A High-Damping Magnesium Matrix to Limit Fatigue in Composite

Abstract

Two phase composites, which consist in a magnesium matrix reinforced with either Mg₂Si, C, Si C aligned long fibres or A1₂0₃ short fibres have been processed. These lightweight composites exhibit a damping capacity which is 10 to 100 times higher than the one of an industrial magnesium cast alloy such as AZ63 and a high Young's modulus. The high damping capacity is interpreted as due to dislocation dissipative mechanisms in the Mg matrix, and the good mechanical properties as due to the fibres. Moreover, the mechanical loss spectra obtained by mechanical spectroscopy are modified by transitory phenomena which appear during thermal cycling. The transient response informs us about the thermal stress relaxation mechanism occurring at ceramic-metal interfaces and thereby about the interface quality and the fatigue behaviour. The comparison between the experimental results and a model of dislocation motion allows one to interpret the relaxation mechanism as due to dislocations which dissipate energy through vibrations, which are controlled by a solid friction mechanism. Furthermore, the composites do not exhibit thermal fatigue over more than 100 thermal cycles (100 K-500 K).