Microstructural evolution and mechanical behavior of pre-compressed ZK60 magnesium with annealing

In this study, the properties of rolled ZK60 magnesium alloys were improved by pre-compression with annealing at different temperatures (200, 250, 300 and 350 degrees C). Pre-compression can induce dense twins in the materials, and subsequent annealing at increasing temperature leads to a transition from a cross-twinned structure to significant recrystallization. For tensile properties, the samples annealed at 300 degrees C and 350 degrees C showed softening, with a yield strength below 150 MPa. In contrast, the samples annealed at 200 degrees C and 250 degrees C had a yield strength of up to 200 MPa because of the hindering effect of the nanoscale second phase at the twin boundaries. In lowcycle fatigue tests, the samples annealed at 350 degrees C had the longest fatigue life, about 3100 cycles at 0.4 % strain amplitude, while those at 200 degrees C had the shortest life of about 2500 cycles, with opposite trends in cyclic stress levels. Half-life interruption tests reveal that fatigue cracks initiate at pre-twin boundaries for samples annealed at 200 degrees C, while the combined effect of basal slip and tensile twinning promotes the formation of microcracks in samples annealed at 350 degrees C.