Effect of friction stir processing and subsequent annealing on microstructure and mechanical properties of a metastable β-Zr alloy

In this work, an effective method to improve the local mechanical properties of β-ZrTiAlV alloy via friction stir processing (FSP) was proposed. A good strength-ductility synergy with high yield strength (896 MPa) and elongation (18.3%) was achieved in the FSPed alloy compared to that of the base material (BM) with low elongation (2.9%) owing to the grain refinement by dynamic recrystallization (DRX) during FSP and the transformation induced plasticity (TRIP) effect caused by deformation-induced α′ martensite transformation. Moreover, FSPed alloy can be further strengthened by annealing treatment. A higher yield strength (1003 MPa) was obtained following 650 °C anneal while a higher ultimate tensile strength (1276 MPa) was acquired in 600 °C annealed samples. The microstructure-properties relationship and underlying deformation mechanisms were also investigated.