Segregation of Mg-6Gd alloy under natural convection: From macro solute distribution to micro dendrite growth

Abstract

Magnesium alloys are widely used in various fields such as automotive, aerospace, and electronics due to their low density, high specific strength, and high specific stiffness [1][2][3][4] . To improve alloy properties, zinc, aluminum, zirconium, and rare-earth (RE) elements are commonly added during casting process. In particular, RE elements can purify alloy melt, improve casting performance, and enhance heat and corrosion resistance. As typical high-strength heat-resistant Mg-RE alloys, Mg-Gd series alloys attract increasing interest, especially in aerospace and defense fields [5][6][7] . However, the significant density difference between Mg and Gd results in serious segregation defect, which deteriorates mechanical properties and shortens lifespan of castings.The segregation defect, occurring in a range over several orders of magnitude, is divided into macro-segregation and micro-segregation based on their scales (from micrometers to meters). The macrosegregation refers to the composition inhomogeneity that is comparable in size to the dimensions of the workpiece, and it arises from relative movement