Abstract
The microstructure evolution of β -Mg 17 Al 12 in as-cast Mg-8.0Al-1.0Nd-1.0Gd alloy during 420 °C solution and then 210 °C aging treatment was investigated. The results indicate that the discontinuous precipitation (DP) distributes along grain boundaries, and the needle-shaped continuous precipitation (CP) with crystallographic orientation relationship (OR) of [ 1 ‾ 101 ] M g / / [ 33 4 ‾ ] β , ( 0 1 ‾ 11 ) M g / / ( 313 ) β , ( 1 ‾ 01 1 ‾ ) M g / / ( 3 3 ‾ 0 ) β are the main intragranular precipitated phases. Compression creep tests of the specimens were carried out at a stress of 60 and 90 MPa at 150 and 180 °C. The microstructure observation reveals that the considerable 86° { 10 1 ‾ 2 } tension twins assist in the creep deformation for all crept specimens. The solid solution treated alloys achieve excellent creep resistance compared with the aged alloys owing to the strong co-segregation between Nd and Gd in α-Mg and β -Mg 17 Al 12 at 180 °C/90 MPa. However, the creep properties of the aged alloys are superior to that of the solid solution treated alloys at 180 °C/60 MPa and 150 °C/90 MPa, which can be attributed to the inhibited dislocation slipping via needle-shaped and spherical CP. In addition, increasing the CP region and reducing recrystallized grains could improve the creep resistance. Combining the micro-morphology of creep structure and creep parameters ( n , Q ), the dominated creep mechanism for solid solution treated alloys is grain boundary sliding ( n = 1.5–1.8, Q = 32–36 kJ/mol), while the dislocation climb combined with grain boundary diffusion ( n = 4–6, Q = 60–80 kJ/mol) is regarded as the controlling creep mechanism for the aged Mg-8.0Al-1.0Nd-1.0Gd alloys.
Published Version
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