New insights into hot tearing mechanisms of alloying elements based on ternary Mg-Gd-Y alloys

The hot tearing susceptibility (HTS) of GW56 (Mg-5Gd-6Y, wt.%), GW74 (Mg-7Gd-4Y, wt.%), GW93 (Mg-9Gd-3Y, wt.%), and GW91 (Mg-9Gd-1Y, wt.%) alloys is studied combining constraint rod casting method, thermodynamic calculation and numerical simulation. The HTS of these alloys is in the sequence of GW56 < GW93 < GW74 < GW91 alloys according to their crack areas at hot spots' vertical section being 0.41 mm(2), 2.77 mm(2), 3.60 mm(2), and infinity (totally cracked), respectively. The effects of alloy compostion on the crack initiation and HTS are relative with the temperature field and average grain sizes. The temperature-field cracking-suscepitibility coefficients (CSCT) of GW56, GW93, GW74, and GW91 alloys are 0.74, 0.85, 1.06, and 1.21, respectively, which perfectly describe the crack initiation and HTS sequence, illustrating that alloy composition affect HTS by temperature field. Moreover, the GW56 alloy's finer average grain sizes resulting from the higher Y content can further decrease its crack initiation temperature and HTS. The idea of studying temperature field-HTS relations could hopefully help clarify the role of alloying elements in HTS and establish a reasonable relation between alloying elements and HTS for multi-element alloys, which contributes to improving the hot tearing theories.