Influence of microstructure on creep strength of MRI 230D Mg alloy

The low density of magnesium alloys makes them attractive for lightweight constructions. However, creep remains an important limitation of Mg alloys. To gain a more detailed understanding of the correlation between microstructure and creep properties in Mg alloys, creep tests have been performed on MRI 230D samples featuring various microstructures. For this purpose, the MRI 230D Mg alloy has been thixomolded into a plate with four steps of different height, which gives different microstructures in each step due to different cooling rates. With an increase in cooling rate (e.g., a decrease in step height) the interconnectivity of the eutectic phase increases at virtually constant volume fraction. The creep strength is found to decrease with decreasing interconnectivity of the eutectic phase. This implies that a eutectic phase morphology, which is highly interconnected, benefits the creep properties and should therefore be one goal in further developments for creep resistant Mg alloys.