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In this study, the precipitation transformation and age hardening of solution-treated Mg-9Gd-4Y-2Zn-0.5Zr(wt.%) alloy were investigated at different aging treatment parameters. The precipitation sequences of the alloy aged at 200 ℃, 250 ℃ and 300 ℃ are β″(DO19) → β′(BCO) → β(FCC), β″(DO19) → β′(BCO) → β1(FCC) → β(FCC) and β(FCC), respectively. The streaks sequences of the alloy aged at 200 ℃, 250 ℃ and 300 ℃ are SF, SF → 14H-LPSO and SF → 14H-LPSO, respectively. For the alloy aged at 200 ℃ and 250 ℃, the increase in hardness with increasing aging time is contributed from the increase in precipitate volume fraction and the transformation from β′′ to β′ phase with basal → prismatic and spherical → spindle-like precipitate changes. The decrease in hardness after the peak-aging stage is attributed to the appearance of micro-sized β precipitates. Because of the smaller size of precipitates and the triangular arrangement of β′ precipitate, the hardness of the alloy aged at 200 ℃ is higher than that aged at 250 ℃. For the alloy aged at 300 ℃, the appearance of only micro-sized β precipitate and its coarsening with increasing aging time leads to the lowest hardness and an overall decrease in hardness with the aging time.

The low-permeability reservoir is one of the important oil production positions in Shengli Oilfield， and its reserves accounts for more than 20% of the total oilfield reserves. The low-permeability reservoir always presents characteristics such as a narrow pore throat and strong heterogeneity， which results in high injection pressure and difficult injection during water flooding. At present， the main measures to improve the development effect include active agents for reducing pressure and increasing injection， water injection under high pressure， and narrowing the distance of drainage wells. However， there are still some production problems， such as short effective time， low well injection per well， low liquid production per well， and small swept volume. Therefore， it is urgent to develop new and efficient development methods. Since the “13th Five-Year Plan in 2016-2020”， the synergistic development modes have been implemented， such as replenishing energy injection enhancement in injectors， increasing production by imbibition in producers， and increasing swept volume by displacement between injectors and producers， which can enhance displacement pressure gradient， water displacement， and recovery. The synergistic development mode has been applied in Chunhua Oilfield. The injection pressure of the well in 62 Block of Chunhua Oilfield has been reduced by 20%； the water injection has been increased by 25%， and the daily oil production of the single production well has increased from 0.45 t/d to 5.08 t/d， with obvious yield increase benefit. The overall recovery has increased by more than 8%.

In this study, the isothermal compression experiments of Mg-Gd-Y-Zn-Zr alloy at 450 °C and 0.01 s−1 under different strains were carried out to investigate the microstructure evolution and the formation mechanism of the heterogeneous microstructure. The microstructure of the sample with a strain of 1.4 exhibited significant heterogeneous microstructure characteristics with bimodal grain and bimodal texture distribution. The particle-stimulated nucleation (PSN) mechanism activated by intergranular block-shaped LPSO phases and the continuous dynamic recrystallization (CDRX) mechanism developed layer by layer towards grain interior promoted grain refinement and the formation of the bimodal grain distribution characteristics. Moreover, the stress-induced dynamic precipitation of Mg5RE particles became more significant with increasing strain, and the interaction of Mg5RE particles with dynamic recrystallization (DRX) grains further refined the DRX grains and exacerbated the degree of bimodal grain distribution. The grains with the axis between CD and TD and grains with the axis perpendicular to CD slipped along basal and prismatic planes, respectively, leading to the gradual deflection of the axis toward CD and the formation of a strong basal texture with axis parallel to CD during thermal compression. At the same time, the coarse deformed grains with strong basal texture were preserved during compression deformation due to small strain energy storage. Inhomogeneous plastic deformation, randomly oriented refined DRX-ed grains and dynamically precipitated Mg5RE particles together lead to the formation of the heterogeneous microstructure. This study provides theoretical guidance for preparing of high-performance Mg-RE alloys with heterogeneous microstructure.

In this study, the precipitate characteristics and precipitation-strengthening mechanism of solution-treated Mg-13Gd-4Y–2Zn-0.6Zr alloy after the upsetting and extrusion were investigated at different aging treatment temperatures. The prismatic plate-shaped nano-sized β′ precipitates and the prismatic rod-shaped micro-sized β precipitates were precipitated in low-temperature (e.g. 170 °C) and high-temperature (e.g. 330 °C) aging treatment, respectively. The critical nucleation resolved shear stresses (CRSSN) for the observed {10–12} and {11–21} extension twins and the twin number fractions of the two-type twins in the total twin number were unaffected by the precipitates. However, the greater total twin number in the alloy aged at 330 °C indicates that the strengthening effect of β precipitates on twinning was greater than that of β′ precipitates. The calculation results of Orowan equation showed that the strengthening effect of β′ precipitates on the pyramidal slip was greater than that of β precipitates. The greater hardness for the alloy aged at 170 °C was attributed to the greater strengthening effect of β′ precipitates on the pyramidal slip.

The hot deformation behavior of the wrought Mg–Gd−Y–Zn–Zr alloy was studied by uniaxial tensile tests conducted at various temperatures (350–500 °C) and strain rates (0.1–0.0001s−1). Furthermore, the effects of the deformation parameter on the true stress−strain curves, microstructure, fracture characteristics, and fracture mechanisms were discussed, and a damage model for predicting fracture strain was established. The results are as follows. The increasing temperature or the decreasing strain rate reduce the peak stress and increase the fracture strain, except for 500 °C/0.0001s−1. The increasing in the fracture strain is attributed to the easier activation of multi−slip, the smaller size of broken 14H−LPSO during deformation, the higher fraction of fine grain generated by DRX. The β phase around the grain boundary will gradually disappear with the decrease of strain rate at high temperature (450 °C and 500 °C), which will cause DRXed−grain coarsening. Especially the alloy deformed at 500 °C/0.0001s−1, the grains are significantly coarsened. Thus, the fracture strain of the alloy deformed at 500 °C/0.0001s−1 is not greater than that of the alloy deformed at 500 °C/0.001s−1. The fracture morphology changes from the coexistence of cleavage surfaces and dimple to dimple with increasing deformation temperature and decreasing strain rate. In addition, the fracture damage predicted using the fracture damage model agreed well with the experimental results, with a maximum relative error of only 8.8%.

As one of severe plastic deformation (SPD) methods, multi-directional forging (MDF) technology is an effective way to refine grains. The microstructure, texture evolution and mechanical properties of homogenized Mg–13Gd–4Y–2Zn–0.5Zr (wt. %) alloy during isothermal MDF process were synthetically investigated in the paper. The results showed that the mean grain size of the alloy decreased gradually with the MDF passes increased. After 4 passes, the average grain size of the alloy was refined to 2.7 μm, and the microstructure distribution was uniform. On the one hand, with the increasing of the MDF passes, the massive intergranular LPSO phases are gradually broken up and formed a deformation zone. The plate-like Mg5(Gd,Y) precipitates were located interior the grains. On the other hand, the spherical Mg5(Gd,Y) phases were randomly distributed with the increasing of MDF passes. In addition, the maximum texture intensity of the MDFed alloy on (0001) basal plane gradually was weaken from 15.993 of the 1MDFed alloy to 4.245 of the 4MDFed alloy, which was attributed to the increasing of volume fraction of dynamic recrystallized (DRXed) grains via MDF method. And the dynamic recrystallization (DRX) mechanisms were continuous DRX (CDRX), discontinuous DRX (DDRX), particle stimulated nucleation (PSN) and kink induced DRX. The maximum ultimate tensile strength (UTS) and tensile yield strength (TYS) after 4 passes were 385 MPa and 360 MPa respectively. The excellent mechanical properties of the alloy were owing to the grain boundary strengthening, dislocation strengthening, texture strengthening and precipitation strengthening. In addition, the second phase particles such as lamellar LPSO phases, broken block-shaped LPSO phases, spherical Mg5(Gd,Y) phases and plate-like Mg5(Gd,Y) phases were demonstrated to be the strengthening phases.

As one of the severe plastic deformation (SPD) methods, repetitive upsetting-extrusion (RUE) technique was an effective way to refine grains for large-sized billet at blank-making stage. The microstructure evolution and mechanical properties of industrial-scale Mg–9Gd–3Y–2Zn–0.4Zr (wt.%) alloys were comprehensively investigated in this paper. The experimental alloys exhibited heterogeneous microstructure in the different regions and directions due to the uneven deformation temperature and strain during the RUE deformation process. In addition, the texture and mechanical properties of the RUEed samples also exhibited obvious anisotropy. In particular, the RUEed sample in the edge region along extrusion direction (EED) showed a superior tensile strength with ultimate tensile strength (UTS) of 357 MPa, tensile yield strength (TYS) of 242 MPa and the failure elongation (FE) of 9.0%, due to the smaller average grain size (12.7 μm) and higher area fraction of the dynamic recrystallized (DRXed) grains (82.2%) than other regions. Furthermore, the results also exhibited that the enhancement of the mechanical properties of the RUEed samples were mainly attributed to Hall–Petch strengthening, Orowan strengthening and texture strengthening.

In this study, the hot deformation of Mg-9Gd-4Y-2Zn-0.5Zr alloy was studied by the hot tensile test conducted at various temperatures (350°C–500 °C) and strain rates (0.0001–0.1s−1). Furthermore, the relationship among the peak stress, the fracture strain, fracture morphology and soften behavior was discussed, and a fracture damage model was proposed to predict the fracture failure. The results were as follows. The soften behaviors, including the twin being replaced by multi-slip and the occurrence of DRX become more obvious with the decrease of Z (Z=ε˙exp(QRT)) value, which leads to the decrease of the strain hardening exponent n determining the peak stress and the increase of the strain-rate hardening exponent m determining the fracture strain. The greater the n, the greater the peak stress; the greater the m, the greater the fracture strain. The transformation of the fracture morphology with the decreasing Z value is cleavage surfaces→ coexistence of cleavage surfaces and dimple→ dimple. The proposed fracture damage model is in good agreement with the experimental results.

The effects of deep cryogenic treatment (DCT) on the tensile property and microstructure of Mg-9Gd-4Y–2Zn-0.5Zr(wt.%) alloy were investigated by comparing the alloy treated by solution treatment, deep cryogenic treatment and aging treatment (ST + DCT + AT) and that treated by solution treatment and aging treatment (ST + AT). The lamellar 14H-type long-period stacking ordered (14H-LPSO) in grain was precipitated in the alloy treated by ST + AT. However, the particle and needle-like Mg5RE (RE = Gd, Y) phases instead of the lamellar 14H-LPSO were precipitated, and a high-density dislocation existed in the alloy treated by ST + DCT. The greater ultimate tensile strength (UTS) and yield strength (YS) of the alloy treated by ST + DCT + AT were obtained because of the precipitation of the Mg5RE phases. The trend, the UTS and YS firstly increased then decreased with the increasing of soaking time, is corresponding to the volume fraction increasing and size-coarsening of Mg5RE precipitates, respectively. The greater elongation (EL) was obtained after the short-time DCT for 0–2 h (DCT0h-DCT2h) and the smaller EL was obtained for the long soaking time (>DCT2h). The fracture mode of the samples is all quasi-cleavage fracture.

At present, there are great technical difficulties in achieving microstructure and mechanical properties uniformity in large-size billets prepared by severe plastic deformation technology. How to improve the process route to realize the microstructure and mechanical properties uniformity of the billets has become an urgent problem to be solved at present. In this paper, GWZ932K alloy is used for two reciprocating upsetting-extrusion (RUE) deformation methods with a cumulative strain of 5.38. The influence of isothermal temperature reciprocating upsetting-extrusion (IT-RUE) and decreasing temperature reciprocating upsetting-extrusion (DT-RUE) on the microstructure and mechanical properties uniformity of GWZ932K alloy is discussed in detail. The results show both IT-RUE and DT-RUE deformation methods can effectively refine grains. IT-RUE can prepare Mg alloy billet with uniform microstructure and mechanical properties from center region (CR) to edge region (ER). The microstructure and mechanical properties of the billet prepared by DT-RUE show obvious gradient characteristics from CR to ER. After 4 passes IT-RUE deformation, double-peak textures appear on the (0001) basal texture of the ER, middle region (1/2R) and CR, which is mainly attributed to the occurrence of dynamic recrystallization (DRX) behavior. It should be noted that changes in the deformation temperature will not cause changes in the DRX mechanism. The deformation mechanisms of continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) jointly promote grain refinement.

This study proposed an effective plastic deformation technique, rotating backward extrusion (RBE), for producing high performance AZ80 magnesium alloy cup-shaped pieces. The RBE process was carried on the Gleeble-3500 test machine at 653 K, and the conventional backward extrusion (CBE) was also conducted for comparison. A detailed microstructure analysis was performed using the optical microscopy (OM) and electron back-scatter diffraction (EBSD). The results shown that the equivalent strain and deformation uniformity of the cup pieces could be substantially increased by the RBE process compared with the CBE process. Furthermore, the RBE process could significantly improve the grain refining capacity and the proportion of dynamic recrystallization (DRX), of which the maximum reduction of grain size was 88.60%, and the maximum increase of DRX proportion was 55.30% in the cup bottom. The main deformation mechanism of the RBE process was the discontinuous DRX (DDRX), while the continuous DRX (CDRX) was also occurred in the cup transition. Compared with the CBE sample, the texture of the cup bottom was weakened for the RBE sample. The microhardness value of the RBE sample was higher than that of the CBE sample, which can be attributed to the grain refinement strengthening.

To achieve high porosity and strength, porous SiC ceramics were fabricated by utilizing α-SiC powder, Si powder and TiO2 powder as starting materials and firing at 1 400 °C for 3 h in an argon atmosphere. The influence of the TiO2 addition (0, 2%, 4% and 8%, by mass) on the phase composition, micro-morphology, pore size distribution and main physical properties of the materials was studied. The results show that as the TiO2 addition increases, the diffraction peak of Si gradually diminishes, while Ti3O5 and TiSi2 are detected in the materials. With the formation of these new phases, SiC particles are bonded more tightly, resulting in reduced apparent porosity and average pore size along with significantly improved mechanical properties. When the TiO2 addition is 8%, exceptional comprehensive properties of the material are achieved in terms of the apparent porosity of 33.6%, cold modulus of rupture of 29.6 MPa and average pore size of 0.27 µm. [ABSTRACT FROM AUTHOR]

Rotating backward extrusion (RBE) is one of severe plastic deformation (SPD) methods used to produce cylindrical components with a very large strain by a single pass. In this study, the microstructure and texture evolution in the different regions of Mg-12Gd-4Y-2Zn-0.5Zr (wt.%) alloys via RBE process were investigated by using optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron back-scatter diffraction (EBSD). The results showed that the cup-shaped sample formed by RBE process exhibited typical gradient microstructure expanding from its inner wall to outer wall along the radial direction (RD). The average grain size of the RBEed sample decreased when the radius decreased from the edge region to the center region along the RD, which was attributed to the different strains and strain rates in the different regions. It also could be observed that the center region showed highest deformation and the edge region exhibited the lowest deformation in the RBEed sample along the RD. In addition, the grain refinement mechanisms of the experimental alloy containing long-period stacking ordered (LPSO) phases after RBE with 100 N were continuous dynamic recrystallization (CDRX), discontinuous dynamic recrystallization (DDRX) and particle stimulated nucleation (PSN).

Abstract Background Guangxi is the province most seriously affected by rabies virus (RABV) in China. Those most affected by RABV each year are people in rural areas, where dogs are the main cause of human infection with the virus. Methods In this study, we established a rabies vaccination demonstration program that included eradication, core, and peripheral areas. This program was implemented for 9 years and comprised three stages: 12 counties in the first stage (2008–2010), 21 counties in the second stage (2011–2013), and then extending to all counties of Guangxi Province in the third stage (2014–2016). The program included a dog vaccination campaign, surveillance of clinically healthy dogs who may be potential RABV carriers, monitoring anti-RABV antibody titers in vaccinated dogs, and compiling and reporting statistics of human rabies cases. Results The target effectiveness was achieved in the eradication, core, and peripheral areas in all three stages. The vaccination demonstration program successfully promoted RABV vaccination of domestic dogs throughout Guangxi Province by drawing upon the experience gained at key points. Compared with a vaccination coverage rate of 39.42–46.85% in Guangxi Province overall during 2003–2007, this rate gradually increased to 48.98–52.67% in 2008–2010, 60.24–69.67% in 2011–2013, and 70.09–71.53% in 2014–2016, thereby meeting World Health Organization requirements. The total cases of human rabies in the province decreased from 602 in 2004 to 41 cases in 2017. Conclusions The present pilot vaccination program obviously increased the rabies vaccination and seroconversion rates, and effectively reduced the spread of rabies from dogs to humans as well as the number of human rabies cases, thus successfully controlling rabies in Guangxi.

Assessing Land Use and Land Cover Change (LULCC) related with aquaculture areas is vital for evaluating the impacts of aquaculture ponds on the environment and developing a sustainable aquaculture production system. Most studies analyze changes in aquaculture land in coastal areas, and little research focuses on the inland area, where the conversions between agriculture and aquaculture land is primarily driven by socioeconomic factors. This study assessed LULCC related to aquaculture areas in Qianjiang City, China, from 1990 to 2022, using multitemporal Landsat images and a combination of decision tree classifier and visual interpretation. The LULCC was analyzed by the transition matrix. Results showed that the main LULC type was farmland, which accounted for more than 70% of the study area from 1990 to 2022. The built-up and aquaculture land showed an increasing trend year by year. In contrast, there was a gradual decline in forest/grass land from 1990 to 2016, and then its area increased slightly from 2016 to 2022 due to the policy of returning farmland to forest. Water areas were mainly composed of rivers and ponds, with subtle changes during the study period. The main driving forces of LULCC in Qianjiang City were economic and policy factors, with rapid GDP growth and government policies being the dominant factors. [ABSTRACT FROM AUTHOR]

The rotating backward extrusion (RBE) process, as a new severe plastic deformation (SPD) process, is based on conventional backward extrusion and rotation, which meets the requirement of modern industrial development with its high performance and production efficiency. However, there is little research on the microstructure evolution and texture modification of the RBE process. Thus, in this study, the effect of different rotating revolutions, e.g., n = 5, n = 10, and n = 50, on the microstructure and texture development for the RBE process based on the AZ80 magnesium (Mg) alloy were investigated at 653 K. The results disclose that the rotating revolution is an influencing processing parameter on the deformation of the RBE process. The grain refining ability is enhanced with the increase of the rotating revolutions, and the minimum grain size of the cup bottom, shearing zone, and cup wall can reach to 16.7 μm, 15.6 μm, and 13.0 μm, respectively, under the condition of n = 50. Furthermore, with the increase in the rotating revolutions, the microstructure of the alloy becomes more uniform and the proportion of dynamic recrystallization (DRX) is also increased. The maximum DRX fractions of the sample for the cup bottom and cup wall are 95.4% and 86.8%, respectively, at n = 50. The DRX mechanism of the RBE process is determined by the continuous DRX and discontinuous DRX. In addition, the texture can be significant weakened during the RBE process, especially at the cup bottom, where the maximum pole intensity can be reduced from 17.6 at n = 10 to 6.5 at n = 50, which can be attributed to the higher proportion of new DRXed grains whose orientations are more random compared with the deformed grains.

The current work systematically investigated the microstructure, texture evolution, and mechanical properties of MDFed Mg-13Gd-4Y-2Zn-0.5Zr (wt%) alloy (GWZ) on the condition of high and low temperature cycle deformation. The high and low temperature cycle deformation was proposed on the basis of the conventional multi-directional forging (MDF) at decreasing temperature and annealing treatment. As a new method, it was aimed to timely uniform the microstructure and strengthen magnesium (Mg) matrix during the deformation process. A low accumulative strain of 3 after 1 pass resulted in a bimodal microstructure with undynamic recrystallized (unDRXed) regions and dynamic recrystallized (DRXed) grains, while a high accumulative strain of 12 after 4 passes lead to a homogeneous microstructure with fine DRXed grains. According to the experimental results, it indicated that the average grain size of 63 μm after homogenization treatment at 520 was refined remarkably to 5.20 μm after 4 passes at 420 °C through high and low temperature cycle deformation. The area fraction of DRXed grains was increased to 98.4%, which can be regarded as achieving complete DRX after 4 passes. The grain refinement was mainly caused by particle stimulation nucleation (PSN) and mechanism. As the MDF passes and accumulative strain increased, the basal texture was weakened and transformed from a strong basal texture to a random distribution gradually. Compared with conventional MDF at decreasing temperature, the mechanical properties were enhanced effectively. After 4 passes, the ultimate tensile strength (UTS), tensile yield strength (TYS), and failure elongation (FE) were 405 MPa, 305 MPa, and 13.1%, respectively.