Effect of process variables on tensile properties of ingot processed versus strip cast iron aluminides

Abstract

The effects of cold rolling and subsequent heat treatment are reported for ingot cast-hot rolled and strip cast iron aluminides (23–29 at.-%Al). Partially recrystallised microstructures obtained by hot rolling at 800°C gave higher strength and elongation to fracture than hot rolling at 1000° C. Elongation increased and proof strength decreased in proceeding from DO₃ to mixed B2 + DO₃ and to B2 order as a result of heat treatment following cold rolling. Variability in the properties of strip cast material was associated with casting defects such as laps, but the best properties were comparable with those of ingot processed material. The detrimental effects of tensile specimen preparation by spark erosion are discussed.     

多级均匀化处理对Al-Cu-Li-Sc-Zr合金微观组织与性能的影响EI北大核心CSCD

通过DSC测定Al-Cu-Li-Sc-Zr合金中Al_(3)(Sc,Zr)弥散相的析出温度,为确定Al_(3)(Sc,Zr)弥散相粒子析出的保温温度与保温时间,制定四种三级均匀化制度。随后将四种均匀化样品经过热轧、固溶、时效等处理后进行室温拉伸对比其力学性能,并通过样品的时效硬化曲线计算表观激活能,采用SEM与EDS分析均匀化后样品的第二相形貌与成分,EBSD表征固溶后样品的晶粒取向特征。结果表明:多级均匀化处理过程中第二阶段温度为460℃的均匀化制度相比于410℃的均匀化制度更利于Al_(3)(Sc,Zr)弥散相粒子的析出,在细化晶粒组织、抑制再结晶的同时,也促进后续时效处理过程中含Li强化相的析出,通过晶界强化、织构成分以及析出相的复合作用提升合金力学性能。另外,由于Al_(3)(Sc,Zr)弥散相粒子的析出,热变形退火后合金中大量亚晶微观组织得以保留,合金在室温拉伸过程中变形均匀,伸长率提高。     

Effect of chromium content on electrical resistivity and tensile properties of Ti–Fe–Cr alloys

Abstract

The effects of substituting chromium for iron and the use of low cost ferrochromium alloys in the production of β-Ti–Fe–Cr alloys have been studied with respect to phase constitution, stability, and mechanical properties, in solution treated and quenched states using resistivity, hardness measurement, X-ray diffraction, and tensile testing. Resistivity at room and liquid nitrogen temperatures, and hardness decreased while the ratio of resistivity at liquid nitrogen temperature to that at room temperature increased with increases in chromium content. Alloys of Ti–Fe–Cr, with almost the same electron per atom value, with higher chromium content have smaller volume fractions of athermal omega than alloys with higher iron content. There is less solution hardening in the former alloys than in the latter alloys. Tensile strength decreased with increases in chromium content, while elongation and reduction in area significantly increased. The balance between tensile strength and ductility (elongation and reduction in area) improved in the alloys with added chromium as a substitute for iron. Therefore, no negative influences of ferrochromium alloying on mechanical properties was observed in this study.     

轧制复合三层铝合金板变形规律及力学性能的研究

采用"热轧+中间退火+冷轧+轧后退火"法复合轧制AA1100/AA7075/AA1100三层铝合金板。利用金相、SEM-EDS观察微观组织变化及界面元素扩散,由显微硬度和拉伸试验测定复合板力学性能。结果表明,AA7075层组织呈拉伸纤维状沿轧向分布;热轧包覆率不变,中间退火后包覆率随冷轧应变的增加先减小后几乎不变;结合界面处存在Mg、Zn元素扩散。轧后退火使复合板强度降低、塑性增加,硬度沿厚度方向呈现梯度变化规律。     

Effect of extrusion parameters on properties of rapidly solidified Al–Mg powder alloys

Abstract

Three rapidly solidified Al–Mg powder alloys have been consolidated by means of cold compaction followed by hot extrusion. The extrusion conditions of temperature, reduction ratio, and ram speed were varied, and it was observed that the mechanical properties of the extrudates were strongly process related. Relationships between properties and the temperature compensated strain rates during extrusion have been established. These alloys have strength/density properties superior to the strongest conventional ingot cast alloys. Good fracture toughness has been recorded in the Al–7 Mg alloy and all three alloys possess good resistance to stress corrosion cracking.

MST/498     

冷轧对Al_(10)Cu_(25)Co_(20)Fe_(20)Ni_(25)高熵合金组织结构及力学性能的影响

对铸态Al10Cu25Co20Fe20Ni25高熵合金进行冷轧处理后进行室温拉伸测试,并利用X射线衍射仪(XRD)和扫描电镜(SEM)分别对其相结构、微观组织形貌及拉伸断口进行分析。结果表明:经冷轧工艺处理后,Al10Cu25Co20Fe20Ni25高熵合金硬度最大为285HV,较轧制前提高了51.6%;在变形量为40%时,抗拉强度达到最大值,为638MPa,是铸态合金的2.7倍。拉伸断口分析表明,铸态合金的断裂模式为树枝晶沿晶断裂和韧窝型延性断裂,而冷轧态合金主要为韧窝型延性断裂模式。     

Strain hardening and orientation hardening/softening in cold rolled AA 5052 aluminum alloy

The tensile properties of cold rolled sheets were measured for the hot band and annealed hot band of AA 5052 aluminum alloy. The variation in yield strength with rolling true strain was used to represent the hardening rate of cold rolled sheets. The Taylor factor (M?) of cold rolled sheets in tension along the rolling direction was calculated based on the measured orientation distribution functions. The strain hardening and orientation hardening/softening produced by cold deformation were analyzed. The results show that the contribution to the hardening rate of cold rolled sheets comes largely from the deformed microstructure and partly from the texture change. For the annealed hot band the orientation softening occurs at strains below 0.5, while the orientation hardening occurs at strains over 0.5. For the hot band the dM?/dε value is always positive, indicating that orientation softening does not occur.     

Texture development in high strength aluminium alloys

Abstract

Texture development during the thermomechanical processing of high strength aluminium alloys is reviewed. The alloys dealt with include both conventional heat treatable alloys, and unconventional materials such as rapidly quenched alloys and metal-matrix composites. The processing routes considered include hot and cold rolling, extrusion, forging, recrystallisation, and superplastic deformation. The information is presented as (111) pole figures and orientation distribution functions, in order to illustrate the much greater degree of detailed information that can be extracted from the latter method of analysis. The implications of texture development are considered by examining the effects that texture can have on tensile property anisotropy and fatigue and fracture behaviour.

MST/1292     

Microstructure and Mechanical Properties of Al25 − xCr25 + 0.5xFe25Ni25 + 0.5x (x = 19, 17, 15 at%) Multi‐Component Alloys

A series of Al_{25 ? x}Cr_{25 + 0.5x}Fe₂₅Ni_{25 + 0.5x} (x = 19, 17, 15 at%) multi‐component alloys are prepared by arc‐melting and rapid solidification of copper molds. The technique of thermal‐mechanical processing is further applied to the master alloys to improve their mechanical properties. These alloys consist of face‐centered cubic (FCC) and body‐centered cubic (BCC) structure. The volume fraction of the BCC phase increases as Al content increase and Cr and Ni contents decrease, accompanied with a microstructural evolution from dendritic structure to lamella‐like structure. Due to the increase of volume fraction of BCC phase, the master alloys exhibit an increased strength and a declined ductility as Al content increases. The rapid solidified alloys have more BCC phase compared with the master alloys, which enhances the strength and decreases the ductility. After homogenization, hot‐rolling, and annealing at 1000 °C, the Al₈Cr_33.5Fe₂₅Ni_33.5 alloy displays excellent combination of strength (yield strength is ～635 MPa and fracture strength is ～1155 MPa) and ductility (tension strain is ～11%).

     

Microstructure and mechanical properties of hot rolled TiNbSn alloys

Titanium alloys with lower elastic modulus and free from toxic elements such as Al and V have been studied for biomedical matters. Ti–Nb–Sn alloys showed up as presenting great potential for the aforementioned purpose. The current study got Ti–35Nb-XSn alloys (x = 2.5; 5.0; 7.5) by applying the following techniques: arc melting, homogenizing and cooling in furnace, homogenizing and water quenched, hot rolling and water quenched. According to each step of the study, the microstructures were featured by means of optical microscopy, by applying a scanning electron microscopy (SEM) analysis as well as X-ray diffraction. The mechanical properties were gotten by means of: Vickers microhardness, tensile and ultrasonic tests. Their ratio between tensile strength and elastic modulus as well as the ductility were compared to other biomedical alloys already available in the literature. The mechanical behavior of the Ti–Nb alloys directly depends on the Sn rates that constitutes the phases as well as on the thermomechanical background to which the alloy was submitted to. The hot rolled Ti–35Nb–2.5Sn alloy showed high ratio between strength and elastic modulus as well as high ductility, just as high as those of some cold rolled Ti alloys.     

Improvement in fatigue characteristics of newly developed beta type titanium alloy for biomedical applications by thermo-mechanical treatments

Tensile and plain fatigue properties of β type titanium alloy, Ti–29Nb–13Ta–4.6Zr, which underwent various thermo-mechanical treatments, were investigated in order to judge its potential for biomedical applications.Microstructures of Ti–29Nb–13Ta–4.6Zr (TNTZ) aged directly at 723 K for 259.2 ks after cold rolling and TNTZ aged at 723 K for 259.2 ks after solution treatment are composed of precipitated α phase in β phase. While, microstructures of TNTZ aged directly at 598 K and 673 K for 259.2 ks after cold rolling and aged at 598 K and 673 K for 259.2 ks after solution treatment are composed of precipitated ω phase, and precipitated α and ω phases in β phase, respectively. Tensile strength of aged TNTZ after solution treatment and aged TNTZ after cold rolling decreases with increasing aging temperature although the elongation shows the reverse trend. TNTZ composed of ω phase or ω and α phases in β phase shows the tensile strength of around 1000 MPa or more. Young's moduli of aged TNTZ after solution treatment and aged TNTZ after cold rolling decrease with increasing aging temperature. TNTZ conducted with solution treatment has the lowest Young's modulus of around 60 GPa. Fatigue strengths of aged TNTZ after solution treatment and aged TNTZ after cold rolling increase with increasing aging temperature. In particular, TNTZ aged directly at 723 K after cold rolling shows the greatest fatigue strength in both low cycle fatigue life and high cycle fatigue life regions, and the fatigue limit, which is around 770 MPa, is nearly equal to that of hot-rolled Ti–6Al–4V ELI conducted with aging, which is one of representative α + β type titanium alloys for biomedical applications.     

Hot workability of an Al-Mg alloy AA5182 with 1 wt% Cu

A comparative study of the hot workability of two aluminium alloys, alloy AA5182 used for automotive applications and a variant modified with 1 wt% copper, has been carried out. Hot torsion tests were performed on both alloys subjected to two different heat treatments: a low temperature preheat to 450 °C and a high temperature preheat at 540 °C. The results from the torsion experiments are interpreted in terms of microstructural features. Both treatments produce the same strength, but the high temperature preheat leads to better ductility. This improvement is related to the homogenization of solute elements in the matrix; and, concerning AA5182 + Cu, also to the dissolution of a non-equilibrium Al-Mg-Cu ternary eutectic present in the as-cast microstructure. The precipitation of (Fe, Mn)Al₆ precipitates in the matrix of both alloys is induced by the high temperature heat treatment. Comparison of the results obtained by hot torsion shows that at low deformation rates AA5182 + Cu has better ductility than the classical alloy, but its ductility is lower at strain rates above 0.6–0.8 s^–1. The null ductility transition temperature is lower compared with that in the classical alloy, restricting the range of hot working temperatures. Inside this range the strength of both alloys is approximately the same, although the strain rate sensitivity coefficient is increased by copper additions. The experimental strength values follow the classical sinus-hyperbolic constitutive equation for hot working.     

Effect of tempering on nitrided and deformed austenitic stainless steel

Abstract

The effect of tempering on nitrided austenitic stainless steel AISI 316 has been studied. Nitrided specimens (with 0.4 wt-%N) were tempered for short times at temperatures up to 900°C and the results show a small effect on the microstructures and mechanical properties. The strength is consistent with a Hall–Petch relationship dependent on nitrogen content in solution. The effect of tempering has also been studied on cold and hot deformed nitrided specimens. In these cases, tempering had a range of different effects on the microstructures and mechanical properties. Specimens that are tempered before cold rolling showed a continuous decrease in strength as the tempering temperature increased, while specimens cold rolled and then tempered had a maximum strength at 550°C. Specimens with 0.4 wt-%N subjected to tempering followed by hot deformation also showed a maximum strength at similar tempering temperatures. The nature of these changes has been analysed and mechanisms have been proposed that relate microstructural effects and properties.     

Fabrication,microstructures, and tensile properties of magnesium alloy AZ91/SiCp composites produced by powder metallurgy

Abstract

The tensile properties and microstructural evolution of hot extruded AZ91 magnesium alloy with and without reinforcement of SiC particles have been investigated in terms of extrusion parameters, such as extrusion ratio and extrusion temperature. Also, the effect of SiC particles on the grain size of the matrix in the composites was evaluated using the Hall-Petch equation. The AZ91 magnesium alloy powders prepared by wet attrition milling from magnesium machined chips were hot pressed with and without SiC particles, hot extruded, and then solution treated. Microstructural observation revealed that both the composites and the magnesium alloy have fine equiaxed grains due to the dynamic recrystallisation during hot extrusion. The tensile strength of both materials increased with increasing extrusion ratio, and the strengths of the composites were higher than that of the magnesium alloy without reinforcement. It was found that the tensile strength of both the materials decreased after solution treatment, and the decrease in tensile strength of the composites was considerably smaller than that of the magnesium alloy. From analyses of the microstructures and the mechanical properties, combined with examination of the H all–Petch relationship, the refinement of the matrix was primarily responsible for the improvement in the yield strength of the composites. The grain growth of the matrix was inhibited by the introduction of the SiC particles.     

Effect of Mn-Bearing Dispersoids on Tensile Properties and Recrystallization Resistance of Al-3Mg-0.8Mn Rolled Alloy

Herein, the precipitation behavior of Mn-bearing dispersoids in Al-3Mg-0.8Mn (AA5454) alloy subjected to different heat treatments is investigated. The effects of Mn-bearing dispersoids on the tensile properties and recrystallization resistance of the abovementioned alloy during hot/cold rolling and postrolling annealing are evaluated. The results show that a low-temperature three-step heat treatment (275 °C/12 h + 375 °C/48 h + 425 °C/12 h) generates a higher number density of Mn-bearing dispersoids with finer sizes compared with the typical high-temperature heat treatment (430 °C/2 h + 480 °C/2 h + 525 °C/2 h), thus resulting in significantly improved tensile strengths of hot/cold-rolled sheets. After annealing at 300 °C, the yield strength (YS) of the alloy reached 196 MPa after hot rolling and 237 MPa after cold rolling, showing an improvement of 30%–32% over samples subjected to high-temperature heat treatment. In addition, the low-temperature heat treatment provides a higher recrystallization resistance after hot and cold rolling owing to the higher number density of Mn-bearing dispersoids and the lower fraction of dispersoid-free zones. The YS contributions of various strengthening components after hot and cold rolling are discussed based on constitutive models. The predicted yield strengths agree well with the experimental values.     

High-strength Mg95Y3Zn1Ni1 alloy with LPSO structure processed by hot rolling

Microstructures and mechanical properties of Mg₉₅Y₃Zn₁Ni₁ alloy containing long period stacking ordered (LPSO) phase processed by hot rolling were systematically investigated in the present work. The results showed that the as-cast alloy was mainly composed of α-Mg and network 18?R LPSO phase. The thermal stability of 18?R LPSO phase in the as-cast alloys decreased with the decrease of Ni content. After solution treatment at 773?K for 40?h, network 18?R phase at grain boundary dissolved, while fine lamellar phase identified as 14H LPSO precipitated in the interior of grains. When the solid-solution alloy was hot rolled at 723?K with six passes and thickness reduction of 62%, some LPSO phases broke down and kinking of varying degrees occurred in LPSO phase. Meanwhile, the as-rolled α-Mg and LPSO phase redistributed aligned along the rolling orientation. The alloy exhibited excellent mechanical properties: yield strength of 282?MPa, ultimate tensile strength of 383?MPa, and elongation to failure of 16% at ambient temperature along the rolling orientation. The remarkable improvement of strength was ascribed to the refined microstructure induced by the deformation kinking and the crush of LPSO phase.     

Effect of Al and C on structure and mechanical properties of Fe–Al–C alloys

Abstract

Effect of aluminium and carbon content on the microstructure and mechanical properties of Fe–Al–C alloys has been investigated. Alloys were prepared by combination of air induction melting with flux cover (AIMFC) and electroslag remelting (ESR). The ESR ingots were hot forged and hot rolled at 1373 K. As rolled alloys were examined using optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to understand the microstructure of these alloys. The ternary Fe–Al–C alloys containing 10·5 and 13 wt-%Al showed the presence of three phases: FeAl with disordered bcc structure, Fe₃Al with ordered DO₃ structure and Fe₃AlC_0·5 precipitates with L′1₂ structure. Addition of high concentration of carbon to these alloys resulted in excellent hot workability and superior tensile at room temperature as well as tensile and creep properties at 873 K. An increase in Al content from 9 to 13 wt-% in Fe–Al–C alloys containing the same levels of carbon has no significant influence on strength and creep properties at 873 K, however resulted in significant improvement in room temperature strength accompanied by a reduction in room temperature ductility.     

Effect of thermal ageing on microstructure,mechanical properties,and fracture behaviour of 50 % cold rolled duplex stainless steel (alloy 2507)

The paper deals with cold rolling and ageing on microstructure and mechanical properties of 2507 duplex stainless steel. Microstructure depicts acicular/Widmanstätten austenite and δ-ferrite with dissimilar volume fraction (∼0.55 for ferrite and ∼0.45 for austenite). Cold rolling and ageing at 950 °C, 1000 °C and 1050 °C result in equiaxed austenite for samples solution treated at 1040 °C and elongated at 1300 °C. By lowering ageing temperature from 1050 °C to 950 °C, structure becomes finer from ∼20 μm to <10 μm grain size. The sigma (σ) phase appears after ageing at 950 °C. Micro-hardness reveals maximum hardness for the hot rolled, solutionized (1040 °C) water quenched, and cold rolled (50 %) sample (380 HV_δF 100 and 430 HV_γ 100), whereas the tensile results reveal the hot rolled, solution treated (1300 °C, 1040 °C), cold rolled and aged at 950 °C samples show higher strength (yield strength=625 MPa, 567 MPa and ultimate tensile strength=892 MPa, 826 MPa) and lower ductility (23 %, 32 %) due to the σ-phase. The solution treated (1040 °C), cold rolled, aged at 1050 °C sample exhibits attractive strength and ductility combination (∼30 GPa %). Fractography supports the tensile results.     

Effects of thermo-mechanical processing and trace amount of carbon addition on tensile properties of Cu–2.5Fe–0.1P alloys

The effects of thermo-mechanical processing, including intermediate aging treatment and/or solution heat treatment, and a trace amount of carbon (C) addition were studied on tensile behavior of Cu–2.5Fe–0.1P alloys. In this study, Cu–2.5Fe–0.1P alloy sheets without and with a carbon content of 0.05 wt.% were cast and subsequently rolled and thermo-mechanically treated following various processing routes. The introduction of intermediate aging treatment between cold rolling improved the tensile strength of Cu–2.5Fe–0.1P alloys. Solution heat treatment prior to aging was proved to be detrimental on the tensile strength, probably due to recovery and recrystallization causing the complete loss of work hardening during previous cold rolling. The present study also suggested that two-step aging is more effective in improving the strength of Cu–2.5Fe–0.1P alloys than one-step aging. The effect of C addition on improving the tensile strength of Cu–2.5Fe–0.1P alloys was real but marginal, probably due to the limited solubility of C in Cu–2.5Fe matrix. The effects of intermediate heat treatments between cold-rolling processes on tensile properties of Cu–2.5Fe–0.1P specimens with and without C addition are discussed based on optical, scanning electron microscope (SEM) and transmission electron microscope (TEM) micrographs, and SEM fractographs.     

Effect of solution treatment temperature on tensile properties of AI-7Si-O.3Mg (wt-%) alloy

Abstract

The effect of solution treatment temperature on the tensile properties of an AI-7 Si-0.3Mg (wt-%) alloy has been studied using tensile and hardness testing, microprobe composition analysis, and differential scanning calorimetry. With a sufficiently long solution treatment time, an increase in solution treatment temperature from 500 to 560°C significantly increases the silicon content in the matrix, but has little effect on the magnesium content. This results in a slight increase in the peak aged yield strength, but a more significant increase in the peak aged ultimate tensile stress and hardness. The alloy ductility is independent of solution treatment temperature, but is clearly influenced by the degree of eutectic silicon particle spheroidisation and coarsening. Using a higher solution treatment temperature can shorten the solution treatment time required to achieve a given tensile elongation value.