Research on flow stress of spray formed 70Si30Al alloy under hot compression deformation

The flow stress of spray formed 70Si30Al alloy was studied by hot compression on a Gleeble- 1500 test machine. The experimental results indicated that the flow stress depends on the strain rate and the deformation temperature. The flow stress increases with an increase in strain rate at a given deformation temperature. The flow stress decreases with the deformation temperature increasing at a given strain rate. The relational expression among the flow stress, the swain rate, and the deformation temperature satisfies the Arrhenius equation. The deformation activation energy of 70Si30Al alloy during hot deformation is 866.27 kJ/mol from the Arrhenius equation.

Research on Development of Dolomite-Ferrosilicon Thermal Reduction Process of Magnesium Production

Up to now, the Pedgion magnesium reduction process is the dominating magnesium production process. In 2004, about 98% of raw magnesium is produced by Pedgion magnesium reduction process in China which equals to 60% of the global output. It shows that the dolomite-ferrosilicon thermal reduction process is the most important method to produce magnesium in the world. Limited by the disadvantage of dolomite-ferrosilicon thermal reduction process, the magnesium producing process always followed by relatively severe pollution, while the resource utilizing efficiency keeps very low. With the rapid development of dolomite-ferrosilicon thermal reduction process in China, many research works have been done aiming at the process technology and the reduction theory, and the magnesium producing process has got great evolution. The history of dolomite-ferrosilicon thermal reduction process was introduced; the process character, the merits and which defects were also discussed. Defects in dolomite-ferrosilicon thermal reduction process were expatiated, and feasible method and idea to upgrade the process was put forward. The main problems and the potential troubles hindering the development of magnesium industry were analyzed. Finally, the probability to further improve the thermal reduction process and the effective approaches to develop Chinese magnesium industry were discussed.

Research on purification and modification of I/S bentonite

Analyzing raw material＇s structure and performance of bentonite from Panzhihua in Sichuan, the authors think that it is adequate for agglomerant of iron smelting. According to its composition and property we have researched the purification and modification of I/S bentonite under conditions of different dispersants and sodium agent. XRD test result reveals that the essential minerals of Panzhihua bentonite are I/S mixed-layer ones, and FTIR analysis shows that when adding 1.5% sodium pyrophosphate to the bentonite slurry during purification, the composition of quartz in bentonite decreases to less than 4% and I/S is more than 90%. The optimized modification technic conditions are Na2CO3 （4%） and CMC-Na （3%） as modified agents, the clay and water are 10 vs. 1, and the temperature is 75℃. It is 40 min for stirring time and reacting time is 4 h. Under the conditions we can get the modified I/S bentonite with colloid index more than 500 nd/15 g.

Semi-solid slurry of AZ91 magnesium alloy prepared by electromagnetic stirring near liquidus temperature

An electromagnetic stirring process near liquidus temperature was designed and demonstrated experimentally to produce semi-solid slurry of AZ91 magnesium alloy,in order to avoid not only contamination from mechanical stirring but also the inflammation of Mg alloy melt at elevated temperature. AZ91 alloy feedstock was isothermally heat treated at 600-610 for 20 min,and then stirred by electromagnetic field. Globular primary particle characteristic was observed optically in the castings. Mechanical properties were also studied.

Relationship between extrusion,Y and corrosion behavior of MgeY alloy in NaCl aqueous solution

The effect of hot extrusion and addition of Y element on the corrosion behavior of MgeY alloy was investigated by weight loss,immersion tests and potentiodynamic polarization measurements.The results showed that the grains became finer and uniform by increasing Y element,after extrusion.The corrosion resistance of MgeY alloy after extrusion was deteriorated with the addition of Y element and corrosion rates decreased in the following order:Mge13.78Y>Mge7.46Y>Mge5.23Y.

The corrosion behaviors of Mg-7Gd-5Y-1Nd-0.5Zr alloy under(NH4)_(2)SO_(4),NaCl and Ca(NO_(3))_(2)salts spray condition

The corrosion behaviors of Mg–7Gd–5Y–1Nd–0.5Zr alloys after T5 treatment under(NH4)_(2)SO_(4),NaCl and Ca(NO_(3))_(2)salt spray condition were investigated by weight loss rates,residual mechanical properties,scanning electron microscope(SEM),X-ray Diffraction(XRD)and potentiodynamic polarization tests.The corrosion degree of Mg–7Gd–5Y–1Nd–0.5Zr alloys in Ca(NO_(3))_(2)salt spray was very shallow by corrosion morphology and the corrosion route was extended along the surface in texture-like shape,while the alloy in NaCl and(NH4)_(2)SO_(4)salt spray were major local corrosion and there were serious corrosion pits on the surface.The weight loss rates in(NH4)_(2)SO_(4),NaCl and Ca(NO_(3))_(2)salt spray was respectively 0.4147,0.1618 and 0.0725 mg/(cm2 d−1).The results of residual mechanical properties indicated that the corrosion order in salts spray of Mg–7Gd–5Y–1Nd–0.5Zr alloys is NH4SO4>NaCl>Ca(NO_(3))_(2),which was consistent with the results of potentiodynamic polarization tests.The type of the salts will play a vital role in the initiation of the corrosion of EW75 alloy when they are used in the atmosphere environments.Inorganic salts with the smaller PH value after dissolution will have a stronger impact on the corrosion of EW75 magnesium alloys.

Evolution of precipitates in Mg−7Gd−3Y−1Nd−1Zn−0.5Zr alloy with fine plate-like 14H-LPSO structures aged at 240℃

The morphology and crystal structure of the precipitates in Mg-7Gd-3Y-1Nd-1Zn-0.5Zr(wt.%)alloy with fine plate-like 14H-LPSO structures aged at 240℃were investigated using transmission electron microscopy(TEM)and high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM).Fine plate-like 14H-LPSO structures precipitate after heat treatment at 500℃for 2 h,andβ-type phases precipitate after the alloy is aged at 240℃.The long-period atomic stacking sequence of 14H-LPSO structures along the[0001]αdirection is ABABCACACACBABA.After being aged at 240℃for 2 h,theβ-type phases are the ordered solution clusters,zig-zag GP zones,and a small number ofβ′phases.The peak hardness is obtained at 240℃for 18 h with a Brinell hardness of 112,theβ-type phases areβ’phases and local RE-rich structures.After being aged at 240℃for 100 h,theβ-type phases areβ’,β1 andβ’F phases.β′phases nucleate from the zig-zag GP zones directly withoutβ″phases,and then transform intoβ1 phase byβ’→β’F→β1 transformations.The Zn not only can form LPSO structure,but also is the constituent element ofβ1 phases.LPSO structures have a certain hindrance to the coarsening ofβ’andβ1 along<0001>α.

Mechanical properties of fine grained superalloy K4169 with addition of refiners

Grain refinement of superalloy K4169 was achieved by adding refiners into the alloy melt and their effects on the mechanical properties were investigated. The tensile properties at room temperature and 700 ℃ and low cycle fatigue properties at room temperature were compared for both conventional and fine grained test bars. The results indicate that the rupture strength, yield strength, elongation and reduction of area for refined grains are all much superior to those for coarse ones. Whereas the elongation and reduction of area of fine grained samples decrease at 700 ℃. Low cycle fatigue properties of samples with refined grains at room temperature are improved significantly. In addition, the degree of dispersion of low cycle fatigue data of samples with refined grains is diminished.

Dynamic precipitation during multi-axial forging of an Mg-7Gd-5Y-1Nd-0.5Zr alloy

The dynamic precipitation behavior during multi-axial forging in an Mg-7Gd-5Y-1Nd-0.5Zr alloy has been investigated and compared with that in static precipitation treatment. The results indicated that dynamic precipitation does occur during multi-axial forging. The dynamic precipitate can be deduced as β phase with face-centered cubic crystal structure (a = 2.22 nm). Most of the β precipitates locate at the dynamic recrystallization grain boundaries. The morphology and orientation relationship is different from that of the β phase formed in the static precipitation treated alloys, although the crystal structure is the same. The precipitation temperature of β phase during MAF is higher than that in the static precipitation treatment.

Influence of aging treatment on corrosion behavior and mechanism of Mg–Y alloys

This paper studied the influence of aging treatment on the corrosion behavior and mechanism of Mg-Y alloys with different Y content through corrosion mass loss test, electrochemical test and corrosion morphologies observation. Results show that the peak-aging times of Mg-（0.25, 2.5, 5, 8 and 15） Y alloys at 250 ℃ were 4, 6, 10, 12 and 16 h. The aging treatment reduced the corrosion resistance of Mg-Y alloys, and the corrosion resistance of Mg-Y alloys became worse with increasing of the aging time. The change magnitude of the open circuit potentials for Mg-（0.25, 2.5）Y alloys was greater than that of Mg-（5, 8 and 15）-Y alloys. The polarization curves of Mg （0.25, 2.5, 5, 8 and 15） Y alloys had the similar shape after aging treatment, and the slopes of the anodic branch were greater than those of the cathodic branches. After aging treatment, the corrosion modes of Mg-0.25Y and Mg-（2.5, 5, 8 and 15） Y alloys were uniform corrosion and pitting corrosion with small local deep corrosion.

EFFECTS OF DISSOLVED MINERAL SPECIES ON THE SURFACE CHEMICAL CHARACTERISTIC,ELECTROKINETIC PROPERTY AND FLOTATION BEHAVIOR OF FLUORITE AND SCHEELITE

Interactions between the dissolved mineral species and other mineralsurface were investigated using solution chemistry calculation, -potential measurement, AES analysis and flotation tests. It has been indicated that there canbe precipitation of scheelite over fluorite in scheelite supernatant at PH> 4.The conversion of fluorite into scheellte was detected by AES. Fluorite in the supernatant of scheelite exhibits nearly identical electrokinetic property andflotation behavior with those of scheelite. The selective flotatlon separation of fluorite from scheelite or vice vasa may be achieved by using selective amphoteric collector for fluorite at PH<4 to avoid surface conversion.

Property measurements on spray formed Si-Al alloys

A novel Si-Al alloy was prepared by spray forming process for electronic packaging. Property measurements on spray-formed Si-Al alloys after hot pressing were carried out. The results indicate that the alloys (Si-(30%-40%)Al) have advantageous physical and mechanical characteristics, including low coefficient of thermal expansion (6.9×10-6-8.7×10-6/K), high thermal conductivity (118-127 W/(m·K)), low density (2.421×103-2.465×103 kg/m3), high ultimate flexural strength (180-220 MPa) and Brinell hardness (162261). The alloys are easy to machine to tight tolerances using standard machine tools and they can be electroplated with gold finishes and soldered with Sn-Pb alloy without any difficulty.

Numerical simulation of die filling behavior of AZ91D in the semisolid process

In this work,numerical simulation of the die filling and solidification process of AZ91D semisolid alloy was investigated to produce a thin walled connecting rod demanding a high dimensional precision.The Carreau viscosity model was implemented to simulate the-ow behavior of semisolid slurry during the filling.The fitted constants for the Carreau model were used to verify the simulation results.The predicted results from this model were in good agreement with the experimental results.Then the verified Carreau model was designed to predict die filling,casting defects and casting process.It was found that the predicted results had a good correlation with those in the experiment.The optimum parameters were obtained with a slurry temperature of 590 °C,a die temperature of 250 °C and an injection velocity of 2 m/s.

Relationship between Heat Treatment and Corrosion Behavior of Mg-15Y Alloy

The corrosion behaviors of a basic type of RE-containing magnesium alloy Mg-15Y processed by different heat treatment methods were studied in 3.5% NaC1 solution at room temperature. The amount of Mg24Y5 phase decreased with the extending of homogenization treatment. The time for achieving dissolving equilibrium of homogenization treatment at 525, 535, and 545 ℃ was 24, 20, and 8 h, respectively. The corrosion behavior of Mg-15Y alloy was studied using immersion, hydrogen evolution and electrochemical tests. The experimental results revealed that the heat treatment improved the corrosion resistance, and the corrosion resistance became better with increasing the heat treatment time. The corrosion mode of the alloy after heat treatment was microgalvanic corrosion consisting of the cathodic Mg24Y5 phase and anodic α-Mg matrix, and Mg-15Y exhibited favorable uniform corrosion mode in NaC1 solution. The volume and increasing tendency of the homogenization treatment samples were both more than those of the as-cast sample.

Cellular automaton modeling of semisolid microstructure formation

Computer modeling of semi-solid structure formation is of significance in both understanding the mechanisms of globular structure formation and determining the effect of solidification conditions on final microstructure.A modified cellular automaton(mCA) model has been developed,which is coupled with macroscopic models for heat transfer calculation and microscopic models for nucleation and grain growth.The mCA model is applied to A356 Al alloy-one of the most widely used semi-solid alloys,to predict grain morphology and grain size during semi-solid solidification,and determines the effects of pouring temperature on the final microstructure.The modeling results show that the lower the initial temperature,the finer grain size will be obtained.In addition,the model can be used to predict the solutal micro-segregation.

Effects of heat treatment and plastic deformation on structure and properties of Mg-9Al-1.2Nd-0.45Y-0.7Zn Mg alloy

The experiments of heat treatment,hot extrusion and hard drawing were employed to study their effects on the structure and mechanical properties of Mg-9Al-1.2Nd-0.45Y-0.7Zn magnesium alloy. The results indicate that the mechanical properties of the ingot are unstable and exhibit typical brittle failure. After heat treatment(693 K,24 h),most β-Mg17Al12 phases decomposed into the α-Mg matrix and the distribution of Rare earths compounds remained the state of as-cast,which have little effects of the mechanical properties of the alloy. As the casting defects disappeared and the grain was refined after hot extruded,the mechanical properties of the alloy were drastically increased. By hard drawing,the ultimate tensile strength and the yield strength of the alloy were sharply increased while the elongation decreased rapidly. The failure of as-cast samples was mainly brittle fracture. After plastic deformation,the fracture patterns all exhibited ductile rupture features.

Effects of Processing Technologies on Mechanical Properties of SiC Particulate Reinforced Magnesium Matrix Composites

Mg matrix composites with SiC particles ranging from 5vol%-25vol% were prepared using stirring casting method. Die casting, squeezing casting, and extrusion were applied for inhibiting or eliminating the defects such as gas porosity and shrinkage void. Through die casting and squeezing casting, most of the defects in Mg matrix composites could be eliminated, but the mechanical properties were improved limitedly. On the other hand, after hot extrusion, not only most of the defects of as-cast composites ingots were eliminated, but also the mechanical properties were improved markedly. With the addition of SiC, the tensile strength, yield strength and elastic modulus of as extrusion SiCp/AZ61 composites increased remarkably, and the elongation decreased obviously.

Corrosion Mechanism and Corrosion Model of Mg-Y Alloy in NaCl Solution

Corrosion of Mg–Y alloy was studied using electrochemical evaluations, immersion tests and SEM observations. Corrosion mechanisms of Mg-（0.25 and 2.5） Y alloy and Mg-（5, 8, and 15） Y alloy were uniform corrosion and pitting corrosion respectively, and the content of Mg_（24）Y_5 phases determined its effect acting as cathode to accelerate the corrosion or corrosion barrier to inhibit the corrosion. Corrosion resistance of Mg-（0.25, 2.5, 5, 8, and 15） Y alloys was as follows： Rt（Mg-0.25Y） 〈 Rt（Mg-8Y） 〈 Rt（Mg-15Y） 〈 Rt（Mg-5Y） 〈 Rt（Mg-2.5Y）. Y could significantly improve the corrosion resistance of the Mg-Y alloy, but the excess of Y deteriorated the corrosion resistance of the Mg-Y alloy. The optimum content of Y in the studied alloys was 2.5%.

Property and performance amelioration of pelagic clay from the East Pacific

To make use of the pelagic clay as polymer filling,the properties of clay sediments from the ocean investigation zone of China in the East Pacific were studied by the SSA,XRF,ICP/MAS,FTIR,XRD,SEM,DTA/TG and granularity distributing etc.,and experiments were settled to improve the whiteness and activation of the clay based on these data.Compared with land clay,pelagic clay holds many particular features,such as fine particles and incompact accumulation,worse crystallization and more defects,high activity,complex mineral and chemical components,and low whiteness etc.Processing the purified pelagic clay with acids and zinc,then baked it at different temperatures,the whiteness of clay can be increased from 23.8% to 73.1%,and the optimized conditions is:consistency of vitriol 25%,ratio of clay to water 4∶1,reaction time 4h,reaction temperature 90℃,dosage of zinc 2.0 g/L,and baking temperature 700℃.And the SSA of whited clay is increased too.Using the dry milling method to modify the pelagic clay with organic reagents,the optimized technique is KH550,concentration 1.5%,reaction time 20 min.XRD,FTIR and SEM testing indicate that the mechanism of organic activation was mainly surface absorbing and chemical combination secondly.

In situ Observation of Mo Implanted HI3 Steel by Transmission Electron Microscopy

In situ observation in high voltage transmission electron microscope(HVEM)was used to investigate the structure of Mo implanted HI3 steel.Instead of tempered Martensite structure,the implanted layer has a fine grain structure.When the implanted specimen is heated inside the HVEM,the fine grain structure does not change until 500℃.The electron diffraction pattern of precipitates FeMo appears at 500℃.Recrystallization and grain growth occur at 650℃.