[en] In order to understand the two-stage A/O process which contained two independent A/O (Anoxic/Oxic) subsystems when applied to treat high-strength ammonia nitrogen wastewater, connection mode of the two A/O subsystems and DO concentration of oxic phase were selected as the influencing factors in this paper. The connection modes of the two independent A/O subsystems were parallel-connected and tandem-connected. Initially, the performance of two-stage A/O process in different connection modes were investigated by comparing the ability to remove COD, NH4+-N and TN. It was observed that tandem-connected two-stage A/O system was suitable for the treatment of high-strength ammonia nitrogen wastewater, and two-stage A/O system which was operated in parallel-connected mode failed to meet the direct emission standard of Discharge Standard of Water Pollutants for Ammonia Industry in China (GB13458-2013) with remanent COD, NH4+-N and final effluent TN concentration of 234.2mg/L, 25mg/L and 74.2mg/L, respectively. Following the above observation, five different levels of DO concentration (2, 3, 4, 5 and 6 mg/L) of stage-one and stage-two were varied to figure out the optimal DO concentration in tandem-connected two-stage A/O system. Examination of effluent quality indicated that 5.0mg/L was determined to be the optimal DO concentration for Stage-one and 2.0mg/L for Stage-two. In this case, the quality of effluent was perfectly satisfied the direct emission standard. (paper)

[en] A new integrated device—inverted A2/O–MBR process for rural domestic sewage treatment was designed and investigated in this study. The device consisted of three components orderly referred to the anoxic zone, anaerobic zone and aerobic zone where a MBR membrane group was arranged. Results showed that the device was favorable to treat rural domestic sewage. Optimal influent percentage of influent to anoxic zone was 70%, with TN, TP removal ratio approaching to 69% and 89%. Reduction of NH4+-N and TN enhanced with the increase of sludge age, but that of TP decreased. 15d was determined to be the best sludge age for simultaneous removal of NH4+-N, TN and TP. Moreover, when DO was 3.0mg/L, NH4+-N, TN and TP reduction reached up to 96%, 70% and 88% respectively. These data verified the good performance of the integrated system, and the quality of effluent could well meet the direct emission standard of Outdoor Drainage Design Specification in China (GB50014-2006) (edition 2014). (paper)

[en] Al/Mg/Al sheet was fabricated by the proposed porthole die co-extrusion and subsequent hot rolling (PCE-R) method. The intermetallic compounds of β-Al₃Mg₂ and γ-Mg₁₇Al₁₂ were formed in transition layer after PCE-R process, and the thicknesses of β and γ layers became larger at higher rolling temperature or higher reduction ratio. Partial dynamic recrystallization (DRX) occurred in Al layer, and Al layer mainly consisted of shear-typed {111} fiber textures. However, if the rolling reduction is as high as 75%, Al layer exhibited quite different texture components. Mg layer consisted of fine equiaxed grains and several elongated grains, implying the occurrence of near complete DRX. With the increase of rolling temperature or reduction ratio, the number of Mg₁₇Al₁₂ particles in Mg layer was reduced, resulting into larger grain size. Mg layer had strong basal plane texture with c-axis parallel to transverse direction. Al/Mg/Al sheet rolled at 300 °C with 65% reduction exhibited two stress-drop fracture mechanism during tensile test, and it showed excellent tensile strength of 149 MPa, and elongation of 0.13. However, Al/Mg/Al sheet rolled with 75% reduction had inferior tensile properties due to the existence of some cracks after rolling.

[en] Highlights: • Selective grains with {0001} orientation achieved abnormal grain growth during solution. • Stored energy gradient was the driving force for abnormal grain growth. • Normal and abnormal grains experienced different precipitates behaviors during aging. • Solution enhanced the overall corrosion resistance, while aging deteriorated it due to the precipitates. • Formation of abnormal grains strongly improved the corrosion resistance of welding zone. Abnormal grain growth (AGG) took place during solution treatment of extruded ZK60 Mg alloy. The driving force of AGG was stored energy gradient, and the {0001} grains acted as candidates. The grain size and topology advantages contributed to the propagation of AGG, while lots of stored energy was consumed by static recrystallization and grain growth, resulting in the ending of AGG. The extruded alloy had the worst corrosion resistance with a corrosion rate of 6.3 mm/y, and the welding zone was preferentially corroded. The corrosion rate dropped to 3.7 mm/y after solution due to the formation of abnormal grains.

[en] Highlights: • Dissimilar AA6063/AA7075 with sound interface was co-extruded by porthole die. • AA7075 was obviously refined, while large grains were remained in AA6063. • The types and intensities of texture were greatly affected by temperature. • Hardness and tensile strength were enhanced with increasing temperature. The dissimilar AA6063/AA7075 plate was fabricated by porthole die co-extrusion method, and the effects of extrusion temperature on microstructure and mechanical properties were investigated. The results showed that the sound AA6063/AA7075 welding interface without crack or impurity was obtained. Few secondary particles existed in extruded AA6063 side, while large amount of fine particles were found in AA7075 side, and the number of particles was decreased with increasing temperature. The coarse initial grains with the formation of substructures were observed in AA6063. However, the microstructure of AA7075 mainly consisted of fine equiaxed grains with several microns due to the occurrence of near complete dynamic recrystallization. The average grains size of the AA6063/AA7075 extruded plate was increased with increasing temperature. The plate extruded at 510 °C has strong texture component with 10° shift of Φ from Cube and some weak recrystallization Cube texture. The elongation was not affected by temperature, while the hardness and ultimate tensile strength were obviously enhanced with increasing temperature.

[en] Highlights: • Dynamic evolution of microstructure during porthole die extrusion was clarified. • Near full DRX occurred in welding zone, while slight DRX occurred in matrix zone. • Texture evolution of welding zone is complex due to the various stress condition. • Fine MgZn₂ with uniform distribution and coarse Al₂₃CuFe₄ existed in the profile. -- Abstract: The porthole die extrusion of high strength Al–Zn–Mg alloy was carried out at 783 K. The reserved materials inside portholes and welding chamber were taken out to investigate the dynamic evolution of grain structure, micro-texture and second phase along streamlines of welding zone and matrix zone. The material of welding zone experienced severe plastic deformation, while the flowing route of matrix zone was relatively smooth. Hence, the welding zone achieved near complete dynamic crystallization after splitting stage, and the grain size kept steady during the subsequent welding and extruding stage. The streamline of matrix zone mainly consisted of elongated grains with small amount of fine equiaxed grains, which indicated the occurrence of dynamic recovery and slight dynamic crystallization. The texture evolution of welding zone was much more complicated due to the combination of compression, shearing and tension stresses. The welding zone of the final extruded profile had the main textures of {112}<111>, {101}<111>, {101}<001> and {111}<112> orientations, while the matrix zone of the profile consisted of {112}<111>, {101}<111> and {101}<211> orientations. The extrusion temperature is sufficient for dissolving MgZn₂ phase, while it is insufficient for the dissolution of Al₂₃CuFe₄. Instead, the coarse Al₂₃CuFe₄ was broke into small pieces due to the effects of mechanical deformation.

[en] Highlights: • Mg-5.80Zn-5.26Al-3.20Sn-0.37Mn alloy suitable for extrusion was designed and fabricated. • High extrusion speed resulted in more second phases, an increase in DRX degree, and a weaker texture. • High extrusion temperature increase the number of second phases, grain size and DRX degree. • The sample extruded under 10 mm/min and 300 °C had the highest strength and corrosion resistance. Mg alloy with the alloying elements of Zn, Al, Sn and Mn was designed, and hot extrusion was carried out under various extrusion speeds and temperatures. The microstructure was well characterized, and the mechanical properties as well as corrosion resistance were tested. The results showed that the high speed extrusion resulted in more second phase particles, an increase in fraction of dynamic recrystallized (DRXed) grains, and a weaker basal plane texture. Moreover, high extrusion temperature increased the number of second phases, grain size, and DRX degree, while decreased the strength of basal plane texture. The sample extruded under the speed of 10 mm/min and temperature of 300 °C exhibited the highest yield strength (YS) and ultimate tensile strength (UTS), and the best corrosion resistance. High extrusion temperature could reduce the strength, while increase the elongation (EL). The corrosion resistance was improved greatly by grain refinement, while it became worse by increasing the number of fine and dispersed second phase particles.

[en] Highlights: • Inhomogeneous microstructure was formed due to the non-uniform temperature and velocity. • The mode of DRX and number/type of precipitates were depended on extrusion speed. • High extrusion speed increased the size and fraction of DRXed grains in matrix zone. • Corrosion rate firstly increased and then decreased during the immersion of Mg profiles. • Corrosion resistance especially in welding zone was enhanced by high extrusion speed. The porthole die extrusion was carried out using ZK60 Mg alloy. The inhomogeneous microstructure was formed on welding and matrix zones of extruded profiles. High extrusion speed induced a temperature rise and made β₁’ precipitate disappear, resulting in an obvious grain growth, change of dynamic recrystallization (DRX) mode, and higher DRX degree. The corrosion rate firstly increased due to the occurrence of localized pitting, and then decreased owing to the formation of a denser and more protective film. Low extrusion speed was harmful on the corrosion behaviors, especially in welding zone, due to the smaller grain size and more precipitates.

[en] Recent research has shown that some intermetallic compound particles with high interfacial hydrogen trap energies (e.g., Mg₂Si) are prone to damage at high hydrogen concentrations. In this study, the acceleration of particle damage in an A6061 alloy was observed in-situ via X-ray CT. The damage behavior of the particles that are located in the crack tip stress field, where high stress triaxiality causes a local increase in the hydrogen concentration, was analyzed. The influence of hydrogen on the damage behavior of the dispersed Mg₂Si particles was investigated by preparing a material charged with hydrogen to achieve extremely high hydrogen concentration, and further hydrogen enrichment in a crack tip region was also utilized. Interfacial debonding of Mg₂Si particles was frequently observed in the vicinity of a crack tip immediately prior to tensile fracture. Even though the fracture is typical of ductile fracture, hydrogen accelerates particle damage and reduces the macroscopic ductility of the aluminum alloy. This can be considered as a form of hydrogen embrittlement of aluminum alloys. Even in materials with relatively low hydrogen concentrations (0.85 mass ppm), interfacial debonding occurred in the hydrogen-enriched crack tip regions. A higher hydrogen concentration promoted interfacial debonding over a wider range of particle sizes and particle shapes. It can be inferred that localized hydrogen enrichment, which is expected to occur due to external hydrogen exposure, stress corrosion cracking, corrosion or crack tips, can directly contribute to debonding at the Mg₂Si particle/aluminum matrix interface. According to the analysis, reduction of the diameter and simplification of the shape of Mg₂Si particles are effective method for suppressing such hydrogen-induced debonding. (author)

[en] Highlights: • Cross rolling and subsequent annealing weakened the intensity of main textures of brass, Dillamore, and S. • Both hardness and electrical conductivity were improved by warm cross rolling. • Cross rolling and subsequent annealing remarkably reduced the degree of anisotropy of tensile strength. • After annealing, rolled sample always showed better corrosion resistance than the extruded sample. -- Abstract: The anisotropy of mechanical properties and poor corrosion resistance are important problems for high strength aluminum plate. In this study, the combined process of hot extrusion and warm cross rolling was conducted on AA7075 alloy, and both the extruded and rolled plates were annealed at various temperatures. The effects of warm cross rolling and annealing on the microstructure, mechanical properties, and corrosion behavior were studied. The results indicated that both cross rolling and annealing weakened the intensity of main textures of brass, Dillamore, and S. Compared to the extruded plate, the cross rolled ones exhibited higher hardness, higher conductivity, and lower anisotropy of tensile strength. Both cross rolling and annealing made the tensile strength of a plate along different directions more uniform. Moreover, annealing greatly enhanced the corrosion resistance by consuming the distortion energy, reducing the number of crystalline defects and increasing the fraction of low-Σ coincident site lattice grain boundaries. After annealing, the rolled AA7075 plates exhibited better corrosion resistance than the extruded ones, since they possessed lower fractions of brass texture, finer grains, and higher fraction of low-Σ coincident site lattice grain boundaries.