Effect of crystal grain orientation on grain boundary fracture in peak-aged polycrystalline Al–Mg–Si alloys

Abstract

Grain boundary fracture was studied in tensile test for peak-aged balanced and excess Si Al–Mg2Si alloys. The route of crack propagation for intergranular fracture in these alloys was considered by Schmid factor (S.F.) and stress transmission factor (Nij) by crystal orientation to tensile axis. The texture of these alloys before tensile test was recrystallized textures, and there were no significant difference of initial texture between these alloys. Fractured grain boundaries has been classified into the following four groups:· Group A: Larger difference in S.F. than 0.05 and higher Nij than 0.5.· Group B: Larger difference in S.F. than 0.05 and lower Nij than 0.5.· Group C: Smaller difference in S.F. than 0.05 and higher Nij. than 0.5.· Group D: Smaller difference in S.F. than 0.05 and lower Nij than 0.5.The cracking was influenced by the grain boundary with larger difference in S.F. and lower Nij in the balanced alloy. The propagation of cracks was influenced by grain boundaries of group B, C, or D with the angles from 60° to 90° to the tensile axis. The cracking and propagation of cracks occurred all together in excess Si alloy at the same time as beginning of tensile test, and grain boundaries in this alloy mostly fractured in the group D with the angle of 30°–90° to the tensile axis.