequency dataset range of 1-100 Hz. Such very low density syntactic foams can be useful in marine vessel and aerospace structures for weight saving. In addition, composites in this density range can directly compete with polymer matrix composites with added advantage of dimensional stability and mechanical property retention at higher temperatures.