Cryorolling Research Articles

Experimental evaluation of mechanical properties and fracture-fatigue simulation of cryo- and room-temperature-rolled zircaloy-2

In this study, the mechanical properties of mercury–quenched, cryorolled (CR) and room–temperature–rolled (RTR) zircaloy–2 have been examined by performing the tensile and hardness tests. The effect of cryorolling and room temperature rolling on the fracture properties has been evaluated by performing two–dimensional (2D) quasi–static crack growth simulations using finite element approach under plane stress condition. J–integral and internal energy of the mercury–quenched, CR and RTR zircalloy–2 are evaluated and compared with each other. The S–N curves for mercury–quenched, CR and RTR zircaloy–2 are obtained through finite element simulations. After performing the fracture and fatigue simulations, it is found that 85% cryorolled zircaloy–2 possesses better fracture and fatigue behaviour when compared with mercury–quenched and 85% RTR zircaloy–2.

Experimental investigations on microstructure and formability of cryorolled AA 5052 sheets

In this paper the effect of cryorolling on tensile and forming behaviour of aluminium alloy (AA) 5052 sheets has been investigated and compared with room temperature rolling of the same. These sheets were rolled up to 50% reduction in thickness at two different temperatures, namely, room and cryogenic temperatures, and compared. The combined forming and fracture limit diagram has been drawn and compared for AA 5052 alloy sheets of both rolling conditions. The formability results obtained for the room temperature rolled (RTR) and cryorolled (CR) conditions have been correlated with tensile properties. Cryorolled AA 5052 alloy with an elongated microstructure exhibited a very high percentage of necking strain during forming compared to the conventional forming limit diagram. This is due to the excessive cross-slip formed during deformation.

Effect of deformation temperature on mechanical properties of ultrafine grained Al–Mg alloys processed by rolling

Aluminum–Magnesium (Al 5083) alloy was subjected to cryorolling (CR) and cryorolling followed by warm rolling (WR) in order to investigate the changes in mechanical behavior and microstructure evolution in the present work. Al alloy specimens were first cryorolled up to 50% thickness reduction followed with warm rolling at 100°C, 145°C, 175°C and 200°C till to achieve total 90% thickness reduction. The final microstructure of all conditions were analyzed and compared through transmission electron microscopy (TEM), Electron back scattered diffraction (EBSD), and X-ray diffraction (XRD) techniques to investigate the effect of WR deformation temperatures on mechanical properties. The mechanical behavior of the processed samples were evaluated through hardness and tensile tests performed at room temperature. An increase in yield strength (522MPa), ultimate tensile strength (539MPa) and ductility (6.8%) was observed in WR specimens at 175°C, hardness also increases to (146HV) as compared to CR samples. These samples were annealed in temperature range from 150°C to 300°C to investigate their thermal stability. The CR samples exhibited severely deformed structure with high dislocation density network while cryorolled followed by warm rolled (WR) samples has shown formation of ultrafine grains associated with dynamic recovery. At elevated temperature of 200°C, WR samples showed decrease in strength accompanied with increase in elongation due to dominant dynamic recovery effect led to reduction in dislocation density.

Effect of aging and cryo rolling on microstructural characterization and mechanical properties of precipitation hardenable 6063Al alloy

The microstructural characterization and mechanical properties of precipitation hardenable 6063 Al alloy subjected to cryo rolling (CR) are reported in this present work. The cryo rolled sheets and solutionized sheets were subjected to aged to induce precipitation. Microstructural and mechanical properties evaluation were investigated by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), conventional test and portable ball indentation technique test. The effect of two types of ageing treatment (peak aging and over aging) on solutionized and cryo rolled samples were investigated in this work. Ultrafine grained microstructure with improved strength was obtained after solutionized and cryo rolling. The mechanical properties of before and after cryo rolling at different ageing treatment were compared.

Effects of warm rolling and ageing after cryogenic rolling on mechanical properties and microstructure of Al 6061 alloy

The mechanical properties and microstructural evolution of Al 6061 alloy subjected to cryorolling and warm rolling have been investigated in the present work. The Al 6061 alloy was subjected to thickness reduction of 70% by cryorolling followed by thickness reduction of 20% by warm rolling. The cryorolled+warmrolled (CR+WR) samples were characterized by Electron back scattered diffraction (EBSD) technique, Differential scanning calorimetry (DSC), X-Ray diffraction (XRD) analysis and Transmission electron microscopy (TEM) technique to substantiate the role of deformation strain and temperature on their microstructural features and compared with cryorolled (CR) samples. The CR+WR samples showed a significant improvement in tensile strength (376MPa) and partial improvement in ductility (5%) as measured from tensile testing. It is mainly due to the combined effect of partial grain refinement, solid solution strengthening, dislocation hardening, dynamic recovery, and dynamic ageing during cryorolling and warm rolling. The effect of ageing on CR+WR samples was investigated and the optimum ageing condition was found to be 45h at 125°C, which gives improved tensile strength of (406MPa) and good tensile ductility (10%). The tensile strength of cryorolled+warm rolled+peak aged (CR+WR+PA) sample (406MPa) was found to be 11.2% more than that of cryorolled+peak aged (CR+PA) sample (365MPa). During peak ageing treatment, the strength has been retained by pinning of dislocations through nanosized precipitates generated during warm rolling and it has been improved further by precipitation of the remnant dissolved second phase in the matrix. However, the observed ductility of CR+PA sample was 13% more than CR+WR+PA sample due to low dislocation density after ageing.

Microstructure Evolution and Mechanical Behaviour of Severe Plastically Deformed Cu

The present study reports the microstructure evolution and mechanical behaviour of severe plastically deformed pure Cu under cryogenic conditions. The samples were severely deformed by cryo rolling upto 50%, 75% and 95% deformation. Microstructure evolution of cryo rolled samples has been characterized by using optical, TEM and EBSD technique. The rolled samples were heat treated at various temperatures so as to control the recrystallization in the severely deformed samples. The effect of recrystallization on the mechanical behaviour was investigated in detail by tensile testing. The EBSD analysis performed on 95% rolled + heat treated samples showed that partial recystallized microstructure demonstrate an optimum combination of strength and ductility in cryo rolled Cu.

Evolution of nanostructure in α-brass upon cryorolling

The microstructure of α-brass has been investigated at 98% and 200% of cryorolling (CR). Severe cryorolling introduces microscopic shear bands, forms primary and secondary twins, and the twin density increases with increase of plastic strain. Even though the average hardness values in CR200 (197 Hv) does not increase significantly than that of CR98 (189 Hv), but the hardness distribution become narrow in CR200 due to the narrow size distribution and refinement of twin lamellar spacing. The microscopic mechanism on the evolution of homogeneous nanostructure in α-brass has been reported.

Fatigue behaviour and crack growth rate of cryorolled Al 7075 alloy

The effects of cryorolling (CR) on high cycle fatigue (HCF) and fatigue crack growth rate behaviour of Al 7075 alloy have been investigated in the present work. The Al 7075 alloy was rolled for different thickness reductions (40% and 70%) at cryogenic (liquid nitrogen) temperature and its tensile strength, fatigue life, and fatigue crack growth mechanism were studied by using tensile testing, constant amplitude stress controlled fatigue testing, and fatigue crack growth rate testing using load shedding (decreasing ΔK) technique. The microstructural characterization of the alloy was carried out by using Field emission scanning electron microscopy (FESEM). The cryorolled Al alloy after 70% thickness reduction exhibits ultrafine grain (ufg) structure as observed from its FESEM micrographs. The cryorolled Al 7075 alloys showed improved mechanical properties (Y.S, U.T.S, Impact energy and Fracture toughness are 430 Mpa, 530 Mpa, 21 J, 24 Mpa m1/2 for 40CR alloy) as compared to the bulk 7075 Al alloy. It is due to suppression of dynamic recovery and accumulation of higher dislocations density in the cryorolled Al alloys. The cryorolled Al alloy investigated under HCF regime of intermediate to low plastic strain amplitudes has shown the significant enhancement in fatigue strength as compared to the coarse grained (CG) bulk alloy due to effective grain refinement. Fatigue crack growth (FCGR) resistance of the ufg Al alloy has been found be higher, especially at higher values of applied stress intensity factor ΔK The reasons behind such crack growth retardation is due to diffused crack branching mechanism, interaction between a propagating crack and the increased amount of grain boundaries (GB), and steps developed on the crack plane during crack-precipitate interaction at the GB due to ultrafine grain formation.

Effect of Annealing on Thermal Stability, Precipitate Evolution, and Mechanical Properties of Cryorolled Al 7075 Alloy

The effect of annealing on microstructural stability, precipitate evolution, and mechanical properties of cryorolled (CR) Al 7075 alloy was investigated in the present work employing hardness measurements, tensile test, X-ray diffraction (XRD), differential scanning calorimetry (DSC), electron backscattered diffraction (EBSD), and transmission electron microscopy (TEM). The solution-treated bulk Al 7075 alloy was subjected to cryorolling to produce fine grain structures and, subsequently, annealing treatment to investigate its thermal stability. The recrystallization of CR Al 7075 alloys started at an annealing temperature of 423 K (150 °C) and completed at an annealing temperature of 523 K (250 °C). The CR Al 7075 alloys with ultrafine-grained microstructure are thermally stable up to 623 K (350 °C). Within the range of 523 K to 623 K (250 °C to 350 °C), the size of small η phase particles and AlZr3 dispersoids lies within 300 nm. These small precipitate particles pin the grain boundaries due to the Zener pinning effect, which suppresses grain growth. The hardness and tensile strength of the CR Al 7075 alloys was reduced during the annealing treatment from 423 K to 523 K (150 °C to 250 °C) and subsequently it remains constant.

Improvement of Fracture Toughness (K<sub>1c</sub>) of 7075 Al Alloy by Cryorolling Process

The effects of cryorolling (Rolling at liquid nitrogen temperature) and optimum heat treatment (short annealing + ageing) on fracture toughness of 7075 Al alloy are reported in the present work. The Al 7075 alloy was rolled for different thickness reductions (40% and 70%) at cryogenic temperature and its mechanical, fracture toughness properties were studied. The microstructural characterization of the alloy was carried out by using Optical microscopy and Field emission scanning electron microscopy (FESEM). The cryo-rolled (CR) Al alloy after 70% thickness reduction exhibits ultrafine grain structure as observed from its FESEM micrographs. It is observed that the yield strength and fracture toughness of the CR material with 70% thickness reduction have increased by 108% and 73% respectively, compared to the starting material. The CR 7075 Al alloy shows improved fracture toughness and tensile strength due to high dislocation density, grain refinement, and ultrafine-grain (UFG) formation by multiple cryorolling passes. The CR samples were subjected to short annealing for 5 min at 190 0C, 170 0C and 150 0C followed by ageing at 160 0C, 140 0C and 120 0C for both 40% and 70% reduced samples. The combined effect of short annealing and ageing improves the fracture toughness, tensile strength, and ductility of cryorolled samples, which is due to precipitation hardening and subgrain coarsening mechanism respectively. The scanning electron microscopy (SEM) fractographs of the Al 7075 alloy samples reveals that starting bulk Al alloy specimens is fractured in a total ductile manner, consisting of well-developed dimples over the entire surface and dimple size got decreased continuously for cryorolled specimens at different percentage of thickness reduction (40% and 70%) as observed in the present work.

Tensile Behavior of Ultrafine-Grained Al-4Zn-2Mg Alloy Produced by Cryorolling

An Al-4Zn-2Mg alloy was subjected to cryorolling (CR) followed by short annealing. An average grain size of ~100 nm was achieved. Cryorolled samples showed large reduction in grain size due to suppression of dynamic recovery and absence of annihilation of dislocations, as compared to room temperature rolled samples. Further, the ultrafine-grained (UFG) Al-4Zn-2Mg alloy when subjected to natural aging showed an improved strength of ~413 MPa with ductility of ~25%, as compared to ~360 MPa and 22% ductility in peak aged condition of coarse-grained alloy. However, UFG alloy in peak aging condition, exhibited a relatively strength (~375 MPa) and 24% ductility combinations than the natural aging condition. The latter is attributed to dynamic precipitation and stored energy. In the present study, it is demonstrated that simultaneous improvement in strength as well as ductility can be achieved for the Al-4Zn-2Mg alloy through CR and controlled heat treatment combinations.

Influence of solutes and second phase particles on work hardening behavior of Al 6063 alloy processed by cryorolling

The effect of solutes, coarse and fine precipitates on work hardening rate and microstructure refinement of cryorolled Al 6063 alloy at different strains was investigated by employing hardness measurements, tensile tests, DSC, XRD, EBSD and TEM characterizations in the present work. The presence of solute in solid solution exhibits a stronger effect on the work hardening of the materials during cryo rolling than the presence of non-coherent and coherent second phase particles. The fine precipitates are sheared and dissolved at a cryorolling strain of 2.3, while the coarse precipitates remain unaffected. The work hardening rate of solutionized material is not saturated even at a cryorolling strain of 2.3, while it is saturated at this strain for the precipitated material. The severe strain induced during plastic deformation of Al 6063 alloy produces ultrafine microstructures with improved strength and hardness. The ageing treatment of the solutionized material after cryorolling at a strain of 2.3 has improved its strength and ductility significantly as compared to precipitated materials due to the precipitation hardening and grain coarsening mechanisms, respectively.

Effect of grain size on corrosion of high purity aluminium

A complete understanding of how grain refinement, grain size, and processing affect the corrosion resistance of different alloys has not yet been fully developed. Determining a definitive ‘grain size–corrosion resistance’ relationship, if one exists, is inherently complex as the processing needed to achieve grain refinement also imparts other changes to the microstructure (such as texture, internal stress, and impurity segregation). This work evaluates how variation in grain size and processing impact the corrosion resistance of high purity aluminium. Aluminium samples with a range of grain sizes, from ∼100 μm to ∼2000 μm, were produced using different processing routes, including cold rolling, cryo rolling, equal channel angular pressing, and surface mechanical attrition treatment. Evaluation of all the samples studied revealed a tendency for corrosion rate to decrease as grain size decreases. This suggests that a Hall–Petch type relationship may exist for corrosion rate and grain size. This phenomenon, discussed in the context of grain refinement and processing, reveals several interesting and fundamental relationships.

A Study on the Combined Treatment of Cryorolling, Short-Annealing, and Aging for the Development of Ultrafine-Grained Al 6063 Alloy with Enhanced Strength and Ductility

High-strength ultrafine-grained (UFG) metals and alloys often show a reduced tensile ductility when compared with their coarse-grained counterparts. The earlier attempts in trying to improve their ductility usually have led to sacrificing its strength. Optimized process conditions are proposed to achieve both high strength and high ductility in the Al 6063 alloy in the current work. It involves solution treatment of the Al 6063 alloy to dissolve the second-phase particles, cryorolling (CR) to produce a high density of dislocations, short annealing (SA) treatment to recrystallize partially the microstructure without affecting the age-hardening effect, and finally aging treatment to generate highly dispersed nano precipitates. The solution treatment prior to CR combined with post-CR SA at 428 K (155 °C) for 5 minutes followed by aging treatment at 398 K (125 °C) for 12 hours are the optimum processing conditions to obtain the UFG microstructure with improved tensile strength (286 MPa) and good tensile ductility (14 pct) in the Al 6063 alloy. It is observed that the accumulation of dislocations and the formation of nanosized precipitates are responsible for improving the strength, whereas both a low dislocation density and a high density of nanosized precipitates contribute to the improvement in ductility of the CR Al 6063 alloy subjected to an optimized treatment of short annealing and aging.

Effect of annealing and aging treatment on mechanical properties of ultrafine grained Al 6061 alloy

A comparative study of aging and a combined treatment of short annealing and aging on mechanical properties and microstructure of cryorolled (CR) Al 6061 alloy is investigated in the present work by using tensile tests, hardness tests, electron backscattered diffraction and transmission electron microscope. The pre-CR solid solution treatment combined with post-CR short annealing (200°C, 5 min) followed by aging treatment (100°C, 57 h) of the Al 6061 alloy showed an improved ductility and well defined ultrafine grain structure as compared to the samples subjected to pre-CR solid solution treatment followed by post-CR aging treatment (100°C, 60 h).

Improving the mechanical properties of 2024 Al alloy by cryo rolling

Ultra fine grained (1 micron size) materials usually exhibit more strength. Most of the approaches to refine microstructure lead to decrease in ductility. Cryo rolling is a successful technique; samples are rolled at cryogenic temperature, to improve strength of an age hardenable alloy with minimum loss in ductility. Aging after cryo rolling ensures good strength and ductility due to bimodal structure and nano sized precipitation of S’ phase. Al 2024 alloy are partially solutionised to retain some T-phase particles, which are very effective in accumulating dislocations during cryo-rolling, and in turn promoted the precipitation of Al2CuMg precipitates with a size of 10–40 nm. The nano sized Al2CuMg precipitates and bimodal grain structure leads to simultaneous increases in strength and ductility.

Development of high strength Al–Mg–Si AA6061 alloy through cold rolling and ageing

Ultrafine grained (ufg) and nanocrystalline (nc) materials are widely researched due to significant improvements in yield and fracture strength. However, achieving a reasonable ductility in these materials is still a challenge. Recent results have shown that the combination of high strength and ductility could be achieved in precipitation hardening alloys through severe plastic deformation followed by annealing/ageing treatments. In the present work, the solutionised plates of an Al–Mg–Si alloy (modified AA6061 alloy) were subjected to severe cold rolling at room and liquid nitrogen temperatures to a true strain ∼1.6. The rolled sheets were aged to induce precipitation. The equilibrium second phase distribution for the above alloy was calculated using CALPHAD. The rolled and aged samples were analysed using differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM), hardness and tensile tests. The stored energy obtained from DSC measurements was found to be independent of the rolling temperature. The volume fraction of S {1 2 3} 〈6 3 4〉 orientation is predominant (∼40%) in both the rolling conditions. The strength and ductility were simultaneously improved following ageing of the cryorolled (CR) and room temperature rolled (RT) samples. Transmission electron microscopy analysis revealed dislocation cell structures in the CR and RT conditions. Analysis of second phases revealed fine spherical Mn rich precipitates (most likely Al 6Mn) following ageing.

SUPERPLASTIC INDENTATION CREEP OF FINE-GRAINED Sn-1% Bi ALLOY

Creep and superplasticity of the fine-grained Sn -1wt.% Bi alloy, processed by conventional rolling (CNR), cryorolling (CRR) and equal channel angular pressing (ECAP) routes, were investigated by indentation testing at room temperature (T > 0.6T m ). Based on the steady-state power law creep relationship, the stress exponents of 4.1, 2.8 and 2.5 were obtained for the CNR, CRR and ECAP routes, respectively. The corresponding strain rate sensitivity (SRS) indices of 0.24, 0.36 and 0.40, corresponding respectively to the grain sizes of 2.8, 2.1 and 1.2 μm, indicate that the materials processed by ECAP and CRR exhibit superplastic deformation behavior for which, grain boundary sliding is the possible creep mechanism.

Development of ultrafine grained Al–Mg–Si alloy with enhanced strength and ductility

Abstract The microstructure and mechanical properties of a precipitation hardenable Al–Mg–Si alloy subjected to cryorolling (CR), short annealing and ageing treatments are reported in this present work. The pre-cryorolled solid solution treatment combined with post-CR short annealing (155 °C for 5 min) and then ageing treatment (125 °C for 12 h) has been found to be the optimum processing condition to obtain the ultrafine grained microstructure with substantial improvement of tensile strength (286 MPa) and good tensile ductility (14%) in the Al–Mg–Si alloy. The significant improvement of the mechanical properties of the cryorolled and peak aged 6063 Al alloys have been observed as compared to its bulk alloys in the peak-aged condition (T6).

A study of shear fatigue crack mechanisms: Hu, Z. Ma, L. and Cao, S. Fatigue Fract. Eng. Mater. Struct. June 1992 15, (6), 563–573

The effects of cryorolling (CR) on high cycle fatigue (HCF) and fatigue crack growth rate behaviour of Al 7075 alloy have been investigated in the present work. The Al 7075 alloy was rolled for different thickness reductions (40% and 70%) at cryogenic (liquid nitrogen) temperature and its tensile strength, fatigue life, and fatigue crack growth mechanism were studied by using tensile testing, constant amplitude stress controlled fatigue testing, and fatigue crack growth rate testing using load shedding (decreasing ΔK) technique. The microstructural characterization of the alloy was carried out by using Field emission scanning electron microscopy (FESEM). The cryorolled Al alloy after 70% thickness reduction exhibits ultrafine grain (ufg) structure as observed from its FESEM micrographs. The cryorolled Al 7075 alloys showed improved mechanical properties (Y.S, U.T.S, Impact energy and Fracture toughness are 430 Mpa, 530 Mpa, 21 J, 24 Mpa m1/2 for 40CR alloy) as compared to the bulk 7075 Al alloy. It is due to suppression of dynamic recovery and accumulation of higher dislocations density in the cryorolled Al alloys. The cryorolled Al alloy investigated under HCF regime of intermediate to low plastic strain amplitudes has shown the significant enhancement in fatigue strength as compared to the coarse grained (CG) bulk alloy due to effective grain refinement. Fatigue crack growth (FCGR) resistance of the ufg Al alloy has been found be higher, especially at higher values of applied stress intensity factor ΔK The reasons behind such crack growth retardation is due to diffused crack branching mechanism, interaction between a propagating crack and the increased amount of grain boundaries (GB), and steps developed on the crack plane during crack-precipitate interaction at the GB due to ultrafine grain formation.