基于弯曲定径带模具挤压的Mg-3Al-1Zn合金力学性能优化

设计了一种采用弯曲定径带模具的新型非对称挤压工艺(TBE),用以改善Mg-3Al-1Zn合金板材的力学性能和成形性能。运用有限元分析揭示了挤压过程中的应变、温度等状态变量的分布。结果表明,在TBE模具的模口处,应变沿板面法向(ND)呈梯度分布,这导致挤压板材显微组织的厚向梯度分布,同时得到TD择优取向的织构,少量基面取向晶粒向挤压方向(ED)偏转。与传统挤压相比,TBE过程中产生更多挤压热,模腔内温度更高,使大量非基面滑移开启,导致板材TD择优取向织构的形成。通过改善织构,TBE板材的塑性和弯曲性能均得到明显提升,沿45°方向的伸长率达到33%,弯曲角度达到83.5°。

Mg−6Zn−1Mn−4Sn−0.5Ca合金在挤压和时效过程中的组织演变和析出强化

采用光学显微镜、扫描电子显微镜、透射电镜、硬度试验和拉伸试验对Mg−6Zn−1Mn−4Sn−0.5Ca(ZMT614−0.5Ca)合金在挤压态和时效态的组织变化及力学性能进行研究。结果表明:铸态ZMT614−0.5Ca合金主要包含α-Mg、Mg−Zn和CaMgSn相。热挤压过程有效地细化晶粒且形成完全动态再结晶组织。挤压态合金的平均晶粒尺寸约为4.85μm。固溶处理后,高熔点CaMgSn仍然存在,起着重要的钉扎作用和阻碍晶界移动。时效处理后,合金ZMT614−0.5Ca具有良好的综合力学性能,屈服强度、抗拉强度和伸长率分别为338 MPa、383 MPa和7.5%。和挤压态相比,合金屈服强度提升约36%,其主要原因是时效过程β相的析出强化。

Mn的添加协同提升挤压态Mg-Gd-Zn合金强度与塑性

采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)和背散射电子衍射仪(EBSD)研究Mn含量对挤压Mg-1Gd-0.5Zn-xMn(x=0、0.3和1,质量分数,%)合金板材显微组织、拉伸性能和应变硬化行为的影响。结果表明,所有挤压板材均呈现出完全再结晶晶粒组织和向挤压方向偏转的织构。随着Mn含量的增加,挤压板材的平均晶粒尺寸逐渐减小,偏转织构减弱,这主要是由于Mn的添加形成新的细小α-Mn颗粒相。拉伸性能结果表明,Mn的添加提高挤压Mg-1Gd-0.5Zn-xMn合金板材的屈服强度、抗拉强度和伸长率,这主要是由于细小的晶粒和α-Mn颗粒。此外,Mg-1Gd-0.5Zn-xMn合金板材中,Mg-1Gd-0.5Zn-1Mn合金板材具有最低的应变硬化指数和最好硬化能力。

Potential red-emitting phosphor GdNbO_4:Eu^(3+),Bi^(3+) for near-UV white light emitting diodes

A red-emitting phosphor GdNbO4：Eu3＋,Bi3＋ was prepared by a high temperature solid-state reaction technique. The phosphor was characterized by X-ray diffraction （XRD）, particle size analyzer and fluorescence spectrometer. The single phase of GdNbO4：Eu3＋,Bi3＋ was obtained at 1150~C and the average particle diameter was about 2.30 μm. Excitation and emission spectra reveal that the phosphor can be ef- ficiently excited by ultraviolet （UV） light （394 nm） and emit the strong red light of 612 nm due to the Eu3＋ transition of SD0~TF2. The opti- mum content of Eu3＋ doped in the phosphor GdNbOn：Eu3＋ is 20mo1%. The phosphor Gdo.80NbO4：0.20Eu3＋,0.03Bi3＋ shows much stronger photoluminescence intensity and better chromaticity coordinates （x=0.642, 0.352） than GdNbO4：Eu3＋. It is confirmed that Gdo.80NbO4：0.20Eu3＋,0.03Bi3＋ is a potential candidate for near-UV chip-based white light emitting diodes.

Microstructure and mechanical properties of Mg-6Zn-0.5Y magnesium alloy prepared with ultrasonic treatment

Ultrasonic effect on microstructure evolution and mechanical properties of Mg-6Zn-0.5Y magnesium alloy was investigated.The results show that ultrasonic treatment can significantly modify the as-cast microstructure of Mg-6Zn-0.5Y alloy.With the application of ultrasonic treatment,the primary a-Mg phase transforms from coarse dendrites to nearly fine equiaxed grains,and the continuous I-phase atα-Mg boundaries is modified into discontinuous one.Interestingly,the area fraction of I-phase decreases after ultrasonic treatment.Besides,the tensile properties of Mg-6Zn-0.5Y alloy are apparently improved after ultrasonic treatment.Compared to those of the untreated alloy,the ultimate tensile strength and elongation of Mg-6Zn-0.5Y alloy are improved by 67%and 56%,respectively.

In vitro corrosion of Mg-6Zn-IMn-4Sn-1.5Nd/0.5Y alloys

The microstructure evaluation, surface morphology, chemical compositions and phase analysis of the biomedical Mg-6Zn-IMn-4Sn-1.5Nd/0.5Y （ZMT614- 1.5Nd/0.5Y） alloys were investigated by means of optical microscopy, EPMA, X-ray EDS, XRD and FTIR. The corrosion behavior was evaluated using weight-loss measurement, hydrogen evolution, electrochemical and pH measurements, The results demonstrate that the microstructure for both ZMT614-1,5Nd alloy and ZMT614-0.5Y alloy is characterized by α-Mg and intermetallic compounds, most of which are distributed along the grain boundaries. These second phases contain Mg2Zn, Mg2Zn11, Mg2Sn and single metal Mn, together with Mg12Nd phase for the ZMT614-1.5Nd alloy, and with Mg24Y5 phase for the ZMT614-0.5Y alloy. Honeycomb-like corrosion product layers form. The corrosion resistance of the ZMT614-0.5Y alloy is higher than that of the ZMT614-1.5Nd alloy, which is ascribed to the addition of the element Y into the alloy delaying the corrosion initiation in comparison to that of Nd element in the alloy.

Effects of Sb Addition on Microstructural Evolution and Mechanical Properties of Mg–9Al–5Sn Alloy

The Mg–9Al–5Sn-xSb(x=0.0,0.3,0.6,1.0,1.5 wt%)alloys were prepared by a simple alloying process followed by hot extrusion with an extrusion ratio of 28.2.The effects of Sb additions on the microstructure and mechanical properties of the Mg–9 Al–5 Sn alloys were investigated by optical microscopy,X-ray diffraction,transmission electron microscopy,scanning electron microscopy equipped with an energy-dispersive X-ray spectrometer.The results indicated that the phasesα-Mg matrix,Mg2Sn,Mg_(3)Sb_(2) and Mg17 Al12 exist in the as-cast Sb-containing alloys.Sb addition results in the precipitation of Mg_(3)Sb_(2).The dendritic size of these alloys decreases with the addition of Sb.Both their ultimate tensile strength and yield strength of extruded alloys increase,and their elongation decreases gradually with increasing the content of Sb.The better mechanical properties of the as-extruded alloys were achieved due to the refined grains and the formation of dispersive second phases Mg_(3)Sb_(2).

Critical damage value of AZ31B magnesium alloy with different temperatures and strain rates

The uniaxial tensile tests were carried out at temperature ranging from room temperature(RT)to 523 K under strain rates of 0.001,0.010 and 0.100 s^(-1) to obtain the flow stress of AZ31 B magnesium alloy.The tensile tests were simulated by the finite element method(FEM)to calculate the critical damage values(Dc)of the CockcroftLatham criterion to predict the occurrence of fracture defects.Finally,the effects of temperature and strain rate on Dc were analyzed to predict the critical damage value’s evolution.The results demonstrate that the critical damage value changes in the range of 0.188-0.718.It increases as strain rate decreases at constant temperature,and increases with the increase of temperature under certain strain rate,but is more sensitive to the temperature.