Role of precipitate-induced [formula omitted] twins on anisotropic fracture behavior in Mg-3Al-0.5Ce alloys

Abstract

Anisotropic fracture toughness (FT) in a hot-rolled Mg-3Al-0.5Ce magnesium alloy has been investigated using fatigue pre-cracked compact tension (CT) specimens with the notch (an)‖ to the rolling direction (RD) and transverse direction (TD). During testing, notable non-linear load–displacement behavior before peak load indicated significant crack tip plasticity. Thus, elastic–plastic FT (JIC) was evaluated and found to be 20.7N/mm and 15.8N/mm for an‖ to RD and TD, respectively. Long-aligned Al11Ce3 precipitates were present in this alloy within the elongated grain boundaries along RD. During FT testing, profuse 101¯2〈101¯1〉 extension twins (ET) with c-axis almost ‖ and lamellae morphology almost ⊥ to RD formed between these elongated precipitates, irrespective of the notch, an‖ to RD or TD. The ET lamellae ⊥ and ∥ to crack path lead to trans and inter lamellar crack for an‖ to RD and TD, respectively. Translamellar crack in an‖ to RD leads to comparatively high strain hardening, dislocation density, geometrically necessary boundaries, and grain refinement, indicating larger plastic energy dissipation and thereby has higher JIC than in an‖ to TD with interlamellar crack.