EFFECTS OF MISCHMETAL ADDITION ON THE CAST MICROSTRUCTURE OF 6063 ALLOYS

Effect of mischmetal addition on the cast microstructure of 6063 alloys has been investigated by means of optical microscopy, TEM and anode filming etc. The results show that there is a critical content of fining dendrite structure by adding mischmetal to 6063 alloys. This critical mischmetal content is about 0.15%. Only when the mischmetal content is above 0.15%, the secondary dendrite arm spacing decreased and eutectic structure fined. The cast grain is obviously refined when the content of mischmetal is lower. Consideration from the cast structure, the suitable mischmetal content in 6063 alloys is 0.20%.

Effect of Ce-base mischmetal addition on the microstructure and mechanical properties of hot-rolled ZK60 alloy

Mg-Zn-Zr(ZK)alloys exhibit notably high mechanical strength amongst all magnesium alloy grades.However,due to the formation of low melting point Mg_3Zn_7-precipitates,these alloys are susceptible to hot cracking,thus compromising their metallurgical processing.The addition of rare earths to ZK alloys is an alternative to form higher melting point intermetallic compounds,speed up dynamic recrystallization,refine grain size,enhance corrosion resistance and extend the service temperature due to improved creep resistance.This work deals with the effect of Ce-base mischmetal addition on the hot rolling behaviour of as-cast ZK60 alloy.The microstructure investigation conducted using electron microscopy and X-Ray diffraction shows that precipitation of Mg_(7)Zn_(3) intermetallics occur during hot rolling,whereas no further precipitation is observed for the ZK60-Mm alloys.The fragmentation of the intermetallic compounds occur during hot rolling and finer particles of Mg_(7)Zn_(3) are observed for the ZK60,whereas Mg_(7)Zn_(3) and Mg Zn_(2) Ce intermetallics are formed in the alloy modified with mischmetal addition.A higher fraction of dynamically recrystallized grains is observed for the ZK60-Mm in comparison to the ZK60.Continuous recrystallization takes place in ZK60 with the formation of sub-grains near to the intermetallics and the addition of mischmetal promotes the occurrence of discontinuous recrystallization with the nucleation of new grains close to the precipitates.The mechanical strength and,in particular,the ductility of the hot-rolled alloys are notably improved when compared to the same alloys in the as-cast condition.The mechanical strength is,however,higher for the ZK60 alloy.Less solid solution strengthening,softer Mg Zn_(2) Ce intermetallics and more extensive recrystallization contribute to reduce the mechanical strength of ZK60-Mm.Failure in both alloys are initiated at coarse intermetallics and propagate through intermetallic-rich regions.

Grain Coarsening Behavior of Mg-Al Alloys with Mischmetal Addition

Small addition of mischmetal （MM） into aluminum alloys can lead to grain refinement. However, it is still uncertain whether the same effect applies to Mg-Al alloys. This work indicated that small amount of mischmetal addition ranging from 0.1% to 1.2% （mass fraction） did not cause grain refinement in Mg-Al alloys. On the contrary, they tended to coarsen the grains. When added into Mg-Al alloys, MM reacted preferentially with Al to form Al11 MM3 phase. As Al11 MM3 phase mainly distributed within α-Mg grains than at grain boundaries, it had little effect in restricting grain growth. In addition, MM reacted with Al8（Mn, Fe）5 or ε-AlMn particles to form Al-MM-Mn compounds, thus it reduced the amount of heterogeneous nuclei in the melt and resulted in remarkable grain coarsening.

Effect of Lanthanum-praseodymium-cerium Mischmetal on Mechanical Properties and Microstructure of Mg-A1 Alloys

The effects of lanthanum-praseodymium-cerium mischmetal （LPC） on the microstructure and mechanical properties of Mg-Al alloy were investigated. With the addition of LPC, an additional rod-like Al11La3 phase was deposited in the alloy. LPC greatly improves the tensile strength of cast Mg-Al alloys but negatively affects the elongation of cast alloys above 473 K. Cast alloys are strengthened by both precipitation strengthening and dispersion strengthening at ambient temperature. When the temperature exceeds 473 K, only the dispersion operates as a strengthening mechanism.

Effect of Mischmetal Addition on Catalytic Performance of PtSnNa/ZSM-5 for Propane Dehydrogenation

The influence of mischmetal addition on physicochcmical properties of PtSnNa/ZSM-5 catalyst was studied by means of XRF, H2 chemisorption, XRD, TPR, NH3-TPD and TPO techniques. The results showed that the presence of mischmetal had an obvious impact on the catalytic performance of the PtSnNa/ZSM-5 catalyst. A suitable content of mischmetal not only could enhance the interactions between Pt species and the support, but also inhibit the formation of coke during the reaction, thus improving the catalytic activity and stability. In our experiments, when the content of mischmetal was 3m%, the catalyst exhibited best catalytic performance. However, the continuous addition of mischmetal could promote the reduction of Sn species to metallic tin, which was disadvantageous to the reaction.

EFFECT OF TRACE MISCHMETAL ON THE MICROSTRUCTURE AND PROPERTIES OF 2618 ALUMINIUM ALLOY

The physical,mechanical properties and microstructures of three 2618 Aluminum alloys containing less than 0.046 wt.-%mischmetal have been studied.lt has been shown that the trace mischmetal has no obvious influence on the physical properties of the.alloy,but can clearly improve plasticity and toughness,and slightly raise the thermal stability.

Influence of Samarium and Neodymium on Production of Mischmetal by Molten Salt Electrolysis Process

In molten salt electrolysis of mixed rare earth chlorides,the influence of the amount of samarium and neodymium containing in the raw material is experimented and discussed.The process of the formation of oxychloride,which is harmful to the production of mischmetal,is described.

Chemical Conversion Film of Mischmetal on Zinc Deposit

A conversion film was obtained on zinc deposit by immersing zinc coated specimens in a mischmetal salt solution. Several factors affecting the anticorrosive efficiency of the conversion film were studied. The suitable technological conditions were established. The composition and the thickness of the conversion film were determined by Auger electron spectroscopy(AES).

The Influence of Mischmetal on Wetting of Steel by Zn+5wt%Al Alloys

The wetting of steel sheet by liquid Zn+5 wt%Al alloy has been measured by the Meniscograph. The result shows that the addition of mischmetal in Zn+5 wt%Al alloy decreases the surface tension of the alloy,reduces the wetting angle of the liquid alloy raising in steel substrate surface and enhances the adhesive power and wettability between them.It is concluded that the mischmetal addition in baths influences the reac- tion between steel sheet and liquid Zn+5 wt%Al alloy and thus improves the wettability of them.

Researches on Mischmetal Preventing Lead Segregation in High Lead Bronze

The effect of mischmetal addition on lead segregation in high lead bronze(grade ZQPb25-5)is studied in this paper.The testing results confirm that 0.5 to 1.0% misehmetal addition can effectively prevent lead from gravity and inverse segregation.The results of preventing lead from segregation respectively by mischmetal and nickel are also compared in the paper.The mischmetal addition in high lead bronze is distributed in the copper matrix mainly in the form of a compound which promotes early precipitation and refinement of α-dendrites, thus restraining the Pb-rich melt from either sinking to the bottom or escaping to the surface layer of the casting.As a result,the tendency of lead segregation is significantly decreased.Proper addition of mischmetal can also improve the mechanical properties,especially the ductility of high lead bronze.In addition,the contents of tin in high lead bronze can partially be substituted by mischmetal addition.

The Quality Specifications of Mischmetal Wire and Rod and the Method of Adding Rare Earth in Steel

The quality of mischmetal wire and rod and the method of adding rare earth into steel are quite important for making high quality steel. This paper proposes a quality specification of wire and rod as well as related adding method. The paper also provides principles for selecting raw material and adding method.

Effects of mischmetal addition on phase transformation and as-cast microstructure characteristics of M2 high-speed steel

The influence of mischmetal （Ce-La） addition on phase transformation and as-cast microstructure characteristics of M2 high-speed steel （HSS） was investigated using Thermo-Calc software, differential scanning calorimetry, X-ray diffractometry and scanning electron microscopy with energy dispersive spectrometry. The results showed that the measured phase transition points of M2 HSS were broadly consistent with the theoretical results. After mischmetal addition, the liquidus peak temperature, the peak temperature of the eutectic precipitation of M6C and MC were all increased, especially for the M6C which was affected significantly and increased about 31 °C. The contents of Mo and V in the eutectic carbide decreased and that of Fe increased, while in the matrix, the Mo, V and Cr contents all increased slightly. Furthermore, the microstructure of as-cast dendrite and ledeburite were refined, the total eutectic carbide content decreased and distributed into a discontinuous network, the lamellar spacing of M2C was reduced and the lamellae became thinner.

Magnetic properties of melt-spun MM-Fe-B ribbons with different wheel speeds and mischmetal contents

In this study, the effect of wheel speed and mischmetal（MM） content on the magnetic properties of MMFeB ribbons was investigated. The samples were prepared via direct solidification technique. The nominal composition of the alloy ingots is MM;Fe;B;with x varying from 9 to 15 in steps of 2. Experimental results show the overall magnetic properties of the ribbons.Analysis of the results shows that the magnetic properties first improve and then degrade with the wheel speed and MM content increasing. Increase in MM content leads to better formation of crystal texture in the ribbons, indicating that the a-Fe phase might undermine the formation of crystal texture. Magnetic properties results show that the coercivity of the ribbons rises with an appropriate increase in both MM content and wheel speed during melt-spun process. The strongest magnetic properties of the ribbons(remanence of M;= 0.72 T, intrinsic coercivity of H;= 352.58 kA·m;, and maximum energy product of（BH）;=72.14 kJ·m;) are obtained for compositions where x = 13 and a wheel speed of v = 20 m·s;.

Effect of Mischmetal on As-cast Microstructure and Mechanical Properties of M2 High Speed Steel

High speed steel has been widely used in various fields due to their excellent red hardness and good wear resistance. However, the influence of mischmetal （Ce-La） on the as-cast microstructures and mechanical properties of high speed steel has rarely been reported. Thus, the microstructure and mechanical properties of M2 high speed steel with addition of mischmetal （Ce-La） were investigated. The morphology and distribution of the eutectic carbides of the steel were observed by using optical microscopy and scanning electron microscopy, and the impact toughness and bending strength were tested. The results show that adding mischmetal has an obvious effect on the microstructure and mechanical properties of M2 high speed steel. The coarse eutectic structure is refined, the weak connection of the carbide networks is broken and the flake carbides become short and fine. More networks of eutectic carbides dissolve into the matrix. When a suitable adding content of mischmetal is selected, for example, 0.3 mass%, the impact strength and bending strength can increase by 27% and 10.76% compared with that without misehmetal, respectively.

Hot Deformation Behavior of As-cast AISI M2 High-speed Steel Containing Mischmetal

The hot deformation behavior of as-cast AISI M2 high-speed steel containing mischmetal （RE） has been investigated on a Gleeble-3500 simulator in the temperature range of 1000--1 150 ℃ and strain rate range of 0.01- 10 s 1 at true strain of 1.0. The mechanical behavior has been characterized using stress-strain curve analysis, kinetic analysis, processing maps, etc. Metallographic investigation was performed to evaluate the mechanism of flow insta- bility. The results show that the deformation activation energy decreases with increasing deformation temperature; the efficiency of power dissipation increases with decreasing strain rate and increasing temperature; flow instability is observed at low-to-medium temperature and higher strain rate region when the strain is smaller, but extends to lower strain rate and high temperature regions with the increment of strain, in which it is manifested as flow localization near the grain boundary. Hot deformation equations and processing maps are obtained. The optimal processing window is suggested and the deformation mechanism is dynamic recrystallization （DRX）.

Effect of Lanthanum on Nodule Count and Nodularity of Ductile Iron

The present study aims at finding out the effect of the addition of a single rare earth element, that is, lanthanum on the nodularity and nodule count of ductile iron under controlled conditions. For this purpose, four melts with different compositions were made, using a 28 kg inductotherm medium frequency induction furnace. The temperature was carefully maintained between 1400 and 1450 ℃ for these heats. A good quality charge consisting of Sorel metal, ferrosilicon, Swedish iron, ferrosilicon magnesium, and ferrosilicon lanthanum was used for the production of melts. A vertically parted sand mould was used for casting of 10 test bars made from local silica sand. Standard coin samples were chill-cast to conduct chemical analysis of the ductile iron. Mierostructure study of the samples was conducted using a Leica optical microscope. Nodule count and nodularity of the samples were carried out using an image analyzer. The results obtained indicated that with the increased addition of lanthanum the nodule count of ductile iron increased, thus making it evident that it played a significant role in increasing the mechanical properties. The highest nodule count of 467 was obtained with the addition of 0.03% lanthanum. However, the effect of lanthanum on nodularity was negligible with nodularity ranging from 81% to 83 %.

Influence of Annealing Treatment on Microstructure and Cycling Stability of La-Rich Ml(NiCoMnAl)_5 Alloy Electrode for Ni/MH Batteries

The crystallographic structure, microstructure, composition homogeneity and electrode charge-discharge cycling stability were investigated of the as-cast and annealed La-rich mischmetal (designating Ml)-based hydrogen storage alloy with a composition of MlNi_(3.55)Co_(0.75)Mn_(0.4)Al_(0.3). X-ray diffraction analysis shows that the MlNi_(3.55)Co_(0.75)Mn_(0.4)Al_(0.3) alloy is composed of the dominant phase with a CaCu_5-type hexagonal structure and small amounts of the second phase with a La_2Ni_7-type structure. The annealing heat treatment conducted at 1273 K for 10 h results in decrease of the crystal lattice strain and composition segregation, disappearance of the dendrite structure and growth of the crystal grain of the MlNi_(3.55)Co_(0.75)Mn_(0.4)Al_(0.3) alloy. The annealing causes the cycle life to be increased by about 30% over the as-cast alloy electrode. The cycling stability of the alloy electrode is improved significantly upon annealing. The cause of the improvement in the cycling stability was discussed based on the alloy composition distribution and microstructure changes due to annealing.

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.

Microstructure and mechanical behavior of similar butt-joints of ZK60 and ZK60-1.5RE magnesium alloys produced by linear friction stir welding

The microstructure and mechanical properties of butt-joints produced by linear friction stir welding of similar plates of as-cast ZK60 and modified ZK60 with 1.5 wt.%RE(ZK60-1.5 RE)are investigated.The thermomechanical affected zone is investigated in both advancing and retrieving sides,and the microstructure is compared to the base metal and the stirred zone.Electron backscattered diffraction measurements provide the average microstructural features of the transformed microstructure.The mechanical properties are assessed using hardness,tensile testing,and surface residual stress measured using X-ray diffraction.Higher torque and heat input are obtained for the ZK60-1.5 RE compared to the ZK60.The thermomechanical affected zone is notably larger for the ZK60 compared to the ZK60-1.5 RE.A gradient microstructure is formed in thermomechanical affected zones where deformed grains are progressively more recrystallised towards the stirred zone.There is no visible interface between the thermomechanical affected zone and the stirred zone.A fine and partially recrystallised microstructure is formed in the stirred zone.The retrieving side of the ZK60-1.5 RE has a slightly more refined microstructure compared to the other investigated zones.Anisotropy measured with increment in the maximum intensity of the(0001)increases towards to stirred zone.The formed microstructure is correlated with the role of twinning,recovery,static,and dynamic recrystallisation that can occur during friction stir welding.Twinning and grains with large misorientation spread are more pronounced in the thermomechanical affected zone and regions towards the base metal.Sharp low angle grain boundaries are observed towards the stirred zone.From refined recrystallised grains decorating the grain in the thermomechanical affected zone,a mosaic-like of low and high angle grain boundaries are observed in the stirred zone.The joints have comparable surface residual stresses.The friction stir welding improved the ductility and strength of the as-cast ZK60-1.5 RE alloy since the tensile samples fractured in the BM.

Kinetics of Hydrogen Absorption in MmNi_（3．55）Co_（0．75）Mn_（0．4）Al_（0．3） Alloy

The kinetic process of MmNi3. 55Co0. 75Mn0. 4Al0. 3 alloy absorbing hydrogen in αand α+βphases at the temperature range of 22￣ 60℃ has been studied. The results show that the kinetic process is controlled by chemical reaction in the α phase and the mechanism of hydrogenation kinetics is not affected by initial hydrogen pressure. In the α+β phase region,the speed of hydrogen absorption is controlled by hydrogen diffusion in the hydride.A reaction rate equation and apparent activation energy have been obtained.