Papers by Author: Wen Jiang Ding

Abstract: Alloy Mg-10Gd-3Y-0,4Zr in as-cast, as-extruded, cast-T6 (peak aged) and extruded-T5 (peak aged) state was tensile creep tested at 200, 250 and 300 °C and stress 50, 80 and 120 MPa. Comparison of minimal creep rate shows that alloy Mg-10Gd-3Y-0,4Zr in cast-T6 conditions is characterized by an excellent creep resistance, which is higher than that of commercially available Mg-alloys. Creep resistance of as-cast, as-extruded and extruded-T5 alloy Mg-10Gd-3Y-0,4Zr is lower. Cavity nucleation is heavily affected by the amount of secondary phases on the grain boundaries and also by the initial grain size of the microstructure. After extrusion and in the extruded-T5 conditions creep cavitation was not observed, whereas in the as-cast and cast-T6 conditions creep cavitation occurred on the high fraction of grain boundaries.

Abstract: Ab inito density functional theory (DFT) and density function perturbation theory (DFPT) have been applied to investigate the thermal properties of the face-center-cubic (fcc) Al3Zr alloy over a wide range of pressure and temperature. Phonon dispersions were obtained at equilibrium and strained configurations by density functional perturbation theory. Using the quasiharmonic approximation for the free energy, several interesting physical quantities such as thermal Grüneisen parameter, heat capacity at constant pressure and volume, thermal expansion coefficient and entropy, as well as adiabatic bulk modulus and isothermal bulk modulus, were calculated as a function of temperature and pressure, and the variation features of these quantities were discussed in details.

Abstract: More and more research has been focused on the improvement of the mechanical properties and the optimal design of the new excellent Mg-based alloys. In spite of many experimental investigations, the theoretical studies of the mechanical properties are very scarce. First-principle calculations of the elastic constants and mechanical properties of typical Mg-based alloys become necessary to understand the fundamental mechanism governing the observed mechanical properties. In this paper, the single-crystal elastic constants Cijs of the typical fcc and hexagonal structured Mg-based alloys (Mg3Zn3Y2 and CaMg2) were calculated, using density functional theory within the generalized gradient approximation. Then the bulk modulus B, shear modulus G, Young’s modulus E, Poisson’s ratio ν and anisotropy value A were derived from single-crystal elastic constants. The mechanical properties such as the ductility and stiffiness of the alloys are analyzed and discussed in comparison with experimental observations.

Abstract: The corrosion behavior of GW63 (Mg-6wt.%Gd-3wt.%Y-0.4wt.%Zr) alloys in 5% NaCl aqueous solution has been investigated by PARSTAT 2273 instrument. The Open Circuit Potential (ECORR) vs. time curve, cyclic polarization (Pitting Scans) curve and Electrochemical Impedance Spectroscopy (EIS) was measured for the GW63 alloys in as-cast and T6 heat treatment conditions. The EIS results indicated that the tendency of impedance variation for as-cast condition was monotonic decreasing, however, the tendency of variation for T6 condition was not completely monotonic but the total tendency was decreasing. The values of impedance of GW63 alloy at 0.1 Hz are about 103 ohm-cm2 for as-cast and T6 condition.

Abstract: The effects of CeCl3-containing fluxes on RE element loss, the high temperature mechanical properties, microstructure and corrosion properties of magnesium alloy containing RE have been studied. The results showed that a certain amount of CeCl3 in purification fluxes restrained the reaction between the Ce element and fluxes to decrease the loss of Ce in alloys. With the flux containing 9% CeCl3, the loss rate of alloy element Ce can be reduced from 26.9% to 3.4%, and the σb and δ of the alloys at 150°C counld be improved from 160.9MPa and 6.2% to 176.5MPa and 7.9% compared with that of conventional MgCl2-containing flux , respectively. Besides, the coarse β phase and rod-like RE phase were refined effectively by CeCl3-containing fluxes.

Abstract: Intermediate phase growth in Mg-Al diffusion couples were studied with different intensity of a strong static magnetic field from 0 to 10 Tesla. Thickness measurement of the intermediate phases (Mg17Al12 and Al3Mg2) shows that with the increasing of magnetic field intensity, the growth rate of both intermediate phases is retarded. The decrease of the phase growth rate is ascribed to the suppressed Al, Mg atom interdiffusion in the diffusion couple under the static magnetic field. It is also found that the orientation relationship between couple interface and magnetic field direction has no influence on the growth of intermediate phases.

Abstract: The microstructure and mechanical properties of Mg-3wt％Nd-0.2wt％Zn-0.4wt％Zr alloy in as-cast, solution-treated and solution-treated + peak-aged were investigated. The alloy had a cast structure with large intergranular Mg12Nd phase between the α-Mg matrix. After solution-treated, the intergranular Mg12Nd phase disappeared and lots of small Zr-containing particles distributed inside the grains. Small plate-like phases precipitated inside the grains strengthened the alloy to a high level after peak-aged at 200°C for 16 hours: the ultimate strength of the alloy up to 305 MPa, with considerable elongation rate 11%, and yield strength 140 MPa. The peak-aged samples also had good creep resistance, with strain rate less than 0.2% after 120 hours creep test under the condition of 110 MPa at 200°C. The minimum creep rate was about 4.64×10-9. The alloy had different fracture pattern in different states: as-cast state, intergranular fracture was the key pattern to failure; after solution-treated, the fracture pattern turned to cleavage transgranular fracture; after peak-aged, the alloy had a mixed fracture pattern of transgranular and intergranular, in which transgranular was the main style.

Abstract: The effect of Nd and Y addition on the microstructure and mechanical properties of as-extruded Mg-Zn-Zr magnesium alloy has been investigated in this study. The Mg-Zn-Zr alloy had 11 μm average grain size due to dynamic recrystallization during hot extrusion; but the average grain sizes of the Mg-Zn-Nd-Y-Zr alloys were markedly reduced to 4 μm by Nd and Y additions. The lamellar α-Mg + T phase or α-Mg + W phase eutectics at grain boundaries in as-cast Mg-Zn-Nd-Y-Zr alloys were broken up and MgZn2 precipitates in the matrix are obtained during hot extrusions. The mechanical properties of as-extruded Mg-Zn-Zr alloy were improved significantly by Nd and Y additions, especially the elevated temperature strength, which was above 150 MPa in ultimate tensile strength at 250 °C. These may be ascribed to the very fine grain size, the dispersed T phase or W phase and the MgZn2 type Laves phase precipitating during hot extrusion.

Abstract: Uniaxial hot compression tests were performed at constant temperature (T) and strain rate (ε& ) in the ranges of 200-500 °C at an interval of 50 °C and 0.001-20 s-1. The flow stress data were used to develop the extrusion limit diagram for AZ31 and AM30 magnesium tubes. The extrusion limit diagram shows a wide region available for extruding AZ31 and AM30 seamless tubes, and comparison of the two extrusion limit diagrams shows that, the extrudability of AM30 alloy is better than that of AZ31 alloy. Actual extrusion trials validated the predicted temperature rise limit curve corresponding to the occurrence of surface cracking during the extrusion process. Magnesium tubes were successfully extruded according to the safe regions identified by the extrusion limit diagram.