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Influences of Zr addition on microstructure and tensile properties at ambient and elevated temperatures have been investigated for precipitation-hardened Mg-3%Nd-0.6%Zn and Mg-3%Nd-0.6%Zn-0.2%Zr casting alloys. By the addition of Zr, the average grain size of α-(Mg) phase decreases remarkably. In T6-treated state, the Mg-3%Nd-0.6%Zn-0.2%Zr alloy shows higher YS, UTS and elongation at RT, 150°C and 200°C, compared to those of the Zr-free alloy. Better creep resistance is observed in the Zr-containing alloy at 175°C/120MPa condition, while its creep resistance becomes inferior to that of the Zr-free alloy at 215°C/80MPa and 250°C/40MPa conditions. The discrepancy between tensile and creep properties is discussed in relation to microstructural evolution.

Aluminum borate whisker (9(Al₂O₃)·(B₂O₃)) reinforced AS52(with and without strontium modification) metal matrix composites (MMC) were fabricated by the squeeze infiltration method. Creep rupture test was carried out at 150°C and 100 MPa condition. Results showed that Alborex reinforcement and modified polygonal shape Mg₂Si phase contributed to the enhancement of mechanical properties and creep resistance. Creep rupture time was increased 11% and minimum creep rate was decreased 17% in the composite. At the Alborex/matrix interface, uniform thin layer of MgO was formed. The initiation of micro-voids at the reinforcement/matrix or Mg₂Si/matrix interface was followed by their growth and coalescence to macro-cracks.