Effect of Grain Refiners and Casting Thickness on the Microstructure Development and Mechanical Properties of DSC‐Cast AZ31B Magnesium Strips**

Abstract This study aims at enhancing subsequent hot rolling properties of AZ31B by reducing the grain size using grain refinement agents (C, SiC, AlSr10, and AlTi5B1) as well as different cast thicknesses. The AZ31B magnesium alloy samples were cast in a direct strip casting process (DSC). The microstructure investigations such as the grain size measurement and the distribution of the secondary precipitates were characterized using light optical microscope (LOM) and scanning electron microscope (SEM). Furthermore, the mechanical properties were determined using tensile and Vickers hardness test. Adding a certain amount of each refiner to an AZ31B alloy leads to a significant reduction of the grain size in the cast structure. As a result of the higher cooling rate at the bottom side the grain size is reduced in comparison to the upper side (convection heat transfer with the protecting gas) across the strip thickness. The minimal grain size was found when using AlTi5B1 master alloy where the grain size is (67 ± 5) µm at the bottom side, whereas it reaches (110 ± 10) µm upside of the strip. At the bottom side and center of the strip can be observed a homogeneous precipitates distribution and similar precipitation rate, size, and distribution in comparison to the upperside. Using SiC powder and AlTi5B1 master alloy refining agents the maximal hardness values compared to the other types of agents were reached. The hardness profile confirms the grain size results considering the temperature gradient across the cast thickness. However, optimum tensile properties were found between bottom side and middle layer.