Influence of Solute Content and Secondary Phases on the Nano-Creep Behavior of Mg-Al-Ca Alloys

Abstract:

Mg-Al-Ca alloys with 1wt.% and 2 wt.% Ca additions (AC51 and AC52) were cast by the Permanent Mold technique. The microstructures of the as-cast Mg-Al-Ca alloys were observed by SEM with EDS analysis. The secondary phases were mainly precipitated along the grain boundaries and exhibited a continuous network microstructure for the AC52 alloy and a divorced microstructure for the AC51 alloy. EDS microanalysis showed that the solute (Ca) content in the grains of the AC52 alloy is higher than that in the AC51. A three-sided pyramidal (Berkovich) diamond indenter was used to characterize the local nano-creep behavior at room temperature within the α-Mg in grains. The nano-creep results showed that the AC52 alloy has better creep resistance than the AC51 alloy at all loads at room temperature. The creep exponent n, obtained from the indentation creep data, changes from 6.3 to 3.0 for AC51 alloy and from 6.6 to 3.2 for AC52 alloy at a critical stress (132 MPa for the AC51 and 145 MPa for the AC52). The transition in creep behavior at higher stresses is associated with a change in the deformation mechanisms.