Comparative Study on Constitutive Models to Predict Flow Stress of Fe-Cr-Ni Preform Reinforced Al-Si-Cu-Ni-Mg Composite

The isothermal compression tests were carried out on Gleeble-3500 thermal-mechanical simulation machine in a temperature range of 298-473 K and strain rate range of 0.001-10 s^-1. The experimental results show that the flow stress data are negatively correlated with temperature for temperature softening, and the strain rates sensitivity of this composite increases with elevating temperature. Based on the experimental data, Johnson-Cook, modified Johnson-Cook and Arrhenius constitutive models were established. The accuracy of these three constitutive models was analyzed and compared. The results show that the values predicted by Johnson-Cook model could not agree well with the experimental values. The prediction accuracy of Arrhenius model is higher than that of Johnson-Cook model but lower than that of the Modified Johnson-Cook model.

Microstructure and creep behaviour of Mg-12Gd-3Y-1Zn-0.4Zr alloy

Microstructure and creep behaviour of Mg-12Gd-3Y-1Zn-0.4Zr alloy prepared by squeeze casting were investigated. Transmission electron microscope （TEM） observation revealed that a kind of lamellar-shaped morphologies 14h long-period stacking order structure （LPSO） and dense β＇-phase precipitates were formed by heat treatment. The alloy exhibited good creep resistance. It was shown that the creep-resistant performance kept stable because of the restriction of dense β＇-phase precipitates and LPSO phases to the movement of dislocations, and the formation of β-phase plates took responsibility for the softening of material during creep. Stress and temperature dependence of the steady-state creep rate were studied over stress range of 50-100 MPa and a temperature range of 250-300 oC, and a dislocation creep mechanism was proposed for the alloy.

Microstructure and mechanical properties of Mg-xY-1.5MM-0.4Zr alloys

Age hardening,microstructure and mechanical properties of Mg-xY-1.5MM-0.4Zr （x=0,2,4,6 wt.%） alloys （MM represents Ce-based misch-metal） were investigated by scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The results showed that the formed precipitates being responsible for age hardening changed from fine hexagonal-shaped equilibrium Mg12MM phase to metastable β＇ phase with bco crystal structure when Y was added into Mg-1.5MM-0.4Zr alloy,and the volume fraction of precipitate phases also increased. With the increase of Y content in Mg-Y-1.5MM-0.4Zr alloys,it was found that the age hardening was enhanced,the grain sizes became finer and the tensile strength was improved. The cubic-shaped β-Mg24Y5 precipitate phases were observed at grain boundaries in Mg-6Y-1.5MM-0.4Zr alloy. It was suggested that the distribution of prismatic shaped β＇ phases and cubic shaped β-Mg24Y5 precipitate phases in Mg matrix might account for the remarkable enhancement of tensile strength of Mg-Y-MM-Zr alloy. It was shown that the Mg-6Y-1.5MM-0.4Zr alloy was with maximum tensile strength at aged-peak hardness,UTS of 280 MPa at room temperature and 223 MPa at 250 oC,respectively.