The pronounced anisotropy in mechanical properties presents a major obstacle to the extensive application of aluminum-lithium(Al-Li)alloys,primarily attributed to heterogeneous precipitate distribution,grain structure...The pronounced anisotropy in mechanical properties presents a major obstacle to the extensive application of aluminum-lithium(Al-Li)alloys,primarily attributed to heterogeneous precipitate distribution,grain structure variations,and crystallographic texture.This study investigates the impact of pre-thermal treatment prior to hot rolling and aging treatment on the anisotropy of mechanical properties of 2195 alloy sheet fabricated by gas atomization,hot pressing and hot rolling.The results demonstrate that pre-treatment at 450℃for 4 h promotes finer and more uniform distribution of precipitates,effectively mitigating mechanical anisotropy of the alloy sheet.Additionally,this treatment facilitates recrystallization during hot rolling,further reducing mechanical anisotropy.The in-plane anisotropy(IPA)factors for ultimate tensile strength(UTS)and yield strength(YS)are 1.15%and 0.77%,respectively.Subsequent aging treatment enhances grain refinement and the uniformity of the T_(1) phase,suppresses the formation of precipitation-free zones(PFZs),significantly improving the strength and toughness of the alloy sheet.After peak aging at 165℃for 48 h,the alloy sheet exhibits YS of 547 MPa,UTS of 590 MPa,and elongation(EL)of 7.7%.展开更多
基于一台高压缩比四缸增压直喷(gasoline direct injection,GDI)发动机和预燃室湍流射流点火(turbulent jet ignition,TJI)系统,开展中低负荷稀燃特性试验研究。研究结果表明:预燃室射流点火的燃烧稳定性存在着明显的负荷边界;在平均指...基于一台高压缩比四缸增压直喷(gasoline direct injection,GDI)发动机和预燃室湍流射流点火(turbulent jet ignition,TJI)系统,开展中低负荷稀燃特性试验研究。研究结果表明:预燃室射流点火的燃烧稳定性存在着明显的负荷边界;在平均指示压力(indicated mean effective pressure,IMEP)为0.4 MPa的低负荷,预燃室射流点火的缸压和瞬时放热率峰值较常规火花点火(spark ignition,SI)下降明显,峰值相位后移,滞燃期长;在平均指示压力为0.7 MPa时其平均指示压力循环波动率(coefficient of variation,COV)达5%;在平均指示压力为1.1 MPa的最佳指示燃油消耗率工况,预燃室射流点火的稀燃边界、指示燃油消耗率、排放等可以达到和常规火花点火相当的水平。中低负荷下,随着负荷增加,预燃室射流点火的滞燃期缩短,燃烧重心提前,燃烧稳定性改善,全碳氢(total hydrocarbon,THC)和CO排放降低。高能点火可以缩短预燃室射流点火的滞燃期,加快燃烧速度,提高燃烧稳定性,改善排放。展开更多
基金Project(52274369)supported by the National Natural Science Foundation of ChinaProject(623020034)supported by the National Key Laboratory of Science and Technology on High-strength Structural Materials,China。
文摘The pronounced anisotropy in mechanical properties presents a major obstacle to the extensive application of aluminum-lithium(Al-Li)alloys,primarily attributed to heterogeneous precipitate distribution,grain structure variations,and crystallographic texture.This study investigates the impact of pre-thermal treatment prior to hot rolling and aging treatment on the anisotropy of mechanical properties of 2195 alloy sheet fabricated by gas atomization,hot pressing and hot rolling.The results demonstrate that pre-treatment at 450℃for 4 h promotes finer and more uniform distribution of precipitates,effectively mitigating mechanical anisotropy of the alloy sheet.Additionally,this treatment facilitates recrystallization during hot rolling,further reducing mechanical anisotropy.The in-plane anisotropy(IPA)factors for ultimate tensile strength(UTS)and yield strength(YS)are 1.15%and 0.77%,respectively.Subsequent aging treatment enhances grain refinement and the uniformity of the T_(1) phase,suppresses the formation of precipitation-free zones(PFZs),significantly improving the strength and toughness of the alloy sheet.After peak aging at 165℃for 48 h,the alloy sheet exhibits YS of 547 MPa,UTS of 590 MPa,and elongation(EL)of 7.7%.
文摘基于一台高压缩比四缸增压直喷(gasoline direct injection,GDI)发动机和预燃室湍流射流点火(turbulent jet ignition,TJI)系统,开展中低负荷稀燃特性试验研究。研究结果表明:预燃室射流点火的燃烧稳定性存在着明显的负荷边界;在平均指示压力(indicated mean effective pressure,IMEP)为0.4 MPa的低负荷,预燃室射流点火的缸压和瞬时放热率峰值较常规火花点火(spark ignition,SI)下降明显,峰值相位后移,滞燃期长;在平均指示压力为0.7 MPa时其平均指示压力循环波动率(coefficient of variation,COV)达5%;在平均指示压力为1.1 MPa的最佳指示燃油消耗率工况,预燃室射流点火的稀燃边界、指示燃油消耗率、排放等可以达到和常规火花点火相当的水平。中低负荷下,随着负荷增加,预燃室射流点火的滞燃期缩短,燃烧重心提前,燃烧稳定性改善,全碳氢(total hydrocarbon,THC)和CO排放降低。高能点火可以缩短预燃室射流点火的滞燃期,加快燃烧速度,提高燃烧稳定性,改善排放。
