摘要
The fatigue behavior of four extruded Mg-Y-Zn alloys containing different volume fractions of long-period stacking ordered(LPSO)grains was investigated through a comparative study combining experiments and crystal plasticity finite element simulations.Strain controlled low-cycle fatigue experiments were conducted at different strain amplitudes and revealed a limited cyclic hardening in Mg_(89)Zn_(4)Y_(7)alloy or softening in Mg_(99.2)Zn_(0.2)Y_(0.6)and Mg_(97)Zn_(1)Y_(2)alloys.A decrease in the fatigue life against the plastic strain with the increase in LPSO phase volume fraction was observed and was related the limited ductility of extruded LPSO grains.Stress-strain hysteresis curves were used to calibrate and validate a crystal plasticity model taking into account twinning and detwinning.The interaction of the different phases on the distribution of local micro-mechanical fields at the grain scale was then analyzed on synthetic microstructures under strain-controlled conditions.Deformation twinning activity was predicted in coarse unrecrystallized grains and tended to disappear with the increase in the LPSO phase volume fraction.Cleavage-like facets observed in LPSO grains were related to high tensile stress,especially at the Mg/LPSO interface,due to the limited number of deformation mechanisms in LPSO crystal to accommodate out-of-basal plane strain.The increase of the fatigue limit with the increase in LPSO phase volume fraction was finally associated with the decreasing presence of coarse unrecrystallizedα-Mg grains due to a higher dynamic recrystallization activity during the extrusion process.
基金
This work was partially supported by the JSPS KAKENHI for Scientific Research on Innovative Areas”MFS Materials Science”(Grant no.JP18H05478)
the JSPS KAKENHI for Early-Career Scientists(Grant no.20K14604).