Rheological properties and concentration evolution of thickened tailings under the coupling effect of compression and shear

Cemented paste backfill(CPB)is a key technology for green mining in metal mines,in which tailings thickening comprises the primary link of CPB technology.However,difficult flocculation and substandard concentrations of thickened tailings often occur.The rheological properties and concentration evolution in the thickened tailings remain unclear.Moreover,traditional indoor thickening experiments have yet to quantitatively characterize their rheological properties.An experiment of flocculation condition optimization based on the Box-Behnken design(BBD)was performed in the study,and the two response values were investigated:concentration and the mean weighted chord length(MWCL)of flocs.Thus,optimal flocculation conditions were obtained.In addition,the rheological properties and concentration evolution of different flocculant dosages and ultrafine tailing contents under shear,compression,and compression-shear coupling experimental conditions were tested and compared.The results show that the shear yield stress under compression and compression-shear coupling increases with the growth of compressive yield stress,while the shear yield stress increases slightly under shear.The order of shear yield stress from low to high under different thickening conditions is shear,compression,and compression-shear coupling.Under compression and compression-shear coupling,the concentration first rapidly increases with the growth of compressive yield stress and then slowly increases,while concentration increases slightly under shear.The order of concentration from low to high under different thickening conditions is shear,compression,and compression-shear coupling.Finally,the evolution mechanism of the flocs and drainage channels during the thickening of the thickened tailings under different experimental conditions was revealed.

Reducing the yield asymmetry in Mg-5Li-3Al-2Zn alloy by hot-extrusion and multi-pass rolling

Reducing the yield asymmetry is very important concern for wrought Mg-Li alloys.In this study,Mg-5Li-3Al-2 Zn(LAZ532)alloy was successfully produced by hot-extrusion followed by multi-pass rolling at 573 K.Microstructure evolution,mechanical properties and yield asymmetry reducing of LAZ532 alloys at different rolling passes were studied.By observing microstructure using transmission electron microscopy showed that a small amount of ultra-fine Al Mg_(4)Zn_(11)and nano Li_(3)Al_(2) phases existed in the alloy.With the increasing of rolling passes,the grains of the alloys were obviously refined,and comprehensive mechanical properties were dramatically improved.Meanwhile,it also showed an excellent tension and compression yield symmetry(TYS/CYS was about 1).The results showed that the combined action of the weak{0001}basal lamellar texture,grain refinement and addition of Li element could effectively improve the yield symmetry.Furthermore,based on theoretical analysis,the yield strength in the alloys mainly depended on the strengthening contributions of LAGBs and HAGBs,and strengthening effect of HAGBs most(~50%)to the yield strength improvement.

A crystal plasticity based approach to establish role of grain size and crystallographic texture in the Tension–Compression yield asymmetry and strain hardening behavior of a Magnesium–Silver–Rare Earth alloy

Existence of tension–compression yield asymmetry is a serious limitation to the load bearing capablities of Magnesium alloys in a number of light weight structural applications.The present work is aimed at nullifying the tension to compression asymmetry problem and strain hardening anomalies in a Magnesium–Silver–Rare Earth alloy by engineering different levels of microstructural conditions via friction stir processing and post process annealing.The existence and extent of yield asymmetry ratio in the range of microstructural conditions was experimentally obtained through quasistatic tensile and compression tests.The yield asymmetry problem was profoundly present in specimens of coarse grained microstructures when compared to their fine grained and ultra fine grained counterparts.The impact of the microstructure and associated mechanisms of plasticity on the macroscopic strain hardening behavior was established by Kock–Mecking’s analysis.Crystal plasticity simulations using Viscoplastic Self Consistency approach revealed the consequential role of extension twinning mechanism for the existence of yield asymmetry and anomalies in strain hardening behavior.This was especially dominant with coarsening of grain size.Electron Microscopy and characterization were conducted thoroughly in partially deformed specimens to confirm the predictions of the above simulations.The role of crystallographic texture for inducing the polarity to Tension–Compression yield asymmetry was corroborated.A critical grain size in Magnesium–Silver–Rare earth alloy was hereby established which could nullify influences of extension twinning in yield asymmetry ratio.

Annealing hardening and deformation behavior of layered gradient Zr–Ti composite

To investigate potential strengthening approaches,multi-layered zirconium–titanium(Zr-Ti)composites were fabricated by hot-rolling bonding and annealing.The microstructures of these composites were characterized using scanning electron microscopy with energy dispersive spectroscopy(SEM-EDS)and electron backscatter diffractometry(EBSD).Their mechanical properties were evaluated by uniaxial tension and compression measurements.It was found that the fabricated Zr–Ti composites are composed of alternating Zr/diffusion/Ti layers,and chemical compositions of Zr and Ti showed a gradient distribution in the diffusion layer.Compared with as-rolled samples,annealing can strengthen the layered gradient Zr–Ti composite,and this is mainly caused by solid-solution strengthening and microstructure refinement-induced strengthening.Compared with the raw materials,a synergistic improvement of strength and ductility is achieved in the Zr–Ti composite as a result of the layered gradient microstructure.Tension–compression asymmetry is observed in the Zr–Ti composites,which may be attributed to twinning and microvoids induced by unbalanced diffusion.

Cooperative effects of Mo,V and Zr additions on the microstructure and properties of multi-elemental Nb-Si based alloys

Eight multi-elemental Nb-Si-based alloys with various Mo,V and Zr contents were prepared by vacuum non-consumable arc melting.The cooperative alloying effects of Mo,V and Zr on the arc-melted and heat-treated microstructure,mechanical properties as well as oxidation resistance at 1250°C of the alloys were evaluated systematically.The results show that except for adding Mo solely,additions of Mo,V and Zr change the microstructure from eutectic to hypereutectic.The additions of Mo,V and Zr suppress the formation ofα(Nb,X)5 Si 3(“X”represents the alloying elements that substitute for Nb in the lattices),whilst promoting the formation ofγ(Nb,X)5 Si 3.The heat treatment at 1450°C for 50 h promotes the formation of(Nb,X)3 Si phase in the Zr-containing alloys.Alloying with either Mo or Zr improves,and their composite additions more obviously improve the compressive yield strength at 1250°C as well as the microhardness ofγ(Nb,X)5 Si 3.The room temperature fracture toughness of the alloys is enhanced by sole and composite additions of V and Zr,while it is deteriorated by the addition of Mo.The sole addition of Mo,V or Zr improves the oxidation resistance at 1250°C,the composite additions of V with Mo/Zr(especially V-Mo-Zr)degrade the oxidation resistance at 1250°C.

Microstructures and properties of Nb-Si-based alloys with B addition

The Nb-16Si-18Ti-xB(at%,similarly hereinafter,x=0,1,2,3)alloys were prepared by arc melting in a water-cooled copper crucible.The influences of B addition on their microstructures and properties were based on the data of X-ray diffraction(XRD),field emission scanning electron microscopy(FESEM),and electronic universal material testing machine.It is found that the addition of B promotes the formation ofα-Nb5Si3phase and suppresses the formation of Nb3Si phase.B addition also tends Nb-16Si-18Ti alloy to form the hypereutectic structures.The content of silicide phases shows a trend of firstly decreasing and then increasing in Nb-16Si-18Ti-xB(x=0,1,2,3)alloys.The size of Nb solid solution(Nbss)phase increases in Nb-16Si-18Ti-xB(x=0,1,2,3)alloys after heat treatment at 1523 K for 10 h.The room temperature compression strength of Nb-16Si-18Ti alloy increases firstly and then decreases with B addition.The high-temperature compression strength of Nb-16Si-18Ti alloy decreases firstly and then increases with B addition.It is found that the volume and size of silicide phases have a synergistic effect on the compression strength of Nb-TiSi-based alloys.