Abstract
High-temperature strengthening mechanisms in various discontinuous magnesium metal matrix composites were examined by performing a close comparison between the creep behaviour of these composites and that of their selected magnesium matrix alloys, AZ91 and QE22. It was found that the magnesium AZ91 and QE22 alloys reinforced with 20 vol.% alumina short fibres exhibit an improved creep resistance arising mainly from the load transfer effect and the existence of a threshold stress, respectively. The creep behaviour of 15 vol.% silicon carbide particle-reinforced magnesium AZ91 and QE22 alloys revealed that the creep resistance of the AZ91 alloy was increased through particle reinforcement; by contrast, the creep resistance of the powder reinforced QE22 alloy was deteriorated. A comparison between the creep characteristics of unreinforced squeeze-cast AZ91 and QE22 magnesium alloys and their hybrid composites reinforced with 8 vol.% carbon short fibres and 15 vol.% SiC particulates indicates the dominant importance of the choice of the composite matrix alloy and the reinforcement used.

Key words
magnesium alloys, composites, creep properties testing, structure, fibres, interfaces

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