用等径角挤压变形法进行奥氏体不锈钢锭开坯的研究

对铸态奥氏体不锈钢的等径角挤压变形(ECAP)试样进行了高温固溶处理,并与锻造试样 固溶处理后的组织、性能进行了对比,研究表明:室、高温ECAP试样在1150℃固溶处理后均可得到完全再结晶组织;增加ECAP道次对完全再结晶后的晶粒尺寸影响不大,但略微增加晶粒尺寸的均匀性;铸态奥氏体不锈钢采用ECAP 固溶处理新工艺后,可以获得与锻造 固溶处理工艺类似的组织、力学性能,有可能实现铸锭的开坯.     

热处理和挤压对WE53镁合金组织与力学性能的影响

为提高WE系列生物镁合金的力学性能,采用重力铸造法制备了Mg-5Y-2Nd-1Gd-0.5Zr （质量分数,WE53）镁合金,并对铸态合金进行了固溶处理（T4）,固溶＋时效处理（T6）和挤压加工.利用光学显微镜和扫描电子显微镜观察了合金的显微组织,并利用拉伸试验机和显微硬度计测试了合金室温力学性能.结果表明,铸态合金屈服强度为130 MPa,伸长率为10.2%,T6处理可显著提高铸态合金的强度和硬度,降低合金的伸长率;挤压变形明显提高合金的强度和硬度,伸长率与铸态相当.通过适当的热处理和挤压变形可显著改善WE53镁合金的力学性能.     

铸态304L奥氏体不锈钢等径角挤压变形研究

 研究了铸态304L奥氏体不锈钢在等径角挤压(ECAP)变形过程中显微组织的演变过程。结果表明,经4道次剪切变形后树枝晶破碎、原始粗大晶粒碎化。显微组织的变化过程可归纳为：原始粗晶粒→晶粒被滑移带分割→位错发展形成高密度位错墙,与滑移带共同作用形成胞块结构→应变增加形成层片状界面→形成大角度晶界的细小晶粒。表明铸态304L奥氏体不锈钢经ECAP变形后塑性变形机制主要由滑移完成。     

Al-Ti-B对AZ91D镁合金显微组织和力学性能的影响

研究了Al-Ti-B对AZ91D镁合金铸态显微组织和力学性能的影响，并探讨其化学成分与组织结构和力学性能之间的变化。研究结果表明：Al-Ti-B加入AZ91D镁合金，能明显细化组织晶粒，从而改善合金的室温力学性能。当加入Al-Ti-B时，合金晶粒细化效果较好，其室温力学性能和硬度比原来都有较大的提高。     

室温ECAP变形纯钛孪生行为研究

室温下对纯钛进行多道次等径弯曲通道变形（ECAP）,分别采用光学显微镜（OM）、透射电镜（TEM）、电子背散射衍射仪（EBSD）、室温拉伸和显微硬度观察,测试纯钛变形过程组织演变和力学性能变化规律,探讨纯钛室温变形机制和孪生行为。结果表明,纯钛ECAP变形过程中出现■拉伸孪晶和■压缩孪晶,随着挤压道次的增大,孪晶数量先增大后减小。孪晶的出现有效改变晶格取向,激发进一步位错滑移,辅助塑性变形过程,使纯钛显微组织有效细化,经过4道次ECAP变形,平均晶粒尺寸由约63.79μm细化至约2.81μm。1道次变形后晶粒细化效果最显著,平均晶粒尺寸比变形前减小约94%;随着变形道次的增加,晶粒细化效果减弱,4道次变形后平均晶粒尺寸累积减小约95.6%。同时,大量位错、孪晶和亚晶的形成,使得位错、孪晶以及亚晶之间的相互作用加强,显著提高了纯钛的屈服强度和显微硬度,4道次变形后,屈服强度从215 MPa增加到600 MPa,增幅为179%;显微硬度从HV 129增加到HV 200。由于1道次变形后晶粒细化效果最显著,并且出现大量孪晶和位错,屈服强度与硬度的增幅也最大。     

高铌TiAl基合金热变形组织的均匀化

研究了热加工和热处理对大尺寸高铌TiAl基合金组织均匀化的影响.结果表明,两次包套锻造能够有效地破碎大尺寸高铌TiAl基合金铸态组织.锻造过程中,铸态组织发生较大程度的动态再结晶,合金锻后组织经过热处理未出现残留的粗大的片层组织.合金在凝固中由于偏析形成的高温β相通过热加工和随后的热处理得到了有效的消除,热处理后所获的双态组织均匀且细小.     

工业纯钛板材室温ECAP变形组织性能研究

选取热轧退火态的工业纯钛(CP-Ti)板材为研究对象,采用通道夹角Φ=135°的模具,在室温下进行CP-Ti板状试样1~8道次等径弯曲通道变形(ECAP),利用金相显微镜(OM)和透射电镜(TEM)观察并分析了纯钛板材在不同道次变形后的组织演变过程。通过力学性能测试实验,分析了X,Y,Z面硬度的变化过程,研究了ECAP变形对CP-Ti力学性能的影响规律。结果表明:CP-Ti板材经过ECAP变形,晶粒逐渐拉长,组织位错大量增加,出现板条状组织;8道次ECAP变形后CP-Ti板材的晶粒明显细化,晶粒尺寸由原始的57.000μm细化到0.668μm;随着挤压道次的增加,组织位错逐渐消失,小角度晶界逐渐转变为大角度晶界,晶粒越来越细,最终达到纳米级别。CP-Ti板材1道次ECAP变形后硬度变化程度最大,X,Y,Z面的硬度增幅分别达32.6%,33.8%和32.9%;随着道次增加,8道次ECAP变形后,力学性能显著提高,X,Y,Z面的硬度最终达到1910,1943和1911 MPa。     

半固态挤压铸造下稀土Y强化机械零件用ZL105铝合金的制备与性能

利用半固态挤压铸造技术制备稀土Y强化后的机械零件用ZL105铝合金,采用光学显微镜(OM)、能谱仪(EDS)、扫描电镜(SEM)研究了不同Y添加量下的ZL105铝合金显微组织和力学性能.结果表明,Y能有效细化铸态铝合金的晶粒,随着Y添加量的增加,α-Al晶粒和Al-Fe-Mn-Si相尺寸均先减小后增大,铝合金硬度、抗拉强度和伸长率均先增大后减小.当Y添加量(质量分数)为0.4%时,铝合金微观组织细化程度最高,稀土相分布在晶间,α-Al晶粒尺寸约为26μm,呈椭球状,Al-Fe-Mn-Si相尺寸减小到22μm,由长针状细化为短棒状,铝合金硬度(HV)达到108.2,抗拉强度为278.6 MPa,伸长率为5.8%;拉伸断口主要由韧窝和一定量的解理面组成.     

镁及镁合金等通道转角挤压研究进展及发展趋势

镁及镁合金属于HCP结构,织构和晶粒尺寸是影响其性能的主要因素.本文对近年来镁及镁合金等通道转角挤压(Equal channel angular pressing,ECAP)的研究状况进行了综述,介绍了ECAP过程中影响镁及镁合金织构的主要因素.根据晶粒细化机制的不同,从两方面介绍了ECAP工艺制备镁及镁合金超细晶、纳...     

双螺旋流变压铸AZ91D镁合金的研究

液态压铸是镁合金最主要的成形方式,但液态压铸件存在气孔等缺陷,限制了镁合金的进一步推广使用。介绍了采用双螺旋流变制浆技术,对镁合金AZ91D进行了流变压铸研究。首先,将镁合金AZ91D熔体浇入到双螺旋流变制浆机中,然后根据不同工艺参数制备流变镁合金浆料,待制浆结束后,将半固态浆料转移到压铸机内,制得半固态压铸件。采用Micro-Image Analysis&Process(MIAP)软件分析了双螺旋流变制浆工艺参数(搅拌温度、搅拌时间和转速)对镁合金AZ91D的初生相晶粒大小的影响,并研究了镁合金压铸成形性。结果表明:随着搅拌温度的降低,晶粒尺寸变化不是很大;随着搅拌时间延长,镁合金晶粒尺寸逐渐增大;随着搅拌速度的增加,镁合金平均晶粒尺寸减少。镁合金流变压铸件中的初生α相由搅拌中形成的球状晶及压铸过程中二次凝固形成的更为细小的球状晶组成。对比了普通压铸件与流变压铸件热处理后的力学性能,流变压铸件的力学性能得到大幅提高,其原因归结为铸态组织的细小和均匀化。     

Microstructure and Corrosion Characterization of Squeeze Cast AM50 Magnesium Alloys

Squeeze casting of magnesium alloys potentially can be used in lightweight chassis components such as control arms and knuckles. This study documents the microstructural analysis and corrosion behavior of AM50 alloys squeeze cast at different pressures between 40 and 120 MPa and compares them with high-pressure die cast (HPDC) AM50 alloy castings and an AM50 squeeze cast prototype control arm. Although the corrosion rates of the squeeze cast samples are slightly higher than those observed for the HPDC AM50 alloy, the former does produce virtually porosity-free castings that are required for structural applications like control arms and wheels. This outcome is extremely encouraging as it provides an opportunity for additional alloy and process development by squeeze casting that has remained relatively unexplored for magnesium alloys compared with aluminum. Among the microstructural parameters analyzed, it seems that the β-phase interfacial area, indicating a greater degree of β network, leads to a lower corrosion rate. Weight loss was the better method for determining corrosion behavior in these alloys that contain a large fraction of second phase, which can cause perturbations to an overall uniform surface corrosion behavior.     

Tensile and Fracture Properties of Cast and Forged Composite Synthesized by Addition of Al-Si Alloy to Magnesium

Cast Mg-Al-Si composites synthesized by addition of Al-Si alloy containing 10, 15, and 20 wt pct of Si, in molten magnesium, to generate particles of Mg₂Si by reaction between silicon and magnesium during stir casting has opened up the possibility to control the size of these particles. The microstructure of the cast composite consists of relatively dark polyhedral phase of Mg₂Si and bright phase of β-Al₁₂Mg₁₇ along the boundary between dendrites of α-Mg solid solution. After hot forging at 350 °C, the microstructure has changed to relatively smaller sizes of β-Al₁₂Mg₁₇ and Mg₂Si particles apart from larger grains surrounded by smaller grains due to dynamic recovery and recrystallization. Some of the Mg₂Si particles crack during forging. In both the cast and forged composite, the Brinell hardness increases rapidly with increasing volume fraction of Mg₂Si, but the hardness is higher in forged composites by about 100 BHN. Yield strength in cast composites improves over that of the cast alloy, but there is a marginal increase in yield strength with increasing Mg₂Si content. In forged composites, there is significant improvement in yield strength with increasing Mg₂Si particles and also over those observed in their cast counterpart. In cast composites, ultimate tensile strength (UTS) decreases with increasing Mg₂Si content possibly due to increased casting defects such as porosity and segregation, which increases with increasing Mg₂Si content and may counteract the strengthening effect of Mg₂Si content. However, in forged composite, UTS increases with increasing Mg₂Si content until 5.25 vol pct due to elimination of segregation and lowering of porosity, but at higher Mg₂Si content of 7 vol pct, UTS decreases, possibly due to extensive cracking of Mg₂Si particles. On forging, the ductility decreases in forged alloy and composites possibly due to the remaining strain and the forged microstructure. The initiation fracture toughness, J _IC , decreases drastically in cast composites from that of Mg-9 wt pct. alloy designated as MA alloy due to the presence Mg₂Si particles. Thereafter, J _IC does not appear to be very sensitive to the increasing presence of Mg₂Si particles. There is drastic reduction of J _IC on forging of the alloy, which was attributed to the remaining strain and forged microstructure, and it is further lowered in the composites because of cracking of Mg₂Si particles. The ratio of the tearing modulus to the elastic modulus in cast composites shows a lower ratio, which decreases with increasing Mg₂Si content. The ratio decreases comparatively more on forging of cast MA alloy than those observed in forged composites.     

原始组织对304L超低碳奥氏体不锈钢等径角挤压变形的影响

304L超低碳奥氏体不锈钢由25kg真空感应炉冶炼,用透射电镜(TEM)研究了该钢铸态组织200℃等径角挤压变形(ECAP)后组织演变和铸态组织1道次ECAP+1150℃1.5 h,AC处理(固溶组织)再进行ECAP后的组织。结果表明,304L钢铸态组织1道次ECAP变形过程中主要的变形机制为滑移变形,同时出现少量的孪晶变形;304L钢固溶组织在ECAP变形过程中孪晶变形数量急剧增加,孪晶和滑移共同进行,细化原始晶粒组织演变。     

Microstructure and Wear Performance of ECAP Processed Cast Al–Zn–Mg Alloys

In the present investigation, wear performance of equal channel angular pressing (ECAP) processed cast Al–Zn–Mg alloys under dry sliding wear conditions was studied against a steel disc. Initially, Al–Zn–Mg alloys (with 5, 10, 15% zinc and 2% magnesium) were ECAP processed. After ECAP, grain size was reduced and enhancement in the hardness was observed. Wear resistance of the alloys increased after ECAP processing. Wear resistance of the alloys also increased when the quantity of the zinc was increased in the alloys. But, wear resistance of all three alloys decreased with increase in the load and the sliding speed. Coefficient of friction of the alloys decreased after ECAP processing. Coefficient of friction of the alloys also decreased when the quantity of the zinc was increased in the alloys. Coefficient of friction of all three alloys increased with increase in the load and the sliding speed. Irrespective of the alloy composition and applied load, worn surfaces of the cast and homogenized samples were composed of plastic deformation, scratches and micro-ploughing. On the other hand, in ECAP processed samples, morphology of the worn surfaces depended on the applied load. Abrasive wear is the main wear mechanism perceived in cast and homogenized samples at all loads. While in ECAP processed samples, the wear mechanism shifted from adhesive and oxidation wear to abrasive wear with increase in the load. Formation of oxide layers on the surface of the sample increased with increase in the ECAP passes. In ECAP processed samples, transfer of iron content from the disc to the sample surface was identified.     

ZK60合金多道次ECAP晶粒组织模拟和实验分析

采用刚粘塑性有限元软件对ZK60合金四道次等通道转角挤压(ECAP)过程进行数值模拟。对一至四道次ECAP试样进行晶粒组织模拟,观察晶粒细化程度的分布和变化规律。通过多道次ECAP实验,利用金相显微观察试样头部和尾部的晶粒尺寸的变化以及动态再结晶形成机理。对比有限元数值模拟与实验组织分析结果,探索利用有限元模拟与实验分析相结合的方法,研究镁合金ECAP成形过程的晶粒组织变化规律。     

Structural transformations during heating of a Zr-2.5% Nb alloy subjected to equal-channel angular pressing

The structure of a Zr-2.5% Nb alloy after equal-channel angular pressing (ECAP) at 690–700 K and annealing in the temperature range 670–1070 K is investigated. The structure of the Zr-2.5% Nb alloy deformed by ECAP is an irregular grain-subgrain oriented structure with an enhanced dislocation density, a cross-section of 30–150 nm of oriented structural elements, and an equiaxed-grain (subgrain) size of 50–200 nm. Heating after ECAP in the temperature range 720–770 K for 3–5 h is proposed for the formation of an ultrafine-grained equilibrium structure in the ECAP deformed Zr-2.5% Nb alloy. Heating of the Zr-2.5% Nb alloy after ECAP at 723 K for 5 h leads to the formation of a predominantly equiaxial submicrocrystalline structure with a grain size of 150–500 nm. Equal-channel angular pressing of the Zr-2.5% Nb alloy increases the yield strength to 622 MPa, which is higher than that in the as-delivered undeformed state by a factor of 1.6. In this case, the relative elongation decreases. Heating of the ECAP deformed Zr-2.5% Nb alloy at 723 K for 5 h decreases the yield strength to 504 MPa, but the relative elongation increases to 14%.     

A thousandfold creep strengthening by Ca addition in die-cast AM50 magnesium alloy

The effect of calcium addition on the microstructure and creep strength of the die-cast AM50 magnesium alloy was investigated. The α-Mg grains with the diameter of 4.9 μm are surrounded by the eutectic phases for the AM50-1.72 mass pct Ca alloy, while the β(Mg₁₇Al₁₂) particles are located mainly on the grain boundaries of the α grains for the AM50 alloy. The minimum creep rates of the AM50-1.72 mass pct Ca alloy are three orders of magnitude lower than those of the AM50 alloy at 423 K typically below 120 MPa. The thousandfold creep strengthening by the Ca addition is ascribed to the thermally stable eutectic phases appearing in the AM50-1.72 mass pct Ca alloy, which is expected to yield effective grain boundary strengthening or to resist the plastic flow of the α-Mg grains.     

Corrosion and mechanical properties of AM50 magnesium alloy after being modified by 1 wt.% rare earth element gadolinium

In order to improve the corrosion and mechanical properties of AM50 magnesium alloy, 1 wt.% Gd was used to modify the AM50 magnesium alloy. The microstructure, corrosion and mechanical properties were evaluated by X-ray diffraction(XRD), scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), electrochemical and mechanical stretch methods. The results indicated that β-Mg17Al12 phase decreased and Al2Gd3 and Al0.4GdMn1.6 phase existed after Gd addition. Because of the Gd addition, the grain of AM50 magnesium alloy was refined significantly, which improved the tensile strength of AM50 magnesium alloy. The decreasing of β phase improved the corrosion resistance of the magnesium alloy. The fracture mechanism of the Gd modified AM50 magnesium alloy was quasi-cleavage fracture. The corrosion residual strength(CRS) of AM50 magnesium alloy was improved after 1 wt.% Gd addition.     

Improving corrosion resistance of RE-containing magnesium alloy ZE41A through ECAP

Significant grain refinement was achieved in rare earth (RE) containing aeronautic magnesium alloy ZE41A through equal-chan-nel angular pressing (ECAP) using rotary die at 603 K. Influence of ECAP pass number on its microstructure change and corrosion behavior was investigated by optical microscope (OM)/scanning electron microscope (SEM) observation and potentiostatic polarization tests in aque-otis solution of NaCl, respectively. The results showed that ultrafine equiaxial grains (about 2.5 μm) were obtained over 16 passes due to plastic-induced grain refinement accommodated by dynamic recrystallization. The lower corrosion current density and nobler corrosion po-tential correlated with large number of pressing passes were attributed to the low tendency toward localized corrosion with broken secondary phase after homogenization on ultrafine-grained Mg matrix. The multi-pass ECAP method made the ZE41A aeronautic magnesium alloy more attractive since severe plastic deformation may significandy improve its corrosion resistance besides superior mechanical properties.     

Effect of Microstructure and Mechanical Properties of Al–Mg Alloy Processed by ECAP at Room Temperature and Cryo Temperature

This research primarily focuses on improving the strength of Al 5083 alloy by both the ECAP and Cryo ECAP methodology. Equal Channel Angular Pressing (ECAP) is one of the best technologies that enable the direct transformation of conventional macro grained metals into sub-micron, ultra-fine and nano grained materials. Fine grain size increases the strength and the fracture toughness of the material and provides the potential for super plastic deformation at moderate temperatures and at high strain rates. The microstructure evolution in Al 5083, subjected to Room Temperature ECAP and Cryo ECAP were analysed. ECAP was carried out using an optimized die with Channel angle ‘?’ = 90°and corner angle ‘Ψ’ = 20° through processing route A and C up to four passes. The results were thoroughly studied using TEM, SEM, and optical microscopic images. Initially the annealed sample had the grain size of 80 µm with the equi-axed grains. In Room Temperature, the hardness values and the mechanical strength were found to be increased from 88 to 410 HV and 306 to 453 MPa after four passes in route A and in route C the strength increased from 390 to 416 MPa after four ECAP passes. Moreover, in Cryo Condition, the sample was processed up to four ECAP passes at route A and route C. The hardness of 153 HV was obtained after four passes in route C and 164 HV obtained after four passes on route A. Additionally, fracture behaviour using SEM, grain size using TEM and crystallite size by X-ray diffraction studies were analyzed. It was observed that the Cryo ECAP showed marginal improvements in mechanical properties relative to the RT ECAP in case of Al 5083.