高温预析出对Al-Zn-Mg系铝合金时效硬化和应力腐蚀的影响

研究了高温固溶后降温处理工艺对中强可使预析出LC52和7039铝合金的组织、时效硬化和应力腐蚀的影响。金相观察发现,高温预析出可优先在晶界处产生,并提高随后时效状态下晶界析出相的不连续分布程度,温度降低到一定程度晶内和晶界产生大量析出。合金拉伸性能和应力腐蚀结果表明,预析出在保持强度和塑性的同时,可提高抗应力腐蚀性能。而预析出温度降低,合金强度呈下降趋势。     

时效制度对1441Al-Li合金抗腐蚀性能的影响

对固溶态1441Al-Li合金板材分别进行T6时效,以及5%冷轧预变形后再进行150℃时效,即T8时效处理,通过晶间腐蚀(IGC)、剥落腐蚀(EXCO)实验、极化曲线测试及透射电镜(TEM)分析,研究时效制度对1441铝锂合金的室温抗晶间腐蚀性能、抗剥落腐蚀性能及微观组织的影响。结果表明,合金经T6或T8时效处理后,随时效时间延长,合金微观组织由欠时效的晶内析出均匀的δ′相,变为晶内析出δ′相和S′相,以及沿晶界析出平衡相δ相和S相,因此合金抗腐蚀性能顺序为欠时效峰时效过时效。与T6时效态相比,经T8时效处理后,晶内析出的δ′相和S′相的数量增加、尺寸减小、分布均匀;同时,沿晶界析出的δ相和S相数量减少,PFZ变窄,合金的抗晶间腐蚀和抗剥落腐蚀能力提高。在3.5%NaCl溶液中进行的极化曲线测试表现出相同的结果。     

多级时效工艺对汽车轮毂铝合金材料组织和性能影响的研究

采用旋转喷吹气净化处理制备A356铝合金汽车轮毂材料,对多级时效工艺后的汽车轮毂铝合金材料进行显微组织分析、硬度试验、拉伸试验,研究多级时效工艺对汽车轮毂铝合金材料组织和性能影响。研究结果表明:多级时效工艺能有效细化改善铝合金汽车轮毂材料的性能,当固溶温度为540℃,保温4h,预时效温度为100℃,保温4h,时效温度为155℃,保温6h时,粗大α-Al初生树枝晶向细小胞状晶与球状晶转变,共晶硅的形态也得到较好的改善,合金表现出较好的力学性能。     

时效温度对粉末FGH96合金的PPB和力学性能的影响

采用等离子旋转电极工艺(PREP)制粉,热等静压工艺制备粉末FGH96合金,研究不同时效温度对其显微组织和力学性能的影响。结果表明:随着时效温度的提高,粉末FGH96合金的晶粒大小和孪晶组织无明显变化,原始颗粒边界(PPB)明显增多;合金的抗拉强度和屈服强度下降,断后伸长率、断面收缩率和蠕变延伸率提高;拉伸断口沿粉末颗粒开裂的形貌明显增多。     

7xxx系铝合金回归再时效的研究现状

7xxx系铝合金作为高强度铝合金的代表,以其较高的强度以及良好的韧性和耐蚀性等优异性能而广泛地应用于航空航天及交通运输领域.该类可热处理强化铝合金对微观组织结构敏感,其性能受合金内部析出相的形核、生长及分布情况的影响.采用三级时效工艺—回归再时效处理,通过预时效、回归、再时效3个过程的有效配合改变合金的析出相状态,可以...     

双级时效对7075合金应力腐蚀性能影响

双级时效处理虽能有效提高7075铝合金抗应力腐蚀开裂(SCC)性能,但同时会导致合金力学性能降低。为了同时提高7075铝合金的拉伸性能和抗SCC性能,并优化双级时效参数,对双级时效处理7075合金进行了正交试验。通过扫描电镜和透射电镜在慢应变速率实验中研究7075合金的SCC行为。结果发现,在130 ℃条件下保温4 h后,在170 ℃条件下保温8 h,合金抗拉强度、伸长率和应力腐蚀指数I_SSRT分别为488 MPa、10.8%和0.095。      

稀土元素Ce对2090铝锂合金强塑性的优化作用

本文研究了稀土元素Ce以及时效温度和时间对2090铝锂合金室温拉伸强塑性的影响。结果表明,在2090铝锂合金中添加微量稀土元素Ce可显著改善其强塑性配合,对其断裂特征亦有影响,热处理制度相同时,2090+Ce合金室温拉伸断口上的滑移条纹多于2090合金。时效温度不同,合金强塑性和断裂特征随时效温度的变化规律亦不同。Ce对合金强塑性的优化作用亦受影响。时效温度较低和时间较短(欠时效至峰值时效)时,断裂方式为主断裂面穿晶断裂+短横向沿晶分层开裂的混合型,强度随时效时间延长而升高,但塑性随之下降。时效温度较高和时间较长(过时效)时,断裂方式主要为沿亚晶断裂,并伴有少量穿晶分量,此时强度和塑性均随时效时间的延长而下降。     

时效制度对喷射成形7055铝合金抗应力腐蚀性能的影响

对喷射成形7055铝合金分别进行T6时效和双级时效处理,然后在空气和3.5%NaCl溶液中进行慢应变速率拉伸实验,测定时效处理后合金的电导率,用扫描电镜观察合金的断口形貌。研究7055铝合金在T6及3种不同双级时效态下在空气和3.5%NaCl溶液中的应力腐蚀开裂行为。结果表明:7055铝合金只在一定的应变速率下应力腐蚀敏感性明显;相同时效制度下,4种应变速率(1.3×10 6,0.8×10 6,0.5×10 6和0.2×10 6s 1)中,应变速率为0.5×10 6s 1时应力腐蚀敏感性大;T6态合金的抗应力腐蚀性能最差,二级时效时间达到15 h后合金对应力腐蚀不敏感;应变速率为0.5×10 6s 1时,喷射成形7055铝合金的应力腐蚀断口的断裂方式为准解理断裂,在惰性介质中慢应变速率拉伸断口断裂方式为韧窝断口。     

铝合金时效硬化模型的研究进展

相对于众多其他合金,铝合金的时效硬化模型经过近几十年的发展已日趋成熟.利用现有模型可以计算球形、片状和针状析出相的尺寸及体积分数与合金成分、时效时间及时效温度的关系,从而可以研究铝合金的屈服强度在时效过程中的演变规律,对铝合金的设计具有重要的指导意义.该文详细地介绍了铝合金时效硬化模型的发展,并指出了现有模型的不足之处,对模型的未来发展进行了展望.     

人工时效前停放时间对7055铝合金挤压管显微组织与性能的影响

采用维氏硬度试验,室温拉伸试验,电导率测试,慢应变拉伸试验和透射电镜等方法,对人工时效前室温停放不同时间的7055铝合金管材的力学性能、电导率、耐应力腐蚀性能和微观组织进行了研究.结果表明:在人工时效前进行室温停放,7055铝合金的晶内会预先析出GP区,为后续人工时效中的η相和η'相的析出提供形核的核心,从而有效地提高合金的力学性能和电导率.人工时效前室温停放6.5 h,7055铝合金的抗拉强度达到最大值即677.9 MPa,电导率和延伸率分别为29.8 % IACS和14.9 %.继续延长室温停放时间,合金的抗拉强度降低,电导率不断增大.在室温停放48 h时,合金的抗拉强度达到649.7 MPa,延伸率为10.6 %,电导率为36.8 % IACS,此时合金的综合性能达到较优.      

Mechanical Property and Intergranular Corrosion Sensitivity of Zn-Free and Zn-Microalloyed Al-2.7Cu-1.7Li-0.3Mg Alloys

The influence of 0.72 pct Zn addition on the tensile properties of Al-2.7Cu-1.7Li-0.3Mg alloys was investigated. Their intergranular corrosion (IGC) dependence on aging [T6 type at 423 K (150 °C) and 448 K (175 °C) and T8 type at 423 K (150 °C)] time was studied. An IGC diagram associated with aging process was established. The addition of 0.72 pct Zn enhanced the strength of the Al-Li alloy with T6 type aging at 448 K (175 °C). With aging process, the corrosion mode of the T6-aged Al-Li alloys was changed in the following order: pitting and local IGC (initial aging stage), general IGC (underaging stage), local IGC (near peak-aging stage), and pitting (overaging stage) again. The IGC depth was increased first and then decreased with aging time extension. The corrosion potential change of grains and the microstructure variation were used to explain the IGC sensitivity of the Al-Li alloy with different tempers. Meanwhile, 0.72 pct Zn addition decreased the IGC sensitivity of the Al-Li alloy, especially the T6-aged Al-Li alloy.     

Effect of homogenization on microstructure and properties of WE91 alloys

The microstructure and properties of the Mg-9Y-1MM-0.6Zr alloy were studied by scanning electron microscopy, optical microscopy, transmission electron microscopy, hardness and tensile testing. Homogeni...     

Effect of test temperature on the dynamic torsional deformation behavior of two aluminum-lithium alloys

The objective of the present study is to investigate the effect of test temperature on the dynamic torsional deformation behavior of two Al-Li alloys, i.e., 2090 and 8090 alloys. Dynamic torsional tests were conducted using a torsional Kolsky bar at room temperature and a low temperature (−196 °C), and the torsionally deformed regions and the fracture surfaces of the tested specimens were examined. The dynamic properties of the two Al-Li alloys at the low temperature were improved, owing to the modification of the deformation behavior. The dynamic deformation behavior at room temperature was dominated by intergranular cracks due to planar slips and by crack propagation along the grain boundaries. At the low temperature, plastic deformation proceeded more homogeneously as planar slip was prevented. These results indicated that the overall deformation mode of both the Al-Li alloys changed from planar slip to homogeneous deformation with decreasing temperature, resulting in the improvement of cryogenic properties under dynamic torsional loading.     

Correlation of deformation mechanisms with the tensile and compressive behavior of NiAl and NiAl(Zr) intermetallic alloys

To identify the mechanisms controlling strength and ductility in powder-extruded NiAl and NiAl + 0.05 at. pct Zr, tensile and compressive testing was performed from 300 to 1300 K for several grain sizes. Grain size refinement significantly increased yield stress in both alloys and, in some cases, slightly lowered the ductile-to-brittle transition temperature (DBTT), although no room-temperature tensile ductility was observed even in the finest grain size specimens. The small Zr addition increased the DBTT and changed the low-temperature fracture mode from intergranular in NiAl to a combination of intergranular and transgranular in the Zr-doped alloy. Scanning electron microscopy (SEM) of compression specimens deformed at room temperature revealed the presence of grain-boundary cracks in both alloys. These cracks were due to the incompatibility of strain in the poly crystalline material, owing to the lack of five independent slip systems. The tendency to form grain-boundary cracks, in addition to the low fracture stress of these alloys, contributed to the lack of tensile ductility at low temperatures. The operative slip system, both below and above the DBTT, was {110} 〈001〉 for both alloys. The change from brittle to ductile behavior with increasing temperatures was associated with the onset of diffusional processes.     

含铒先进铝合金

综述了Er在高纯铝、Al-Mg,Al-Zn-Mg,Al-Li以及Al-Cu合金中的作用情况,分析讨论了Er在铝及其合金中的作用机制。结果表明:对于高纯铝、Al-Mg,Al-Zn-Mg,Al-Li合金来说,适量Er可以显著细化合金铸态晶粒,能够在一定程度上抑制再结晶,提高合金热稳定性,与此同时可以提高不同热处理状态下的合金的拉伸强度与硬度,Er的细化及强化作用主要与Al3Er相的形成有关;对于Al-Cu合金,Er能够细化枝晶网胞组织,提高再结晶温度,然而对合金的力学性能并无益处。     

Hydrogen embrittlement of Ni-Cr-Fe alloys

The purpose of this work was to investigate the role of chromium on hydrogen embrittlement of Ni-Cr-Fe alloys and thus to develop a better understanding of the low-temperature stress corrosion cracking (SCC) phenomenon. The effect of chromium on hydrogen embrittlement was examined using tensile tests followed by material evaluation via scanning electron microscopy (SEM) and light optical microscopy. Four alloys were prepared with chromium contents ranging from 6 to 35 wt pct. In the uncharged condition, ductility, as measured by the percent elongation or reduction in area, increased as the alloy chromium content increased. Hydrogen appeared to have only minor effects on the mechanical properties of the low-chromium alloys. The addition of hydrogen had a marked effect on the ductility of the higher-chromium alloys. In the 26 pct chromium alloy, the elongation to failure was reduced from 53 to 14 pct, with a change in fracture mode from mixed ductile dimple and ductile intergranular failure to a brittle appearing intergranular failure. A maximum in embrittlement was observed in the 26 pct Cr alloy. The maximum in embrittlement coincided with the minimum in stacking-fault energy. It is proposed that the increased hydrogen embrittlement in the high-chromium alloys is due to increased slip planarity caused by the lower stacking-fault energy. Slip planarity did not appear to affect the fracture of the uncharged specimens.     

On the mechanisms of high-temperature intergranular embrittlements of Ni3Al-Zr Alloys

Recent studies on the room-temperature fracture behavior of Ni₃Al-Zr alloys after preexposure at elevated temperatures show various types of intergranular failure. In the presently studied Ni₇₈Al₂₁Zr₁B_0.2 alloy, a strong intergranular fracture tendency at room temperature has been found after preexposure at 750 °C, which is caused by the grain boundary precipitation in this alloy. After short-term exposure above 1200 °C and bending fracture at room temperature, the alloy also suffers intergranular embrittlement due to grain boundary melting. The intergranular fracture appearance is quite different from that observed in a previous study for a Ni_77.4Al₂₂Zr_0.6B_0.2 alloy after air exposure for 100 hours at 1200 °C. In that case, the intergranular fracture was accompanied by grain boundary diffusion (invasion) and segregation of oxygen. The mechanisms of these types of grain boundary failure are discussed. Formerly Doctoral Candidate, Institute of Materials Science and Engineering, National Taiwan University.     

The effect of carbide precipitation on the hydrogen-enhanced fracture behavior of alloy 690

Alloy 690 is susceptible to hydrogen embrittlement where hydrogen reduces the ductility and causes the fracture morphology to change to predominantly intergranular. The role of carbide precipitation in the embrittlement behavior is not well defined. The objective of this work is to understand the effect of intergranular carbide precipitation on the hydrogen embrittlement of alloy 690. The work reported herein used tensile and compact-tension specimens in both the solution-annealed condition (minimal grain-boundary carbide precipitation) and in the solution-annealed condition followed by an aging treatment to precipitate grain-boundary carbides. By performing the mechanical tests on materials in both uncharged and hydrogen-charged conditions, it was possible to evaluate the degree of embrittlement as a function of the carbide precipitation. It is shown that the embrittlement due to hydrogen increased as the material was aged to allow grain-boundary carbide precipitation. It is proposed that the increase in embrittlement was caused by increased hydrogen at the carbide/matrix interface due to the trapping and increased stresses at the precipitate interface, which developed from strain incompatibility of the precipitate with the matrix. It is further shown that increasing the hydrostatic stress increased the tendency for intergranular fracture, as is consistent with other nickelbase alloys.     

Mechanical Properties and Fracture Behavior of Cu-Co-Be Alloy after Plastic Deformation and Heat Treatment

Mechanical properties and fracture behavior of Cu-0.84Co-0.23 Be alloy after plastic deformation and heat treatment were comparatively investigated.Severe plastic deformation by hot extrusion and cold drawing was adopted to induce large plastic strain of Cu-0.84Co-0.23 Be alloy.The tensile strength and elongation are up to 476.6 MPa and 18%,respectively.The fractured surface consists of deep dimples and micro-voids.Due to the formation of supersaturated solid solution on the Cu matrix by solution treatment at 950℃for 1h,the tensile strength decreased to271.9 MPa,while the elongation increased to 42%.The fracture morphology is parabolic dimple.Furthermore,the tensile strength increased significantly to 580.2 MPa after aging at 480℃ for 4h.During the aging process,a large number of precipitates formed and distributed on the Cu matrix.The fracture feature of aged specimens with low elongation(4.6%) exhibits an obvious brittle intergranular fracture.It is confirmed that the mechanical properties and fracture behavior are dominated by the microstructure characteristics of Cu-0.84Co-0.23 Be alloy after plastic deformation and heat treatment.In addition,the fracture behavior at 450 ℃ of aged Cu-0.84Co-0.23 Be alloy was also studied.The tensile strength and elongation are 383.6 MPa and 11.2%,respectively.The fractured morphologies are mainly candy-shaped with partial parabolic dimples and equiaxed dimples.The fracture mode is multi-mixed mechanism that brittle intergranular fracture plays a dominant role and ductile fracture is secondary.     

Gallium-induced magnesium enrichment on grain boundary and the gallium effect on degradation of tensile properties of aluminum alloys

By applying a controlled amount of gallium (3 mg or 5 mg) to double-notched samples, the effects of the gallium on the grain boundary chemistry and tensile properties of AA6061-T4 alloy were investigated. Commercial-purity aluminum AA1050 was used for comparison to determine whether alloying elements would correlate with Ga-induced embrittlement and to elucidate the physical reason that governed the occurrence of intergranular fracture in the AA6061 Al-Mg-Si alloy. The AA6061 and AA1050 samples wetted by 3 mg or 5 mg of Ga were held statically for 7 days before tensile tests were conducted. The 6061 Al-Mg-Si samples with gallium were fractured intergranularly. However, the Ga-treated AA1050 samples had a mixed fracture mode, showing better strength and ductility than the Ga-treated AA6061 alloy, independent of whether the samples had their longitudinal axis parallel or perpendicular to the rolling direction, or the holding temperatures before tensile tests. Auger electron spectroscopy scanning the intergranular facets on fracture surfaces showed that the Auger peak-to-peak ratio I_Ga/I_Al of 6061 samples was similar to that of 1050 samples, but the high intensity of Mg signal was detected from the intergranular fracture surface of the AA6061 alloy. Magnesium being induced by Ga to enrich on the grain boundary and free surface of the AA6061 alloy was confirmed. The intergranular embrittlement of the 6061 T4 Al-Mg-Si alloy wetted by small amount of Ga involves the combination of the following two effects: Ga metal on grain boundary embrittlement, and Ga-induced magnesium enrichment on grain boundary that further decreases the strength of the grain boundary.