Electron Theory Research in Mg-Y Alloy

Adding yttrium to magnesium can improve the mechanical properties, especially the mechanical behavior at high temperature. The valence electron structures of Mg-Y alloy were analyzed with the empirical electron theory of solids and molecules (EET). Calculation shows that yttrium is on the fifth hybrid level and magnesium is on the third one in pure metal crystals. By comparing with aluminum in Mg-Al alloy, it is shown that the reason why the solution strengthening effect of yttrium is better than that of aluminum in Mg-Al alloy is the enhanced bond energy according to EET. And it is concluded from EET analysis that intermetallies Mg24Y5 can significantly improve the properties of magnesium alloys because yttrium atoms oceupy the centers of the oetahedron and Mg-Y bonds efficiently strengthen the alloy matrix.     

Study on Ignition Proof AZ91D Magnesium Alloy Chips with Cerium Addition

The effect of Ce on ignition point of AZ91D magnesium alloy chips was studied. For the AZ91D and the AZ91D-xCe magnesium alloys, changing the sizes of the chips in the range of 58 - 270 μm has a limited influence on ignition point, however, the shift of the content of Ce has much effect on ignition point. Increasing the Ce content, x from 0.15 to 0.25, the ignition point increases with increasing of Ce; however, x from 0.25 to 0.45, the ignition point decreases with increasing of Ce. By the addition of Ce of 0.25 %. the ignition point is raised by 43℃.     

Effect of erbium on microstructures and properties of Mg-Al intermetallic

The effect of the rare earth element Er on the microstructures and properties of Mg-Al intermetallic were studied in this experiment. Metallographic and X-ray diffraction（XRD） results showed that the microstructures of Mg-Al-Er alloys varied with Er content. The Mg-44Al-0.5Er and Mg-43.8Al-1.0Er alloys were both composed of Mg17Al12 matrix and Al3 Er phase, whereas Mg-43Al-3.0Er and Mg-42Al-5.0Er were composed of Mg17Al12 matrix, Al3 Er phase, and Mg-Mg17Al12 eutectic. The Mg-42Al-5.0Er alloy showed the highest microhardness, and the values remained nearly stable as Er content increased from 1.0 wt.% to 5.0 wt.%. The dispersed second phase Al3 Er caused the grain refinement of the Mg-Al-Er alloy, which was the main reason for the improvement in microhardness. The corrosion resistance of the Er-containing alloys initially increased and then decreased with increasing Er content. All the Er-containing alloys had the ability to suppress hydrogen evolution, which was the main reason for the higher corrosion resistance of the modified alloys than that of the Mg-44.3Al alloy. Considering the higher hardness and dispersity of the Al3 Er phase, Mg-43.8Al-1.0Er exhibited higher wear resistance than the as-cast Mg-44.3Al alloy.     

Preparation and Corrosion Resistance of Rare Earth Conversion Coatings on AZ91 Magnesium Alloy

The feasibility of forming Ce-containing rare earth conversion coating (short for RECCs),which is nonpoisonous and green to the environment,onto the AZ91 magnesium alloy surface in order to increase the corrosion resistance was studied. And the optimum technological conditions, such as the appropriate concentrations of the components in the solution,temperature and duration of the coatings formation were also settled. The protection of conversion coatings on magnesium alloy surface was evaluated by moisture/heating test, anodie polarization, etc.     

Effects of RE on Microstructures and Mechanical Properties of Hot-Extruded AZ31 Magnesium Alloy

Effects of rare earth (RE) additions on microstructure and mechanical properties of the wrought AZ31 magnesium alloy were investigated. The results show that, by adding 0.3%, 0.6% and 1.0% RE elements, the as-cast microstructure can be refined, and the as-cast alloys‘ elongation and tensile strength can be improved. After extrusion, the alloy with 0.3 % and 0.6% RE additions obtain a finer microstructure and the best mechanical properties, but the alloy with 1.0% RE addition has the coarse A1-RE compound particles in grain boundaries which decreased elongation and tensile properties. Usually, Rare earth (RE) elements were used to improve the creep properties of aluminium-containing magnesium pressure die cast alloys at elevated temperatures. In this paper, it is also found that the high temperature strength of extruded materials can be increased by RE elements additions.     

Microstructures and properties of SnZn-xEr lead-free solders

The Sn9Zn eutectic alloy is the nontoxic lead-free solders alternative having a melting temperature which is closest to that of the eutectic SnPb alloy. In order to improve the properties of SnZn lead-free solders, 0-0.5 wt.% of rare earth Er was added to the base alloys, and the microstructures were studied. Results showed that the addition of rare earth Er could enhance the wettability of SnZn solders, with 0.08%Er addition, the spreading area gave an 19.1% increase. And based on the mechanical testing, it was found that the tensile force and shear force of SnZn-xEr solder joints could be improved significantly. Moreover, the oxidation resistance of SnZn0.08Er solder was better than that of SnZn solder. In addition, it was found that trace amounts of rare earth Er could refine the microstructures of SnZn solders, especially for Zn-rich phases, and excessive amount of rare earth Er led to a coarse microstructure.     

Effect of samarium on microstructure and corrosion resistance of aged as-cast AZ92 magnesium alloy

The effects of samarium（Sm） on microstructure and corrosion resistance of AZ92 magnesium alloy were characterized and analyzed by scanning electronic microscopy, X-ray diffraction, mass loss test, electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy and potentio-dynamic polarization test. The results showed that the added Sm could promote continuous precipitation of β-Mg17Al12 phase in grains, and meanwhile restrain discontinuous precipitation of the same phase along the grain boundaries. Thus, the precipitations distributed more uniformly in the aged AZ92 magnesium alloys. When the content of Sm was 0.5 wt.%, the corrosion resistance of aged AZ92 alloy tended to be the best, which was due to the β-phase distributes more homogeneous reducing the galvanic corrosion. The corrosion product film had more integrality and compactness than AZ92 alloys without Sm. However, it resulted in worse corrosion resistance of AZ92 alloy because of the formation of mass cathodic Al2 Sm phase coming from excess Sm in AZ92 alloy.     

The Rare Earth Aluminium Alloys in China

The development and application of rare earth aluminium alloys began in the 1960s in China.The represen-tative work was the usage of rare earth metals in alumino-silicon alloys for piston.In the 1970s,its initial stage.rare earths were used in enhanced AIMgSi alloy transmission line and FeCr Al alloy electric heating wire.Duringits developing period(from 1980 to 1985),in the field of smelting,after the electrolytic preparation of RE-Almaster alloys at relatively low temperature,a new technique was invented that rare earth compounds were addedto commercial aluminium electrowinning cell to produce RE-Al alloys directly.It opened the way for the appli-cation of rare earths in industry on a large scale.In the field of application,it was found that the addition ofrare earths could improve the conductivity and processing property of aluminium alloys.The application of rareearths to aluminium conductors and products had made a breakthrough progress.Since 1986,its golden age,thestudy,production and application of aluminium alloys containing rare earths have been developing at an amazingspeed,running neck and neck with the application of RE in agriculture,textile dyeing,and cast iron.     

Research on microstructure and high-temperature friction and wear properties of a cobalt-based alloy for hot extrusion die

The hot extrusion die is a key tool for determining the surface quality and dimensional accuracy of extruded products.Because its service process is subject to high temperature,high pressure,and wear,it must be resistant to these conditions.In this paper,the high-temperature friction and wear properties of a cobalt(Co)-based alloy were investigated and compared with those of a titanium carbide(TiC)cemented material.The results show that the high-temperature wear performance of the Co-based alloy is better than that of the TiC cemented material,and that Co-based materials have the potential for replacing TiC cemented materials as hot-extrusion-die materials.Due to the high density and good combination of the matrix and carbide,the carbides do not easily peel off from the matrix during the wear process.Due to the higher impact toughness of the Co-based alloys,microcracks that can cause worn-surface peeling are not easily generated.As a result,the high-temperature wear performance of Co-based alloys is found to be better than that of TiC cemented materials.     

Influence of Cerium on Corrosion of AZ91 Magnesium Alloy

Effect of cerium addition on corrosion resistance of AZ91 magnesium alloy was investigated using the static weight loss and polarization curve method as well as metallographical observation. The results indicate that a small amount of cerium （0.2% - 0.8%） in AZ91 magnesium alloy can significantly reduce the corrosion rate, enhance the electrode voltage and lower corrosion current density in 3.5%NaCl aqueous solution, and AZ91-0.8% Ce alloy has better corrosion resistant performance. The reason for increasing corrosion resistance is attributed to the addition of Ce, refining the α-Mg grain, reducing the segregation of element Al, and improving the morphologies of β-Mg17 Al12 phases.     

Nitride Nanoparticle Addition to Beneficially Reinforce Hybrid Magnesium Alloys

This study is aimed at understanding the function of two nitride nanoparticles regarding altering the mechanical properties of hybrid magnesium alloys in relation to nanoparticle-matrix reactivity. Nitride nanoparticles were selected for reinforcement purposes due to the affinity between magnesium and nitrogen (in parallel with the well-known magnesium-oxygen affinity). AZ91/ZK60A and AZ31/AZ91 hybrid magnesium alloys were reinforced with AlN and Si₃N₄ nanoparticles (respectively) using solidification processing followed by hot extrusion. Each nitride nanocomposite exhibited higher tensile strength than the corresponding monolithic hybrid alloy. However, AZ91/ZK60A/AlN exhibited slightly lower tensile ductility than AZ91/ZK60A, while AZ31/AZ91/Si₃N₄ exhibited higher tensile ductility than AZ31/AZ91. The formation of high strain zones (HSZs) (from particle surfaces inclusive) during tensile deformation as a significant mechanism supporting ductility enhancement was addressed. AZ91/ZK60A/AlN exhibited lower and higher compressive strength and ductility (respectively) compared to AZ91/ZK60A, while AZ31/AZ91/Si₃N₄ exhibited higher and unchanged compressive strength and ductility (respectively) compared to AZ31/AZ91. Nanograin formation (recrystallization) during room temperature compressive deformation (as a toughening mechanism) in relation to nanoparticle-stimulated nucleation (NSN) ability was also discussed. The beneficial (as well as comparative) effects of the respective nitride nanoparticle on each hybrid alloy are studied in this article.     

Preparation and Corrosion Resistance of Rare Earth Ceramic Film on AZ91 Magnesium Alloy

With the purpose of improving corrosion resistance and solving environmental pollution caused by traditional protective technique, rare earth ceramic film on AZ91 magnesium alloy was prepared by dip coating process, and technical parameters of preparation were defmed. Microstructure and composition of the film were studied and corrosion resistance was evaluated as well. The results show that rare earth ceramic film is uniform,dense, with strong cohesion and intact coverage. The film is mainly made up of CeO2 and MgCeO3. The results of corrosion experiments approve that the film acts as a barrier to isolate the contact of the substrate with corrosion media and decreas corrosion rate. Polarization curve of the coated sample shiftes to positive potential obvito 2.7 × 104 Ω. These facts indicate that rare earth ceramic film could effectively improve corrosion resistance of AZ91 magnesium alloy.     

Modification of AZ91?Mg Alloys for High Temperature Applications

The good specific strength and specific modulus of magnesium alloys had drawn the attention of the automotive manufacturers for use in fuel efficient vehicles. Among the cast magnesium alloys, AZ91 (Mg?C9Al?C1Zn) is the most sought alloy because of its good casting properties. However, this alloy loses its strength and creep resistance properties above 120?°C due to softening of the ?? phase (Mg₁₇Al₁₂). Hence, this alloy cannot be used for making heavier engine components (power train), which require the thermal stability up to about 250?°C. The paper discusses the approach of modifying the AZ91 alloy by minor alloying additions to improve the high temperature withstanding capability without significantly affecting its casting properties. Additions of Ca to AZ91 alloy to the levels of about 0.4?wt% increased the ambient and high temperature strength of the base alloy. Additions of other minor alloying elements such as Sb, Pb, rare earths etc. can also increase the high temperature capability of the AZ91 by further modifying the ?? phase structure. The paper overviews the work carried out by the authors on the role of different alloying additions on the microstructure and mechanical properties of AZ91 magnesium alloys.     

Effect of Ca and Rare Earth Elements on Impression Creep Properties of AZ91 Magnesium Alloy

Creep properties of AZ91 magnesium alloy and AZRC91 (AZ91 + 1 wt pct RE + 1.2 wt pct Ca) alloy were investigated using the impression creep method. It was shown that the creep properties of AZ91 alloy are significantly improved by adding Ca and rare earth (RE) elements. The improvement in creep resistance is mainly attributed to the reduction in the amount and continuity of eutectic β(Mg₁₇Al₁₂) phase as well as the formation of new Al₁₁RE₃ and Al₂Ca intermetallic compounds at interdendritic regions. It was found that the stress exponent of minimum creep rate, n, varies between 5.69 and 6 for AZ91 alloy and varies between 5.81 and 6.46 for AZRC91 alloy. Activation energies of 120.9 ± 8.9 kJ/mol and 100.6 ± 7.1 kJ/mol were obtained for AZ91 and AZRC91 alloys, respectively. It was shown that the lattice and pipe-diffusion-controlled dislocation climb are the dominant creep mechanisms for AZ91 and AZRC91 alloys, respectively. The constitutive equations, correlating the minimum creep rate with temperature and stress, were also developed for both alloys.     

Preparation and Corrosion Resistance of Rare Earth Conversion Coatings on AZ91 Magnesium Alloy

Magnesiumalloysarewidelyusedinweaponin dustry,spacenavigationandhavegoodpotentialof applicationanddevelopmentindailycommunication facilitiesduetotheirpropertiesoflightweightandhighstrength[1].Appliedasstructuralmaterials,mag nesiumalloysmayeasilycrackduet…     

Forecasting Tribological Properties of Wrought AZ91D Magnesium Alloy Using Soft Computing Model

The wear characteristics of wrought magnesium alloy AZ91D is assessed by varying the wear test parameters namely sliding velocity, sliding distance and normal load in the pin-on-disc tribometer. The experimental results are used to develop a statistical model, and soft computing models based on artificial neural network and Sugeno–Fuzzy logic to predict the wear rate of AZ91D alloy. Sugeno–Fuzzy model had the highest accuracy in prediction and hence used to study the effect of wear test parameters on the wear rate of AZ91D alloy. It is observed that the wear rate increases with decrease in load, increase in sliding velocity, and increase in sliding distance.     

Fabrication of a novel Mg-RE(Nd,Ce) intermetallic compound coating by molten salt diffusion and its effect on corrosion resistance of magnesium alloys

A novel Mg-rare earth(Nd,Ce) coating containing intermetallic compound was fabricated on the surface of the AZ91D magnesium alloy by bathing the sample in a NaCl-KCl-LiCl-NdCl_3-CeCl_3 molten salt. The cross-sectional morphology, microstructure and phase composition of the coating were investigated by scanning electron microscopy(SEM), transmission electron microscopy(TEM) and energy dispersive spectroscopy(EDS). The corrosion resistance was characterized by the potentiodynamic polarization curves. The SEM observation indicated that a continuous and compact diffusion coating was obtained on the surface of SMATed AZ91D magnesium alloy and the XRD and TEM investigations revealed that the new phases were Al_2Ce and Al_2Nd intermetallic. The potentiodynamic polarization curves showed that the Mg-RE coating improved the corrosion resistance of the AZ91D magnesium alloy, and the corrosion current density of the coated sample was about 1510 mA /cm~2 lower than the uncoated sample.     

稀土元素铈对镁合金AZ91D显微组织和力学性能的影响

利用光学显微镜、X射线衍射和扫描电镜等分析研究含铈镁合金AZ91D（0．25％Ce、0．7％Ce、0．95％Ce）的显微组织，并对其力学性能进行了测试，同时与不含铈镁合金AZ91D进行了比较。结果表明，加入一定量Ce后的镁合金AZ91D形成杆状化合物Al4Ce，被推移到生长界面，阻碍枝晶的自由生长，从而细化合金显微组织；Ce能提高镁合金AZ91D抗拉强度和硬度，而对其屈服强度和延伸率影响不大；加入0．7％Ce的AZ91D镁合金晶粒细化效果和综合力学性能比较理想。