Creep resistance in magnesium alloys and their composites

A considerable improvement in the creep properties of magnesium alloys can be potentially achieved by non-metallic reinforcement (metal matrix composites - MMCs). This paper provides a comparative report on experiments which were conducted on the two representative magnesium alloys (AZ91 and QE22) and their composites in order to evaluate the creep properties and to clarify the direct and indirect strengthening effects of reinforcement in creep. A comparison between the creep characteristics of squeeze-cast AZ91 and QE22 magnesium alloys reinforced with 20 vol.% Al2O3 short fibres and unreinforced matrix alloys shows that the creep resistance of the reinforced materials is considerably improved compared to the monolithic alloys. By contrast, the investigations of the creep behaviour of a particulate QE22-15 vol.% SiC composite prepared by powder metallurgy and the squeeze-cast hybrid QE22 matrix composites have revealed no substantial increase in the creep strength of the composite compared to the matrix alloy and AZ91 matrix composites. These results indicate a paramount importance of the choice of the composite matrix alloy and the reinforcement used.