Cryorolled Samples Research Articles

Microstructure and mechanical properties of cryorolled Al–6Zn–3Mg–2Cu–0.5Sc alloy

Abstract Al–6Zn–3Mg–2Cu–0.5Sc alloy with 85% rolling reduction from the original thickness at room and cryogenic temperatures leads to high tensile strength and higher dislocation density for the cryorolled (CR) (−80 °C) sample. Microstructural investigation and their properties on mechanical behaviour of Al–6Zn–3Mg–2Cu–0.5Sc alloy were noted in detail during rolling as-cast, room temperature rolling (RTR) and cryorolling (−80 °C) conditions. The CR (−80 °C) sample revealed greater work hardening value than the as-cast alloy, due to the effect of CR and the presence of Al3CuMg precipitates. The Hierarchical Grain Size Distribution (HGSD) reported in cryorolled samples via Electron Back Scattered Diffraction (EBSD) studies, and it leads to a high strength of 537 MPa and 17% ductility in CR (−80 °C) samples. Transmission electron microscope (TEM) studies revealed that the high dense dislocations and nano sized intermetallic compounds are equally distributed alongside the matrix in the CR (−80 °C) among the rolled samples. Al–6Zn–3Mg–2Cu–0.5Sc alloy showed improved mechanical properties during various rolling conditions.

High thermal stability and excellent mechanical properties of ultrafine-grained high-purity copper sheets subjected to asymmetric cryorolling

For most ultrafine-grained metals, the yield stress increases with finer grain size, but the thermal stability reduces. In this study, high purity (99.999%) copper sheets were fabricated using three different techniques: symmetric rolling, asymmetric rolling and asymmetric cryorolling. In each case, the sheets were annealed at a temperature ranging from 50 °C to 125 °C for 1 h. Their mechanical properties were tensile-tested using dog-bone samples, and their microstructure evolution was examined using electron backscatter diffraction and transmission electron microscopy. The results show that the asymmetric-cryorolled copper sheets have finer grains and higher tensile strength, and better thermal stability compared with the copper sheets subjected to symmetric rolling and asymmetric rolling and low-temperature annealing. The finer grains in copper sheets subjected to asymmetric cryorolling result from the additional shear strain and severe plastic deformation at low temperature. The improvement in the thermal stability may be due mainly to the vacancy clusters, small laminate thickness, low-angle grain boundary and high misorientation angle in asymmetric cryorolled samples. These results can provide significant insights into the development of ultrafine-grained metal sheets with both excellent mechanical properties and high thermal stability.

Correlation of Tensile Properties and Fracture Toughness with Microstructural Features for Al–Li 8090 Alloy Processed by Cryorolling and Post-rolled Annealing

The influence of cryorolling and post-deformation annealing on the tensile and fracture behaviour of aluminium–lithium (Al 8090) alloy is reported in the present investigation. The solution-treated (ST) alloy was cryorolled (CR) up to the true strain of 2.3 to achieve ultrafine-grained (UFG) microstructure and then annealed at different temperature ranging from 100 to 350 °C. CR samples showed a significant increase in tensile strength (~ 373 MPa), hardness (~ 120 HV), and fracture toughness [KQ (21.9 MPa $$ \surd m $$ ), Kee [27.9 MPa $$ \surd m $$ ), J integral (21.8 kJ/m2)], while huge drop in ductility of CR alloy is observed as compared to coarser grain ST alloy. After annealing in the temperature ranging from 100 to 350 °C, the significant changes in the tensile and fracture behaviour of bulk UFG Al 8090 alloy were noticed. The tensile strength and fracture toughness were gradually improved up to the temperature 150 °C and observed to be maximum (~ 561 MPa) at 150 °C, while beyond this temperature, a significant drop in these properties was observed. The improved tensile and fracture properties of cryorolled followed by annealed alloy at 150 °C could be attributed to the precipitation of S′ (Al2CuMg) and $$ \delta $$ (Al3Li) phase as observed from XRD and TEM studies.

Effect of Pre-heat Treatment on Microstructure and Mechanical Properties of Cryorolled Low Carbon Steel

Abstract Low carbon steel cannot meet the requirements of most manufacturing and production industry in modern society due to its limited strength. In recent years, ultrafine-grained (UFG) structure steel with grain size below 1 µm has been studied aggressively, because they are expected to provide superior mechanical properties. The present works aim at producing UFG in low carbon steel using cryorolling and investigated its effect on microstructure, mechanical properties and corrosion behaviour. The samples were prepared by pre-annealed at different annealing temperatures (550°C, 750°C and 900°C) followed by cryorolling at 50% thickness reduction. Microstructure and mechanical properties of the cryorolled low carbon steel at different pre-heat treatment were investigated by means of optical, scanning electron microscope (SEM), X-ray Diffraction (XRD), Vicker microhardness and tensile test. The grain aspect ratio decreases for both annealed and cryorolled samples. However the cryorolled samples have the higher grain aspect ratio as compared to annealed sample. All the cryorolled samples have lower crystallite size and higher lattice strain than annealed sample. Among the cryorolled, sample pre-annealed at 500°C has the highest grain aspect ratio, lowest crystallite size, and the highest lattice strain. The high hardness (162.3 Hv) recorded for sample annealed at 550°C followed by cryorolling with 58.1% increment. The cryorolled sample pre-annealed at 550°C showed a remarkable increase in both tensile and yield strength with the value of 567 MPa and 566.6 MPa respectively.

Microstructure and mechanical properties of Al – 3Mg – 0.25 Sc alloy sheets produced by cryorolling

Al-3Mg-0.25Sc alloy with 50% and 75% rolling reductions from the initial thickness at room and cryogenic temperatures resulted in a higher dislocation density, enhanced lattice strain and reduced crystallite size for the cryorolled (CR) sample with 75% reduction (CR 75). A hierarchical grain size distribution was noted in CR samples through electron backscattered diffraction studies that led to a combination of 490 MPa of strength and 27% of ductility in CR 75. Also, due to hierarchical grain distribution, during the tensile test, deformation was expected to follow a complex strain distribution rather than localised necking, which had resulted in higher elongation. Further, a low mechanical anisotropy and a proportional decrement in texture index with a higher fraction of Cube texture enhanced the ductility of CR 75 among the rolled samples. Higher work hardening rate was reported by the CR samples than that of room temperature rolled (RTR) ones due to the influence of cryorolling and the existence of Al3Sc precipitates. Among the rolled samples, the CR 75 sample reported a higher necking percentage of 24% based on the stress based necking limit and fracture limit diagram, which indicated its ability to withstand higher strain before failure was consistent with the mechanical properties reported.

Effect of Initial Microstructure on Properties of Cryorolled Al 5052 Alloy Subjected to Different Annealing Treatment Temperatures

Al 5052 alloy sheets were subjected to different pre-annealing temperatures (150, 200, 250, 300, and 350 °C) prior to cryorolling. The process resulted in Al 5052 alloys with different initial microstructures. The pre-annealed alloy sheets were compared with a cryorolled sample not subjected to pre-annealing. The thicknesses of the alloy samples after cryorolling was reduced by 30%. The pre-annealed cryorolled samples exhibited low crystallite size, and high lattice strain. Among them, the cryorolled sample pre-annealed at 300 °C had the lowest crystallite size, and the highest lattice strain. Changes in initial microstructure of this sample resulted in a significant improvement in its hardness (88 Hv), tensile strength (333 MPa), and corrosion resistance. The sample had the highest corrosion resistance among the cryorolled samples.

Enhancement of mechanical properties of bulk copper processed by room temperature rolling and cryorolling

Objectives: In the present work, we have examined and reported the mechanical and microstructures properties of bulk Cu subjected to Room Temperature Rolling (RTR) and Cryorolling (CR) in Liquid Nitrogen temperature (LN2). Samples deformed plastically to obtain 90% Reduction in Area (RA). Methods/Statistical analysis: The mechanical properties of samples at room temperature rolling and cryorolled samples investigated by tensile testing and hardness measurement. Brittle type of fracture was identified for 90% RA cryorolled samples from fractography analysis, whereas the presence of the small dimples in the fractured surfaces of Room Temperature Rolled (RTR) tensile specimens shows a ductile failure. Findings: The increase in tensile strength is due to the refinement of the grains due to collective effect of inhibition of dynamic recovery and the recrystallization processes, an increase of the high density dislocations in the cryorolling. The grain size refinement has been confirmed by TEM analysis. Application/Improvements: Cryorolled samples with 90% RA show tensile yield strength (380 MPa) with an elongation only ~3.2%. The enhancement in yield strength of the cryorolled samples were found more compared to the Room Temperature Rolled (RTR) samples (YS = 230 MPa). Keywords: Cryorolling (CR), Electron Microscopy, Room Temperature Rolling (RTR), Tensile Yield Strength, Ultrafine Grains, Work Hardening

Pseudo-texture memory in AISI 321 austenitic stainless steel

In this study, a 45 µm-sized AISI 321 austenitic stainless steel was cryo-rolled at -196 °C to 50 % thickness reduction to completely transform the γ-austenite phase to α'-martensite. The cryo-rolled sample was subsequently annealed in the temperature range of 923 - 1073 K for 30-28800s (0.5 - 480 mins) to reverse the α'-martensite back to γ-austenite and develop ultrafine grain (UFG) structure at an optimum annealing condition. Average austenite grain sizes of 0.22 and 0.31 µm were obtained at an optimum annealing conditions of 923 K for less than 480 minutes and 1023 K for 10 minutes, respectively. High resolution EBSD and XRD texture results shows that ζ-fibre ({110}<uvw>) is the major texture component of austenite grains in the UFG structure and it is stronger in specimen annealed at 923 K than those of higher temperatures (973, 1023 and 1073 K) used in this study. The strong intensity of ζ-fibre in UFG is attributed to pseudo-texture memory in AISI 321 i.e. the ability of the steel to memorize the crystallographic orientation of the deformed austenite, rather than the conventional as-received austenite phase that is random.

Formability and fracture behaviour of cryorolled Al-3 Mg-0.25 Sc alloy

The rolling of an Al-3Mg-0.25Sc alloy at room and cryogenic temperature to 50% and 75% reduction in thickness resulted in the formation of a bimodal microstructure. The grain size distribution based on electron backscattered diffraction (EBSD) analyses showed an enhanced fraction of ultra-fine grains with nearly 100 nm in cryorolled samples whereas; room temperature rolled samples exhibited sub-micron grains with 300 nm. The transmission electron microscopy (TEM) studies revealed the dense dislocation cell structures for cryorolled samples due to the restriction of dynamic recovery. The better forming and fracture limit strains were noted for cryorolled samples compared to room temperature rolled ones in the forming and fracture limit diagrams. A good correlation of formability with void coalescence parameters based on larger void size, lower ligament thickness and lower d-factor were obtained. This indicated better accumulation of plastic deformation and improved formability of cryorolled samples. Further, the reduced aspect ratio (L/W) of void signified delayed fracture behaviour of cryorolled samples compared to room temperature rolled samples and showed better fracture resistance. The improved fracture limit strain in combined forming and fracture limit diagram exhibited by cryorolled samples was consistent with the void coalescence parameters.

Effect of Pre-Ageing on the Age Hardening Response of Cryorolled Al-Mg-Si Alloy

The present work investigates about the effect of pre-ageing on hardening behavior of Al-Mg-Si alloys processed by cryorolling and its age hardening behavior. Ageing conditions were examined at natural ageing for 2days and pre-ageing at 100 °C, 130°C and 170 °C for 4 hours, 2 hours and 30 minutes respectively. The observations revealed that, the pre-ageing before cryorolling is useful to enhance the dislocation density during cryorolling. However artificial ageing of cryorolled samples is not influenced much with pre-ageing. It is revealed that, maturing at room temperature of CR samples for 30 days has resulted better hardening response during artificial ageing.

Mechanical Properties and formability of Cryorolled Commercial Pure Aluminium at various reductions

This paper deals with the Mechanical properties, formability for Commercial pure Aluminium (CPAl) sheets that were rolled up to 50%, 75% reduction at two different temperatures viz., room temperature and cryogenic temperature. For this, the tensile properties and formability of rolled sheets were examined at both the temperatures and were correlated with Electron Back Scattered Diffraction (EBSD) analysis. The cryorolled (CR) samples exhibit relatively better mechanical properties than the room temperature rolled (RTR) samples. Lower values of 'n' were observed both rolled conditions than base material was observed. Grain refinement is more for the CR condition than in RTR condition as shown in OIM micrographs, which is indicated by the crystallite sizes obtained from X-ray diffraction line profile analysis, (XRDLPA) to be low in CR than in RTR. It is believed that heterogeneous slip in CR condition resulted contributed to higher necking percentage.

Influence of cryorolling and followed by annealing on high cycle fatigue behavior of ultrafine grained Al 2014 alloy

Effects of cryorolling (CR) and followed by annealing (CR+AN) on the high cycle fatigue strength of bulk ultrafine grained (UFG) Al 2014 alloy were investigated in the present work. Al 2014 alloy was cryorolled (CR) for the thickness reduction of 75% at liquid nitrogen temperature (−196°C). The cryorolled (CR) samples were heat treated for the temperature range of 100–250°C for the duration of 45min in order to investigate its influence on tensile strength, yield strength and high cycle fatigue behavior. The microstructural characterization of the alloy was made through TEM and FESEM. The cryorolled (CR) sample shows the improved high cycle fatigue strength as compared to ST alloy due to the formation of ultrafine grain (UFG) microstructure. The reduced flaw size in UFG prevents accumulation of stress concentration near the crack tip. However, the improvement in high cycle fatigue properties of cryorolled followed by annealed (CR+AN) alloy up to 200°C as compared to solution treated (ST) alloy observed is due to improvement in crack growth resistance facilitated by crack tip/precipitate interaction at grain boundaries (GBs). The high cycle fatigue strength gradually decreases with increasing annealing temperature from 100 to 250°C, due to gradual coarsening of metastable precipitate (θ′ phase), which transformed in to stable coarser precipitate ‘θ’ phase at 250°C.

Comparison of Microtexture Evolution During Cryo and Room Temperature Rolling of Ti–5Ta–2Nb Alloy

An α + β Ti–5Ta–2Nb alloy has been developed for applications under severe oxidizing conditions of boiling concentrated nitric acid in spent fuel reprocessing plant. The formation of nanocrystalline grains has been observed in the cryo-rolled sample accompanied by a significant improvement in yield strength whereas the grain refinement is not significant in case of room temperature rolled sample. Suppression of dynamic recovery plays a major role in the formation of nanostructured material. The evolution of micro-texture during room temperature rolling and cryo-rolling has been compared in this study. The rolling texture of room temperature and cryo-rolled samples are similar to the rolling texture predicted for hexagonal materials with c/a <1.6. XRD analysis indicates peaks shift to lower 2θ with increase in rolling strains indicating the presence of tensile residual strains. Peak broadening is also observed indicating an increase in defect density and decrease in grain size.

A Comparative Study on Tensile and Fracture Behavior of Al–Mg Alloy Processed Through Cryorolling and Cryo Groove Rolling

In the present work, Al–Mg alloy (AA 5052) was subjected to cryorolling followed by post-deformation annealing, in order to investigate its effect on tensile and fracture behavior. The solution-treated Al alloys were cryorolled (CR) and cryo groove rolled to different true strains. The microstructure of the samples (deformed and post-annealed) was characterized by optical microscopy, x-ray diffraction, and TEM to substantiate the mechanisms of grain refinement and its influence on tensile and fracture properties. Fractography of the tensile as well as three-point bending test samples was carried out using a scanning electron microscope (SEM) to reveal the fracture mode. The deformed samples (90% thickness reduction) exhibit significant improvement in strength (291 MPa) and hardness (110 HV) in CR samples and 313 MPa and 122 HV in cryo groove rolled samples, which is due to high dislocation density and grain size reduction. Post-annealing of the deformed samples (90% thickness reduction) led to improvement in its ductility as well as fracture toughness. The cryo groove rolled samples and post-annealed samples have shown better fracture toughness (142 kJ/m2) as compared to cryo rolled samples (29 kJ/m2) due to the relatively larger grain and dimples as observed from TEM and fractography studies.

Microstructural evolution and mechanical properties of low SFE Cu-Al alloys processed by cryorolling followed by short-annealing

Cu-2% Al and Cu-4.5% Al alloys were developed by metal mould casting followed by homogenization at 800°C for cryorolling. The homogenized samples were cryorolled (CR) up to the maximum possible reduction in area (~75%). Activation energy for recrystallization of the CR samples was estimated by isoconversion methods using differential scanning calorimetry data; whereas, stored strain energy was determined by X-ray diffraction analysis. The activation energy for recrystallization correlated well with the stored energy of the corresponding sample. Microstructural evolution was analyzed by optical and transmission electron microscopy. The CR+annealed (225°C) sample showed an improved yield strength (YS) of 810MPa with a reasonable ductility of 5.1%. The YS found to be 10 times higher than that of the cast+homogenized sample (76MPa). This is attributed to the recovery of low angle grain boundaries, increasing grain boundary spacing, formation of nanotwins and decrease in the dislocation density without any recrystallization. The YS obtained by analytical modeling of the active strengthening mechanisms is highly corroborated with the experimental YS of the annealed sample. The Hall-Petch strengthening and dislocation strengthening found to play the pivotal role in the improvement of mechanical properties.

Effect of solution treatment on Al 1100 cryorolled sheet alloy

Influence of cryorolling (CR) on Al 1100 alloy was investigated. Prior to cryorolling process, samples were solution treated at various temperatures (500°C, 540°C and 580°C) and times (2, 4, 6 hrs) to study the effect of solution treatment on the percentage reduction and microhardness of cryorolled samples. Sample solution treated at 540°C for 2 hrs showed the highest hardness of 69.74 Hv and the highest percentage reduction of 32%.

Mechanical anisotropy and microstructural changes during cryorolling of Al–Mg–Si alloy

Rolling was performed on Al–Mg–Si alloy sheets to true strain values of 0.69 and 1.38 at both room temperature and at cryogenic (liquid nitrogen) temperature and the influence of rolling temperature on microstructure and mechanical properties was studied. At both the reductions, cryorolled samples exhibited enhanced hardness and strength compared to room temperature rolled samples. The enhanced properties of cryorolled samples are attributed to the high dislocation density, increased microstrain and a reduced crystallite size compared to room temperature rolled samples. Besides, at high true strain condition, anisotropy behaviour was studied and correlated with X-ray bulk texture components. Evaluation of the percentage volume fraction of individual texture components revealed that cryorolled samples exhibited ~16% and ~33% increase in S and brass deformation texture components, respectively compared to room temperature rolled samples. Cryorolled samples also showed an enhanced texture index value compared to room temperature rolled samples.

Mechanical and Electrical Properties of Aluminium Alloy by Cryorolling Process

The mechanical and electrical properties of aluminium alloy 6061 are reported in this present work. Aluminium alloys were homogenized at 550 ◦C, for 5 hours and cooled in the furnace. The different thickness reductions of 60-90% on homogenized aluminium alloy plates were achieved by cryo-rolling. Later, the as rolled samples were aged by solution treatment at the temperatures of 520 ◦C for 1 hour, water quenched; subsequently aged at 160 ◦C for 8-24 hours and partial aged (not solution treatment) at 160 ◦C for 824 hours. Mechanical and electrical properties of samples were investigated. The experimental result showed that the microhardness of cryo-rolled samples were increase with increasing the percentage of the thickness reduction. Moreover, the microhardness of cryo-rolled, aged by solution treatment samples were higher than those of the cryo-rolled and cryo-rolled, partial aged samples. The cryo-rolled alloys subjected to full aged at 160 ◦C for 24 hours exhibited the hardness of 125 HV and electrical conductivity values was 45.76 %IACS and the cryo-rolled alloys subjected to partial aged at 160 ◦C for 20 hours exhibited the hardness of 67 HV and electrical conductivity values was 49.67 %IACS

Effects of rolling temperature and subsequent annealing on mechanical properties of ultrafine-grained Cu–Zn–Si alloy

The effects of rolling temperature and subsequent annealing on mechanical properties of Cu–Zn–Si alloy were investigated by using X-ray diffraction, transmission electron microscope, electron back scattered diffraction and tensile tests. The Cu–Zn–Si alloy has been processed at cryogenic temperature (approximately 77K) and room temperature up to different rolling strains. It has been identified that the cryorolled Cu–Zn–Si alloy samples show a higher strength compared with those room temperature rolled samples. The improved strength of cryorolled samples is resulted from grain size effect and higher densities of dislocations and deformation twins. And subsequent annealing, as a post-heat treatment, enhanced the ductility. An obvious increase in uniform elongation appears when the volume fraction of static recrystallization grains exceeds 25%. The strength–ductility combination of the annealed cryorolled samples is superior to that of annealed room temperature rolled samples, owing to the finer grains, high fractions of high angle grain boundaries and twins.

High cyclic fatigue behaviour of ultrafine grained Al 5083 alloy

The effects of cryorolling (CR) and CR followed by warm rolling (WR) on high cycle fatigue behaviour of Al 5083 alloy have been investigated in the present work. The Al 5083 alloy samples were rolled for different thickness reductions of 50 and 85% at cryogenic (liquid nitrogen) temperature. Fifty per cent cryorolled samples were subsequently warm rolled at 175°C for 70% reduction (WR). Hardness, tensile strength and fatigue life using constant amplitude stress controlled fatigue were investigated. The microstructural evolution of the alloy was characterised using optical microscopy, SEM and TEM techniques. The cryorolled Al alloy after 85% thickness reduction exhibits high dislocation density due to suppression of dynamic recovery, whereas WR alloy has shown fine subgrain structure in the range of 100–150 nm, associated with dynamic recovery and dynamic aging during WR. The Al 5083 alloy after WR has shown significant enhancement in fatigue strength as compared to the coarse grained solution treated (ST) bulk alloy and CR material. It can be attributed to the formation of fine precipitates during WR, which inhibits dynamic recovery during cyclic deformation; precipitate–dislocation tangled zones inhibits the crack propagation in the alloy.