Papers by Keyword: Cold Rolling

Abstract: A new rolling process, which combined asymmetric rolling with symmetric rolling, was adopted in age-hardenable 6xxx series Al-Mg-Si alloy promising as automotive body panels in order to develop favorable textures for the deep drawability after solution treatment. Symmetric cold rolling at high reduction and subsequent asymmetric warm rolling at low reduction for AA6022 sheets led to the formation of “TD-rotated β-fiber texture” including moderate {111}<uvw>-oriented components, resulting in noticeable evolution of {111}<110> recrystallization texture during the solution treatment at a high temperature. The results of texture analysis and microstructural observation suggested that the low stored energy after asymmetric warm rolling, the high fraction of high angle boundaries with neighboring deformed matrices and the approximate 40° <111> orientation relationship with deformed matrices would strongly affect the evolution of {111}<110> recrystallization texture.

Abstract: The cold rolling and annealing texture formation has been investigated in electro deposited pure iron which has an extremely sharp and isotropic <111>//ND fiber. Regardless of cold rolling reduction, {111}<112> intensified texture is formed after cold rolling. Similar texture remains after recrystallization in 65% cold rolled material while {111}<110> type texture forms in 80% and 90% cold rolled ones. The recrystallized grains at the stage of 5% recrystallization have {111}<112> orientation in 65% cold rolled sheet, whereas {111}<110> is observed in 80% cold rolled one. From this aspect, it is considered that the nucleation orientation plays an important role in the recrystallization texture formation. In the meanwhile, the growth of the recrystallized nuclei is also supposed to affect the recrystallization texture formation. The nuclei with {111}<112> orientation in lightly cold rolled sheet are easier to consume the deformed matrix than they do in heavily cold rolled sheets because their frequency to encounter a deformed grain with nearly the same orientation is much smaller in lightly cold rolled specimen, which can result in a large mobility for growth. Cross cold rolling makes cold rolling texture rather homogeneous <111>//ND fiber, which gives rise to an almost homogeneous <111>//ND fiber after annealing.

Abstract: The development of ultrafine grained structures in 316L and 304-type austenitic stainless steels subjected to large strain cold working and subsequent annealing and their effect on mechanical properties were studied. The cold rolling was accompanied by a mechanical twinning and a partial martensitic transformation and resulted in the development of elongated austenite/ferrite grains with the transverse size of about 50 nm at a strain of 4. The grain refinement by large strain cold working resulted in an increase of tensile strength above 2000 MPa in the both steels. Annealing at temperatures above 500°C resulted in ferrite-austenite reversion. However, the transverse grain/subgrain size remained on the level of about 100-150 nm after annealing at temperatures up to 700°C.

Abstract: In this communication we report the effect of macro and microstructure on the hydrogen storage properties of magnesium based materials. Magnesium hydride is an attractive material for hydrogen storage applications since it has a high hydrogen volumetric density. Furthermore, the high enthalpy of hydride formation makes it attractive for thermal energy storage applications. Besides, magnesium is an abundant and low cost material. However, the Mg/MgH₂ system requires high operating temperatures due to its thermodynamic stability and slow hydrogen absorption and desorption kinetics. Magnesium’s first hydrogenation is a very long and costly process. This work aims to ameliorate this process which would effectively reduce the cost of MgH₂. Commercial pure magnesium samples were processed by cold rolling. After processing, the samples presented limited hydrogen absorption due to their small surface area to volume ratio. To overcome this problem the samples were then reduced to powder using a bastard file. The samples were characterized by scanning electron microscopy and presented different morphology. Hydrogen storage properties and morphology are discussed and correlated. Results show an important improvement on the hydrogen absorption and desorption kinetics for the comminuted samples.

Abstract: The microstructural evolution and mechanical properties of an Al-5.4Mg-0.4Mn-0.2Sc-0.09Zr alloy subjected to cold rolling with a total strain up to ~1.6 was studied using high resolution EBSD analysis and TEM. It was shown that cold rolling induces elongation of initial grains and the formation of deformation bands along rolling direction in addition to dramatic increase in density of lattice dislocations. Two types of deformation bands evolve. Deformation bands initially bounded by low-angle boundaries (LABs) with misorientation higher than 2^o and spacing ranging from 0.8 to 4 μm gradually transform to lamellas delimited by high-angle boundaries (HABs). Thin deformation bands delimited by LABs with misorientation of 2^o or less evolve within these coarse bands. First type of deformation bands is subdivided due to mutual intersection with second order deformation bands or shear bands to elongated crystallite evolving to micron scale grains with strain. The thin deformation bands may be also subdivided to nanoscale crystallites. It was shown that the formation of well-defined deformation bands yield very high anisotropy in strength and ductility, while a strong increase in lattice dislocation density with strain diminishes this anisotropy.

Abstract: Activation of different slip and twinning systems in cold-rolled Mg-3Al-1Zn at different thickness reductions was investigated by using orientation distribution function and electron backscattered diffraction techniques. The results show that the activation of slip coincides with the most compressive strain, resulting in little need for deformation twinning. The importance of prismatic slip was reinforced and <c+a> pyramidal slip was not a major deformation mechanism during cold rolling. The crystal texture in the cold rolled samples was weakened by twinning but strengthened by slip.

Abstract: The pure copper tube with strong axial orientation columnar grain and equiaxed grain respectively were rolled using a three-roller precision tube mill. Optical microscope, hardness testing machine and universal testing machine were used to investigate the microstructure and mechanical properties of the pure copper tube rolled with different deformation degrees. The results show that the pure copper tube with two kinds of microstructure can be directly rolled from the dimension of Φ68.5mm×57.9mm to Φ34.7×30.4mm by 8 passes with accumulated deformation degree nearly 80% and without intermediate annealing. With the increasing deformation degree, the primary columnar grain boundaries of the pure copper tube with columnar grain blurred gradually until completely disappeared. However, the microstructures of pure copper tube with equiaxed grain completely transformed into fibrous microstructures when the deformation degree reaches to 79.11%. The columnar grain is without transverse grain boundaries but with small-angle boundary, which is conducive to axial deformation. It is also found that with the increasing deformation degree, the tensile strength of pure copper tube increased steadily, while the elongation decreased gradually. The elongation of pure copper tube with columnar grains is higher and the microhardness is lower than that of equiaxed grains, indicating that the cold deformation properties of pure copper tube with columnar grain was more excellent.

Abstract: Strip profile control during rolling is required to assure the dimensional quality of rolled thin strip is acceptable for customers. Throughout rolling, the strip profile is controlled by using the advanced shape control rolling mill, such as the combination of work roll crossing and shifting during asymmetrical rolling, the one of the valuable methods to control the strip profile quality in rolling process. In this paper, the influences of cold rolling parameters such as the crossing angle and axial shifting value of work rolls on the strip profile are analysed. The strip shape control is discussed under both symmetrical and asymmetrical rolling conditions. The obtained results are appropriate to control the rolled thin strip profile in practice.

Abstract: The MMS-2B wear machine was used to study abrasion wear of work rolls in cold rolling by simulating emulsion cooling during the cold rolling process. The work roll materials used were 4%Cr, same as those in industrial production. The surface SEM scanning photographs were taken every 30 minutes until the friction experiment finished, and erosive appearance of emulsion on the work roll surface could be seen in the photos. The corrosive wear of the work roll surface is discussed. Findings show that the main causes of stress corrosion and pitting corrosion are uneven microstructure on the work roll surface and a large number of dislocation accumulations, which form microscopic cells. Water in steel rolling emulsion is the main conductive medium of electrochemistry reaction, and this intensifies the corrosive wear.

Abstract: Fe-10Ni-7Mn (wt. %) steel is a member of ultrahigh strength steels which shows good ductility in the solution annealed condition and excellent age hardenability. In the current research, this alloy was subjected to heavy cold rolling in which the reverse transformation of martensitic to austenite was brought about. From the XRD, DSC and dilatometric analyses, it is resulted that after 60 % cold rolling the austenite phase may be formed by displacive mechanism. Stability of austenite at room temperature is referred to the ultrafine/nanograin size of austenite after deformation which prevents the austenite to martensite transformation. The presence of ultrafine/nanoaustenite formed by displacive mechanism leads to the observation of new mechanical properties during cyclic tensile test. This behavior is known as pseudoelastic phenomenon. In this behavior, during loading-unloading tensile cycle, the shape of the specimen return to its original configuration with a hysteresis loop in its path to the zero strain point.