Role of multi-microalloying by rare earth elements in ductilization of magnesium alloys

The present work investigates the influences of microalloying with rare earths on the mechanical properties of magnesium alloys.The amount of each rare earth element is controlled below 0.4 wt.%in order not to increase the cost of alloy largely.The synergic effects from the multi-microalloying with rare earths on the mechanical properties are explored.The obtained results show that the as-cast magnesium alloys multi-microalloying with rare earths possesses a quite high ductility with a tensile strain up to 25-30%at room temperature.Moreover,these alloys exhibit much better corrosion resistance than AZ31 alloy.The preliminary in situ neutron diffractions on the deformation of these alloys indicate that the multi-microalloying with rare earths seems to be beneficial for the activation of more slip systems.The deformation becomes more homogeneous and the resultant textures after deformation are weakened.

Effect of rare earth additions on microstructure and mechanical properties of AZ91 magnesium alloys

In order to meet the demands of high temperature components in automobile, the microstructure and mechanical properties of several new die-casting AZ91-rare earth (RE) magnesium alloys were studied. The alloys were characterized by optical microscopy (OM), scan electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), tensile and creep tests. The results show that Ce addition has little effect on the mechanical properties of AZ91 alloy at high temperature, while Y and Nd addition play important role in the improvement of creep resistance. New alloys containing Y or Nd with excellent high temperature performance are selected to produce cylinder head cover of high power diesel engine of Red Flag car and oil pan of Besturn car. The new magnesium alloys with RE addition for die-casting have potential to produce power-train parts, and can greatly decrease weight.

Unexpected formation of hydrides in heavy rare earth containing magnesium alloys

Mg–RE(Dy,Gd,Y)alloys show promising for being developed as biodegradable medical applications.It is found that the hydride REH_(2) could be formed on the surface of samples during their preparations with water cleaning.The amount of formed hydrides in Mg–RE alloys is affected by the content of RE and heat treatments.It increases with the increment of RE content.On the surface of the alloy with T4 treatment the amount of formed hydride REH_(2) is higher.In contrast,the amount of REH2 is lower on the surfaces of as-cast and T6-treated alloys.Their formation mechanism is attributed to the surface reaction of Mg–RE alloys with water.The part of RE in solid solution in Mg matrix plays an important role in influencing the formation of hydrides.

Study on Rare Earth-Containing Phases in TiAl Based Alloys Prepared by Non-Equilibrium Solidification Processing

Microstructure evolution of rare earth rich phase of rapidly-solidified (RS) TiAl based alloys was investigated. The two rapid-solidification techniques employed are melt-spinning technique (MS) and Hammer-and-Anvil technique (HB). MS ribbons and HA foils were obtained in the experiment. The results demonstrate that with the increasing of cooling rates of TiAl based alloys great changes are taken place in the microstructures of rare earth rich phase, from scattering mainly on grain boundaries of as-cast ingot to distributing homogeneously as very fine fibers or powders (nanometer grade) on the matrix. The fine paralleling second phase fibers in the HA foils are considered to be connected with gamma/alpha (2) lamellar colonies. Selected area electronic diffraction (SAED) patterns of the rare earth rich phase is in accordance with that of intermetallic AlCe.

Phase Structure and Electrochemical Properties of Rare Earth Based Hydrogen Storage Alloys

The rare earth based hydrogen storage alloys MmxM1 1 - x ( Ni3.55 Co0.75 Mn0.4 A10.3 ) ( x = 0 ～ 0.5 ) were investigated in this work.Adjusted Ml: Mm ratio to change the content of La,Ce,Pr and Nd in the alloys and then to change the phase structure, the influences of phase structure on the electrochemical properties were analyzed.The results indicate that the main phase of all alloys is LaNi5 with CaCu5 type structure and the crystal lattices constants of LaNi5 are changed with increasing x value, i.e, decreased a-axis, increased c-axis and axis ratio and nonlinear decreased crystal volume.The crystal volume of the alloy with x = 0.3 is larger than others.There is second phase A1LaNi4 in alloys when x≥0.3, which decrease the discharge capacity, but increase the cycling stability and high rate discharge ability.Compared comprehensively, the alloy with x = 0.3 shows the higher discharge capacity and the better cycling stability.

Thermodynamics and kinetics of phase transformation in rare earth–magnesium alloys:A critical review

Magnesium and its alloys are significant superior metallic materials for structural components in automobile and aerospace industries due to their excellent physicomechanical properties.The Mg–rare earth(RE)systems have attracted great interests because RE additions can improve both the deformability and the strength of Mg alloys through solid solution strengthening and precipitation hardening mechanisms.This paper focuses on the interface stability,together with thermodynamics and kinetics of nucleation and growth of the key phases and matrix phases in Mg–RE alloys.In this paper,the theory and recent advances on Mg–RE alloys,especially for the interface stability,thermodynamics and kinetics of nucleation and growth of the key phases and matrix phases,together with their relationships with micro-structures,and macroscopic properties,are reviewed.By combining the thermodynamics/kinetics integrated simulations with various advanced experimental techniques,“reverse”design of Mg–RE alloys starting from the target service performance is put forward as a kind of scientific paradigm with rational design.

TEM STUDIES OF THE W PHASE AND ITS ORDERED W'PHASE IN RARE EARTH Mg ALLOYS

By means of transmission electron microscopy（TEM）,the W phase and its ordered W’phase in as-cast Mg-Zn-Zr-Y system alloys were studied.The W phase,which distributes alongthe grain boundaries in the form of a lamellar eutectoid with Mg,is of FCC structure with α=0.865 nm.The W’phase,which is an ordered structure of the W phase with α=2.055 nm,was found in the alloy with lower Y content.The W and W’phases have a simple orientationrelationship of（100）W//（100）W’,（010）W//（010）W’,and（001）W//（001）W;but they do nothave an orientation relationship with the α-Mg matrix.The results of convergent electroncliffractions（CBD）on these phases show that their point group is m3m and that the space group isFm3m.

Study on Phase Structure and PCT Characteristics of Rare Earth Based Hydrogen Storage Alloys

The rare earth based hydrogen storage alloys Mm_xMl_ 1-xNi_ 3.55Co_ 0.75Mn_ 0.4Al_ 0.3(x=0～0.50) were investigated in this work. The influences of phase structure on the PCT characteristics were analyzed by means of electrochemical measurements. The results indicate that there is a strict relationship between crystal volume and PCT characteristics.

Preparation of RE-containing magnesium alloys via molten-salt-mediated magnesiothermic reduction

RE-containing magnesium alloys were prepared via molten-salt-mediated magnesiothermic reduction by using RE_(2)O_(3)(RE=Y,Nd and Gd)and Mg metal as raw materials.The thermomechanical analysis of the magnesiothermic reduction reactions in molten salt was investigated.Then the molten-salt-mediated magnesiothermic reduction process was studied from three different perspectives.After that,the RE-containing magnesium alloy was characterized by using chemical analysis,XRD analysis and SEM analysis.The magnesiothermic reduction was a liquid-liquid reaction with relatively weak driving force.During the melting process and the magnesiothermic reduction process,magnesium metal and the obtained alloy went up and down as a whole in molten salt,which improved the process safety without introducing chloride inclusions.Meanwhile,the hydrolysis of the RECl_(3^(-))containing molten salt occurred at elevated temperature,which severely impeded the magnesiothermic reduction process.After the magnesiothermic reduction at 750°C for 2.0 h,the content of RE and the common impurity elements in the obtained RE-containing alloy met the both requirements of the commercial WE43A and WE43B.

Mechanism of Effects of Rare Earths on Microstructure and Properties at Elevated Temperatures of AZ91 Magnesium Alloy

By using real-space recursion method,the energetics of the undoped and Al and/or RE atoms doped 7（1450）〈0001〉 symmetric tilt grain boundaries（GBs）in AZ91 alloys were investigated.Similar calculations were performed on undoped and doped bulk α Mg for comparison.The results showed that Al atoms segregated at GBs in AZ91 alloys.When RE atoms were added,they also segregated at GBs,and their segregation is stronger than Al atoms＇.Therefore,RE atoms retard the segregation of Al atoms.Calculations of interaction energy indicated that Al atoms repelled each other,and could form ordered phase with host Mg atoms.On the contrary to the case of Al,RE atoms attracted each other,they could not form ordered phase with Mg,but could form clusters.Between RE and Al,there existed attractive interaction,and this attractive interaction was the origin of Al11RE3 precipitation.Precipitation of Al11RE3 particles with high melting point and high thermal stability along GB improves high temperature properties of AZ91 alloys.

Effects of rare earths on the microarc oxidation of a magnesium alloy

The effects of rare earths on the properties of the microarc oxidation（MAO） coating on a magnesium alloy were investigated by means of scanning electron microscopy（SEM）,energy dispersive X-ray spectroscopy（EDS）,and electrochemistry methods.The results show that a nice and compact MAO coating was successfully obtained when the magnesium alloy was treated in nitrate solutions as the pre-treatment of MAO.However,the MAO was not successfully completed for the silicate electrolytes with the addition of rare earths.After the magnesium alloy being treated by rare earth nitrate,the obtained MAO coating has advantages such as uniform distribution of thickness,improved corrosion resistance,and nice-uniform surface,as compared with the untreated magnesium alloy.In addition,the time of non-ESP,the voltage and current density of the MAO process obviously decrease.Cerium oxide doped on the surface of the magnesium alloy can significantly improve the corrosion resistance of the MAO coating and decrease the current density of the MAO process,as compared with lanthanum oxide,whereas the doped rare earths have no significant effect on the components of the MAO coating.

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

The feasibility of forming pollution-free and environmentally benign Ce-based rare earth conversion coatings （short for RECCs） on AZ91 magnesium alloy to enhance corrosion resistance was studied. The effect of optimum processing parameters on corrosion resistance of RECCs, such as density of treating solution, temperature and time of coating formation were discussed. Protective performance of conversion coatings on magnesium alloy was evaluated by moisture/heating test, anodic polarization, etc. The results show that Ce-based RECCs under moisture/heating condition can remain intact, with high coverage and no obvious corrosion phenomenon. Corrosion potential increases and passive phenomenon occurs while current density decreases, therefore Ce-based RECCs can improve corrosion resistance of AZ91 magnesium alloy. The morphology of Ce-based RECCs prepared under optimum process through SEM observation is found to be a few particles coherent to the base coating, and the coating has no cracks and exhibits apparent corrosion resistance during corrosion courses of AZ91 magnesium alloy.

Preparation and Performance of Rare Earths Chemical Conversion Film on Magnesium Alloy

Golden yellow cerium conversion film was obtained on magnesium alloys surface by immersion method and the preparation parameters were established. The influence of different process parameters on the surface morphology and performance of the conversion film were analyzed by means of SEM and electrochemical method. Formation dynamics about cerium conversion film on magnesium alloy in solution containing cerium salt and the anti-corrosion behavior of the conversion film in 3.5% NaCl solution were studied by electrochemical method respectively. The results shows that the conversion film is more compact at room temperature when concentration of cerium sulfate is 10 g·L-1 in the solution; the open circuit potential of the magnesium sample moves up to positive direction about 100 mV, the surface of conversion film becomes even and lustrous, and the adhesion intensity of conversion film increases when adding aluminum nitrate into the solution containing cerium salt. The pH value of the solution and immersion time of the sample in the solution also affect the surface morphology and anti-corrosion property of the conversion film. After covered by rare earths conversion film, the anti-corrosion property of magnesium alloy is obviously improved. Rare earth conversion film has self-repairing capability in corrosion medium.

Effects of rare earth elements on the microstructure and properties of magnesium alloy AZ91D

The effects of rare earth elements on the microstructure andproperties of magnesium alloy AZ91D alloy were studied. The differentproportion of rare earth elements was added to the AZ91D and thetensile tests were carried out at different temperatures. Theexperimental results show that at room temperature or at 120 deg. Cthe AZ91D's strength decrease with the increasing amount of the rareearth elements. However, the ductility is improved. The influence of0.14/100Sb(mass fraction)on the AZ91D's strength is like that of rareearth elements(0.2/100-0.4/100)(mass fraction). Microstructure graphsdemonstrate that appropriate amount of rare earth elements(0.1/100-0.2/100)can fine AZ91D's grain and improve its ductility.

Evolution and distribution of Al_2Sm phase in as-extruded AZ61-xSm magnesium alloys during semi-solid isothermal heat-treatment

The evolution and distribution of Al2Sm phase in as-extruded AZ61-xSm（x=0, 1.5, 2.0 and 2.5, mass fraction, %） magnesium alloys during semi-solid isothermal heat treatment were investigated. The results showed that when as-extruded AZ61 magnesium alloys were modified with Sm, the smaller and rounder grains were obtained during semi-solid isothermal heat treatment. When the Sm content is 2.0%（mass fraction）, the average size of the globular grains reached the smallest value of 90 μm. Although a few Al2Sm particles existed in the α-Mg grains, most of Al2Sm particles solidified at the edge of the globular grains with the width of 20 μm. These phenomena are mainly attributed to the forces acting on Al2Sm particles in front of the solid-liquid interface, leading to Al2Sm particles accumulating at the solid-liquid interface and then solidifying at the edge of the globular grains in the quenching process.

Ignition-proof mechanism of ZM5 magnesium alloy added with rare earth

The ignition-proof mechanism of ZM5 magnesium alloy added with 0.1% （mass fraction） rare earth （RE） was investigated. The oxide scales and substrates were characterized by scanning electronic microscope （SEM）, X-ray diffraction （XRD）, energy dispersive spectrometer （EDS） and tensile test. And an oxidation model of ZM5 alloy with RE was established. The results show that the ignition temperature of ZM5 alloy is particularly elevated from 654 to 823 ℃, the microstructure is refined, and the tensile strength is slightly improved from 168.2 to 174.6 MPa by adding 0.1% RE. A double-layer oxidation film formed on the alloy surface under high temperature mainly consists of MgO, RE203 and A1203, which is 2.5-3.5 μm in thickness. It is found that the forming of protective oxidation film on the thermodynamics is attributed to RE elements congregating on the surface of molten Mg alloy.

Effect of rare earth elements on the microstructure and property for magnesium alloy AM60B

The effects of rare earth elements on the microstructure and properties ofmagnesium alloy AM60B alloy were studied. Different proportions of rare earth elements were added toAM60B and the tensile tests were carried out under different temperatures. The experimental resultsshow that at room temperature the tensile strength of AM60B can be improved with the addition ofrare earth elements. The ductility of which at room or elevated temperature (120 deg C) can also beimproved, and the ductility is to some extent in proportion with the amount of rare earth elements.The ductility at 120 deg C is better than that at room temperature. The microstructure graphsdemonstrate that appropriate amount of rare earth elements (0.1 percent-0.2 percent, mass fraction)can fine AM60B's grain and improve its ductility.

Effects of rare earths on friction and wear characteristics of magnesium alloy AZ91D

The influence of various rare-earth contents on the friction and wear characteristics of magnesium alloy AZ91D was studied. The results show that the wear resistance properties of rare-earth magnesium alloys are better than those of the matrix alloy under the testing conditions. Magnesium alloys undergo transition from mild wear to severe wear. The addition of rare earths refines the structure of alloys, improves the comprehensive behaviors of the magnesium alloys, increases the stability of oxidation films on worn surfaces, enhances the loading ability of rare-earth magnesium alloys, and delays the transition from mild wear to severe wear effectively.

Study on Ignition-Proof AZ91D Magnesium Alloy Added with Rare Earth

Magnesium alloy is prone to burning during its melting and casting processes in air, which is a major factor of obstructing its application. Fluxes and cover gases are currently used for the melting and production processes, and semi-solid casting is also used to shape composites made of magnesium alloy, but there still remain many problems. Alloying is a promising method of preventing magnesium from burning. The effect of RE additions on the ignition temperature of AZ91D magnesium alloy was investigated. The changes of the quality of oxidation film and the as-cast microstructure were analyzed, and the mechanical property was compared with that without rare earth. For AZ91D with RE in the range of 0.08% to 0.12%. It is shown that the ignition temperature point can be greatly heightened, the quality of oxidation film is obviously improved, the as-cast microstructure is refined greatly, and the mechanical property is bettered a little, therefore, such an alloy is promising.

Influence of Solution Composition on Formation of Golden Yellow Rare Earth Conversion Film on Magnesium Alloy

Cerium sulfate was used as main composite in solution to prepare golden yellow chemical conversion film on magnesium alloy. The influence of solution composition on the surface morphology of golden yellow rare earth conversion film on magnesium alloy was studied by means of SEM; potential-time curves in the formation process of rare earth conversion film and the anti-corrosion property of the conversion film were tested through ECT. The results show that, when there is no other component in the solution besides cerium sulfate, yellow film can be obtained on magnesium alloy, but there are some dusts on the film surface and the solution is not stable. The stability of cerium sulfate solution increases with adding hydrogen peroxide, while the film is thin and its color turn light. After adding combination additive containing Al 3+, smooth and compact golden yellow film was obtained on magnesium alloy. The polarization curves tested in 3.5% NaCl solution show that the anti-corrosion property of magnesium alloy is increased obviously by rare earth conversion film, and the film has self-repairing capability in the corrosion process.