Cryorolling Research Articles

Effect of cold and cryo rolling on microstructure and mechanical properties of low carbon steel

The influence of microstructure and mechanical properties of low carbon steel by cold and cryo rolling have been investigated in the present work. Low carbon steel was rolled at 50% thickness reduction at room temperature and cryogenic temperature and its microstructure and mechanical properties were studied. All the samples showed severely deformed grains, which were elongated along the rolling direction. Cryorolled low carbon steel showed the finest crystallite size compared to the cold rolled low carbon steel with average crystallite size of 25.42 nm. The mechanical properties like hardness and tensile strength of cryorolled were improved compared with the cold rolled sample. This was because of higher dislocation density accumulation during lower temperature rolling. Cryorolled sample has higher hardness and tensile strength with improvement of 23.6% and 27.2% compared with cold rolled low carbon steel.

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 reverse austenitic transformation on mechanical property and associated texture evolution in AISI 316 austenitic stainless steel processed by low temperature rolling and annealing

The tensile behaviour of austenitic stainless steel after cryorolling and subsequent annealing has been reported. The defect structures generated during cryorolling, lead to the formation of α’ and ε-martensite. Subsequent annealing leads to the formation of refined austenitic grains surrounded by martensitic islands. These martensitic islands consist of α’ phase only. The dislocation-martensite interaction leads to discontinuous yielding for high Ultimate Tensile Strength (UTS)/Yield Strength (YS) ratio. In case of annealing at 923 K (650 °C) for 10 min after 30% cryorolling leads to nearly 30% untransformed martensite whereas only 7% martensite remains after annealing for 1 h. The effect of remnant martensite on tensile behaviour leading to yield plateau has been discussed in this work. It can be noticed that sample with 20% cryo rolling and annealed at 650 °C for 1 h shows higher YS (721 MPa) with YS/UTS ratio of 0.79 and ~ 18% uniform elongation. Sample with 30% cryo rolling and annealed at 650 °C for 1 h shows YS of 305 MPa with YS/UTS ratio of 0.27 and uniform elongation of ~ 24%. Therefore, 20% cryo rolled and annealed at 650 °C for 1 h has the best combination of mechanical properties.

Cryorolling-Induced Texture, Mechanical Properties and Fracture Behavior of Al-Mg-Si Alloys During Cold Deformation

This study investigated the texture, mechanical properties, and fracture behavior during cold working of cryorolled (CR) Al-Mg-Si alloys. An x-ray texture goniometer was used to examine the crystallographic texture, and tensile tests were performed to understand the deformation behavior in more detail. SEM/EBSD/TEM was used to observe the microstructures and fracture morphology of the alloy during cryorolling. The microstructures indicated that a large number of ultrafine grains and dislocations formed after cryorolled. The recrystallization was prohibited due to low temperature during deformation. The ultrafine grains and dislocation strength improved the tensile strength from 279.38 MPa for the room-rolled alloy to 313.98 MPa for the cryorolled alloy; better plasticity (4.6%) was observed in the CR sheet. Ductile and intergranular fractures were observed in the CR sheet deformation from 20 to 90%.

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

Correlation of fracture toughness with microstructural features for ultrafine‐grained 6082 Al alloy

AbstractIn the present work, cryorolling (CR) and room temperature rolling (RTR) followed by annealing (AN) at 200°C were carried out to investigate the effects of grain size, precipitates (Mg‐Si‐phases), and AlFeMnSi‐phases on the fracture toughness of 6082 Al alloy. Using the values of the conditional fracture toughness, (KQ), in the critical fracture toughness (KIC) validation criteria, it was found that the sample size is inappropriate, which implies that the conditional fracture toughness obtained cannot be considered as the critical fracture toughness. Therefore, to establish the relative improvement in fracture toughness, the equivalent energy fracture toughness (Kee) and J‐integral were calculated and used. The results show that the values of Kee (89.91 MPa √m) and J (89.86 kJ/m2) obtained for the sample processed via CR followed by AN (CR + AN) are the highest when compared with the other samples processed through CR, RTR, and RTR followed by AN, RTR + AN. Microstructural features such as high fraction of low Taylor factor, high fraction of kernel average misorientation, Si‐rich particles, small size AlFeMnSi‐phases, and mixed mode of failure (transgranular shear and micro‐void coalescence) also support the high fracture toughness in the CR + AN sample. It was also observed that the effect of residual stresses on the fracture toughness of CR and RTR samples is minimal. Therefore, the correlation between microstructure and residual stresses is not considered in the present work due to very small values of the residual stresses for CR and RTR samples and the absence of residual stress from the heat‐treated samples.

Precipitation hardening behaviour of Al-Mg-Si alloy processed by cryorolling and room temperature rolling

The precipitation hardenable aluminium alloy (Al-Mg-Si) plates were solutionized and subjected to rolling at room temperature and liquid nitrogen temperature (RTR, CR) up to a true strain of ∼2.7. The rolled sheets were uniformly aged at room temperature and above room temperature (125 °C) to induce precipitation. 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 strength and ductility were simultaneously improved after controlled ageing of the cryorolled (CR) and room temperature rolled (RTR) samples. However, the increment in strength is more in RTR material than CR material with same ductility. Transmission electron microscopy analysis revealed the formation of ultrafine grains (UFG) filled with dislocations and nanosized precipitates in the CR and RTR conditions after ageing treatment. The behaviour of CR and RTR alloy is same under natural ageing conditions.

CORROSION PROPERTIES OF CRYOROLLED AA2219 FRICTION STIR WELDED JOINTS USING DIFFERENT TOOL PIN PROFILES

The purpose of this paper is to present the corrosion behavior of the Cryorolled (CR) material and its Friction Stir Welded joints. Due to the thermal cycles of Friction Stir Welding (FSW) process, the corrosion behavior of the material gets affected. Here, the cryorolling process was carried out on AA2219 alloy and CR material was joined by FSW process using four different pin tool profiles such as cylindrical, threaded cylindrical, square and hexagonal pin. The FSW joints were analyzed by corrosion resistance with the help of potentiodynamic polarization test with 3.5% NaCl solution. From the analysis, it is found that CR AA2219 material exhibits good corrosion resistance compared to the base AA2219 material, and also a hexagonal pin profile FSW joint exhibits high corrosion resistance. Among the weld joints created by four different tools, the lowest corrosion resistance was found in the cylindrical pin tool FSW welds. Further, the corroded samples were investigated through metallurgical investigations like OM, Transmission Electron Microscopy (TEM), Energy-Dispersive X-ray Spectroscopy (EDX) and X-Ray Diffraction (XRD). It was found that the amount of dissolution of Al2Cu precipitate was present in the weld nugget. The amount of dissolution of Al2Cu precipitate is higher in the weld nugget produced by hexagonal pin tool. This is due to the enhancement of the corrosion resistance.

The influence of metallurgical factors on low cycle fatigue behavior of ultra-fine grained 6082 Al alloy

In the present work, ultrafine grained Al 6082 alloy was produced by cryorolling (CR), room temperature rolling (RTR), CR + annealing (CR + AN) at 200 °C and RTR + annealing (RTN + AN) at 200 °C processes to study the effects of metallurgical factors (ultrafine grain structure, precipitates and secondary phase particles) on its low cycle fatigue behavior. Various characterization techniques such as the transmission electron microscopy, electron back scattered diffraction, scanning electron microscopy and differential scanning calorimetry were used to investigate the low cycle fatigue (LCF) behavior of the 6082 Al alloy. It was observed that the sample produced via CR + AN exhibits the highest LCF life when compared to the other samples investigated. The improvement in the LCF life of the 6082 Al alloy after CR + AN is attributed to the presence of small sized Si-rich precipitates, secondary phase particles, sub grains formation (200–400 nm) and high stored energy (32.16 × 10−4 J/mol).

Plane stress fracture toughness of cryorolled 6082 Al alloy

In this paper, the plane stress fracture toughness of 6082 Al alloy produced by cryorolling is reported for the first time. The rolling was performed to achieve a 75% reduction in the sample thickness at two different temperatures, namely, liquid nitrogen temperature (−196 °C), and room temperature (25 °C). The plane stress fracture toughness was evaluated for cryorolled (CR), room temperature rolled (RTR), cryorolled and annealed (CR + AN), and room temperature and annealed (RTR + AN) samples using ASTM E1820-13 standard and compact tension specimens. Two methods, i.e., the Load point displacement (LPD)-load and the J-Integral-resistance (J-R) curves, were used to calculate the plane stress fracture toughness. The results showed that the fracture toughness calculated using the J-R curve is more accurate since it accounts for all the constraints for evaluating the critical plane stress fracture toughness of the alloy for all the processing routes. The values of the critical plane stress fracture toughness (JIC) obtained via the J-R curve were 49 kJ/m2 for CR, 31 kJ/m2 for RTR, 69 kJ/m2 for CR + AN and 39 kJ/m2 for RTR + AN samples. Microstructural features obtained through scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) were also correlated with the fracture toughness. It is found from the SEM results that Mg-Si phases evolved at the crack tip/path during crack propagation in all the investigated samples. The EBSD results showed that CR + AN sample exhibits high kernel average missorentation and crack branches due to the evolution of small sized Mg-Si (Si-rich) precipitates during the fatigue testing. The presence of mixed grains (coarse and fine), fractographic features such as shallow ridges, transgranular facets, flat circular and elongated dimples, small sized Si-rich precipitates and high kernel average missorentation support the high plane stress fracture toughness observed for the CR + AN sample.

Effects of various tool pin profiles on mechanical and metallurgical properties of friction stir welded joints of cryorolled AA2219 aluminium alloy

Friction stir welding (FSW) process was conducted on cryorolled (CR) AA2219 plate using different tool pin profiles such as cylindrical pin, threaded cylindrical pin, square pin and hexagonal pin profiles. The FSW was carried out with pairs of 6 mm thick CR aluminium plates with different tool pin profiles. The different tool pin profile weld portions' behaviors like mechanical (tensile strength, impact and hardness) and metallurgical characteristics were analyzed. The results of the mechanical analysis revealed that the joint made by the hexagonal pin tool had good strength compared to other pin profiles. This was due to the pulsating action and material flow of the tool resulting in dynamic recrystallization in the weld zone. This was confirmed by the ultra fine grain structure formation in Weld Nugget (WN) of hexagonal pin tool joint with a higher percentage of precipitate dissolution. The fractograph of the hexagonal tool pin weld portion confirmed the finer dimple structure morphology without having any interior defect compared to other tool pin profiles. The lowest weld joint strength was obtained from cylindrical pin profile weld joint due to insufficient material flow during welding. The Transmission Electron Microscope and EDX analysis showed the dissolution of the metastable θ″, θ′ (Al2Cu) partial precipitates in the WN and proved the influence of metastable precipitates on enhancement of mechanical behavior of weld. The XRD results also confirmed the Al2Cu precipitation dissolution in the weld zone.

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.

Influences of metastable θ″, θ′ and stable θ intermetallics formed during cryorolling and friction stir welding process on AA2219

This paper presents a detailed investigation on the formation of θ′ and θ″ precipitates in the Cryorolled (CR) material of AA2219 alloy and the Friction Stir (FS) welded portion of CR AA2219 and their influence on material characterizations. The ultrafine grain formation and precipitate dissolutions in CR AA2219 and FS weld were characterized using optical, Scanning Electron (SEM) and Transmission Electron Microscopes (TEM). X-Ray Diffraction (XRD) was carried out to distinguish the phase changes of base AA2219, CR AA2219 and FS weld portion.

Deformation twin and martensite in the Fe–36%Ni alloy during cryorolling

ABSTRACTIn this paper, the microstructural evolution and deformation mechanism of the cryorolled Fe–36%Ni alloy was investigated. Deformation twinning was confirmed to be activated at the early stage of cryorolling (CR) and subsequently suppressed due to microstructure refinement. The existence of and peaks revealed that the (α′-M) phase transformation was induced during the CR process. The stress-assisted martensite and strain-induced martensite were detected to be transformed at the grain boundary and intersection of deformation twins, respectively. Owing to the co-effect of the temperature raise and mechanical stabilisation, the α′-M phase transformation was suppressed during the CR process. Therefore, the amount of the α′-M was limited in the tested alloy.

Parameter optimization of friction stir welding of cryorolled AA2219 alloy using artificial neural network modeling with genetic algorithm

In this paper, parameter optimization of FSW of cryorolled AA2219 alloy was carried out to obtain defect free weld joint with maximum weld strength. To achieve this, artificial neural network (ANN) was used to model the relationship between the input parameters and the mechanical and corrosion properties (output) of the weld joints. The optimal FSW parameters were determined by genetic algorithm (GA). The feasible solution of the GA was tool rotational speed of 1005 rpm, tool travel speed of 20 mm/min and tool tilt angle of 3°. The feasible parameter was used to weld and check the ability of the parameter to produce better weld joint than the L9 orthogonal array parameters. The weld, subjected to the confirmation test, was investigated by means of metallurgical, mechanical, and corrosion testing. This process reduces the costs associated with trial runs to obtain optimal parameters and also the production cost of the cryorolled (CR) plate which is high.

Fatigue Behavior of Ultrafine-Grained 5052 Al Alloy Processed Through Different Rolling Methods

In the present study, 5052 Al alloy was processed through different rolling methods to obtain ultrafine grains and its high-cycle fatigue behavior were investigated. The solution-treated Al-Mg alloys (AA 5052) were deformed through different methods such as cryorolling (CR), cryo groove rolling (CGR) and cryo groove rolling followed by warm rolling (CGW), up to 75% thickness reduction. The deformed samples were subjected to mechanical testing such as hardness, tensile and high-cycle fatigue (HCF) test at stress control mode. The CGW samples exhibit better HCF strength when compared to other conditions. The microstructure of the tested samples was characterized by optical microscopy, SEM fractography and TEM to understand the deformation behavior of deformed Al alloy. The improvement in fatigue life of CR and CGR samples is due to effective grain refinement, subgrain formations, and high dislocation density observed in the heavily deformed samples at cryogenic condition as observed from SEM and TEM analysis. However, in case of CGW samples, formation of nanoshear bands accommodates the applied strain during cyclic loading, thereby facilitating dislocation accumulation along with subgrain formations, leading to the high fatigue life. The deformed or broken impurity phase particles found in the deformed samples along with the precipitates that were formed during warm rolling also play a prominent role in enhancing the fatigue strength. These tiny particles hindered the dislocation movement by effectively pinning it at grain boundaries, thereby improving the resistance of crack propagation under cyclic load.

Investigation of tensile behaviour of cryorolled and room temperature rolled 6082 Al alloy

In this paper, 6082 Al alloy has been worked upon at cryogenic and room temperatures. With the help of tensile testing, the influence of cryorolling and room temperature rolling have been observed. Further, the tensile properties shows the optimality in the heat treatment schedule. The microstructure of the cryorolled (CR) and room temperature rolled (RTR) 6082 Al alloy with different thickness reduction i.e. 40%, 70% and 90%, are featured by EBSD and TEM owing to the grain refinement, grain fragments, high angle boundaries and ultrafine grains formation. The tensile strength of CR and RTR alloy are improved and CR results better mechanical properties.

Effect of deformation temperature on precipitation, microstructural evolution, mechanical and corrosion behavior of 6082 Al alloy

The influence of cryorolling (CR), room temperature rolling (RTR) and post annealing on precipitation, microstructural evolution (recovery, recrystallisation and grain growth), mechanical and corrosion behavior, was investigated in the present work. The precipitation kinetics and microstructural morphology of CR, RTR, and post annealed samples were investigated by differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and electron back scattered diffraction (EBSD) to elucidate the observed mechanical properties. After annealing at 200 °C, UTS and hardness of CR samples (345 MPa and HV 127) were improved as compared to RTR samples (320 MPa and HV 115). The increase in hardness and UTS of CR samples after annealing at 200 °C was due to precipitation of β″ from Al matrix, which imparted higher Zener drag effect as compared to RTR samples. The improvement in corrosion and pitting potentials was observed for CR samples (−1.321 V and −700 mV) as compared to RTR samples (−1.335 V and −710 mV). In CR samples, heavy dislocation density and dissolution of Mg4Al3Si4-precipitates in the Al matrix have improved corrosion resistance of the alloy through formation of protective passive layer and suppression of galvanic cell, respectively.

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.

EXPERIMENTAL INVESTIGATION ON FRICTION STIR WELDING OF CRYOROLLED AA2219 ALUMINUM ALLOY JOINTS

In this paper, experimental investigation on cryorolled aluminum AA2219-T87 plate by using friction stir welding (FSW) process is carried out. AA2219-T87 plates with a size of 200[Formula: see text]100[Formula: see text]22.4 mm were rolled and reduced to 12.2[Formula: see text]mm thickness (more than 45% of reduction in total thickness of the base material) at cryogenic temperature (operating temperature range [Formula: see text]90–[Formula: see text]30[Formula: see text]C). The cryorolled (CR) plates have reduced grain size, improved hardness and increased corrosion resistance property compared with the uncryorolled AA2219-T87 plates. FSW joints of cryorolled AA2219-T87 plates were prepared using cylindrical threaded FSW tool pin profile. Mechanical and metallurgical behaviors of friction stir welded joints were analyzed and the effects of the FSW process parameters are discussed in this paper. The variation of microhardness in the FSW joint regions were correlated with the microstructure of FSW joints. Cryorolled plate and FSW joints were tested for corrosion resistance using potentiodynamic polarization test. FSW joints shows better result during the corrosion resistance analysis compared to base AA2219-T87. The X-ray diffraction (XRD) test results showed that fine [Formula: see text]-Al grains with eutectic phase (Al2Cu) were present in the weld nugget (WN). The large clusters of strengthening precipitates were reduced in size and merged with the weld nugget portion.