In this paper, we are concerned with a weighted quasilinear elliptic equation involving critical Hardy-Sobolev exponent in a bounded G-symmetric domain. By using the symmetric criticality principle of Palais and varia...In this paper, we are concerned with a weighted quasilinear elliptic equation involving critical Hardy-Sobolev exponent in a bounded G-symmetric domain. By using the symmetric criticality principle of Palais and variational method, we establish several existence and multiplicity results of positive G-symmetric solutions under certain appropriate hypotheses on the potential and the nonlinearity.展开更多
The secondary phases of the steels have significant effects on the microstructure and mechanical properties, making controlling these secondary phases important. The control of MnS inclusions and A1N precipitates in a...The secondary phases of the steels have significant effects on the microstructure and mechanical properties, making controlling these secondary phases important. The control of MnS inclusions and A1N precipitates in a N-alloyed high-Mn twin-induced plastic cryogenic steel via solution treatment was investigated with several different techniques including microstructural characterization, 298 K tensile testing, and 77 K impact testing. The solutionizing temperature （ST） increased from 1323 to 1573 K, where the elongated MnS inclusions and large-sized AlN precipitates became spheroidized and dissolved. The aspect ratio of the MnS inclusions decreased as the ST increased and the number density increased. The impact toughness of the steels showed anisotropy and low impact energy values, due to the elongated MnS inclusions and large-sized AIN precipitates. The anisotropy was eliminated by spheroidizing the MnS inclusions. The impact energy was improved by dissolving the large-sized AlN precipitates during the solution treatment. The austenite grain size increased when the dissolution of the AlN precipitate increased, but the effect of the grain size on the yield strength, toughness, and the strength--ductility balance was weak.展开更多
Recently results were presented for an R & D program for handling the as-cast billets of an Al-Si-Mg A6060 Al alloy at the solutionizing heat treatment temperature. A reduction in the solutionizing temperature of ...Recently results were presented for an R & D program for handling the as-cast billets of an Al-Si-Mg A6060 Al alloy at the solutionizing heat treatment temperature. A reduction in the solutionizing temperature of the as-cast billets from 585℃ to 540℃ was found. This leads to substantial energy savings without lowering the quality of the final commercial Al profiles. The alloy was treated from the microstructural point of view as an Aluminum Metal-Matrix Composite (Al-MMC). Strengthening of the Al matrix grains during the process was quantified and measured by micro-Vickers hardness testing. A possible application of this is to apply the suggested lower temperature solutionizing process to billets stockpiled in the factory for some months. The alloy undergoes natural aging, a physical process at ambient temperature that alters its microstructural features. Does this aging affect the quality of the lower temperature solutionizing treated profiles? The effect of the natural aging by micro-Vickers hardness testing on some of the same samples of our original work stockpiled in our lab for 10 months was investigated. We applied, further, the Image-Pro Plus image processing software on them in an effort to collect microstructural data and compared them to values taken 10 months earlier. Also we tried an interconnection between the two experimental processes treating the alloy as an Al-MMC.展开更多
Duplex stainless steels are gaining global importance because of the need for a high strength corrosion resistant material. Three compositions of this group were selected with three different nitrogen contents ciz, 0....Duplex stainless steels are gaining global importance because of the need for a high strength corrosion resistant material. Three compositions of this group were selected with three different nitrogen contents ciz, 0.15 wt pct （alloy 1）, 0.23 wt pct （alloy 2） and 0.32 wt pct （alloy 3）. The steels were melted in a high frequency induction furnace and hot forged to various reductions from 16% to 62%. In this work, the effect of hot forging on the ferrite cont.ent, hardness, yield strength, impact strength and grain orientation （texture） were studied. Fracture analysis on all the forged specimens using SEM reveals that a size reduction of 48% results in maximum ductility and impact strength as well as minimal ferrite content and grain size. Thus the mechanical properties are found to have a direct correlation to ferrite content and grain size. The highest impact strength was observed in specimens with the smallest grain size, which was observed in specimens forged to 48% reduction in size.展开更多
In recent decades, aluminium alloy based metal matrix composites are used in several applications. Al6061 has been used as matrix material due to its good formability, excellent mechanical properties and etc., wide sp...In recent decades, aluminium alloy based metal matrix composites are used in several applications. Al6061 has been used as matrix material due to its good formability, excellent mechanical properties and etc., wide spectrum of the applications in industrial sectors. Inclusion of Frit particulates as reinforcement in Al6061 alloy material system improves its hardness and decrease in density. In the present investigation Al6061-Frit particulate composites were produced by ‘VORTEX’ method with varying weight percentages of Frit particulate from 0 wt% to 10 wt% in steps of 2.The as cast matrix alloy and its composites have been subjected to solutionizing treatment at a temperature of 530℃ for 2 hours followed by quenching in different media such as air, water and ice. The quenched specimens were subjected to artificial ageing. Aged specimens were subjected to ultra-sonic test using ultra-sonic flaw detector testing apparatus to identify the common casting defects like porosity, blow holes. Macrostructure and microstructure studies were conducted on as cast and composites in order to investigate the distribution of frit particles retained in matrix material system. Micro structural studies were carried out to understand nature of structure. Density measurement was carried out on both Al6061matrix alloy and Al6061-Frit particulate composite. Hardness tests have been conducted both on Al6061 matrix alloy and Al6061-Frit particulate composite before and after heat treatment. It has been observed under identical heat treatment conditions adopted, Al6061-Frit particulate composites exhibited significant improvement in hardness when compared with Al6061 alloy.展开更多
Heat treatable Al alloys of the 6xxx series are produced by the industry following a path that consolidates melting of raw materials, casting the melt in billets, solutionizing the billets following a suitable thermal...Heat treatable Al alloys of the 6xxx series are produced by the industry following a path that consolidates melting of raw materials, casting the melt in billets, solutionizing the billets following a suitable thermal cycle, pre-heating and extruding the material to profiles and finally aging the profiles. Although this procedure is known for pure materials from the scientific point of view, the introduction of scrap to the raw materials for melting modifies to an extent the fabrication conditions that follow casting. This fact affects the production cost. In this article we propose a research way based mainly on micro-Vickers tests that lead to an optimization of the treatment conditions for solutionizing the billets.展开更多
基金Supported by the Natural Science Foundation of China(1107118011171247)Project supported by Scientific and Technological Research Program of Chongqing Municipal Education Commission(KJ130503)
文摘In this paper, we are concerned with a weighted quasilinear elliptic equation involving critical Hardy-Sobolev exponent in a bounded G-symmetric domain. By using the symmetric criticality principle of Palais and variational method, we establish several existence and multiplicity results of positive G-symmetric solutions under certain appropriate hypotheses on the potential and the nonlinearity.
基金the financial support of the National Key Research and Development Program of China(Grant No.2017YFB0305101)
文摘The secondary phases of the steels have significant effects on the microstructure and mechanical properties, making controlling these secondary phases important. The control of MnS inclusions and A1N precipitates in a N-alloyed high-Mn twin-induced plastic cryogenic steel via solution treatment was investigated with several different techniques including microstructural characterization, 298 K tensile testing, and 77 K impact testing. The solutionizing temperature （ST） increased from 1323 to 1573 K, where the elongated MnS inclusions and large-sized AlN precipitates became spheroidized and dissolved. The aspect ratio of the MnS inclusions decreased as the ST increased and the number density increased. The impact toughness of the steels showed anisotropy and low impact energy values, due to the elongated MnS inclusions and large-sized AIN precipitates. The anisotropy was eliminated by spheroidizing the MnS inclusions. The impact energy was improved by dissolving the large-sized AlN precipitates during the solution treatment. The austenite grain size increased when the dissolution of the AlN precipitate increased, but the effect of the grain size on the yield strength, toughness, and the strength--ductility balance was weak.
文摘Recently results were presented for an R & D program for handling the as-cast billets of an Al-Si-Mg A6060 Al alloy at the solutionizing heat treatment temperature. A reduction in the solutionizing temperature of the as-cast billets from 585℃ to 540℃ was found. This leads to substantial energy savings without lowering the quality of the final commercial Al profiles. The alloy was treated from the microstructural point of view as an Aluminum Metal-Matrix Composite (Al-MMC). Strengthening of the Al matrix grains during the process was quantified and measured by micro-Vickers hardness testing. A possible application of this is to apply the suggested lower temperature solutionizing process to billets stockpiled in the factory for some months. The alloy undergoes natural aging, a physical process at ambient temperature that alters its microstructural features. Does this aging affect the quality of the lower temperature solutionizing treated profiles? The effect of the natural aging by micro-Vickers hardness testing on some of the same samples of our original work stockpiled in our lab for 10 months was investigated. We applied, further, the Image-Pro Plus image processing software on them in an effort to collect microstructural data and compared them to values taken 10 months earlier. Also we tried an interconnection between the two experimental processes treating the alloy as an Al-MMC.
文摘Duplex stainless steels are gaining global importance because of the need for a high strength corrosion resistant material. Three compositions of this group were selected with three different nitrogen contents ciz, 0.15 wt pct （alloy 1）, 0.23 wt pct （alloy 2） and 0.32 wt pct （alloy 3）. The steels were melted in a high frequency induction furnace and hot forged to various reductions from 16% to 62%. In this work, the effect of hot forging on the ferrite cont.ent, hardness, yield strength, impact strength and grain orientation （texture） were studied. Fracture analysis on all the forged specimens using SEM reveals that a size reduction of 48% results in maximum ductility and impact strength as well as minimal ferrite content and grain size. Thus the mechanical properties are found to have a direct correlation to ferrite content and grain size. The highest impact strength was observed in specimens with the smallest grain size, which was observed in specimens forged to 48% reduction in size.
文摘In recent decades, aluminium alloy based metal matrix composites are used in several applications. Al6061 has been used as matrix material due to its good formability, excellent mechanical properties and etc., wide spectrum of the applications in industrial sectors. Inclusion of Frit particulates as reinforcement in Al6061 alloy material system improves its hardness and decrease in density. In the present investigation Al6061-Frit particulate composites were produced by ‘VORTEX’ method with varying weight percentages of Frit particulate from 0 wt% to 10 wt% in steps of 2.The as cast matrix alloy and its composites have been subjected to solutionizing treatment at a temperature of 530℃ for 2 hours followed by quenching in different media such as air, water and ice. The quenched specimens were subjected to artificial ageing. Aged specimens were subjected to ultra-sonic test using ultra-sonic flaw detector testing apparatus to identify the common casting defects like porosity, blow holes. Macrostructure and microstructure studies were conducted on as cast and composites in order to investigate the distribution of frit particles retained in matrix material system. Micro structural studies were carried out to understand nature of structure. Density measurement was carried out on both Al6061matrix alloy and Al6061-Frit particulate composite. Hardness tests have been conducted both on Al6061 matrix alloy and Al6061-Frit particulate composite before and after heat treatment. It has been observed under identical heat treatment conditions adopted, Al6061-Frit particulate composites exhibited significant improvement in hardness when compared with Al6061 alloy.
文摘Heat treatable Al alloys of the 6xxx series are produced by the industry following a path that consolidates melting of raw materials, casting the melt in billets, solutionizing the billets following a suitable thermal cycle, pre-heating and extruding the material to profiles and finally aging the profiles. Although this procedure is known for pure materials from the scientific point of view, the introduction of scrap to the raw materials for melting modifies to an extent the fabrication conditions that follow casting. This fact affects the production cost. In this article we propose a research way based mainly on micro-Vickers tests that lead to an optimization of the treatment conditions for solutionizing the billets.
