Effect of Start‐Up Levels on the Stress–Strain Field and Cracking Tendency during Direct‐Chill Casting of Magnesium Alloy AZ80

The stress field of magnesium alloy AZ80 billets at different start‐up levels in direct‐chill (DC) casting is calculated, including equivalent stresses, equivalent strains, sump depth, and temperature fields. The equivalent stresses and strains are highest in the center of the billet for all start‐up levels considered. A new criterion called cracking damage index (CDI) is used to predict the cracking susceptibility of the billets. At dangerous position of the billets, increasing start‐up levels is benefit for the decrease of CDI, equivalent stresses, and equivalent strains. Consequently, reasonably increasing start‐up levels can reduce the risk of cracks in the billets.