多级强化固溶处理对7050铝合金厚板强度和断裂韧性的影响

采用光学金相、示差扫描量热分析、扫描电镜、室温拉伸及断裂韧性实验,研究多级固溶处理对7050铝合金强度和断裂韧性的影响。结果表明:7050铝合金厚板经多级强化固溶后,随最后一级温度的增加,可溶性粗大第二相减少,其强度和断裂韧性增加,当最后一级温度为493℃时,合金的断裂韧性和强度达到峰值,其断裂韧性(KIC)、屈服强度(σ0.2)和抗拉强度(σb)分别为37.4 MPa.m1/2、500.6 MPa和534.0 MPa;当最后一级温度超过493℃时,由于再结晶分数急剧增加、晶粒快速长大,断裂韧性和强度又逐渐降低;当多级固溶最后一级的温度和时间与单级固溶一致时,经多级强化固溶后的7050铝合金具有比单级固溶时更高的断裂韧性和强度。     

Strengthening-toughening of 7xxx series high strength aluminum alloys by heat treatment

1　INTRODUCTIONAerospaceand groundtransportationvehicleswithreducingstructuralmasscanenhancecarrycapa bilityandflexibility ,decreasefuelconsumption ,andextendflightvoyageevidently .Highstrengthstruc turalmaterialswithlightdensityplayapivotalroleonreducingmassinstructure .Presently ,confrontedwithcompetitionofresinbasedcomposites ,alu minumalloysas primarystructuralmaterialsforspacecraftandgroundtransportationvehiclesarede velopinginlinesofsuperhighstrength ,corrosionen durance ,lowdensitya…     

Characterization of Fracture and Fatigue Behavior of 7050 Aluminum Alloy Ultra-thick Plate

The microstructure, mechanical property, fracture toughness, and fatigue behavior of 7050 aluminum alloy pre-stretched ultra-thick plate were investigated by means of optical microscopy, scanning electron microscopy, transmission electron microscopy, tensile test, fracture toughness test, and high-cycle fatigue test. The results showed that the microstructure of the ultra-thick plate consisted of recrystallized grains, subgrains, constituent particles, precipitated phases, and precipitate-free zone. Mechanical tests indicated that anisotropy of fracture toughness existed in L-T, T-L, and S-T orientation. Fractographic features suggested that this anisotropy was significant due to the difference of recrystallized grain on different metallographic planes. Compared to 7050 aluminum alloy plate in less thickness, the ultra-thick plate showed deterioration on fracture toughness due to the increase of recrystallized grains but improvement on fatigue property ascribed to the less densely populated particles. Fractographic observations showed that fatigue initiation of this ultra-thick plate was primarily related to the constituent particles and promoted by increase of the stress amplitude.     

热处理对选区激光熔化GH3536合金晶界与拉伸行为的影响

采用选区激光熔化制备了GH3536合金,并分别进行固溶处理和热等静压处理,研究不同热处理手段对GH3536合金的组织形貌、晶界形态及室温拉伸行为的影响。结果表明:沉积态试样的组织由超细柱状亚晶粒与熔池界组成,存在气孔与微裂纹等缺陷;选区激光熔化试样分别经固溶处理和热等静压处理后,二者致密度均上升,组织转变为由交替分布的大小不等等轴晶粒组成,但热等静压的沿晶界析出M_(23)C_6相,形成锯齿状的弯曲晶界;沉积态试样的拉伸性能表现出各向异性的特点,固溶处理可消除拉伸性能的各向异性,但抗拉强度和屈服强度均有下降,延伸率明显上升。热等静压态试样与固溶态试样相类似,但其抗拉强度、屈服强度和延伸率均有进一步的提高;3种形态合金的断裂机制均为微孔聚集型的韧性断裂。     

双级固溶处理对7075高强铝合金组织和性能的影响

采用光学显微镜、电子万能试验机、维氏硬度计等对比研究了单级固溶处理与双级固溶处理对7075铝合金显微组织和力学性能的影响。结果表明:相对单级固溶处理,双级固溶处理7075铝合金中第二相粒子可以更为充分的溶入基体,固溶度更高。7075铝合金经460 ℃×1 h+480 ℃×0.5 h双级固溶处理后,组织中第二相粒子体积分数为0.303%,晶粒均匀细小,固溶效果理想。经460 ℃×1 h+480 ℃×0.5 h+120 ℃×24 h固溶时效处理后,7075铝合金硬度、抗拉强度和伸长率分别达到199 HV5、637 MPa和14.1%,综合性能最佳。     

形变诱导析出对7A20铝合金组织与性能的影响

采用光学显微镜、扫描电镜、透射电镜、X射线衍射仪和拉伸试验机等手段研究了预变形温度和预析出时间对7A20铝合金中第二相析出行为和组织性能的影响。结果表明:300~450 ℃预变形温度下析出的MgZn₂相,粒子尺寸基本在0.1 μm左右,400 ℃析出的粒子数量最多,分布更均匀。不同预处理制度下,合金在400 ℃保温2 h的预析出处理后,屈服强度和抗拉强度达到最高值,分别为170 MPa和310 MPa,同时伸长率也达到20%。拉伸断口均表现为韧性断裂特征。热轧形变和预析出处理后,MgZn₂析出相衍射峰主要出现在40°~45°之间。试验合金1、2和4 h预析出处理后,MgZn₂相的尺寸分别为0.1~0.2、0.3~0.8和0.6~1.0 μm。第二相粒子密度随预析出时间的延长逐渐降低。     

热变形条件对7085铝合金晶粒结构和性能的影响(英文)

通过光学显微镜、透射电镜和力学与断裂性能测试,研究热变形条件对7085铝合金晶粒结构和性能的影响。结果表明,动态再结晶的体积分数随着Z值的减少而增加,静态再结晶的体积分数随着Z值的减少而降低。经固溶时效后,合金的力学性能和断裂性能随着Z值的增加先升高后降低。建立了综合变形和固溶过程中的显微组织演化图。在考虑显微组织和性能的基础上,合金优化的Z参数变形条件为1.2×10109.1×1012.     

热处理对挤压态7090/SiC_p复合材料组织和力学性能的影响(英文)

采用喷射沉积的方法制备SiCp增强超高强Al-10%Zn-3.6%Mg-1.8%Cu-0.36%Zr-0.15%Ni复合材料。使用透射电镜(TEM)和能谱仪(EDS)对挤压并热处理过的合金棒进行微观组织取样观察。双级时效后的复合材料的晶粒比单级时效合金的晶粒更小。经单级时效处理,在晶界上和晶粒内部都可以观察到细小的η相和富AlZnMgCu 相的析出颗粒。双级时效后在 SiC 颗粒与基体的界面上发现了一层5nm厚的Si-Cu-Al-O非晶层。Ni、Zr的添加可以改善双级时效的效果,并且抑制7090/SiCp复合材料晶粒的生长。固溶时效处理可以显著提高复合材料的断裂韧性,而断裂韧性随着时效时间的延长而先减小后增加。     

损伤容限型钛合金的等温锻造温度研究

研究了TC21钛合金在5.5×10-4s-1恒应变速率、40%变形程度条件下,等温锻造温度变化对锻件组织和性能的影响。结果表明:TC21钛合金显微组织对温度变化敏感,在两相区锻造时,显微组织由初生α相和β转变组织组成,并且随着变形温度的提高,初生等轴α相的含量逐渐减少,晶粒尺寸增大;在相变点温度锻造时得到网篮组织;在相变点以上温度锻造时得到片状组织。室温拉伸强度和断裂韧性随锻造温度的升高呈现增加趋势,室温拉伸塑性明显降低。在965℃等温锻造时,显微组织为较细的片状组织,强度、塑性和断裂韧性达到较佳匹配,获得较好的综合力学性能。965℃为较佳等温锻造温度。     

Enhanced fracture toughness and strength in bulk nanocrystalline Cu with nanoscale twin bundles

Bulk nanocrystalline pure Cu samples with embedded nanoscale twin bundles were prepared by means of dynamic plastic deformation (DPD) at cryogenic temperature. By adjusting the DPD parameters, we increased the volume fraction of nanotwin bundles, resulting in an increase in both tensile strength and fracture toughness. The enhanced strength is attributed to the strengthening effect of the nanotwin bundles. The highly anisotropic nanotwin lamellar structures are found to be effective in energy absorption and arresting crack propagation during fracture. Coarse and deep dimples associated with obvious recrystallization underneath were detected in the fracture surfaces, owing to the presence of the nanotwin bundles. The enhancement of fracture toughness is closely correlated with the formation of these deep dimples.     

Al-Cu-Mg合金的断裂韧性与拉伸延性模拟

基于铝合金中的脆性结晶相在外力作用下发生断裂而形成微裂纹的过程服从Weibun分布，建立了Al-Cu-Mg合金断裂韧性与拉伸延性的细观力学模型。模型的解析表明，在外力作用下由结晶相断裂而形成的微裂纹的体积分数随着外加应力的增加而增加：在相同的外加应力作用下，结晶相含量较高时微裂纹的体积分数也较高。同时模型的计算表明，Al-Cu-Mg合金的拉伸延性及断裂韧性与结晶相的含量及尺寸有很大关系；拉伸延性与断裂韧性随着结晶相体积分数与尺寸的增加而减小；因此通过对铝基体的纯化，减少Fe与Si元素的含量或者通过强化固溶处理可以降低结晶相的体积分数与尺寸，从而提高Al-Cu-Mg合金的拉伸延性与断裂韧性。     

Effects of extrusion and heat treatments on microstructure and mechanical properties of Mg–8Zn–1Al–0.5Cu–0.5Mn alloy

The effects of extrusion and heat treatments on the microstructure and mechanical properties of Mg–8Zn–1Al–0.5Cu– 0.5Mn magnesium alloy were investigated. Bimodal microstructure is formed in this alloy when it is extruded at 230 and 260 °C, and complete DRX occurs at the extruding temperature of 290 °C. The basal texture of as-extruded alloys is reduced gradually with increasing extrusion temperature due to the larger volume fraction of recrystallized structure at higher temperatures. For the alloy extruded at 290 °C, four different heat treatments routes were investigated. After solution + aging treatments, the grains sizes become larger. Finer and far more densely dispersed precipitates are found in the alloy with solution + double-aging treatments compared with alloy with solution + single-aging treatment. Tensile properties are enhanced remarkably by solution + double-aging treatment with the yield strength, tensile strength and elongation being 298 MPa, 348 MPa and 18%, respectively. This is attributed to the combined effects of fine dynamically recrystallized grains and the uniformly distributed finer precipitates.     

Effect of internal stresses on the fracture toughness of a TiAl-based alloy with duplex microstructures

A series of fine duplex microstructures with different volume ratios of equiaxed γ and lath colonies (α₂+γ) were achieved from an isothermally forged Ti–46.5Al–2Cr–2Nb alloy. The internal stress determination using X-ray diffraction techniques and plane-strain fracture toughness tests were carried out at room temperature, and the effects of the internal stresses on the fracture toughness were investigated. It was found that the internal stresses play an important role in determining the fracture toughness of the TiAl-based alloy. The compressive internal stresses in γ phase and the tensile internal stresses in α₂ phase may be responsible for the delamination along the γ/α₂ boundaries. For the microstructures with different volume fraction of lamellar grains, the fracture toughness increases with the internal stresses, which facilitate the formation of shear ligaments; and the effects of the α₂ phase and equiaxed gamma grains on the internal stresses and the fracture toughness were discussed.     

固溶处理对TiB2/7050Al复合材料组织与性能的影响

研究了固溶处理对TiB₂/7050Al复合材料组织与性能的影响规律。结果表明,TiB₂/7050Al复合材料内的可溶性第二相主要为MgZn₂(η相)、AlZnMgCu(T相)和Al₂CuMg(S相)。η相在470℃已完全溶解,T相在476℃开始溶解,S相在491℃下可完全溶解。随固溶温度的升高,复合材料的强度整体呈上升趋势,但伸长率先增加后降低。在480℃固溶时,复合材料同时具备高强度和高塑性,其屈服强度、抗拉强度和伸长率分别为658 MPa、719 MPa和11.3%;继续升高固溶温度至490℃,虽然可使铝基体内残余S相完全溶解,但也使基体再结晶晶粒异常长大,降低了复合材料的塑性。     

轧制变形速率对7050铝合金板材淬火敏感性的影响

通过光学显微镜、扫描电镜、透射电镜、电子背散射衍射以及硬度测试研究轧制变形速率对7050铝合金微观组织演变的影响,分析轧制变形速率影响合金淬火敏感性的微观机理。结果表明:变形速率较小时(5 s?1和8 s?1),合金再结晶分数低,试样中存在大量的亚组织结构,亚晶粒的尺寸较小,晶界较难分辨,为小角度晶界,固溶慢速淬火的试样中少量η平衡相在亚晶界上形核析出;随着变形速率的增加,亚晶长大,晶界平直逐渐向大角度晶界转变,η平衡相在晶界上析出增加,在亚晶内部亦有明显析出;当变形速率升高至15 s?1时,固溶后试样的再结晶百分数明显增加,在大角度晶界处以及再结晶晶粒内出现大量非均匀形核析出,同时,在亚晶区域观察到较多析出,与微观组织演变对应,合金时效态硬度性能测试结果表明:随着轧制变形速率增加,慢速淬火的试样力学性能损失变大,合金淬火敏感性增加。     

Strength and ductility of 316L austenitic stainless steel strengthened by nano-scale twin bundles

By means of dynamic plastic deformation (DPD) with high strain rates, a bulk nanostructured 316L austenitic stainless steel consisting of nano-sized grains embedded with bundles of nanometer-thick deformation twins was synthesized. The average transverse grain size is ∼33 nm and the twin/matrix lamellar thickness is ∼20 nm. The nano-twin bundles constitute ∼24% in volume. The nanostructured samples exhibit a high tensile strength of ∼1400 MPa but a limited ductility with a uniform elongation of ∼2%. Subsequent thermal annealing of the as-DPD samples in a temperature range of 730-800 °C led to a single-phased austenite structure consisting of static recrystallized (SRX) micro-sized grains embedded with remaining nano-twin bundles and nano-grains. The annealed DPD samples exhibit an enhanced strength-ductility synergy and much more enhanced work-hardening rates than the as-deformed samples. Work-hardening rates of the annealed DPD samples can be even higher than that of the original CG sample. Tensile ductility was found to increase almost linearly with the volume fraction of SRX grains. A combination of 1.0 GPa tensile strength with an elongation-to-failure of ∼27% is achieved in the annealed DPD 316L stainless steel samples.     

固溶处理和人工时效对Al-Cu合金显微组织和力学性能的影响(英文)

对Al-Cu合金进行析出强化和人工时效处理以获得优异的力学性能,如高的强度、好的韧性。其热处理工艺条件为:510～530℃固溶处理2h;60℃水淬;160～190℃人工时效2～8h。采用光学显微镜、扫描电镜、能谱分析、透射电镜和拉伸实验对经固溶和人工时效处理的Al-Cu合金的组织和力学性能进行表征。固溶处理实验结果表明,Al-Cu合金的力学性能随着固溶处理温度的升高先增加,然后降低。这是由于Al-Cu合金的残余相逐渐溶解进入基体中,从而导致析出相的数量和再结晶晶粒尺寸不断增加。相较于固溶处理温度,固溶处理时间对Al-Cu合金的影响较小。人工时效处理实验结果表明,合金经180℃时效8h,可以获得最大的拉伸强度。合金的最大拉伸强度和屈服强度随着时效时间的延长和温度的升高而升高。     

The influence of powder characteristics on mechanical properties of Al2O3–TiC–Co ceramic materials prepared by Co‐coated Al2O3/TiC powders

Ultrafine Al₂O₃–TiC–Co (ATC) ceramic is prepared in order to improve the bending strength and fracture toughness of ceramic materials. The ultrafine Co‐coated Al₂O₃ and TiC powders have been synthesized by electroless plating at room temperature, and the composite powders were sintered by hot‐pressing to compact ATC samples. The average bending strength, average hardness and average fracture toughness values of ATC ceramic with different particle sizes and Co contents were investigated. The toughening mechanism of the ultrafine ATC ceramic was studied by transmission electron microscopy (TEM) and ceramic performance testing methods. The results show that the relative density, bending strength and fracture toughness values increase remarkably with the increase of Co content. The ultrafine grain of original powders is beneficial to improve the relative density, strength and toughness values of ATC ceramic. The Co phase hinders the growth of ATC ceramic grains during sintering. The Co phase forms a three‐dimensional mesh skeleton structure during sintering, improving the fracture toughness and strength of the composite ceramic.     

Effects of single- and multi-stage solid solution treatments on microstructure and properties of as-extruded AA7055 helical profile

The effects of single-stage solution treatment (SST), enhanced solution treatment (EST), high-temperature pre-precipitation (HTPP) and multi-stage solution treatment (MST) on the microstructure, mechanical properties and corrosion resistance of the as-extruded 7055 aluminium alloy (AA7055) helical profile were investigated using differential scanning calorimetry (DSC), optical microscopy (OM), scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM). It was observed that EST and MST could promote the dissolution of the second-phase particles compared with the traditional SST, and the intergranular phases were distinctly discontinuously distributed after HTPP and MST. There was obvious difference in the main texture type and texture strength for the alloy after different solid solution treatments. HTPP could improve the corrosion resistance of the alloy by regulating the intergranular phases, but the mechanical properties were severely weakened. While the good corrosion resistance of the alloy could be obtained by MST without obvious strength loss. As a result, the MST is an ideal solid solution treatment scheme for AA7055.     

固溶处理对Al-Zn-Mg-Cu系超强铝合金组织与硬度的影响

利用光学显微镜(OM)、扫描电镜(SEM)及维氏硬度计等研究了不同固溶处理参数对Al-Zn-Mg-Cu系超强铝合金7050固溶态组织与固溶时效态硬度的影响。结果表明:锻态7050铝合金组织中含有粗大块状初生相和针状、点状的η(MgZn₂)相。随着固溶温度的升高和固溶时间的增加,合金组织中的未溶相减少,再结晶组织体积分数增高。经过470 ℃×4 h固溶+120 ℃×24 h时效处理7050铝合金的硬度值达到最大,为189 HV0.2。