ScholarWorks@성균관대학교

초록

This study investigates the impact of grain size on the quality index of tensile properties for various levels of microporosity in commercial AZ series magnesium alloys, together with the relative contribution of damage evolution due to premature fracture of the Mg17Al12 phase to the quality index. To explore the effects of grain size in commercial Mg-xAl-1Zn alloys (where x = 3, 6, 9), 3-cavity multi-step molds with varying dimensions were utilized. Various microstructural characteristics were analyzed, and the volume fraction of the Mg17Al12 phase was quantified using X-ray diffraction with the internal standard method. The tensile strength and elongation decrease in a parabolic relationship with increasing microporosity, and the quality index by combination of ultimate tensile strength and elongation similarly exhibits a parabolic dependence on microporosity. Moreover, the quality index with respect to microporosity change can be described by a linear relationship based on the defect susceptibility concept in a logarithmic function. As the Al content in the alloy increases, the defect susceptibility coefficient rises with the increase of precipitation fraction, leading to improved maximum tensile properties under defect-free conditions. The increase of grain size by decrease of solidification rate induces the increase of defect susceptibility coefficient and maximum value. However, when considering the effective void area fraction, including premature fracture of the Mg17Al12 phase, the defect susceptibility coefficients and maximum values are lower compared to those based solely on microporosity. The relative contributions to the quality index decrease in the following order: microporosity, grain size, and precipitation fraction.

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