Yuan Guangyin

Effects of bismuth and antimony additions on the microstructure and mechanical properties of AZ91 magnesium alloy

The effects of bismuth and antimony additions on the microstructure and mechanical properties of AZ91 alloy have been studied. Results show that a small amount of bismuth or antimony additions to AZ91 increases the yield strength and creep resistance significantly at elevated temperatures up to 200°C. The highest creep resistance has been obtained from the alloy with combined additions of bismuth and antimony. The activation energies of the steady-state creep for AZ91-based alloys studied were close to that of pure magnesium self-diffusion, indicating that dislocation climb is responsible for the creep mechanism under the present conditions. Microstructural observations reveal that the additions of bismuth or antimony have the effect of refining the b (Mg17Al12) precipitates in as-cast alloys and suppressing discontinuous precipitation of the b phase effectively during the aging process. Some rod-shaped Mg3Bi2 or Mg3Sb2 particles distributed mainly at grain boundaries have been observed in the alloys with bismuth or antimony additions. Both Mg3Bi2 and Mg3Sb2 have a high thermal stability and play important roles in improving creep resistance of the alloys at elevated temperatures.

Microstructure and mechanical properties of Mg–Zn–Si-based alloys

Abstract A new type of magnesium alloy based on Mg–Zn–Si system has been developed for automobile application. The solidification process, microstructure, mechanical properties and creep resistance of the new alloy have been studied. Results show that the Mg–6Zn–1Si alloy has good comprehensive mechanical properties and its creep resistance is better than that of AZ91 alloy. Proper additions of Ca were found to be efficient in refining the microstructure of Mg–6Zn–1Si alloy. A morphological change in Mg 2 Si particles from coarse Chinese script shape to a small polygonal type was also observed. The modification mechanism of Ca is polygonal type Mg 2 Si particles nucleate from CaSi 2 particles. Such improved microstructure of the Mg–6Zn–1Si–0.25Ca alloy results in significant improvement in tensile properties and creep resistance as compared to the Mg–6Zn–1Si base alloy.

High temperature deformation behavior of permanent casting AZ91 alloy with and without Sb addition

AbstractThe elevated temperature deformation behavior of permanent cast magnesium alloy AZ91 with and without Sb addition has been investigated using slow strain rate (5.0 × 10−4s−1) elevated temperature tensile and constant load creep testing at 150°C and 50 MPa. The alloy with 0.4 wt% Sb showed a higher elevated temperature tensile strength and creep resistance due to the formation of thermal stable Mg3Sb2 precipitates and a smaller microstructure as well as the suppressing of the discontinuous precipitation. Plastic deformation of AZ91 based alloys is determined by motion of dislocation in basal plane and non-basal slip systems. The dislocation motion in a slip system is influenced by temperature, precipitates and other lattice defects. Dislocations jog, grain boundaries and/or precipitates are considered as obstacles for moving dislocations. The

Structure refinement founding process of magnesium alloy containing Mg2Si reinforcing phase

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Mechanical Properties and Microstructure of Mg-Al-Zn-Si-base Alloy

deformation twinning were founded in the creep process by TEM. Cross slip of dislocations was taken into account as the main softening mechanism for permanent cast AZ91 alloy during elevated temperature deformation process.