Microstructure and mechanical properties of friction stir weld of dissimilar AZ31-O magnesium alloy to 6061-T6 aluminum alloy

Dissimilar friction stir welding between AZ31-O Mg and 6061-T6 Al alloys was investigated. 3 mm thick plates of aluminum and magnesium were used. Friction stir welding operations were performed at different rotation and travel speeds. The rotation speeds varied from 600 to 1400 r/min, and the travel speed varied from 20 to 60 mm/min. Defect-free weld was obtained with a rotation speed of 1000 r/min and travel speed of 40 mm/min. Metallographic studies showed that the grain size in the stir zone is much finer than that in the base metals. Complex flow pattern was formed in the stir zone. Microhardness measurement revealed an uneven distribution in the stir zone. Tensile test results indicated that the tensile strength of the welded specimen is about 76% of AZ31 Mg alloy and 60% of the 6061 Al alloy in tensile strength. SEM fracture surface image of the welded specimen indicated that the welded specimen failed through brittle-mode fracture.

Microstructural evolution and mechanical properties of nanostructured Cu-Al-Ni shape memory alloys

The melt spinning technique, with an applied cooling rate of about 106 K/s, was used to produce a nanostructured Cu＋13.2Al＋ 5.1Ni （in wt%） shape memory alloy. The properties of nanostructured ribbons were then compared with those of conventional coarse struc- ture. The microstructural evolution was characterized using scanning electron microscopy （SEM）, atomic force microscopy （AFM） and X-ray diffraction （XRD） techniques. Microhardness measurements indicate a two-fold increase in hardness because of the produced nanos- lructure. Comparing to its coarse structure, the nanostructured Cu-A1-Ni shape memory alloy exhibited the enhanced mechanical properties including a ductility of 6.5% and a pronounced plateau in the stress-strain curve.

Geostatistics Studies and Geochemical Modeling Based on Core Data,Sheytoor Iron Deposit,Iran

In general,the purpose of the mineralization modeling is the advancement of a mineral exploration project and ultimately,the extractive design of a deposit,which is one of the most important stages in mining engineering.Mineralization modeling is divided into two general categories,superficial and deep modeling.In surface modeling,the aim is finding abnormal locations in terms of mineralization at the study area,which is commonly used in the early stages of exploration as one of the means for locating exploratory boreholes.After drilling in the study area with the aim of identifying mineralization and reserve estimation it is necessary to obtain deep mineralization position and its geometric features,using statistical and modeling methods.Using mathematical,statistical and modeling methods,we can predict the position of iron mineralization in places where drilling is not done and eventually reach a three-dimensional model of the mineral materials underground.As a case study,the deep information about the boreholes of the sheytoor mining area in Yazd province of Iran was investigated.Iron mineralization was modeled as 2D cumulative model and 3D block model,and the results were presented.Finally the geochemical threshold and the anomalous limit of iron element are calculated by concentration-volume(C-V)fractal method in this deposit.Geochemical threshold and the anomalous limit for Fe in this deposit are 24.7%and 34.3%respectively.

Estimating and Plotting of Groundwater Quality Using WQI UA and GIS in Assiut Governorate, Egypt

This paper aims to turn complex groundwater data into comprehensible information by indexing the different factors numerically comparative to the standards of World Health Organization (WHO) to produce Water Quality Index (WQI). Water Quality Index (WQI) has been used to assess groundwater quality and Geographic Information Systems (GIS) has been used to create maps representing the spatial distribution of groundwater categories in Assiut governorate, Egypt. Water Quality Index has been computed by Un-weighted Arithmetic Water Quality Index (WQIUA) method and applied on 796 wells over eight years from 2006 to 2013. The results showed that WQIUA values for drinking purposes were high and most of them reached higher or close to 100, which indicated that the groundwater was polluted and unsafe for drinking. On the other hand, the quality index of groundwater for irrigation purposes in most of the study area ranges between 55.78 and 78.38 (poor and very poor category);this means that groundwater is moderately polluted and rather suitable for irrigation.

Numerical analysis of confinement effect on crack propagation mechanism from a flaw in a pre-cracked rock under compression

In many situations rocks are subjected to biaxial loading and the failure process is controlled by the lateral confinement stresses. The importance of confinement stresses has been recognized in the literature by many researchers, in particular, its influence on strength and on the angle of fracture, but still there is not a clear description for the influence of confining stress on the crack propagation mechanism of rocks. This paper presents a numerical pro- cedure for the analysis of crack propagation in rock-like ma- terials under compressive biaxial loads. Several numerical simulations of biaxial tests on the rock specimen have been carried out by a bonded particle model （BPM） and the influ- ence of confinement on the mechanism of crack propagation from a single flaw in rock specimens is studied. For this purpose, several biaxial compressive tests on rectangular spec- imens under different confinement stresses were modeled in （2 dimensional particle flow code） PFC2D. The results show that wing cracks initiate perpendicular to the flaw and trend toward the direction of major stress, however, when the lat- eral stresses increase, this initiation angle gets wider. Also it is concluded that in addition to the material type, the initiation direction of the secondary cracks depends on confine- ment stresses, too. Besides, it is understood that secondary cracks may be produced from both tensile and shear mechanisms.

Serviceability analysis of deep underground openings driven in jointed-rock

The performance of underground excavations is inevitably influenced by rock mass characteristics, presence of joints and their geometrical properties, depth below surface and state of in-situ stress field. The objective of this paper is to investigate the behaviour of deep underground tunnel opening existed between two bedding planes, Such planes weaken the strength of rock mass and may cause rock slippage/rotation along them. Therefore, the state of stress-displacement, after tunnel opening has been introduced, is examined using two-dimensional elasto-plastic finite-elements code, RS^(2D). The results indicate that, there is significant drop in the normal stress along joints over tunnel opening; slip occurs due to reversal in the direction of shear stress(e.g., inward shear displacement is produced) and there is discontinuity in the strength contours of rock surrounding tunnel after they have been intersected by bedding planes.

Studies of Grinding Media Corrosion from Galvanic Interaction on Galena Flotation

This study has been done to determine the galvanic interaction between five types of grinding media (mild steel, cast iron, 10% chromium, 20% chromium, and ceramic media) and galena, in situ of the mill. The ceramic media has a significantly not galvanic interaction with galena and high chromium media has a significantly weaker galvanic interaction with galena, and produces a very much lower amount of oxidize iron species in the mill discharge than mild steel medium. The investigation of the various reactions occurring on the galena surface was investigated by ethylene diamine-tetra acetic acid disodium salt (EDTA) extraction and X-ray photoelectron spectroscopy (XPS) measurements. The floatability of galena is dependent on the galvanic current between grinding media and galena during grinding because the current is relative to the amount of iron oxidation species and the reduction rate on galena. Iron oxidation species depressed galena flotation. The optimum galena flotation was achieved by selecting grinding conditions that enabled iron oxidation to be controlled.

Advantages of employing multilevel monitoring wells for design of tunnels subjected to multi-aquifer alluvial

For tunnels being excavated through multiple knowledge of the aquifers’hydraulic head becomes essential for determining groundwater inflow into the tunnel and analyzing its stability,specifically using multilevel monitoring systems.In the multi-aquifer alluvial section of the Glas tunnel(Iran),since the hydraulic head calculations were based on the data obtained from single-piezometer boreholes,the excavation risk was assessed to be at high level and the tunnel seemed to be unstable,thus an incorrect conclusion was derived from the misleading data.To take cost mitigation measures into account,it was necessary to calculate the hydraulic head at tunnel level accurately.By installing nested and clustered wells the mean hydraulic head was measured to be 70 m,significantly different from the 90 m previously determined by boreholes.Considering the updated value,the groundwater inflow and bulkhead load,formerly calculated as 0.65 m^(3)/s and 9.5 bars,were determined to be 0.49 m^(3)/s and 7.5 bars,respectively.

A Study of Heavy Metals in the Dust Fall around Assiut Fertilizer Plant

A study of an environmental assessment of dust fall and the associated heavy metal contents was conducted during the period from the first of March 2011 to the end of February 2012 at adjoining area of a phosphate fertilizer plant. Around the industrial area 8 dust fall stations were established and one of them was built upwind far from pollution activities to be taken as a control sample. Dust fall samples collected monthly weighed and then prepared to be analyzed through Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS) to obtain heavy metal concentration. Meteorological parameters influencing the distribution of dust fall such as wind speed and direction, temperature, humidity, rain fall and pressure were determined. Results showed that deposition flow rates were 38.2. 47.5, 57.7, 44.3, 39.4, 38.2, 42.7 and 5.9 g/m2·month for the sites No., 1, 2, 3, 4, 5, 6, 7 and 8 respectively, and were compared with the findings of other investigators of like industrial areas worldwide. Levels of heavy metal As, Cu, Pb, Zn, Cd, and Hg in the deposited dust fall were 3.30, 26.46, 22.33, 235.00, 4.53 and 3.80 μg/g respectively. Enrichment coefficients of the heavy metals in the dust fall were found to be significant and reached the values 1.81, 0.90, 0.85, 0.65, 0.41 and 0.35 for zinc, lead, cadmium, copper, mercury and arsenic respectively. The paper ends with results and recommendations suggesting a methodology to remediate the investigated area polluted with heavy metals and control measures for the fertilizer plant to reduce pollution into the surrounding environment.

High Temperature Deformation Behavior of 4340 Steel: Activation Energy Calculation and Modeling of Flow Response

The 4340 steel is extensively utilized in several industries including automotive and aerospace for manufac- turing a large number of structural components. Due to the importance of thermo-mechanical processing in the pro- duction of steels, the dynamic recrystallization （DRX） characteristics of 4340 steel were investigated. Namely, hot compression tests on 4340 steel have been performed in a temperature range of 900-- 1200 ℃ and a strain rate range of 0.01--1 s-1 and the strain of up to 0.9. The resulting flow stress curves show the occurrence of dynamic recrys- tallization. The flow stress values decrease with the increase of deformation temperature and the decrease of strain rate. The microstrueture of 4340 steel after deformation has been studied and it is suggested that the evolution of DRX grain structures can be accompanied by considerable migration of grain boundaries. The constitutive equations were developed to model the hot deformation behavior. Finally based on the classical stress-dislocation relations and the kinematics of the dynamic recrystallization; the flow stress constitutive equations for the dynamic recovery period and dynamic reerystallization period were derived for 4340 steel, respectively. The validity of the model was demon- strated by demonstrating the experimental data with the numerical results with reasonable agreement.

Mechanical and microstructural variations in ECAP of Ti-6Al-4V alloy with equiaxed microstructure

The aim of this study is to investigate mechanical and microstructural variations of Ti-6 Al-4 V acquired through various equal channel angular pressing(ECAP)cycles.The ECAP of Ti-6 Al-4 V alloy with the first equiaxed micros tructure was carried out by an isothermal warm and isothermal die method.EC A pressing carried out on cylindrical samples at 650℃.Mechanical and microstructural investigations were performed concerning Ti-6 Al-4 V in the first state after 2,4,and 8 passes.Optical microscopy(OM)investigation shows that alpha grain size increases and beta grain size decreases with the pass numbers increasing.Beta phase content initially decreases in the first two ECAP passes.The results show that more equiaxed alpha grains are achieved after four ECAP passes.Results of X-ray diffraction(XRD)analysis show that crystallite size decreases with the number of passes increasing.After two ECAP passes,a vivid increase in mechanical strength is observed;however,the increment dramatically slows down by the increasing number of passes.

Comparison of indirect boundary element and finite element methods A case study:Shiraz-Esfahan railway tunnel in Iran

Because of the high importance of transportation tunnels,most precise analyses of stress concentration and displacement around them are essential to provide safety of them as much as possible.Recently,various numerical methods such as finite element method(FEM),discrete element method(DEM),finite difference method(FDM)and boundary element method(BEM)have been used extremely in geosciences problems,but among these numerical methods,BEM has been used less than others because the computational algorithm is not so straightforward.This paper suggests the implementation of the indirect boundary element method(IBEM)as a formulation of BEM to analyze displacement around Shiraz-Esfahan railway tunnel in Zagros Mountains southwest of Iran.For this purpose,this tunnel has been modeled numerically using two-dimensional fictitious stress method(TWOFS)algorithm.To validate the results,they were compared with FEM results as a commonly used numerical method.Results of current theoretical study have shown that the presented approach using IBEM is reasonably accurate and can be used for analysis of displacement in geosciences problems.In rock mechanics,for problems with a low ratio of boundary surface to volume,FEM is not very well suited and may be cumbersome,but use of such a proposed IBEM approach can be particularly attractive.

Comparing the Fatigue and Corrosion Behavior of Nanograin and Coarse-Grain IF Steels

In the present work,a nanograin layer of about 150 μm thick was formed on the surface of an interstitial-free（IF） steel via friction stir processing.Then,the fatigue and corrosion behaviors of IF steel with nanograin layer were compared with that of coarse-structure counterpart.More than threefold increase in the hardness was observed due to the formation of nanograin layer.The size of nanograms in the stir zone was within 30-150 nm.This resulted in 50%increase in the fatigue strength of nanostructured specimen.Furthermore,the fracture surfaces were characterized using field emission scanning electron microscopy and scanning electron microscopy.As for the fatigue behavior of nanograin IF steel,the fracture surface was characterized by the formation of nanospacing striations and nanodimples.Besides,the nanograin structure pronounced the passivity and exhibited higher corrosion resistance.

Ga-(Nb+Ta)-(Nb/Ta)(Zr/Hf) Ternary Diagram: An Excellent Tool for Discriminating Barren and Ta-Hosting Granite-Pegmatite Systems

Discriminating barren and fertile intrusions is one of the main challenges in the search for rare-element pegmatites.Diagrams comprising more than one element can make discrimination of productive and barren samples more valid.These diagrams distinguish samples by simultaneous means of positive and/or negative correlations between variables.A ternary diagram for S-type peraluminous granites has been obtained in this study.Firstly,a database composed of Ta-bearing and barren granitic systems was created,then geochemical behavior of trace elements was studied,and statistical investigations were done using GCDkit software,which resulted in the Ga-(Nb+Ta)-(Nb/Ta)(Zr/Hf)ternary diagram which can distinguish the non-mineralized granites from productive ones.The Ta-bearing samples,which are situated in the fertile field in the diagram,are those which have high Nb and Ta contents,elevated Ga content and the lowest Nb/Ta and Zr/Hf values.

Hot Deformation Characteristics of 34CrMo4 Steel

The 34CrMo4 （AISI 4130） steel is extensively utilized in the compressed natural gas cylinders. Due to the importance of thermomechanical processing in the production of these cylinders, the dynamic reerystallization （DRX） characteristics of 34CrMo4 steel were investigated. The effect of hot deformation parameters such as temperature and strain rate on the dynamic restoration processes of a 34CrMo4 alloy was studied. Hot compression tests were performed in the temperature range of 900 to 1 100 ℃ and the strain rate range of 0. 001 to 0.1 s-1. Hot workability of this alloy has been analyzed by employing flow localization parameter. The flow curves observed are typical of occurrence of dynamic recrystallization and have exhibited single or multiple peaks in flow stress curve before reaching steady state, depending on the temperature and strain rates. The flow stress decreases with the increase of deformation temperature and the decrease of strain rate. Finally the activation energy obtained in this research is 490. 749 kJ/mol.

Hot Ductility of Severe Plastic Deformed AA6061 Aluminum Alloy

The hot ductility of 6061 aluminum alloy,which was subjected to two different severe plastic deformations（SPD）,was studied at different temperatures and strain rates.The tensile tests were carried out at the temperature range of 300-500 ℃ and at the strain rates of 0.0005-0.01 s^（-1）.The microstructure evolution was characterized using optical microscopy,transmission electron microscopy and X-ray diffraction technique.The influences of the microstructure after SPD,thermomechanical parameters（temperature and strain rate） and specimen size on the hot formability of this alloy were then analyzed.The results show that a decrease in grains/subgrains exhibited significant effect on the hot ductility of SPDed samples.The constitutive equations were then developed to model the hot formability of the studied alloy.The developed model can be represented by Zener-Hollomon parameter in a hyperbolic sinusoidal equation form.Both the changes of elongation to failure and Zener-Hollomon parameter indicate that the hot ductility of the alloy is more sensitive to the temperature rather than to the strain rate.The uniform elongation is independent of the specimen size,but the postnecking elongation increases dramatically as the ratio of l/A^（1/2） decreases.

Lattice parameters of Ti–4Al–2V alloy with thermal oxidation

In this study, the effect of thermal oxidation on the lattice parameters of Ti-4Al-2V alloy was studied.Samples were oxidized at 450, 600 and 650 °C for 1-7 h in electric furnace under air atmosphere. The lattice parameters were determined using the Cohen method as a function of oxidation time at each temperature. The lattice parameters of as-received alloy are calculated as a = 0.29289 nm and c = 0.46652 nm. The thermal oxidation at 450 °C results in a gradual increase in a-parameter, whereas it goes through a maximum at higher temperatures（600 and 700 °C）. The results show that these maximums are reduced to an approximately constant value after a long-time oxidation. The c-parameter generally increases over the whole treatment condition. It is believed that these variations could be due to the dissolution of oxygen atoms in octahedral sites of hcp lattice of titanium.