An algorithm for automatic identification of double twin variants in Mg alloys

101¯1−101¯2 double twins (DTs) are profuse in Mg alloys after rolling at a large reduction (>10%). In many cases, the secondary twins completely occupy the primary ones, causing difficulty in variant analysis. Here, we propose an algorithm for automatic identification of twin variants. This is applicable for the 101¯1−101¯2 DTs without knowing the primary twins. In addition, two kinds of stereographic projections are constructed to assist such variant selection. By this method, the variants of 67 DTs observed in a rolled AZ31 sheet are determined. Based on 14 sets of DTs with known primary twin orientations, the high efficiency and reliability of this proposed algorithm is verified. The reason for unreliable variant identification in two special cases is also discussed.