Mechanical-stress relaxation in magnesium-based composites

In metal matrix composites (MMCs), the metal matrix is exposed to plastic deformation and damage accumulation in the region close to the reinforcements, following mechanical or thermal stresses. Mechanical spectroscopy has been used to study interface stress–relaxation in Mg–2%Si based MMC reinforced with either C aligned long fibers or Al2O3 short fibers. In the Al2O3/Mg–2%Si composite, the damping capacity is low; the mechanical stresses are relaxed by damage accumulation at interfaces. The elastic shear modulus decreases until rupture, when the composite is cycled at high vibration amplitude. On the contrary, the damping capacity is high in the C/Mg–2%Si composite and the interface stresses are relaxed by reversible motion of dislocations in the matrix, leading to a strong increase in fatigue resistance.