Development of heat-resistant magnesium alloys with superior strength by utilizing fine lamellar microstructure

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The creep behavior of hypoeutectic Mg1-xCax (x = 2.8, 8.7, and 14.8 mass%) cast alloys was investigated at 473 K under stresses between 30 and 60 MPa. The microstructure of the alloys is characterized by the discontinuously distributed primary α-Mg phase in a continuous eutectic fine lamellar structure consisting of α-Mg and C14-Mg2Ca phases. The creep curves of the alloys exhibit three stages: a normal transient creep stage, a minimum creep rate stage and finally an accelerating stage. The decrease in creep rate during the transient stage becomes pronounced and the onset of the accelerating stage is delayed with increasing calcium concentration. The stress exponent of the minimum creep rate is four for each alloy for stresses below the yield stress. The creep of the alloys is controlled by the high-temperature climb of dislocations. The effect of the eutectic fine lamellar structure on creep strength is prominent when the volume fraction is below 50%.