Xiaodong Peng

Effects of Sr and Y on Microstructure and Corrosion Resistance of AZ31 Magnesium Alloy

The effects of Sr and Y with different contents on the microstructure and corrosion resistance of AZ31 alloy were investigated. The results indicate that the addition of Sr can obviously reduce the grain size of AZ31 alloy and transform β-Mg17Al12 phase from continuous network to scattered form. Simultaneously, Al 4 Sr phase distributed along the boundaries of grains is formed in AZ31-Sr magnesium alloys. The addition of Sr is not as effective as the simultaneous addition of Sr+Y for the refinement of grains, and Al2Y and Al3Y phases are distributed both in intracrystalline and along grain boundaries. The corrosion resistance is improved slightly in AZ31 alloy with simultaneous addition of 0.5%Sr+Y. Due to its smallest corrosion current density and corrosion rate, the corrosion resistance of AZ31-0.5%Sr-1.5%Y magnesium alloy is proved the best.

Effect of Sr content on microstructure and mechanical properties of Mg-Li-Al-Mn alloy

Abstract The as-cast Mg-8Li-3Al-0.5Mn- x Sr (LAM830- x Sr, x =0-1.0) alloys were designed and prepared in a vacuum induction furnace under controlled argon atmosphere. The alloys were then processed by hot extrusion, and their microstructural evolution and mechanical properties were analyzed. Results indicate that the LAM830 alloy mainly consists of α -Mg, β -Li, Al 2 Mn 3 , and LiMgAl 2 phases. Sr addition results in the precipitation of Al-Sr. Moreover, Sr addition results in a fact that the secondary dendrite arm spacing (DAS) of the primary a -Mg phase is obvious refined. Microstructure of the investigated alloys is further refined as a result of the hot extrusion treatment. The content and morphology of the secondary phases have important effects on the mechanical properties of the alloys. The as-extruded LAM830-0.5Sr alloy exhibits an optimal elongation of 22.43% and as-extruded LAM830-0.75Sr alloy shows an optimal tensile strength of 265.46 MPa.

Deformation behavior and constitutive model for dual-phase Mg–Li alloy at elevated temperatures

In order to study the deformation behavior and evaluate the workability of the dual-phase Mg–9Li–3Al–2Sr alloy, isothermal hot compression tests were conducted using the Gleeble–3500 thermal-mechanical simulator, in ranges of elevated temperatures (423–573 K) and strain rates (0.001–1 s−1). Plastic instability is evident during the deformation which is in the form of serrated flow; serrated yielding is attributed to the locking of mobile dislocations by the Mg and Li atoms which diffuse during the deformation. The relationships between flow stress, strain rate and deformation temperature were analyzed and the deformation activation energy and some basic material factors at different strains were calculated using the Arrhenius equation. The effects of temperature and strain rate on deformation behavior were represented using the Zener-Hollomon parameter in an exponent-type equation. To verify the validity of the constitutive model, the predicted values and experimental flow curves under different deformation conditions were compared, the correlation coefficient (0.9970) and average absolute relative error (AARE=4.41%) were calculated. The results indicate that the constitutive model can be used to accurately predict the flow behavior of dual-phase Mg–9Li–3Al–2Sr alloy during high temperature deformation.

Microstructure and Mechanical Properties of Superlight Mg-Li-Al-Zn Wrought Alloy

Abstract Superlight alloys, including Mg-7Li-3Zn, Mg-7Li-3Al and Mg-7Li-1.5Al-1.5Zn, were prepared using a resistance furnace under the protection of argon atmosphere. The microstructures and phases of the alloys were studied by optical microscopy, scanning electronic microscopy (SEM), X-ray diffraction (XRD). The mechanical properties of these alloys were measured by a tensile tester. The results show that the Zn and Al added in Mg-Li alloy mainly dissolve in α-Mg phase and β-Li phase. However, there still exists a part of the Al and Mg compound such as Mg17Al12 which is mainly distributed discontinuously at α phase boundary while the most of them in the β phase are granular. The as-extruded Mg-7Li-3Al alloy has the maximum tensile strength and yield strength of 239 MPa (34% higher than the as-cast) and 178 MPa (31% higher than the as-cast), respectively, and the maximum elongation reaches to 27% (93% higher than the as-cast).

Influence of I-phase and W-phase on microstructure and mechanical properties of Mg–8Li–3Zn alloy

Abstract Microstructures and mechanical properties of LZ83–xY alloys containing I-phase and W-phase were investigated by XRD, OM, SEM and EDS. The experimental results show that the content of I-phase and W-phase changes by varying Zn/Y mass ratio in the LZ83–xY alloys. The cohesion of I-phase/α-Mg eutectic pockets can enhance the strength in the as-cast LZ83–0.5Y and LZ83–1.0Y alloys, while the W-phase has no obvious strengthening effect on the LZ83–1.5Y alloy. In the extruded alloys, the I-phase and W-phase were extruded into the particles with nanoscale size in the β-Li matrix phase. The dispersion strengthening of W-phase was more obvious because of the higher volume fraction. The ultimate tensile strength of extruded LZ83–1.5Y alloy is up to 238 MPa while the elongation is up to 20%.

A comparison between DCCAE and conventional extrusion of Mg-9.5Li-3Al-1.6Y alloy

Abstract Double change channel angular extrusion (DCCAE) was performed in dual-phase Mg-9.5Li-3Al-1.6Y (wt.%) alloy to develop fine-grained microstructures. The microstructure evolution during DCCAE and conventional extrusion (CE) was investigated. The microstructure of the extruded dual-phase Mg-Li alloy consisted of recrystallized β-Li grains, banded α-Mg phases, and Al2Y phases distributed in β-Li phases and phase-interface uniformly. Compared with CE, the specimens after DCCAE had smaller β-Li grain size (3–5 μm by the DCCAE and 6–10 μm by the CE) and the α-Mg phases were refined during the DCCAE. The distribution of the Al2Y phases was improved a lot by DCCAE. Furthermore, the specimens after DCCAE had better tensile strength than conventional extrusion ones.

Dynamic Recrystallization Behavior and Corrosion Resistance of a Dual-Phase Mg-Li Alloy

The hot deformation and dynamic recrystallization behavior of the dual-phase Mg-9Li-3Al-2Sr-2Y alloy had been investigated using a compression test. The typical dual-phase structure was observed, and average of grain size of as-homogenized alloy is about 110 µm. It mainly contains β-Li, α-Mg, Al4Sr and Al2Y phases. The dynamic recrystallization (DRX) kinetic was established based on an Avrami type equation. The onset of the DRX process occurred before the peak of the stress–strain flow curves. It shows that the DRX volume fraction increases with increasing deformation temperature or decreasing strain rate. The microstructure evolution during the hot compression at various temperatures and strain rates had been investigated. The DRX grain size became larger with the increasing testing temperature or decreasing strain rate because the higher temperature or lower strain rate can improve the migration of DRX grain boundaries. The fully recrystallized microstructure can be achieved in a small strain due to the dispersed island-shape α-Mg phases, continuous the Al4Sr phases and spheroidal Al2Y particles, which can accelerate the nucleation. The continuous Al4Sr phases along the grain boundaries are very helpful for enhancing the corrosion resistance of the duplex structured Mg-Li alloy, which can prevent the pitting corrosion and filiform corrosion.

Comparative study on the microstructure and mechanical properties of Mg-Li-Al based alloys with yttrium and strontium addition

The effects of yttrium and strontium on the microstructure and mechanical properties of Mg-11Li-3Al magnesium alloy (LA113) are compared and analyzed. Microstructures and phases of the alloys were studied with optical microscope (OM), scanning electron microscope (SEM), X-ray diffractometer (XRD) and energy dispersive spectrometer (EDS). Mechanical properties of alloys were measured with tensile tester. The results show that yttrium and/or strontium additions produce a strong grain refining effect in LA113 alloy. Al2Y and Al4Sr, etc. phases with different morphologies are verified and exist inside the grain or at the grain boundaries, which directly impact on the mechanical properties of LA113 alloy. The results of tensile tests show that, the as-extruded LA113-1Y-1Sr alloy obtains the optimal tensile property of which the tensile strength and elongation are 253.56 MPa and 18.12%, the tensile strength is increased by almost 25% compared with the asextruded LA113 alloy.

Effects of Ce on microstructure of semi-continuously cast Mg-1.5Zn-0.2Zr magnesium alloy ingots

Mg-1.5Zn-0.2Zr-xCe (x=0, 0.1, 0.3, 0.5, mass fraction, %) alloys were prepared by conventional semi-continuous casting. The effect of rare earth Ce on the microstructure of Mg-1.5Zn-0.2Zr-xCe alloys was studied and the distribution of Ce was analyzed by optical microscopy (OM), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results indicate that Ce element exists in the form of Mg12Ce phase and has an obvious refining effect on the microstructure of test alloys. As the Ce content increases, the grain size reduces, the grain boundaries turn thinner, and the distribution of Mg12Ce precipitates becomes more and more dispersed. The Mg-1.5Zn-0.2Zr alloy with 0.3%Ce has the best refinement effect. From center to periphery of the ingot, the amount of granular precipitates in the grain reduces. In longitudinal section of the ingot, some relative long columnar grains appear.

Microstructure, dielectric and ferroelectric properties of (1− x ) BaTiO 3 – x BiYbO 3 ceramics fabricated by conventional and microwave sintering methods

Abstract(1−x) BaTiO3–xBiYbO3 (abbreviated as (1−x) BT−xBY, x = 0, 0.03, 0.06 and 0.09) ferroelectric ceramics have been fabricated by conventional sintering (CS) and microwave sintering (MWS) methods. The microstructure, dielectric and ferroelectric properties of (1−x) BT–xBY ceramics have been investigated systematically. X-ray diffraction patterns indicate all samples possess single perovskite phase and the crystal structure transforms from tetragonal to pseudo-cubic phase with increasing x. It can be also found that denser microstructure and finer grains can be obtained by MWS compared to CS as indicated by scanning electron microscopy. Dielectric measurements reveal that the addition of BY can lead to an obvious relaxation behavior in all samples, and the relaxation characteristics of MWS samples are stronger than those of CS samples. Moreover, the dielectric constant decreases with increasing BY content and the temperature stability and frequency stability of dielectric properties can be enhanced by using MWS method and addition of BY. P–E hysteresis loops become slimmer with the increase of BY content, and the ferroelectric properties of MWS samples are similar to those of CS samples. The leakage current of MWS sample is smaller than that of CS sample from J–E curve. The energy storage efficiency (η) increases with increasing BY content, while the energy storage density (U) increases and then decreases, Umax is obtained at x = 0.06. These results demonstrate that MWS technique and moderate BY content are effective methods to prepare materials for energy storage application.