Strengthening in Mg–Li matrix composites

Mg–xLi (x = 4, 8, 12) matrix composites reinforced with short δ-alumina (Al2O3) fibres were manufactured by the pressure infiltration process. Mg–8Li composite reinforced by SiC was prepared by the powder metallurgical technology. With increasing lithium content, the Mg–Li matrix exhibits phase transitions from hcp, to hcp + bcc and to bcc phase. Compression tests of cylindrical composite samples were carried out at temperatures between 20 and 300 °C. The deformation behaviour of composites is significantly influenced by the structure of matrix and the preparation technique. The results obtained revealed that the flow stresses of the composites are substantially higher than those of unreinforced alloy. The reinforcing effect of fibres and particles decreases with increasing temperature. Different contributions to the strength of composites were evaluated. The shear stresses at fibre/matrix interface were of greatest importance in the fibres reinforced composites, while in the particles reinforced composites, the small grain size plays the crucial role. The contribution resulting from the increased dislocation density is also important.