Abstract
Mechanical properties of two magnesium alloy based composites were studied. Composite with QE22 matrix reinforced by 20 vol.% of Al₂O₃ short fibres and hybrid composite (QE22 + 5 vol.% Al₂O₃ fibres and 15 vol.% SiC particles) were deformed in compression at temperatures from RT up to 400 °C. Two types of specimens were investigated - one with fibres plane oriented parallel to the stress axis and the other with perpendicular fibres plane orientation. Temperature dependences of the characteristic stresses σ₀₂ and σ_max were studied. Mechanical properties of composite materials were compared with the monolithic QE22 matrix alloy. Optical and scanning electron microscopy were used for study of microstructure of materials. Possible hardening and softening mechanisms are discussed. Main hardening mechanism in composite is probably the load transfer in which the part of the external load within the matrix is transferred to reinforcement. Increased dislocation density plays also important role. The cross slip and subsequent annihilation of dislocations cause very probably softening in the matrix. Local climb of dislocations in the vicinity of fibres supported by interfacial diffusion is probably important recovery mechanism.

Key words
composite, hybrid composite, hardening, softening

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