Aiming at potential emergency discharge required during at-sea testing of deep-sea polymetallic nodules lifting system consisting of pipeline and lifting pump, a theoretical calculation was conducted for the hydraulic system of emergency discharge mechanism for at-sea testing, and also a simulation analysis was conducted with AMEsim. It is found that the reliability coefficient of AMEsim for the system is 0.86. An AMEsim-based hydraulic system model was established for the actuator in an at-sea test at 500 m depth. The simulation results show that the oil pipeline in the hydraulic system is 16 mm in diameter, with the set pressure not less than 10.47 MPa, and the action time of actuator is 6 s. This research results can provide a reference for the design of emergency discharge mechanism.

A free fall backfill (FFB) system with high-concentration slurry in a mine was taken as an example to study pipeline parameters and resistance characteristics of FFB system by conducting theoretical analysis, laboratory test and verification with field measurement. The results show that the FFB system has many working procedures, with flowrate for normal backfilling fluctuating within the range of 100-240 m³/h, and the pressure at 1.2-2.2 MPa. The flowrate at specific points of the pipeline presents a quasi-normal distribution, averaging 190 m³/h. There are two characteristic peaks for the pressure, being 1.86 MPa and 3.04 MPa, respectively. The parameters at a single point of pipeline cannot be used to analyze and judge the working conditions, such as pipe blockage and leakage. The pressure difference and flowrate difference between sections of the pipeline present obvious normal distribution, with mathematical statistics expectations of 4.62 m³/h and 0.64 MPa, respectively. The difference in instantaneous flowrate and pressure can be used to judge blockage and leakage of the pipeline. The flow resistance in the laminar-turbulent transition zone predicted by the Swamee-Aggarwal formula is 2.08 MPa/km, which is consistent with the measured value of 2.15 MPa/km.

With a tailings pond in Lesser Khingan Mountains region as an example, experiments were carried out on tailings embankment respectively by upstream construction with discharged wet metallic tailings, by filling a pond with metallic tailings, and by construction with overflow and underflow of tailings separately from cyclone. It is shown that the embankment construction with overflow and underflow separately from cyclone is superior over other two methods based on comparison. It can not only effectively improve consolidation of the tailings in front of the embankment through drainage, prolong the length of dry beach and increase the strength of the tailings in front of the embankment, but also create a wide sloping sediment, keep the embankment within the freeboard, improve the seepage condition of the dam body, as well as increase the bearing capacity of beach surface and the efficiency of embankment construction. By improving the cycloning process, a scheme including constructing embankment during non-winter seasons and discharging tailings in winter to build a wide sub-dam is proposed, which can solve the previously existing problems to a certain extent, such as sediment beach with high water content and low bearing capacity, as well as inability to build sub-dam with tailings sand. However, both the utilizing rate of coarse sand, the width of sub-dam of high-grade tailings pond and development of frozen soil still need to improve. Finally, it is found that the embankment construction by adopting technique of building wider sub-dam with underflow and overflow of tailings from cyclone combined with geofariform method can effectively resolve the existing problems for tailings dam. Thus, this technique can be promoted as an effective embankment construction scheme with fine-grained tailings in regions with high altitude and cold weather.

The numerical simulation was used to establish a single-hole blasting model, which was then used to simulate the blasting effect with different stemming length. Otsu thresholding technique was adopted for image segmentation, and the data, such as percentage of cracked rock area, fractal dimension of pore structure, and fragmentation of rock mass, were extracted for comparative analysis, so as to explore the influence of stemming length on damage effect under deep-hole blasting. The results show that fractal dimension and percentage of cracked rock area are in an uptrend before falling down as stemming length increases. The fractal dimension reaches the maximum value with stemming length of 3.0 m, and the percentage of cracked rock area reaches the maximum value with stemming length of 1.7 m. Stemming length of 2.2 m can bring the highest number of fragments, and stemming length of 2.0 m can result in the smallest average area of fragments. It is found that the blasting with the stemming length of 2.0-2.2 m can lead to better rock fragmentation effect. As the stemming length increases, the flyrock becomes bigger, and the displacement distance decreases. The research results can be taken as reference in selection of stemming parameters for blasting operation.

A slope of ionic rare earth mine was taken to study the variation of pore water pressure in the slope during and after rainfall events with different rainfall intensity, and the varied critical slip surface during these two periods of time was also studied by using the finite element Morge nstern-Price method. The results show that the rainfall intensity is a significant factor affecting the pore water pressure of shallow slope of ionic rare earth mine. The hysteresis property of rainwater infiltration into the slope is the internal reason for hidden risk of potential slope instability after rainfall events. The greater rainfall intensity will lead to faster formation of the 289 slip surface, higher peak value of greatly changed safety factor, as well as longer influence time. It is proposed for the first time that the development of ionic rare earth mine slope under rainfall conditions may experience four stages: safety, drastic internal variation, high landslide susceptibility, and relative safety.

The influence of hydraulic properties of geogrid on the stability of expansive soil slope was explored by conducting fluid-solid coupling analysis with Plaxis software. On this basis, the principle of flexible support for expansive soil slope under different rainfall conditions was analyzed. It is found that the axial forces on geogrid in each layer of the reinforced slope increase with the continuous infiltration of rainwater, presenting a “convex” shape variation. Without taking consideration of the hydraulic properties of geogrid, the axial forces on the geogrid will be underestimated and the stability of the slope will be overestimated. Flexible support structure can effectively control rainfall infiltration into slope and maintain the shear strength of expansive soil, meanwhile control the slope deformation and displacement growth. Thus, it is regarded as an effective way to support expansive soil slope.

In order to solve the problem of parameter selection for smooth blasting in tunnel/roadway excavation, a parameter selection model based on random forest algorithm was constructed. The input parameters in the model include quality classification BQ of surrounding rock, tunnel (roadway) section area and borehole diameter, and the output parameters include minimum burden, borehole spacing and borehole depth. Then, 24 training samples and 7 test samples were used for training and testing of model, and the results show that the relative errors between the output parameters of borehole spacing, minimum burden, borehole depth and the corresponding parameters of test samples are 17%, 8.8% and 22% respectively on average, indicating that the model is good in selecting minimum burden, but less effective in selecting blasthole spacing and blasthole depth.

To study the effect of sand content on the rheological properties of lacustrine soft soil in northern Hunan, one-dimensional rheological consolidation tests under single-stage load were carried out with soft soil samples prepared with different sand content in the laboratory. The results show that the sand content has a significant effect on consolidation deformation of lacustrine soft soil in northern Hunan. The time of primary consolidation is almost unaffected by consolidation pressure, and decreases linearly with the sand/soil ratio. The higher the sand content in soil, the greater the consolidation pressure, and the smaller the secondary consolidation coefficient. The relationship between the secondary consolidation coefficient and the sand/soil ratio can be well represented by a power function. The higher the content of coarse particles in soft soil, the greater the fractal dimension. There is a linear relationship between the secondary consolidation coefficient and the fractal dimension.

With a flake graphite ore from Africa as the raw material, a beneficiation technique was adopted to recover graphite resource according to ore size fraction. The results show that the fixed carbon content of the graphite feed ore is 32.54%, and the large flake graphite mainly in sheet or banded structure is intergrown with feldspar minerals. The optimized roughing condition is determined as follows: grinding fineness of -0.074 mm 72.87%, kerosene dosage of 50 g/t and terpineol dosage of 150 g/t. A flotation process with one stage of roughing, one stage of scavenging and four stages of cleaning is adopted, in which the large flake graphite is screened from the flotation production of the 1st-stage of cleaning, while the undersize is treated further by three stages of grinding and three stages of cleaning to recover fine flake graphite. The closed-circuit test shows that the fixed carbon content in the large flake graphite (+0.150 mm) concentrate and the fine flake graphite (-0.150 mm) concentrate reaches 96.53% and 96.21%, respectively. The recovery rate of the large flake graphite reaches 22.74%, which is higher by 7.66 percentage points compared to that by conventional regrinding-separation approach.

The effect of hydroxamic acids on flotation of fluorapatite and dolomite was studied. The flotation results show that salicylhydroxamic acid exhibits certain selectivity but low recovery for fluorapatite and dolomite; octylhydroxamic acid shows poor selectivity but high recovery for fluorapatite and dolomite; while benzohydroxamic acid possesses high selectivity and recovery for fluorapatite. The flotation mechanism of fluorapatite and dolomite in the presence of benzohydroxamic acid was studied by performing zeta potential measurement, adsorption capacity test and XPS analysis. It is found that benzohydroxamic acid is an ideal collector for fluorapatite and dolomite.

As for the thickener designed for the new concentrator of a multi-metal mine in Hunan, aiming at the problems of covering a large area, high cost and long period of time for construction, efforts were made to increase the concentration of products from classification for reducing thickener area or even cancelling thickening operation, so as to actualize a simple, efficient and low energy-consuming pre-treatment of feed ore. For this purpose, experiments were carried out to determine parameters, such as hydrocyclone replenishment water, cone angle, cylinder height and apex diameter. It is found that by using a hydrocyclone consisting of a long cylinder and a short cone with cone angle of 90°, cylinder height of 800 mm and apex diameter of 50 mm, the overflow concentration can be increased from 34% to more than 44%, with the classification efficiency up by 0.77 percentage points, and the content of -74 μm size range is stabilized at more than 70%. Therewith, the content of easy-to-separate range increases by 2.19 percentage points and the WO₃ distribution increases by 9.87 percentage points. Furthermore, the grade and recovery of tungsten, molybdenum and bismuth all become stabilized in the follow-up flotation operations.

Experimental study was carried out to realize comprehensive recovery of non-metallic mineral resources from granite tailings in Henan Province, and explore the feasibility of preparing high-purity quartz. The results show that the granite tailings, mainly containing minerals of plagioclase feldspar, quartz, potassium feldspar and mica, have potential to be comprehensively utilized. With a flowsheet consisting sequentially of scrubbing-magnetic separation, pre-treatment of desliming, and mica-feldspar-quartz preferential flotation, a mica concentrate with Al₂O₃, K₂O, Na₂O, SiO₂ and Fe₂O₃ contents of 33.84%, 8.13%, 0.32%, 56.78% and 0.121%, a feldspar concentrate with Al₂O₃, K₂O, Na₂O, SiO₂ and Fe₂O₃ contents of 15.89%, 2.16%, 10.68%, 71.06% and 0.124%, and a quartz concentrate with Al₂O₃, K₂O, Na₂O, SiO₂ and Fe₂O₃ contents of 1.05%, 0.17%, 0.56%, 97.76% and 0.106%, respectively, can be collected. The quartz concentrate can be further purified to obtain a high-purity quartz sand with SiO₂ content of 99.994%.

Based on the properties of Shizhuyuan molybdenum-bismuth sulfide ore, a new eco-friendly collector CYB-06 was developed. The results of industrial experiment show that, when using collectors CYB-06 and ethyl thiocarbamate coordinately, the recovery of molybdenum, bismuth and sulfur in the bulk sulfide concentrate attains respectively to 84.12%, 67.90% and 83.28%, up by 2.32 percentage points, 2.82 percentage points and 6.55 percentage points respectively, and the COD in the wastewater from processing plant is 117 mg/L, declined correspondingly by 41.21%, compared to the concentrate obtained with the combined collector of butyl xanthate and ethyl thiocarbamate. As CYB-06, without pungent odor, exhibits good selectivity index, and leads to low COD in the wastewater from processing plant, its application is of significance for improving product quality and operation efficiency, cleaning production and environmental protection of mining enterprises.

Aiming at the problem of insufficient sorting of low-grade rock ore in the western Inner Mongolia region, the processing technique and equipment were improved to solve the problems including the concentrate of low-grade rock ore with the grade failing to meet the requirement and the grain refinement. By applying automation and intelligent technologies in new equipment, the processing index can be largely improved, which complies with the requirement for the development of green and intelligent mine. Simultaneously, by implementing remote connection, the connection of remote-control center and remote units can be actualized, facilitating the communication between customers and equipment manufacturers, tracking of equipment operation status, as well as the maintenance of operation indicators and observation of component operation status.

Based on the process mineralogy study, an experimental study on grinding-separation technique was performed for JISCO's magnetite obtained from its suspension magnetization roasting process. In the experiment, a 110 mT low-intensity magnetic separator was firstly adopted for pre-concentration. The middlings were reground and processed by magnetic separation for enrichment and tailings discarding, and the obtained concentrate was subjected to reverse cationic flotation. Finally, the whole process produced the comprehensive concentrate grading 60.06% TFe and containing 5.17% SiO₂, with metal recovery of 84.27%. In comparison with the previous processing technique, the TFe grade of concentrate is improved by 1.96 percentage points and the metal recovery is increased by 1.38 percentage points, while the SiO₂ content falls by 1.06 percentage points.

An experimental study on a metallurgical grade fluorite concentrate with CaF₂ content of 70.34% was conducted to upgrade fluorite concentrate quality by reducing impurities therein. The results of the full process test show that by adopting a process of high intensity magnetic separation for reducing silicon, followed by flotation of non-magnetic minerals for reducing calcium, the experiment produces a fluorite concentrate grading of 91.95% CaF₂ at 76.52% recovery, with a yield of 58.30%. It is shown that the concentrate meets the raw material standards for anhydrous hydrofluoric acid production.

SAG mill grinding and conventional crushing-grinding processes adopted in Baima Iron Mine are introduced. Based on the detailed comparison of processing flowsheet, production index, equipment operation parameter, construction investment, operation cost, it can be concluded that the SAG milling process has the advantages of simple process, low construction investment, good adaptability to ores and fine grinding fineness, also some disadvantages like high equipment failure rate, short service life for lining plate, relatively low equipment operation rate and high production cost. These results can be referred in the construction of similar mines.

High gradient magnetic separation technique was adopted to separate the (tantalum-niobium)-tin bulk concentrate obtained from gravity separation. The effects of magnetic intensity, pulsating frequency, magnetic rod matrix diameter and rotating speed of ring on (Ta-Ni)/Sn separation efficiency were studied. The test results show that, from the bulk concentrate with grades of Ta, Ni and Sn respectively as 11.65%, 9.33% and 19.59%, the final tantalum-niobium concentrate containing 22.31% Ta, 17.38% Ni and 3.22% Sn can be collected with the recoveries of Ta, Ni and Sn respectively as 95.48%, 92.88% and 8.20%, respectively. Meanwhile, a tin concentrate with Sn grade of 35.87% and Sn recovery of 91.80% can be obtained. The tantalum-niobium and tin minerals can be effectively separated.

The dissolution characteristics and mechanism of heavy metal ions (As, Cr, Cu, Mn, Ni, Pb) and Na⁺, K⁺ in red mud were studied in a simulated natural environment. The results show that the dissolution of heavy metal ions, Na⁺ and K⁺ out of red mud can be promoted by reducing pH value, increasing contact time, raising leaching temperature, and increasing liquid-solid ratio. After dissolution, the characteristic peak values of calcite, magnesium chlorite, gosilicate and triploidite significantly become lower, and elements of As, Cr, Ni, Cu, Mn, Na and K, after dissolution out of red mud, exist in the forms of As₂O₃, Cr³⁺, NiO, CuO, MnO, Na⁺ and K⁺.

Based on the experience from production practices, an orthogonal experiment was performed by simulating a grate-rotary kiln process to investigate factors affecting compressive strength of preheated pellets and also find measures to improve the process. It is found that both OA iron ore and OB iron ore are fine-grained, with -0.074 mm grain content greater than 85%, which meets the basic requirements for particle size in pelletizing process. With 90% OA iron ore blended with 10% OB iron ore, the obtained pellet after drying and preheating process can have FeO content reduced from 26% to less than 4%, with the oxidation degree greater than 85%. With the following optimal thermal parameters of chain grate, including a drying temperature of 200 ℃ for air blowing and a drying temperature of 360 ℃ for ventilation, 720 ℃ for I-stage preheating and 990 ℃ for II-stage preheating, the obtained preheated pellet can have a compressive strength of 1 056 N/pellet. It is verified that the experimental result is in accordance with the anticipation.

Fluoride-containing industrial wastewater was treated by using a composite coagulant of polymerized aluminum chloride (PAC) and polyacrylamide (PAM), and effects of PAC dosage, PAM concentration, pH value, reaction time and stirring speed on fluoride removal efficiency were explored. The results show that by adding 4 400 mg/L PAC, with PAM concentration of 1 mg/L, solution with pH of 7.0, reaction time of 20 min and stirring speed of 300 r/min, the fluoride removal rate can reach 97.98%, leading to the residual concentration of fluoride ion at only 0.81 mg/L. However, the presence of impurity ions can reduce the fluoride removal rate by PAC.

In order to determine a new type of gold leaching system, which can not only bring good leaching effect with low consumption of thiosulfate, but also make the gold in the lixivium to be efficiently recovered, the leaching effects of gold with thiosulfate catalyzed by different combination of metal ions and organic ligands were compared, and then the gold in the lixivium was recovered by resin adsorption. The results indicate that the Ni²⁺-glycine-thiosulfate system can bring good Au leaching effect, showing Au leaching rate up to 89.72% with thiosulfate consumption of 15.28 kg/t. During the gold leaching process in this system, glycine catalyzes the coordination of Au⁺ with S₂O₃^2- and also stabilizes Ni²⁺ under alkaline conditions, and Ni (C₂H₄NO₂)₂⁰ catalyzes the reduction of O₂. When Au is recovered by resin adsorption, Ni ions in the lixivium are hardly adsorbed on the resin, and do not compete with Au ions for adsorption, resulting in Au adsorption rate up to 98.13%. Then, only one-step process is required for desorption of gold-loaded resin, that is, Au can be directly desorbed.

Experimental study was carried out on continuous leaching of mixed wolframite-scheelite concentrate with soda in a horizontal continuous autoclave reactor, and the effects of various processing parameters on the decomposition rate of the mixed ore were investigated. Under the processing conditions, including grinding fineness of -0.050 mm for the mixed ore, leaching temperature of 200 ℃, liquid-to-solid ratio of 2.1∶1, soda usage at four times of the theoretical dosage, addition of NaOH at 25 kg/t of ore, and feeding rate of 10 m³/h, the decomposition rate of tungsten in the mixed wolframite-scheelite concentrate reaches 99.55%, with only WO₃ content of 0.28% in the slag. It is found that the continuous leaching with soda offers the advantages of easy operation, higher production efficiency, lower energy consumption, stable decomposition rate, as well as higher automation.

A two-step acid leaching process was used to leach scandium and yttrium from red mud. Phosphoric acid was used in the first stage of leaching to achieve dealkalization, desilication and enrichment of rare earth elements (scandium and yttrium). Then, the leaching residue was leached with sulfuric acid in the second stage. The effects of sulfuric acid concentration, liquid-solid ratio, reaction temperature and reaction time on the leaching process of scandium and yttrium were investigated, and the leaching kinetics was also analyzed. It is found that leaching of red mud with phosphoric acid can bring better dealkalization and desilication effect, showing the leaching rates of K, Na and Si at 75.62%, 87.82% and 80.25%, respectively. Then, in the second stage of leaching process with sulfuric acid concentration of 2.5 mol/L and liquid-solid ratio of 7∶1, reaction runs at 70 ℃ for 45 min, leading to the average leaching rates of Sc and Y up to 74.49% and 80.02%, respectively. It is shown that the leaching processes of Sc and Y with sulfuric acid follow the liquid-solid reaction model, which is controlled by diffusion, and the apparent reaction activation energies are calculated to be 18.50 kJ/mol and 16.74 kJ/mol, respectively.

The iron-carbon (Fe-C) micro-electrolysis was adopted to treat arsenic-containing wastewater from copper smelting, and the effects of processing parameters, including pH of inlet water, air blowing rate, contacting time, vibration frequency, solid-liquid ratio (mass ratio of Fe-C micro-electrolysis material to inlet water per minute), on the arsenic removal efficiency were explored. Results show that during the treatment by Fe-C micro-electrolysis, the generated oxides such as FeAsO₄, Fe₂O₃, and Fe₃O₄ are deposited on the surface of the Fe-C micro-electrolysis material, making passivation of the Fe-C micro-electrolysis material ineffective, thus resulting in poor arsenic removal efficiency. The use of vibration can effectively solve such problem. It is shown that after 90 d continuous treatment under the conditions, including pH of inlet water at 2.0, air blowing rate at 5 L/min, contacting time of 2 min, solid-liquid ratio of 2.5∶1, vibration frequency rate at 2 min every 4 h, the arsenic removal rate can be up to 99.99% and the arsenic content in water falls down to 0.033-0.036 mg/L, presenting a good and stable removal effect. It is concluded that this arsenic removal approach by adopting Fe-C micro-electrolysis can provide a new idea for treatment of arsenic-containing wastewater from copper smelting.

According to the existence of manganese, an experiment was carried out by adopting a processing technique consisting of reduction roasting and acid leaching to treat high-silicon manganese oxide ore. The effects of roasting temperature, roasting time, mass ratio of coal to ore, leaching temperature and time, initial sulfuric acid concentration, and liquid-solid ratio on the manganese leaching rate were all investigated. The results show that the leaching rate of manganese can reach 95.83% under the conditions including roasting temperature of 880 ℃, roasting time of 1.5 h, a mass ratio of 18% for coal to ore, leaching temperature of 55 ℃, leaching time of 2 h, initial sulfuric acid concentration of 1.80 mol/L, as well as liquid-solid ratio of 5 mL/g.

By adjusting the pH value of electrokinetic remediation cathode and adding enhancers, the total removal rate of Cr from the contaminated soil by electrokinetic remediation technology was increased. Then, the change of energy consumption and law of Cr migration and distribution during the electrokinetic remediation project were explored. The results show that EDTA, citric acid and hydrochloric acid can significantly enhance the total Cr removal rate during the electrokinetic remediation process. The total removal rates of Cr were 24.47% and 23.24% respectively after 7 days of electrokinetic remediation without adjusting the pH value of the cathode, by adding EDTA and citric acid into the soil. The pH value of the cathode isn't adjusted, which results in an obvious polarization effect. In contrast, the total removal rates of Cr were 44.20% (4.9 times as much as the blank) and 36.80%, respectively, after 7 days of electrokinetic remediation with the pH value of the cathode controlled, by adding hydrochloric acid and citric acid to the soil, respectively. Controlling the pH value of the cathode can effectively prevent the precipitation of Cr in the cathode region, thus enhancing the removal rate of Cr, but won't significantly increase the energy consumption of the electrokinetic remediation process. This method can greatly increase the total removal rate of Cr in contaminated soil by electrokinetic remediation, which is of significance in guiding the remediation of heavy metal contaminated soil.

Hydrothermal carbon generated by hydrothermal carbonization of waste jujube branches was activated with zinc chloride as an activator, and a kind of modified biochar was prepared with highly porous and aromatic structure on its surface, which was then used to adsorb Zn²⁺ in aqueous solution. It is shown that for the solution with pH of 9 and initial Zn²⁺ concentration of 30 mg/L, after 80 min adsorption at a temperature of 55 ℃ by adding 700 mg/L modified biochar, the removal rate of Zn²⁺ therein exceeds 99%. The adsorption process is well-fitted to the Freundlich adsorption model, indicating that the adsorption process with the modified biochar is a multilayer molecular adsorption. The removal rate of Zn²⁺ by the modified biochar, after 5 cycles of adsorption and desorption, can still remain over 97%.

The effect of laser remelting (LR) on the microstructure property and thermal stability of Ti-6Al-4V alloy prepared by laser powder bed fusion (LPBF) was investigated. The results show that after LR treatment, the thermal stability of the α′ phase within the LRed-Ti-6Al-4V titanium alloy samples is significantly improved, and the temperature at which β-Ti phase appears is up from 500 ℃ to 700 ℃. After heat treatment, the grains in LPBF-Ti-6Al-4V titanium alloy grow continuously, and obviously appear to be “short bar-like” and “coarse lamellar” at the temperature above 700 ℃; while the grains in the melting zone of the surface layer of the LRed-Ti-6Al-4V sample are still maintain equiaxial, and the relatively uniform and fine needle-like microstructure are observed in the melting zone and heat affected zone above 700 ℃. The surface microhardness of those two groups of samples decreases with the increased temperature, especially significant at 700 ℃ and 850 ℃ respectively. It is found that the rapid coarsening of β-Ti grains is the main reason for the falling down of hardness.

The surface of 38CrMoAl steel was processed by ion nitriding at 560 ℃ with the mixture of nitrogen and argon as nitrogen source. After that, the friction and wear property of 38CrMoAl steel was studied. The results show that as the N₂ volume fraction in the mixed gas increases, the thickness of nitrided layer increases, and the surface hardness of the nitrided layer increases first and then decreases. By adjusting the volume fraction of N₂ in the mixed gas, the number of active nitrogen atoms can be changed, thus leading to the change in the phase composition of the nitrided layer. With N₂ and Ar in a volume ratio of 2∶3, γ′-Fe₄N phase is the major phase and ε-Fe_2-3N phase is the minor phase in the nitrided sample. With N₂ and Ar in a volume ratio of 3∶2, the nitrided layer has ε-Fe_2-3N phase as the major phase andγ′-Fe₄N as the minor phase. Compared with the substrate material, the ion-nitrided sample has a smaller friction coefficient and higher wear-resistance. With N₂ and Ar in a volume ratio of 3∶2, the ion-nitrided sample has its compound layer in a thickness of 21.4 μm, and its average friction coefficient up to 0.26, presenting good wear resistance. The mechanisms of friction and wear include fatigue, abrasion and oxidation.

In order to improve surface hardness and corrosion resistance of 304 stainless steel, a medium-entropy alloy (CoCrNi) coating was prepared on the surface of 304 stainless steel by laser cladding, and phase composition, element distribution and corrosion resistance of the cladded coating were studied. The results show that the treatment has achieved good metallurgical bonding between the cladded CoCrNi coating and the substrate, with no cracks, pores and other defects. The cladded coating is composed of single FCC phase, and exhibits dendrite and inter-dendrite structure. The elements are uniformly distributed on the cladded coating without obvious segregation. The uniform distribution of Cr element plays a positive role in improving corrosion resistance of the coating. The CoCrNi coating has its polarization resistance (101.65 kΩ) higher than that of 304 substrate (90.56 kΩ), and also significantly higher corrosion resistance.

Based on the current situation and demand in the field of commercial aircraft engine bracket, analysis and review of research progress in magnesium alloy were presented in terms of formability, corrosion resistance and flame retardancy, and the prospects of applications of magnesium alloys in aircraft engine bracket were also discussed.

The effects of Zr content on solidification process of Al-Si-Mg-Mn alloy, and its microstructure and mechanical properties after aging treatment were investigated by means of numerical simulation, microstructure observation and mechanical property testing. The research results reveal that with increasing Zr content, the solidification path of the alloy become significantly different, and grains evolve from initial dendrites to equiaxed grains. After aging treatment at 175 ℃ for 7 h, an addition of Zr can significantly improve the hardness of the alloy. The addition of Zr promotes the precipitation of precipitates at lower aging temperature, which may be attributed to grain refinement of Zr, thus leading to improved diffusion efficiency. The main precipitates of the alloy are β″ phase and Q′ phase during peak aging.

Aiming at the shortcomings of single crystalline high-nickel ternary cathode material, including high residual alkali on the surface, poor cycle performance at high temperature, co-doping with niobium and yttrium was proposed to modify the cathode material for improving its electrochemical performance. With monocrystalline high-nickel ternary precursor (Ni_0.6Co_0.1Mn_0.3(OH)₂) as raw material, a series of cathode materials co-doped with two different elements were synthesized by high-temperature solid-state reaction. The results show that the niobium and yttrium co-doped sample presents excellent cycling stability and rate capability at high temperature. Compared to niobium-doped sample, it can have capacity retention rate higher by 2.58 percentage points after 50 cycles at 45 ℃, and discharge capacity higher by 6.2 mAh/g at 2C charge-discharge rate.

The effect of Cr content on microstructure and heat exposure of Al-Cu-Mg-Ag alloys was investigated. It is found that strength of the alloys at room temperature decreases after an initial increase as Cr content increases, and the 0.2%Cr alloy exhibits excellent room-temperature mechanical properties. Transmission quantitative calculation results suggest that an addition of 0.2%Cr can promote precipitation of Ω phase and improve coarsening resistance of Ω phase in the alloy after heat exposure. With the addition of Cr exceeding 0.3%, the (Al, Cr, Mn, Ti)-enriched phases precipitate at the grain boundaries of the alloy, leading to coarser grains.

The phase structure, microstructure and mechanical properties of Fe_46-xNi₂₀Co₂₀Cr₁₀V₄Al_x (x=5, 8, 12, 15) high-entropy alloys with different Al contents (atom fraction, %) were systematically investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and performing uniaxial tensile test. The results show that with the increase of Al content, the phase structure of Fe_46-xNi₂₀Co₂₀Cr₁₀V₄Al_x high-entropy alloys transforms from single-phase structure of face-centered cubic (FCC) to dual-phase structure of FCC and body-centered cubic (BCC). Also, the strength increases and ductility decreases. The Fe₃₄Ni₂₀Co₂₀Cr₁₀V₄Al₁₂ high-entropy alloy annealed at 900 ℃ exhibits an excellent strength-ductility balance, with yield strength, tensile strength and elongation to failure at 593 MPa, 1009 MPa and 32.13%, respectively. With Al content of 5%, the as-cast and annealed high-entropy alloys remain single FCC phase. However, with Al content of 8%, 12% and 15%, the high-entropy alloys all become FCC-BCC phase. The annealing treatment promotes the precipitation of BCC phase, and the proportion of BCC phase increases with increasing annealing temperature.

When ultra-high strength steel with tensile strength more than 1 600 MPa and BS700 high-strength steel with tensile strength more than 760 MPa are joined together by metal active gas welding, weld cracks are prone to occur in the seam of joint. To solve this problem, comparative welding tests were performed by using ER70-G or ER307Mo welding wire with diameter of 1.0 mm, respectively, with initial welding current of 160-180 A, voltage of 21-24 V, and final welding current of 190-210 A, voltage of 23-26 V. The comparison of process and weldability show that welding with ER307Mo can lead to the sample with bending property obviously better than that by welding with ER70-G. The sample after welding with ER70-G can be found to have micro-cracks not going through the whole cross section of welding seam, with cracking rate on the cross section of seam reaching 35.29%, but no cracks are found on the section of welding seam by using ER307Mo. It is concluded that the ER307Mo welding wire is more suitable for welding ultra-high strength steel and BS700 high strength steel. The study has solved the cracking problem in the joint of ultra-high strength steel and BS700 high strength steel, which can provide a solution for the welding of dissimilar high-strength steel with larger difference in tensile strength.