High-temperature tensile properties and deformation mechanism of polycrystalline magnesium alloys with specifically oriented columnar grain structures

A Mg-4.78Zn-0.45Y-0.10Zr (wt%) alloy with specifically oriented columnar grain structures (crystal growth direction < 10(1) over bar0 >) was prepared using directional solidification. The columnar grain structures possessed parallel growing primary arms and straight longitudinal grain boundaries. The results from an electron backscatter diffraction analysis demonstrated that the angle between the c-axis and the growth direction was 74-87 degrees. As the tensile tests were performed along the (01(1) over bar0) growth direction, the Schmid factors for the < a > cylindrical and < c + a > conical plane slips were as high as 0.45. When the tensile test temperature was 300 degrees C, dynamic recovery was observed and the < a > cylindrical, < a > conical, and < c + a > conical slip systems were all activated. This phenomenon, together with the high orientation consistency between the adjoining grains, resulted in an elongation increase up to 42%. Fractography of the Mg alloy revealed extended or parabola-shaped dimples with specifically oriented columnar grain structures, suggesting good ductility for this material.