初始组织对热挤压Mg-6Al-2Ca-2Sm合金显微组织和力学性能的影响

对铸态Mg-6Al-2Ca-2Sm合金分别进行经固溶和固溶+时效处理获得不同初始组织试样,然后对不同初始组织的试样进行热挤压,研究了不同初始组织对热挤压Mg-6Al-2Ca-2Sm合金显微组织和力学性能的影响。结果表明：铸态合金经热挤压后发生明显的部分再结晶,显微组织得到显著细化;经固溶或固溶+时效处理能够改善合金组织,热挤压后合金显微组织分布更加均匀。初始组织分布能够改善热挤压Mg-6Al-2Ca-2Sm合金室温和高温力学性能,固溶+时效后进行热挤压,Mg-6Al-2Ca-2Sm合金具有最高的抗拉强度和延伸率。     

预时效对A357合金组织与力学性能的影响

研究了低温预时效对含钪A357合金组织与力学性能的影响。结果表明,较理想的合金预时效工艺为120 ℃×4~6 h;120 ℃×4 h+175 ℃×5 h双级时效工艺使合金抗拉强度增至362 MPa,伸长率增至6%,分别较单级时效提高4.6%和7.1%。低温预时效能促进细密、弥散GP区的形成,有利于二次时效获得高密度、弥散分布的细小强化相Mg₂Si,从而提高合金力学性能。     

时效工艺对纳米结构2297铝锂合金力学性能与微观组织的影响

采用535 ℃×2 h固溶制度,将热锻态2297铝锂合金固溶水淬后冷轧,冷轧压下量为95%,然后将轧制样品在不同温度(120~190 ℃)和时间(0~80 h)范围内进行时效处理。采用拉伸、扫描电镜(SEM)和透射电镜(TEM)等测试方法,分析时效温度和时间对铝锂合金组织与性能的影响。结果表明:时效前的大塑性变形能获得纳米结构组织,能促进T₁相均匀细小地析出,缩短合金达到峰时效的时间,最终成功制备了高强高塑性铝锂合金。在120~140 ℃温区内时效时,时效温度越高,达到峰时效的时间越短、强度越高。140 ℃达到峰时效时间缩短为40 h,此时合金的抗拉强度、屈服强度和伸长率分别为525 MPa、478 MPa和7.7%,主要强化相为细小的T₁相。在170~190 ℃温区内时效时,时效温度越高,达到峰时效的时间越短,但抗拉强度与屈服强度迅速下降。170 ℃时效8 h达到峰时效状态,此时合金的抗拉强度、屈服强度和伸长率分别是503 MPa、462 MPa和5.0%,主要强化相仍为T₁相,但已经明显粗化。     

Effect of abruptly changing withdrawal rate on solidification microstructure in directionally solidified Al-4.5wt%Cu alloy简

Al-4.5wt.%Cu alloy has been directionally solidified at constant and abruptly changing withdrawal rates, respectively. The effects of the withdrawal rate on solidification microstructure, primary dendrite arm spacing(PDAS) and liquid solute distribution in front of the solid-liquid interface were investigated. The experimental results for the PDAS at a constant withdrawal rate agree well with the values calculated by the Hunt, Trivedi and Hunt-Lu models. At an abrupt change in the withdrawal rate, the maximum to minimum ratio of the PDAS at a given solidification parameter, i.e. λ1max/λ1min, is more than 2, and the PDAS values are remarkably history-dependent. Further, the liquid-solute distribution curve based on theoretical calculation shows that the larger the initial withdrawal rate is, the smaller the minimum of liquid solute concentration in front of the solid-liquid interface is after the abrupt change in withdrawal rate.     

Effect of Y2O3 on microstructure and mechanical properties of hypereutectic Al-20%Si alloy

The effect of Y203 on the microstructure and mechanical properties of the hypereutectic Al-20%Si（mass fraction） alloy was investigated. The results show that, with the addition of Y203 into the Al-P-Ti-TiC modifier, the average size of primary silicon in the Al-20%Si alloy modified by Al-P-Ti-TiC-Y203 modifier （approximately 15μm or less） is significantly reduced, and the morphology of eutectic silicon changes from coarse acicular and plate like to refined fibrous. The Brinell hardness （HB189） and tensile strength （301 MPa） of Al-20%Si alloy modified by the Al-P-Ti-TiC-Y2O3 increase by 11.6% and 10.7%, respectively, for the alloys aider heat treatment.     

Ti-22Al-25Nb合金热机械处理组织与性能研究

研究了Ti-22Al-25Nb合金的显微组织和力学性能,重点介绍了等温锻造温度、固溶时效处理对合金力学性能的影响规律。结果表明:随着等温锻造温度的升高,合金的强度和塑性先增加后降低。在O+B2两相区固溶时,随着固溶温度的升高,具有较高塑性的B2相体积分数的增加和等轴颗粒的减少是合金具有较高塑性的主要原因;而在α_2+B2+O3相区固溶时,片层厚度的减小有利于合金强度的提高,但过大的B2相晶粒尺寸和较细的片层厚度则对合金的塑性不利。相的含量、形态、尺寸对合金力学性能的影响较大,尽可能在B2相变点附近进行等温锻造,以控制等轴颗粒数量和B2相晶粒尺寸,在低温时效以获得较细的片层组织从而提高合金的强度和塑性。     

时效时间对FeNiCoAlNbB合金组织和性能的影响

以Fe_39.35Ni₃₀Co₁₈Al_10.5Nb₂B_0.15形状记忆合金为研究对象,运用X射线衍射仪、扫描电镜、压力试验机、金相显微镜和能谱仪研究了时效时间对合金组织结构和性能的影响。结果表明,随着时效时间的增加,γ'相和B2相相继析出,γ'相的析出强化了奥氏体母相,B2相的析出降低了合金的塑性。从伪弹性曲线可以看出,在873 K温度下时效时,随着时效时间的增加,合金的抗压强度、可恢复应变和维氏硬度均随着时效时间的增加呈现先增大后减小的趋势,而合金的最大应变则随时效时间的增加先快速后缓慢增大。时效时间为60 h时,合金的抗压强度、可恢复应变及硬度均达到最大值,分别为1239.05 MPa、10.76%、496 HV10,合金的残余应变相对最小。     

Influence of yttrium on microstructure and mechanical properties of as-cast Mg-5Li-3Al-2Zn alloy

The influence of Y on microstructure and mechanical properties of as-cast Mg-5Li-3Al-2Zn alloy was investigated. The results show that the phase compositions of Mg-5Li-3Al-2Zn consist of α-Mg and AlLi phases. Adding Y to the alloy results in the formation of Al₂Y compound and facilitates grain refinement. The addition of 0.8 wt.% Y produces the smallest grain size. The tensile tests performed at room temperature show that the additions of Y can improve the mechanical properties of the alloy; the tensile strength and ductility reach peak values when the Y additions are 0.8 wt.% and 1.2 wt.%, respectively. The mechanisms of improvement are related to grain refinement and compound strengthening effects.     

Effect of deformed microstructure on mechanical properties of Ti-22Al-25Nb alloy

Effect of the deformed microstructure on mechanical properties of an orthorhombic （Ti2klNb） based alloy of Ti-22Al-25Nb （mole fraction, %） has been investigated. It was found that the deformed microstructures in different portions of a flee forged rod with diameter of 30 mm were quite different and thus resulted in the different mechanical properties after the same subsequent heat-treatment. One deformed microstructure with less primary α2/O particles and a larger and equiaxed B2 grains resulted in poor RT ductility, but the other one with a relatively larger amount of the primary α/O particles and non-equiaxed B2 grains had good combination of the tensile strength and ductility both at RT and 650 ℃. It was also found that two different deformed microstructures were obtained for the hot rolling plates with thickness of 3 mm even processed under an identical nominal rolling and the same post-deforming heat treatment conditions. One only has 3.5% of RT tensile elongation and the other up to 8%.     

Heat-treated microstructure and mechanical properties of laser solid forming Ti-6Al-4V alloy

The effects of heat treatment on the microstructure and mechanical properties of laser solid forming (LSF) Ti-6Al-4V alloy were investigated. The influences of the temperature and time of solution treatment and aging treatment were analyzed. The results show that the microstructure of LSFed samples consists of Widmanstätten α laths and a little acicular in columnar prior β grains with an average grain width of 300 µm, which grow epitaxially from the substrate along the deposition direction (Z). Solution treatment had an important effect on the width, aspect ratio, and volume fraction of primary and secondary α laths, and aging treatment mainly affects the aspect ratio and volume fraction of primary α laths and the width and volume fraction of secondary α laths. Globular α phase was first observed in LSFed samples when the samples were heat treated with solution treatment (950°C, 8 h/air cooling (AC)) or with solution treatment (950°C, 1 h/AC) and aging treatment (550°C, above 8 h/AC), respectively. The coarsening and globularization mechanisms of α phase in LSFed Ti-6Al-4V alloy during heat treatment were presented. To obtain good integrated mechanical properties for LSFed Ti-6Al-4V alloys, an optimized heat treatment regimen was suggested.     

Regarding the processing associated microstructure and mechanical properties improvement of an Al-4.5 Cu alloy

In the present study, an Al-4.5 wt. % Cu alloy was synthesized using a casting technique and a new disintegrated melt deposition technique. Microstructural characterization studies conducted on the samples taken from disintegrated melt deposition technique revealed a relatively more equiaxed grain morphology when compared to the cast samples. Microporosity, which is unavoidable for the columnar-equiaxed matrix microstructure was found to be less in case of disintegrated melt deposited samples when compared to the cast samples. Results of ambient temperature mechanical tests demonstrate that disintegrated melt deposited samples exhibited similar 0.2% yield stress, 1.52 times ultimate tensile strength and 3.69 times ductility when compared to the cast samples. All attempt is made to correlate the results of microstructural characterization and mechanical testing with the nature of processing technique employed to synthesize Al-4.5 wt. % Cu alloy.     

Effects of annealing time on microstructure and mechanical properties of MosSi3 alloy

以纯金属Mo和纯Si为原料，采用电弧熔炼法制备了Mo5Si3合金。在1200℃对其进行不同时间真空退火，并对合金的相组成、显微结构及力学性能进行分析。结果表明，随退火时间的延长，合金致密度、显微硬度和抗压强度提高，其压痕断裂韧性表现出先增加后降低的趋势，退火20h后合金断裂韧性为3．23MPa·m^1/2。退火50h后，合金主要物相为Mo5Si3和少量MoSi2，在合金中形成M05Si3／MoSi2层片状组织结构，层片间距在20-50μm之间。M05Si3晶粒尺寸和点阵畸变分别为87．3nm和0．0986％，合金具有纳米晶结构。     

Effect of La addition on microstructure and mechanical properties of hypoeutectic Al-7Si aluminum alloy

The effect of La addition (0, 0.1, 0.2, 0.4, wt.%) on the microstructure, tensile properties and fracture behavior of Al-7Si alloy was investigated systematically. It is found that the La appears in the Al-7Si alloy in the form of Al₄La and Al₂Si₂La phases. La addition can refine the secondary dendrite arm spacing (SDAS) and eutectic Si particles, which are decreased by 7.9% and 7%, respectively, with the optimal La content of 0.1wt.%. Because when 0.1wt.% La is added, a relatively higher nucleation undercooling of 37.47 °C is observed. Higher undercooling degree suggests that nucleation is accelerated and subsequent growth is restrained. After T6 heat treatment, compared with the without La, the ultimate tensile strength of the alloy with 0.1wt.% La is enhanced by 5.2% from 333 MPa to 350.2 MPa and the elongation increases by 73% from 7.37% to 12.75%, correspondingly. The fracture mode evolves from the ductile-brittle mixed fracture to ductile fracture mode. However, when La element content reaches a certain value of 0.4wt.%, serious segregation takes place during the solidification process. The formed brittle phases deteriorate the tensile properties of the alloy and the fracture mode of Al-7Si-0.2/0.4 La changes to mixed ductile-brittle fracture mode.

     

时效对Ti-22Al-24Nb合金显微组织及力学性能影响

研究了经1000℃/2 h/WC(水冷)固溶处理的Ti-22Al-24Nb合金在不同时效条件下的组织演变规律,且进行了不同时效时间下组织的力学性能测试。结果表明:时效时间对显微组织中相的含量和尺寸的变化影响较为明显。随时效时间增至24 h时,部分晶粒发生了长大,且次生α2/O相长大明显,初生的α_2相长大并等轴化。随时效温度的升高,晶粒尺寸变化不明显。经780℃/20 h/AC(空冷)时效处理后,合金常温力学性能提升较小,抗拉和屈服强度分别提升至1022和950 MPa,但塑性却大大降低至3%左右,随时效时间延长至24 h,强度增加,塑性变化不大;合金高温力学性能为强度增加不明显,但塑性明显增加,其伸长率为20.27%,随时效时间延长至24 h,合金的高温强度进一步增加,抗拉强度为1019 MPa,屈服强度为977 MPa,但高温塑性出现了下降。     

Ti-48Al-2Cr-2Nb-( TiB2, Ni)合金凝固组织演变规律及力学性能研究

TiAl合金已成为航空航天工程升级换代的关键材料,然而其铸态晶粒尺寸粗大,室温塑性和强度低,限制其进一步工程应用。本文采用真空感应凝壳熔炼工艺系制备铸锭,系统研究TiB2和Ni元素共同添加对Ti-48Al-2Cr-2Nb合金凝固组织和力学性能的影响。结果表明,TiB2及Ni合金化后,合金的凝固路径和初生相并未改变,晶粒尺寸从700μm细化至100μm,生成片状TiB2和富镍τ3相。T4822-( Ni, TiB2)合金的室温拉伸强度与基体合金相近,断裂伸长率提高30%。700-900℃时,T4822-(Ni, TiB2)合金的抗拉强度始终高于基体合金,在900℃时抗拉强度达到365MPa,较基体合金提高9%。800℃和900℃时T4822-(Ni, TiB2)合金的断裂伸长率分别达到25.3%和36.1%,远高于基体合金。晶粒尺寸的细化和晶界处的块状γ相是T4822-(Ni, TiB2)合金塑性提升的主要原因,其良好的高温强度则可以归因于片层团内部和界面处的硬质硼化物和富镍τ3相。     

Effect of Fe addition on microstructure and mechanical properties of Ti-25V-15Cr-2Al-0.2C alloy

1　INTRODUCTIONTitaniumalloyshavebeenextensivelyappliedtoaerospaceindustriesduetotheirexcellentspecificstrength ,goodcorrosionresistanceandmechanicalproperties .However ,conventionaltitaniumalloysarehighlyreactiveandcanundergosustainedcombustionunderconditionsencounteredingasturbineenginescompressors.Intheearly 1990s ,Pratt&Whit ney[13] intheUSAdevelopedanew βtitaniumalloywithgoodburnresistance ,designatedAlloyC (Ti 35V 15Cr) .Theproductioncostofthisalloyisveryhighbecauseofalargeamou…     

热处理对真空压铸Mg-7Al-2Sn合金组织性能的影响

利用光学显微镜、扫描电子显微镜,能谱分析仪、X射线衍射分析及差热分析研究了T4和T6热处理对真空压铸Mg-7Al-2Sn(AT72)合金组织和力学性能的影响。结果表明,真空压铸使得AT72合金组织更加致密,进而通过热处理可以进一步提高合金的力学性能。特别是T4固溶处理(400℃×20 h)后,晶粒尺寸变化较小,Al、Sn元素固溶到基体中产生固溶强化;同时,由于Mg17Al12相分解,使得高熔点的Mg2Sn颗粒相的析出强化效果更加明显。T4处理后的AT72合金的抗拉强度、屈服强度和伸长率达到276 MPa,202.6 MPa和10.6%,其比压铸态合金分别提高了18.2%,7.0%,24.7%。T6(400℃×20 h+200℃×15 h)处理后由于脆性相Mg17Al12的非连续析出以及Mg2Sn相粗化,使得合金的强度和塑性均有所下降。由于耐热相Mg2Sn的存在,提高了Mg17Al12相的开始熔化温度,使得AT72合金表现出比商用AZ91合金具有更好的高温力学性能。     

停放时间对6061铝合金性能及微观组织的影响

采用宏观检测与显微分析相结合的手段,研究不同停放时间下6061铝合金的力学性能与微观组织的变化规律。结果表明:停放时间对6061铝合金的晶粒尺寸有较大影响,晶粒尺寸呈先增大后减小的趋势;停放时间对6061铝合金弹塑性变形过渡阶段有较大影响,但对弹性及塑性阶段变形的影响很小。6061铝合金在停放为0～2 h时,力学性能无明显变化,变形后试样表面光滑,变形协调性较好;停放时间为12 h时,材料的抗拉强度和屈服强度降至最低,但伸长率提高,试样表面呈橘皮形貌,变形均匀性较差;停放时间为24 h～15 d时,合金的强度回升并逐渐趋于稳定。结果表明:随着停放时间的增长,6061铝合金断口的韧窝直径和深度不断增加,第二相粒子的尺寸也不断增大,形状由球状、带状逐渐转变为板状、块状。通过研究得到6061铝合金满足汽车结构强韧化需求,综合性能最优需求的停放时间为12～24 h。此研究结果能够为6061铝合金加工工艺优化提供理论指导。     

淬火转移时间对Ti-1023合金组织与力学性能的影响

通过室温拉伸性能测试、断口分析和显微组织分析,研究了淬火转移时间对Ti-1023合金组织演变和力学性能的影响规律和机理。结果表明,随淬火转移时间的增加,淬火转移过程中过饱和β相中析出α相,导致等轴α相含量增加,过饱和β相基体的相对含量降低,时效析出的次生αs相含量和弥散程度下降,致使合金强度降低、塑性提高。对于厚80 mm的Ti-1023合金板材或锻件,将淬火转移时间控制在120 s之内,合金组织性能不会受到明显的影响。