Formation and characterization of cerium conversion coatings on magnesium alloy

Chemical conversion treatment by rare earth metal salt solution was considered as an alternative to chromium chemical conversion treatment to improve the corrosion resistance of magnesium alloys. In this study, cerium conversion coatings formed on AZ31 magnesium alloy were characterized and the formation mechanism was discussed. X-ray photoelectron spectroscopy （XPS） analysis showed that cerium conversion coating consisted of cerium hydroxides/oxides, in which both tetravalent cerium Ce（Ⅳ） and trivalent cerium Ce（Ⅲ） species co-existed. Cerium conversion coating was a two-layer structure. Atomic force microscopy （AFM） images revealed that the morphology of the inside layer was different from that of the outside one, which was responsible for the inherent adhesive weakness of the coating. Corrosion potential （Ecorr） measurements indicated that poor adhesion limited the improvement of the corrosion resistance of the coating. During the treating process, the increased pH value of the cerium salt solution led to the precipitation of cerium hydroxides/oxides. The formation kinetics of the coating followed a parabolic curve.

Ultra-precision machining of cerium-lanthanum alloy with atmosphere control in an auxiliary device

Cerium–lanthanum alloys are the main component of nickel–metal hydride batteries,and they are thus an important material in the greenenergy industry.However,these alloys have very strong chemical activity,and their surfaces are easily oxidized,leading to great difficulties in their application.To improve the corrosion resistance of cerium–lanthanum alloys,it is necessary to obtain a nanoscale surface with low roughness.However,these alloys can easily succumb to spontaneous combustion during machining.Currently,to inhibit the occurrence of fire,machining of this alloy in ambient air needs to be conducted at very low cutting speeds while spraying the workpiece with a large amount of cutting fluid.However,this is inefficient,and only a very limited range of parameters can be optimized at low cutting speeds;this restricts the optimization of other cutting parameters.To achieve ultraprecision machining of cerium–lanthanum alloys,in this work,an auxiliary machining device was developed,and its effectiveness was verified.The results show that the developed device can improve the cutting speed and obtain a machined surface with low roughness.The device can also improve the machining efficiency and completely prevent the occurrence of spontaneous combustion.It was found that the formation of a build-up of swarf on the cutting tool is eliminated with high-speed cutting,and the surface roughness(Sa)can reach 5.64 nm within the selected parameters.Finally,the oxidation processes of the cerium–lanthanum alloy and its swarf were studied,and the process of the generation of oxidative products in the swarf was elucidated.The results revealed that most of the intermediate oxidative products in the swarf were Ce^(3+),there were major oxygen vacancies in the swarf,and the final oxidative product was Ce^(4+).

Effect of Microadditional Cerium on Annealing Embrittlement of Fe－B－Si Amorphous Alloy

it is reported in literature those the effect of microadditional cerium on annealing embrittlement of Fe-B-Si amorphous alloy is negligible even negative.The test result of present paper shows that the annealing embrittlement temperature of Fe76B15Si9 can be increased by 80℃after cerium has been microadded.The cause of the divergence of the test result from those in the literature was analysed.The condition with the positive effect of microadditional cerium on annealing embrittlement temperature of Fe-B-Si amorphous alloy was approached.The reason why microadditional cerium may be ineffective even negative on annealing embrittlement temperature was preliminarily elucidated.

Combined “Gateway” and “Spillover” effects originated from a CeNi_(5) alloy catalyst for hydrogen storage of MgH_(2)

Efficient catalysts enable MgH2 with superior hydrogen storage performance.Herein,we successfully synthesized a catalyst composed of Ce and Ni (i.e.CeNi_(5) alloy) with splendid catalytic action for boosting the hydrogen storage property of magnesium hydride (MgH_(2))The MgH2–5wt%CeNi_(5) composite’s initial hydrogen release temperature was reduced to 174℃ and approximately 6.4wt%H_(2) was released at 275℃ within 10 min.Besides,the dehydrogenation enthalpy of MgH_(2) was slightly decreased by adding CeNi_(5).For hydrogenation,the fully dehydrogenated sample absorbed 4.8wt%H_(2) at a low temperature of 175℃.The hydrogenation apparent activation energy was decreased from(73.60±1.79) to (46.12±7.33) kJ/mol.Microstructure analysis revealed that Mg_(2)Ni/Mg_(2)NiH_(4) and CeH_(2.73) were formed during the process of hydrogen absorption and desorption,exerted combined“Gateway”and“Spillover”effects to reduce the operating temperature and improve the hydrogen storage kinetics of MgH_(2).Our work provides an example of merging“Gateway”and“Spillover”effects in one catalyst and may shed light on designing novel highly-effective catalysts for MgH_(2) in near future.

Thermodynamic Properties of Cu-Ce-O and Cu-RE-O Melts

The oxygen activities in the Cu-RE-O melts containing different amount of cerium or mischmetal have been measured by galvanic cell with solid electrolyte in the temperature range from 1440 to 1573 K. The rare earth dissolved in the melts has been determined by ICP-AES (inductively coupled plasma) after the quenched samples were electrolyzed in an organic electrolyte at low temperature (&le20°C) for separating the inclusions. A series of thermodynamic calculation have been done by using the experimental results.

Corrosion behavior of as-cast Mg–8Li–3Al+xCe alloy in 3.5wt% NaCl solution

Mg-8Li-3Al＋xCe alloys（x = 0.5wt%, 1.0wt%, and 1.5wt%） were prepared through a casting route in an electric resistance furnace under a controlled atmosphere. The cast alloys were characterized by X-ray diffraction, optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The corrosion behavior of the as-cast Mg-8Li-3Al＋xCe alloys were studied under salt spray tests in 3.5wt% NaC l solution at 35°C, in accordance with standard ASTM B-117, in conjunction with potentiodynamic polarization（PDP） tests. The results show that the addition of Ce to Mg-8Li-3Al（LA83） alloy results in the formation of Al_2Ce intermetallic phase, refines both the α-Mg phase and the Mg_（17）Al_（12） intermetallic phase, and then increases the microhardness of the alloys. The results of PDP and salt spray tests reveal that an increase in Ce content to 1.5wt% decreases the corrosion rate. The best corrosion resistance is observed for the LA83 alloy sample with 1.0wt% Ce.

Influence of Rare Earth Element on Short Fatigue Crack Threshold for Al－Li Alloy 2090

Curves of △Kth vs.△ath and △Kcl·th vs.△ath for aluminum-lithium alloy 2090 have been determined and compared with those for traditional aluminum alloy 2024.The growth resistance of short fatigue cracks for aluminum-lithium alloy 2090 is quantitatively evaluated.The essential reason resulting in stronger short cracks effect has been ascertained.Influence of cerium on the growth behavior of short fatigue cracks for aluminum-lithium alloy 2090 was investigated.The results show that by adding cerium into this alloy a significant improvement in △Ki can be achieved and at the same time △Kcl·th is increased.Consequently,the essential factor resulting in lower growth resistance of short fatigue cracks for this alloy is removed and the growth resistance of long and short fatigue cracks is increased.

Effect of solution temperature and cooling rate on microstructure and mechanical properties of laser solid forming Ti-6Al-4V alloy

The effect of solution temperature and cooling rate on microstructure and mechanical properties of laser solid forming （LSF） Ti-6A1-4V alloy is investigated. The samples are solutions treated at 900, 950, and 1000 ℃, followed by water quenching, air cooling, and furnace cooling, respectively. It is found that the cooling rate of solution treatment hasα more important effect on the microstructure in comparison with the solution temperature. The martensite α formed during water quenching results in the higher hardness and tensile strength but lower ductility of samples. With decreasing the cooling rate and increasing the solution temperature, the width of primary α laths increases, and the aspect ratio and volume fraction decrease, which make the hardness and tensile strength decrease and the ductility increase.

Microstructure characteristics of laser forming repaired Ti60 alloy

The microstructure characteristics of laser forming repaired （LFR） Ti60 （Ti-5.6Al-4.8Sn-2Zr-1Mo-0.35Si- 0.3Nb） as-deposited and annealed samples are analyzed. The microstructure of as-deposited repaired zone （RZ） consists of epitaxial columnar prior β grains, in which fine woven α laths and βphase between α laths exist. The heat-affected zone （HAZ） experiences a continuous microstructural transition from duplex microstructure of the base metal zone （BMZ） to the microstructure of RZ. The presence of silicide precipitates is observed in both RZ and BMZ in an annealed sample by transmission electron microscopy. They are identified as （Ti, Zr）6Si3 distributed mainly at The fine α2 precipitates are detected in BMZ by electron the α/β interface with the size of 100-300 nm diffraction; there was no α2 detected in RZ.