锆、铜及均匀化处理对高导耐热铝合金电工圆杆性能的影响

通过扫描电镜、X射线物相分析等方法,研究了Zr、Cu元素及均匀化工艺对高导耐热铝合金电工圆杆组织及性能的影响。结果表明,通过"添加Zr(0.10%)Cu(0.08%)+300℃×16h均匀化+83%轧制"处理后,试样综合性能较优,试样导电率为59.5%IACS,抗拉强度达到149 MPa,230℃保温1h,强度残存率为94.3%。     

Al-B-N中间合金对1070铝合金力学性能及导电性的影响

目的研究Al-B-N中间合金对1070铝合金力学性能和导电性的影响。方法向1070铝合金熔体中添加适量Al-B-N中间合金,借助其中的纳米AlN颗粒(AlN_P)强化铝基体,同时以AlB_2相去除铝中降低导电率的过渡族金属元素(如Zr,Cr,V等)。结果添加质量分数为2%的Al-B-N中间合金,1070铝合金强度由66MPa提高至85 MPa,导电率由60.14%IACS提升至62.12%IACS,较未添加之前分别提高了28.8%和3.2%,此时合金伸长率为35.8%。结论适量Al-B-N中间合金可以同时提高1070铝合金抗拉强度与导电率,实现协同强化。     

CMT电弧增材制造Cu-Ni-Al-Mn-Fe铝青铜合金微观组织性能研究

目的研究冷金属过渡技术(Cold metal transfer,简称CMT)增材制造Cu-Ni-Al-Mn-Fe铝青铜合金的微观组织成形规律。方法采用CMT电弧增材的方式制备了Cu-Ni-Al-Mn-Fe铝青铜合金的薄壁试样件,研究了试样件在不同位置、不同方向的微观组织。结果 CMT电弧增材制造Cu-Ni-Al-Mn-Fe铝青铜合金的微观组织分为3个区域,前3层的不稳定区域主要是由基材树枝晶到柱状晶的转变区域;第3层到最后一层的稳定区域主要是外延生长的柱状晶区;在最后一层靠近空气侧约360μm厚度范围内,出现转向枝晶。交替往复电弧增材的Cu-Ni-Al-Mn-Fe铝青铜合金,在每层顶部均会形成转向枝晶,但随后新一层电弧增材的熔池会熔化顶部形成的转向枝晶,最终在微观组织形貌上表现出柱状晶外延生长的形式。结论通过控制合适工艺参数,可以获得致密无缺陷的CMT电弧增材制造Cu-Ni-Al-Mn-Fe铝青铜合金薄壁试样,在试样的稳定区域,微观组织是外延生长的柱状晶,柱状晶的晶界上Al,Ni,Mn元素产生富集现象,质量分数高于平均值。在柱状晶的晶内,Cu元素高于均值,而Al,Ni,Mn元素质量分数均低于均值,这与柱状晶的形核顺序有关。     

固溶时效和快速凝固时效对Cu-Cr-Zr-Mg合金时效性能的影响

研究了固溶时效和快速凝固时效工艺对Cu Cr Zr Mg合金的显微组织、硬度和导电率性能的影响。结果表明快速凝固态晶粒比固溶态晶粒细小得多,细晶强化作用显著。合金经920℃×1h固溶和550℃×0.5h时效后,硬度为100HV,导电率达71%IACS;快速凝固和同样的时效条件下,硬度为126HV,导电率达70%IACS。     

CMT电弧增材制造铝青铜的微观组织及耐腐蚀性能研究

目的研究冷金属过渡技术(Cold metal transfer,CMT)增材制造Cu-Ni-Al-Mn-Fe铝青铜合金的微观组织演变规律以及在不同温度下的耐腐蚀性能。方法采用CMT电弧增材的方式制备了铝青铜合金的薄壁试样件,通过光学显微镜研究了试样件在不同位置的微观组织演变规律,并通过电化学工作站测试试样在质量分数为3.5%的NaCl溶液中的电位极化曲线,进而分析其耐腐蚀性能。结果 CMT电弧增材制造铝青铜合金的微观组织主要表现为3个区域。前3层微观组织由基材树枝晶转变为柱状晶的区域;中间稳定区域主要是垂直于基板方向生长的均匀柱状晶微观组织;以及在最后一层出现柱状晶转向树枝晶的区域。当温度由20℃上升到60℃时,该材料的稳定电位ER由-0.2540 V下降到-0.2745 V。自腐蚀电流密度由2.84×10-6 A/cm~2增加到了5.149×10-6A/cm~2。结论采用合适工艺参数,可以获得致密无缺陷的CMT电弧增材制造铝青铜合金薄壁试样,在试样的稳定区域,微观组织是外延生长的柱状晶。同时试样在质量分数为3.5%的NaCl浓度溶液中有着良好的耐腐蚀性能,并且由于腐蚀过程介质温度的升高,电极反应速度加快、溶液的对流和扩散加强,从而加快了阳极过程和阴极过程,加速了金属的腐蚀。由此可见,介质温度对腐蚀速率的影响是非常重要的。     

激光选区熔化成形含钛6061铝合金的显微组织与力学性能EI北大核心

激光选区熔化(selective laser melting,SLM)成形6061铝合金易形成粗大的柱状晶和热裂纹。采用低能球磨组装修饰法制备TiH_(2)/AA6061铝基复合粉末,采用激光选区熔化技术制备含钛6061铝合金试样,分析不同TiH_(2)添加量对试样显微组织和力学性能的影响。结果表明:添加1%TiH_(2)(质量分数,下同)即可使合金熔池边界形成连续的等轴晶区,平均晶粒尺寸从59.8μm减小到2.53μm,粗大的柱状晶粒和裂纹被抑制,添加1.5%TiH_(2)时,SLM试样的粗大柱状晶组织绝大部分消失。显微组织转变归因于Ti元素增强成分过冷以及原位反应形成L12-Al_(3)Ti形核质点,该质点与铝基体形成共格界面,具有较强的异质形核作用,显著促进Al基体柱状晶向等轴晶转变及晶粒细化。经激光选区熔化成形后,添加1%TiH_(2)的试样抗拉强度为274 MPa,屈服强度为238 MPa,断后伸长率为18%。     

Ni、Si元素配比对Cu-Cr-Zr合金组织与性能的影响

在Cu-Cr-Zr合金中添加Ni、Si元素,制备Cu-0.6Cr-0.15Zr、Cu-2.8Ni-0.7Si-0.6Cr-0.15Zr(w(Ni)/w(Si)=4∶1)、Cu-2.8Ni-0.9Si-0.6Cr-0.15Zr(w(Ni)/w(Si)4∶1)、Cu-2.8Ni-0.56Si-0.6Cr-0.15Zr(w(Ni)/w(Si)4∶1)共4种合金。研究了Ni、Si元素及其配比对合金组织及性能的影响。结果表明:Ni、Si元素细化了合金组织,增强了合金高温力学性能。合金时效初期先析出CrSi2化合物,时效后期析出相颗粒主要有CrSi2、Ni2Si、ZrCrSi2,形态为长条形、椭圆形及圆盘状。时效处理后,与Cu-0.6Cr-0.15Zr合金相比,加入Ni、Si元素后合金硬度从131HV上升到240HV以上;导电率从88%IACS左右降到40%IACS左右。Ni、Si元素配比对导电率的峰值影响有限,在4%IACS~9%IACS;对硬度峰值的影响在20HV~30HV之间。     

激光选区熔化成形含锆7×××系铝合金的显微组织与力学性能

热裂问题是激光选区熔化成形(SLM)7× × ×系铝合金面临的主要障碍之一.通过低能球磨工艺制备ZrH2/7075复合粉末,采用激光选区熔化技术制备含锆7×××系铝合金材料,分析了不同ZrH2添加量(0.5％,1.0％,1.5％,质量分数,下同)对试样显微组织和力学性能的影响规律.结果表明:随着ZrH2含量的增加,SLM试样的柱状晶组织逐渐消失,热裂纹逐渐减少,当ZrH2含量为1.5％时,试样显微组织完全转变为细小等轴晶(平均晶粒尺寸为1.6μm),热裂纹完全消除.ZrH2在SLM成形过程中与铝熔体原位反应形成L12型Al3 Zr相,L12型Al3 Zr相的异质形核作用促进了柱状晶到等轴晶的转变,抑制了热裂纹的产生.经T6热处理后,试样抗拉强度为(550±10)MPa,屈服强度为(490±5)MPa,伸长率为(12±1)％,断口处存在大量韧窝,表现为韧性断裂.     

Y对耐热铝导体材料铸态组织和性能的影响

随着特高压输电技术在我国的大力发展,铝合金导体材料作为特高压输电线路的主要组成部分,受到业内的广泛关注.本文采用电导率测试、硬度测试、金相显微镜和扫描电镜观察等手段,研究添加不同含量稀土Y对铸态Al-Zr耐热铝导体材料的影响.研究结果表明:Y元素和Fe、Si等杂质元素形成金属间化合物,可净化基体,改变杂质相的形态和分布,使其粒子化、球化和细化.Y元素在枝晶网络和晶界分布,从而细化晶粒和枝晶组织,但添加量达到0.5%时晶粒细化不均匀.当Y含量为0.2%时,电导率达到60%IACS;当Y含量为0.3%时,硬度达到最高值20.9HBS,且电导率并无明显下降.加入0.3%Y可使耐热铝导体材料获得较好的综合性能.     

Cu-0.7Cr-0.13Zr合金时效强化行为的研究

研究了不同时效工艺对Cu-0.7Cr-0.13Zr合金的硬度和导电性能的影响,利用透射电镜分析了合金的时效析出微观组织.研究表明:500℃时效6 h后硬度和电导率具有141HV和76%IACS,强度的提高主要是由扩展位错以及共格弥散析出所造成的;合金在550℃时效2 h硬度和电导率仍具有126HV和77%IACS,析出相仍较细小,但与基体失去共格关系;最佳时效工艺条件为500℃时效4～6 h,硬度为134～141HV,电导率达72%～76%IACS.     

Effect of solid solution state of zirconium and Al3Zr (L12) precipitates on the recrystallization behavior of Al-0.2 wt.%Zr alloy

Effect of homogenization annealing on the existence form of zirconium in Al-0.2wt.%Zr alloy and effect of various existence form of zirconium on the recrystallization behavior of Al-0.2wt.%Zr cold-rolled (total deformation is 92.8 %) sheet are studied. The results show that large numbers of nearly spherical Al₃Zr (L1₂) nanoparticles precipitated from aluminum matrix after homogenizing at 475 °C for 24 h. Moreover, due to the precipitation of Al₃Zr particles, the hardness and electrical conductivity of the as-cast Al-0.2wt.%Zr alloy is increased from 25.1±0.5 HV 3 and 54.0±0.2 %IACS to 28.6±0.7 HV 3 and 56.2±0.1 %IACS, respectively. Hence, zirconium exists as solid solution state in the as-cast Al-0.2wt.%Zr alloy and metastable Al₃Zr phase in the homogenized alloy. Moreover, the recrystallization temperature of the pure aluminum without addition of zirconium is 300 °C, while the recrystallization temperature of the Al-0.2wt.%Zr alloy without and with homogenization is about 350 °C and 400 °C, respectively. Obviously, the solid solution state of zirconium has certain effect on retarding the recrystallization of aluminum alloy, while the nanometer Al₃Zr particles can inhibit the recrystallization of aluminum alloy effectively and increase the recrystallization temperature remarkably.     

Real time synchrotron X-ray observations of solidification in hypoeutectic Al–Si alloys

This paper demonstrates how recent advances in synchrotron technology have allowed for the real-time X-ray imaging of solidification in Al–Si alloys, despite the small difference in atomic number of these elements. The experiments performed at the SPring-8 synchrotron, involved imaging the solidification of Al–1wt.%Si and Al–4wt.%Si alloys under a low-temperature gradient and a cooling rate of around 0.3 °C/s. The nucleation and growth of the primary aluminum grains as well as the onset of eutectic solidification were clearly observed. In the alloys containing Al–4wt.%Si, contrast was sufficient to characterize the nucleation rate and growth velocity of the aluminum grains. The importance of improving observation of solidification in the Al–Si system by increasing the time resolution during critical events is discussed.     

Microstructure and Hardness of Laser Shocked Ultra-fine-grained Aluminum

Ultra-fine-grained commercial purity aluminum was produced by severe cold rolling, annealing and then strain- ing at ultra-high rate by a single pass laser shock. Resulted microstructure was investigated by transmission electron microscopy. Microhardness of annealed 0.6 μm ultra-fine grained aluminum increased by 67% from 24 to 40 HV. Many 0.3 μm sub-grains appeared at the shock wave center after a single pass laser shock, while high density dislocation networks were observed in some grains at the shock wave edges. Accordingly, microhardness at the impact center increased by 37.5% from 40 to 55 HV. From the impact center to the edge, microhardness decreased by 22% from 55 to 45 HV.     

Effects of Sc(Zr) on the microstructure and mechanical properties of as-cast Al–Mg alloys

Both the addition of 0.6% Sc and simultaneous addition of 0.2% Sc and 0.1% Zr exerted a remarkable effect on grain refinement of as-cast Al–Mg alloys, changing typical dendritic microstructure into fine equiaxed grains. Such effect was found to be related to the formation of primary particles, which acted as heterogeneous nucleation sites for α-Al matrix during solidification. Primary particles formed in Al–Mg–Sc–Zr alloy could be identified as the eutectic structure consisting of multilayer of ‘Al₃(Sc,Zr)?+?α-Al?+?Al₃(Sc,Zr)’, with a ‘cellular-dendritic’ mode of growth. In addition, an attractive comprehensive property of as-cast Al–5Mg alloy due to the addition of 0.2% Sc and 0.1% Zr was obtained.     

Microstructure and mechanical property of sintered Fe-Cr-Mo steels due to phase transformations with fast cooling rates

The influence of carbon content in the range of 0.01–0.3 wt.% on microstructure, hardness and tensile property of sintered Fe-Cr-Mo steels was investigated. The sintered Fe–3.0 wt.%Cr–0.5 wt.%Mo–(0.1, 0.2, 0.3) wt.% C steels were prepared by using powder metallurgical process. After sintering, the specimens were rapidly cooled by nitrogen at the rate of 5.4 °C/s. It was found that in the sintered steels with a lower carbon content of 0.01 and 0.1 wt.%, the allotriomorphic ferrite and Widmanstӓtten ferrite formed at austenite grain boundaries and grew to occupy the whole prior austenite grains. With higher carbon contents of 0.2 and 0.3 wt.%, the microstructures consist of bainite, martensite and some retained austenite. These steels exhibited increases of hardness, tensile strength and elongation at break with increasing carbon content. Increase of strength is due to the transformations from austenite, formed during sintering, to hard bainite and martensite structures.     

Nanotubular surface and morphology of Ti-binary and Ti-ternary alloys for biocompatibility

The nanotubular surface of Ti-binary and Ti-ternary alloys for biomaterials has been investigated using various methods of surface characterization. Binary Ti-xNb (x = 10, 20, 30, and 40 wt.%) and ternary Ti-30Ta-xNb (x = 3, 7 and 15 wt.%) alloys were prepared by using the high-purity sponges; Ti, Ta and Zr spheres. The nanotube on the alloy surface was formed in 1.0 M H₃PO₄ with small additions of NaF (0.5 and 0.8 wt.%), using a potentiostat. For cell proliferation, an MC3T3-E1 mouse osteoblast was used. The surface characteristics were investigated using field-emission scanning electron microscope, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy.Binary Ti-xZr alloys had a lamellar and a needle-like structure, whereas, ternary Ti-30Ta-xZr alloys had equiaxed grains with a lamellar martensitic α′ structure. The thickness of the needle-like laths of the α-phase increased as the Zr content increased. The nanotubes formed on the α phase and β phase showed a different size and shape appearance with Zr content. As the Zr content increased from 3 to 40 wt.%, the diameter of the nanotubes in Ti-xZr and Ti-30Ta-xZr alloy decreased from 200 nm to 50 nm. The nanotubular Ti-30Ta-15Zr alloy surface with a diameter of 50 nm provided a good osseointegration; cell proliferation, migration and differentiation.     

Microstructure and mechanical properties of friction stir welded Al/Mg2Si metal matrix cast composite

In this research, friction stir weldability of 15 wt.% Mg₂Si particulate aluminum matrix cast composite and effects of tool rotation speed and number of welding passes on microstructure and mechanical properties of the joints were investigated. Microstructural observations were carried out by employing optical and scanning electron microscopy of the cross sections perpendicular to the tool traverse direction. Mechanical properties including microhardness and tensile strength were evaluated in detail. The results showed fragmentation of Mg₂Si particles and Mg₂Si needles existing in eutectic structure in stir zone. Also, homogeneous distribution of Mg₂Si particles was observed in the stir zone as a result of stirring with high plastic strains. Tension test results indicated that tensile strength of the joint had an optimum at 1120 rpm tool rotation speed and decreased with increasing of the number of welding passes. Hardness of the joint increased due to modification of solidification microstructure of the base composite. This research indicates that friction stir welding is a good candidate for joining of 15 wt.% Mg₂Si aluminum matrix composite castings.     

Influence of ultrasonic melt treatment on the formation of primary intermetallics and related grain refinement in aluminum alloys

Ultrasonic melt treatment (UST) is known to induce grain refining in aluminum alloys. Previous studies have clearly shown that in Al–Zr–Ti alloys, the primary Al₃Zr intermetallics were dramatically refined by cavitation-assisted fragmentation, and a good refinement effect was achieved. In this article, Al–Ti, Al–Ti–Zr alloys, and some commercial aluminum alloys are used to analyze the effect of UST on primary intermetallics and grain refinement. The addition of a small amount of Al–3Ti–B master alloy is also studied in order to compare with the addition of Ti and Zr in commercial aluminum alloys. Experimental results show that the ultrasonic grain refining effect is not only related to the size of particles which are refined and/or dispersed by UST, but also related to an undercooling available for activation of these particles in the solidification process. Athermal heterogeneous nucleation theory is considered to explain the effect of size and distribution of substrate particles on the grain structure with different undercoolings. The distribution of primary particle sizes results in the distribution of required undercoolings. Grain refining occurs when the undercooling is large enough to activate the refined primary intermetallics or dispersed inoculants.     

Laser-based directed energy deposition of novel Sc/Zr-modified Al-Mg alloys: columnar-to-equiaxed transition and aging hardening behavior

The control of grain morphology is important in laser additive manufacturing(LAM), as grain morphology further affects the hot cracking resistance, anisotropy, and strength–ductility synergy of materials. To develop a solidification-control solution and achieve columnar-to-equiaxed transition(CET) in Al-based alloys during LAM, Sc-and-Zr-modified Al-Mg alloys were processed via directed energy deposition(DED).CET was achieved by introducing high potent primary Al_3(Sc,Zr) nucleation sites ahead of the solidification interface. Furthermore, the relationship between the solidification control parameters and precipitation behavior of primary Al_3(Sc,Zr) nucleation sites was established using the time-dependent nucleation theory. Then, the CET was studied according to the Hunt criterion. The results indicated that coarse columnar grain structure was still obtained at the inner region of the molten pool at low Sc/Zr contents owing to the effective suppression of the precipitation of the primary Al_3(Sc,Zr) nucleation sites via rapid solidification during DED. In addition, the relatively low melt temperature at the fusion boundary unavoidably promoted the precipitation of primary Al_3(Sc,Zr) nucleation sites, which resulted in a fine equiaxed grains band at the edge of the molten pool. As the Sc/Zr content increased, the solidification cooling rate was not sufficient to suppress the precipitation of the primary Al_3(Sc,Zr) nucleation sites, and a fully equiaxed grain structure was obtained. Furthermore, the effect of the layer-by-layer manufacturing process on the subsequent precipitation strengthening of secondary Al_3(Sc,Zr) precipitates was discussed.Both the remelting and subsequent aging during thermal cycling should be considered to achieve greater precipitation strengthening.     

Microstructures and tensile properties of Al-Zn-Cu-Mg-Zr alloys modified with scandium

We melted five types of Al-Zn-Cu-Mg-Zr alloys and added 0.0, 0.1, 0.2, 0.3, and 0.5 (wt.%) of scandium. Its influence on the microstructure of alloys and their mechanical properties is studied with the help of optical transmission and scanning electron microscopes. An insignificant amount of scandium promoted the formation of Al₃ (Sc, Zr) particles. These particles efficiently clean the microstructure, decelerate and preserve recrystallization, and fix dislocations and substructures. The strength of the alloys increases for high levels of plasticity. It is shown that the optimal properties of the alloys with 0.21% Sc are attained after holding in a solution for 40 min at 475°C and aging for 24 h at 120°C. The strength of the alloys increases mainly as a result of dispersion solidification and microstructural hardening with Al₃ (Sc, Zr) particles. Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 1, pp. 100–103, January–February, 2008.