重固溶再多级时效处理对7175铝合金组织和性能的影响

采用拉伸试验、电导率测试及电镜观察等方法,研究了重固溶制度后高温-低温-高温(HLH)再多级时效制度对7175铝合金组织与性能的影响。结果表明,经过HLH处理以后,材料的综合性能有所提高。经过480℃×2h重固溶、180℃×1h+110℃×6h+180℃×5h三级时效处理后,7175铝合金能得到最佳的综合性能。     

过时效-重固溶-再时效处理对 7055铝合金组织与性能的影响

采用拉伸试验、电导率测试及透射电镜观察等方法,研究了重固溶温度和过时效处理时间对7055铝合金组织与性能的影响.结果表明,120℃×3h+180℃×8h过时效处理后,经过不同温度(440℃～490℃)重新固溶处理以及120℃/24h再时效后,7055铝合金的电导率随重固溶温度的上升而降低,但强度升高;延长过时效时间(120℃×3h+180℃×4h～20h),470℃×1h重固溶处理后,合金电导率略微上升,而强度逐渐降低.组织观察表明,过时效处理形成的粗大析出相在不同温度重固溶时的重新溶解程度不同,重固溶温度越低,粗大析出相溶解越不充分,从而形成与回归再时效处理相类似的组织结构;同时,过时效及重固溶处理也有利于Fe、Si和Zr等残留固溶原子以化合物的形式充分析出,因此利用该工艺可以在保持强度不降低的前提下,提高合金的电导率,并最终提高合金的抗应力腐蚀性能.     

2196铝锂合金重固溶-时效组织与性能研究

基于2196-T8511铝锂合金,对其进行重固溶-再时效处理,研究时效时间对其力学性能与组织演化的影响。结果表明:重固溶处理后的晶界清晰。再采用适当的温度和时间进行时效处理,合金可以回复到原始态的力学性能。2196铝锂合金的重新固溶-再时效析出相包括T1相(Al_2Cu Li)、δ'相(Al_3Li)和θ'相(Al_2Cu);较短时效时间可形成较多δ'相和θ'相。随着时效时间的延长,T1相逐渐增多,δ'相和θ'相减少;重新固溶-时效后,断口韧窝增加,仍以分层断裂为主。     

重固溶-不同温度T8再时效2195铝锂合金的力学性能与显微组织演化

以5.2 mm厚度2195-T8铝锂合金为对象,进行重固溶、4.5%预变形后不同温度(145C~160℃)的T8再时效处理,研究其力学性能与晶内显微组织演化。结果表明:重固溶处理后的晶粒形态与原始2195-T8态晶粒形态一样,仍然保持为拉长的带状晶粒组织。重固溶并经4.5%预变形后,再采用适当的温度和时间进行T8时效处理,2195铝锂合金可以回复到原始T8态的显微组织和力学性能,即2195铝锂合金采用重固溶-T8再时效处理不会明显损害其力学性能。2195铝锂合金的晶内时效析出相包括T1相(Al2Cu Li)、δ′相(Al3Li)、θ′相(Al2Cu)及θ″相(Al2Cu),其中优先析出相为T1相;较低温度及较短时间时效可形成较多δ′相和θ″相;随着时效时间延长,T1相生长,θ″相转化为θ′相并减少,δ′相消失;时效温度提高可促进该转变过程,加快铝锂合金的时效响应速度。     

2195铝锂合金重固溶-T8再时效的组织与力学性能

以5.2 mm厚2195-T8铝锂合金为基础,进行了重固溶及后续152℃的T8(预变形3%~6%)再时效处理,研究了其微观组织与拉伸性能。结果表明,重固溶处理未显著改变2195铝锂合金的晶粒组织,仍然保持为拉长的扁平状(带状)晶粒组织态。合金的主要时效强化相为T1相(Al_2Cu Li)和θ'相(Al_2Cu)。T1相数量随预变形量增大而明显增加,而峰时效后θ'相数量及尺寸随预变形量增加呈降低的趋势。合金中T1相分数随时效时间延长而增加并主要沿长度方向长大,而峰时效后θ'相随时效时间延长逐渐减少。重固溶T8再时效处理未明显损害2195铝锂合金拉伸性能。     

固溶工艺对Ti12LC合金组织性能的影响

Ti12LC合金是西北有色金属研究院研制的一种低成本钛合金,用于取代TC11合金进行推广应用。本文对420mm Ti12LC合金铸锭进行常规锻造,得到等轴组织的170mm Ti12LC合金棒材。采用单重固溶＋时效、双重固溶＋时效两种不同的工艺对Ti12LC合金进行热处理,分析不同固溶工艺对Ti12LC合金显微组织及室温拉伸、室温冲击性能的影响。研究表明,在相同的固溶冷却速率下,增加单重固溶温度,初生等轴α相含量减少,合金强度增加、塑性减小、冲击韧性减小。单重固溶＋时效热处理后合金冲击韧性低、强韧性匹配差。与单重低温固溶＋时效相比,合金经高温预固溶慢冷＋低温固溶处理后,初生α相尺寸及相含量变化不明显,但可以获得更大尺寸的次生α相,合金的塑性稍有降低、强度增加、冲击韧性改善明显,综合力学性能匹配良好。     

固溶时效对激光熔化沉积TC17钛合金显微组织的影响

研究了激光熔化沉积TC17钛合金原态及固溶时效后的显微组织,分析了一重固溶+时效和两重固溶+时效热处理对初生α相含量、长宽比的影响。结果表明,激光熔化沉积态TC17钛合金凝固组织为粗大的柱状β晶,显微组织为细密的片层α+β两相网篮组织。当固溶温度从800℃升高到835℃时,初生α相体积分数由53%减少到34%,宽0.4～0.5μm,长宽比约从9∶1减小到5∶1;时效后初生α相片层显著粗化,宽0.7～0.8μm,次生α相极其细密,均匀分布于初生α片层之间,含量随固溶温度升高逐渐增多。当进行两重固溶处理时,第一步固溶温度决定初生α相含量,而对初生α相的宽度及长宽比几乎没有影响,第二步固溶时间主要影响初生α相的长宽比,而对初生α相的含量及宽度几乎没有影响。     

回归再时效对7075-T8铝合金显微组织及力学性能的影响

对7075-T8铝合金进行重固溶处理、T6时效处理和不同温度(160～205℃)、不同时间(20～80 min)的回归再时效(RRA)处理,采用扫描电镜、透射电镜、显微硬度仪和万能试验机等研究了合金经不同热处理后的显微组织和力学性能。结果表明：重固溶处理后,相较于T8及T6处理,采用适当的回归温度和回归时间的RRA处理,不会改变合金析出相的种类,但能提高析出相的密度,减小析出相的尺寸;且晶界处第二相尺寸随回归温度的升高不断增大,含铜相随回归时间延长不断富集在晶界附近。经重固溶-RRA(470℃×4 h+120℃×24 h+175℃×20 min+120℃×24 h)处理后的7075-T8合金的抗拉强度和伸长率达到696 MPa和12.7%,与T8和T6时效处理相比,合金的抗拉强度分别提高了29%和20%、伸长率分别提高了46%和41%。合金的强度随着回归温度的升高先升高后降低,在175℃回归处理20 min后达到峰值。     

固溶热处理对AA7085铝合金组织与性能的影响

采用拉伸试验、电导率测试、剥落腐蚀试验、金相观察及透射电镜分析等方法,研究了不同固溶热处理工艺(包括常规固溶、高温预析出固溶与部分重固溶)对AA7085铝合金的强度、剥落腐蚀性能及显微组织的影响。结果表明,采用部分重固溶工艺并时效处理后,合金的抗拉强度降低,但电导率与抗剥落腐蚀性能明显得到提高。其原因是通过部分重固溶处理并时效处理后,合金中的晶界析出细小且非连续分布的η析出相,从而提高了AA7085铝合金的抗腐蚀性能。     

热处理工艺对羽毛球拍杆铝基复合材料性能的影响

采用4种不同的热处理制度对羽毛球拍杆用铝基复合材料进行热处理,并对材料的抗弯刚度、阻尼性能和耐磨损性能进行分析。结果表明,双级固溶较单级固溶、双级时效较单级时效均能提高材料的抗弯刚度、阻尼性能和耐磨损性能。热处理制度优选为:双级固溶+双级时效;与单级固溶+单级时效的热处理制度相比,优选的热处理工艺使材料的抗弯刚度增大12%、阻尼系数增大58%、磨损体积减小55%     

7175铝合金锻件毛坯高温均匀化处理工艺研究

对7175铝合金大型锻件生产过程中的关键工艺－－高温均匀化处理进行了研究；分析了锻造毛坯经过高温处理和未经高温处理的锻件的组织、性能差别及其机理。     

Effect of Cr elimination on flow behavior and processing map of newly developed ECO-7175 aluminum alloy during hot compression

ECO-Al alloys are introduced as a game-changer for the aluminum industry and it is of utmost importance to determine the role of alloying elements in their processing characteristics. In this study, the effects of Cr on the hot deformation behavior of newly-developed ECO-7175 alloy were investigated. ECO-7175 samples with and without Cr were hot-compressed using a Gleeble simulator (temperature range of 350?500 °C and strain rates of 0.001?1 s^?1). The results were used to study the constitutive equations, the processing maps, and the microstructural evolution of the alloys. In Cr-containing alloy, the analysis of the deformation activation energy reveals that the rate-controlling mechanisms of the deformation change gradually from self-diffusion of Al (or diffusion of Mg in Al) to diffusion of Cr in Al by decreasing the Zener?Hollomon parameter. The analysis of the processing maps of Cr-containing alloy shows that the dynamic recrystallization (DRX) zone is limited to the deformation at high temperatures and low strain rates and expands with increasing applied strain. On the other hand, it is found that the self-diffusion of Al (or Mg in Al) is the only rate-controlling mechanism during hot deformation of Cr-free alloy in all processing conditions and its DRX zone is independent of the plastic strain.     

Laser alloying of aluminium alloys with chromium

The microstructure and corrosion resistance of laser-alloyed aluminium and ANSI 7175 aluminium alloy with chromium were investigated. Surface layers alloyed with chromium contain relatively large amounts of intermetallic compounds dispersed in a matrix of -Al. The intermetallic compound particles present needle-like morphologies, organized in a dense network or distributed radially. Al₇Cr, Al₁₁Cr₂ and -Al phases have been identified by X-ray diffraction. The alloyed layers may contain cracks, pores, inclusions and undissolved chromium particles, depending on the chromium concentration and the particle size. However, homogeneous layers were produced by a two-step process, consisting of laser alloying followed by remelting. The second treatment eliminates porosity and refines the structure. The hardness attains a Vickers hardness of 155 HV in chromium-alloyed aluminium and exceeds 300 HV in chromium-alloyed 7175. The corrosion behaviour of the above alloys was assessed using anodic polarization techniques. Laser alloying of aluminium and 7175 with chromium improves the pitting corrosion resistance of the alloys. The effect depends on the chromium content of the alloyed layers and is more significant in 7175 alloy.     

Avoiding crevice corrosion by laser surface treatment

The present work shows that laser surface alloying of the creviced area on Al 7175-T7351 with chromium can avoid crevice corrosion. Corrosion takes places outside the crevice in conditions where the ratio of anodic area to cathodic area is favourable to minimize corrosion. As laser surface processing is adequate for treating small areas there is an enormous potential in this technology.     

7175铝合金大型锻件热处理工艺研究

通过对7175铝合金大型锻件均匀化、淬火、时效工艺的试验研究，阐述了7175铝合金大型锻件经过特殊的热处理工艺不仅能够得到高强度，而且具有良好的耐蚀性和断裂韧性。     

Investigation of Cr, Cu and Zn sites in corroded/ uncorroded aluminum by X-ray absorption spectroscopy (XAS)

X-ray absorption spectroscopy (XAS) was used to characterize the Cr, Cu and Zn sites in 7175 T736 aluminum which had exhibited corrosion at the bond between the Al and ethylene propylene diene monomer (EPDM) during 9.8 years of storage. The characterization was concerned with the Cr, Cu and Zn coordination chemistry (chemical valence, coordination number, bondlength, disorder, and species of surrounding atoms) of corroded and uncorroded samples. The results show that only the Cu site in the Al alloy significantly changed during the process of corrosion. After corrosion no chemical shift was observed in the Cu K-edge (8979 eV) nor was the significant presence of Cu oxide, sulfide, chloride or hydroxide found. Analysis of the data using XAS methods indicated that ˜20% ± 10% of the Cu sampled (to a depth of ˜ 104 μm using fluorescent yield) was present as disordered, metallic Cu after corrosion. The remainder of the Cu was present in the alloy as it would be found in uncorroded 7175 T736. Very little Cu was found in the top ˜ .235 μm of the corrosion layer as sampled by electron yield methods.     

Improved FE model for simulation of friction stir welding of different materials

Abstract

One of the most relevant aspects of friction stir welding is the possibility to weld different materials. In the present paper, the authors present an improved continuum finite element model for the simulation of friction stir welding processes aimed to obtain T joints, made of a stringer in AA7175-T73511 and of a skin in AA2024-T4. The model, taking into account the thermomechanical behaviours of the two different materials, is utilised to study the occurring material flow and residual stress state. Numerical results are compared with experimental observations: the model is able to predict the material flow, obtaining important information on the joint failure mode.     

维斯塔金属公司的特大2×××系及7×××系铝合金锭铸造

扼要地介绍了美国维斯塔金属公司(Vista Metals Corporation)铸造超大硬铝合金(2×××系、7×××系)圆锭及扁锭的工艺。维斯塔金属公司在铸造硬铝合金特大锭方面居世界领先地位,2003年初铸出直径1 068 mm的7175合金圆锭,2004年秋铸出宽2 438 mm、厚1 067 mm、长4 369 mm的2618铝合金扁锭,这都是创世界记录的。特大2×××系及7×××系铝合金锭在航天航空工业、交通运输工业、模具制造业有着重要用途。     

Black anodic coatings for space applications: Study of the process parameters,characteristics and mechanical properties

Black inorganic anodized aluminium alloys are used for managing passive thermal control on spacecraft and for avoiding stray light in optical equipment. Spalling of these coatings has sometimes been observed after thermal cycling on 2XXX and 7XXX aluminium alloys. This phenomenon could generate particulate contamination in satellites and may affect mission lifetime. In this work, the influences of the four main steps of the process (pretreatments, sulphuric anodizing, colouring and sealing) on the coating characteristics have been studied for a 7175T7351 aluminium alloy. The chemical heterogeneity of the coating has been underlined, and its mechanical behaviour observed through crazing. Scratch-testing, used to evaluate coating adhesion to its substrate, revealed the negative impact of thermal cycling.