Microstructure and texture formation in high strength cold rolled and annealed sheet and their correlation with formability property

A comprehensive understanding was developed on the evolution of microstructure and texture during annealing of Nb bearing microalloyed drawing quality high strength cold rolled (HSCR) sheet with specific reference to cold rolling and annealing practices. Further, this study aimed at establishing the best combination of these processing parameters to achieve an YET value of 1.4 min. For a hot rolled microstructure of moderately coarse ferrite grain of size 16 μm, it was observed that 70% cold reduction guaranteed high intensity of (222) component accompanied with minimum intensity of (200) component. Further, investigation was carried out to understand the influence of annealing time on recrystallization behavior and texture development during intermediate annealing of 60% and 70% cold reduced specimens at 550 °C. It was found that recrystallization ceased after 12 h of intermediate annealing at 550 °C. The textures and microstructures produced during final annealing of 70% cold rolled specimens at various temperatures like 670, 690, 710, and 730 °C with varied duration of soaking (12–18 h) were critically examined. An YET value of ∼1.5 was achieved in HSCR microalloyed steel when 70% cold rolled specimens were intermediately annealed at 550 °C for 12 h followed by final annealing at 710 °C for 12 h.     

Dynamic recrystallization,texture and mechanical properties of high Mg content Al–Mg alloy deformed by high strain rate rolling

The Al–Mg alloy with high Mg addition (Al–9.2Mg–0.8Mn–0.2Zr-0.15Ti, in wt.%) was subjected to different passes (1, 2 and 4) of high strain rate rolling (HSRR), with the total thickness reduction of 72%, the rolling temperature of 400 °C and strain rate of 8.6 s⁻¹. The microstructure evolution was studied by optical microscope (OM), scanning electron microscope (SEM), electron backscattered diffraction (EBSD) and transmission electron microscope (TEM). The alloy that undergoes 2 passes of HSRR exhibits an obvious bimodal grain structure, in which the average grain sizes of the fine dynamic recrystallization (DRX) grains and the coarse non-DRX regions are 6.4 and 47.7 μm, respectively. The high strength ((507±9) MPa) and the large ductility ((24.9±1.3)%) are obtained in the alloy containing the bimodal grain distribution. The discontinuous dynamic recrystallization (DDRX) mechanism is the prominent grain refinement mechanism in the alloy subjected to 2 passes of HSRR.     

Influence of warm deformation on the formation of a fragmented structure in low-carbon martensitic steels

Methods of optical metallography and scanning and transmission electron microscopy were used to investigate the structure of low-carbon steels of martensitic classes VKS-7 and VKS-10 subjected to warm rolling or upsetting at temperatures of 600 and 700°C (in the α state) and 800°C (in the γ state). It has been shown that the deformation by rolling at 600°C to degrees of 40 and 60% does not lead to the destruction of the lath structure of the initial martensite; an increase in the rolling temperature to 700°C and of the degree of deformation to 80% favors the development of recrystallization in situ. It has been found that, upon warm deformation by upsetting, recrystallization occurs at lower temperatures than in the case of the warm rolling. It has been shown that warm deformation by upsetting at a temperature of 700°C leads to the formation of a fragmented structure with a high fraction of ultrafine grains with a size less than 2 μm.     

Effect of Cu on the Superplastic-like Behavior of Coarse-Grained Al-Mg Alloys

In this study, the effect of Cu content on the superplastic-like behavior of Al-Mg alloys in coarse grain size condition has been studied. Five hot-rolled Al-Mg alloys with different Cu concentrations (0.5, 1.0, 1.5, and 2.0?wt.%) and without Cu were prepared. Tensile test specimens were machined parallel to the rolling direction. High-temperature elongation to failure tests were performed under a constant cross-head speed condition at different strain rates and temperatures. Grain size refinement is observed as Cu addition increases. Maximum tensile elongation of 373% could be achieved in the Al-4.5%Mg-1.5%Cu alloy with an average grain size of 28???m at 500?°C and 1?×?10^?2?s^?1. Grain size refinement after superplastic deformation was also observed.     

Evolution of microstructure and microtexture upon recrystallization of submicrocrystalline niobium

Laws of recrystallization in niobium after a submicrocrystalline structure was formed in it by high pressure torsion at room temperature are studied by transmission and scanning electron microscopy. Recrystallization is shown to begin at 300 °C due to the growth of individual microcrystallites. Continuous recrystallization develops in the temperature range 300–800°С. As isothermal annealing temperature is increased, the area occupied by recrystallized grains, which (110) planes are parallel to the sample surface, increases to 90%. Discontinuous and continuous recrystallization that takes place simultaneously upon annealing at 900°С results in grain refinement and more pronounced size inhomogeneity in the structure. The grain refinement is accompanied by a smearing of the recrystallization texture.     

Structure and Microtexture of Niobium Recrystallized after Cryogenic Deformation by Shear under Pressure

Annealing of the submicrocrystalline (SMC) structure of niobium obtained by high pressure torsion to e = 7 at the temperature of liquid nitrogen was carried out. The influence of the annealing temperature in the range of 100–1100°C on the recrystallization of the SMC structure and the formation of texture was investigated. This paper discusses the role of static recovery and thermoactivated formation of recrystallization nuclei. The submicrograined recrystallized structure characterized by an average grain size of 0.8 μm, by a high homogeneity, and by the lack of the texture has been obtained. The sharpest recrystallization texture is formed as a result of annealing at 900°C; the average grain size is 10 μm in this case.     

Microstructure Evolution and Hardness of an Ultra-High Strength Cu-Ni-Si Alloy During Thermo-mechanical Processing

Microstructure evolution and hardness changes of an ultra-high strength Cu-Ni-Si alloy during thermo-mechanical processing have been investigated. For hot-compressive deformation specimens, dynamic recrystallization preferentially appeared on deformation bands. As deformation temperature increased from 750 to 900 °C, elongated grains with the Cubic texture {001} 〈100〉 were substituted by recrystallized grains with Copper texture {112} 〈111〉. For the samples having undergone cold rolling followed by annealing, static recrystallization preferentially occurred in the deformation bands, and then complete recrystallization occurred. Goss, Cubic, and Brass textures remained after annealing at 600 and 700 °C for 1 h; R texture {111} 〈211〉 and recrystallization texture {001} 〈100〉 were formed in samples annealed at 800 and 900 °C for 1 h, respectively. For samples processed under multi-directional forging at cryogenic temperature, the hardness was increased as a result of work hardening and grain refinement strengthening. These were attributed to the formation of equiaxed sub-grain structures and a high dislocation density.     

Superplastic deformation behavior of 7075 aluminum alloy

A study has been made to investigate the effect of a prior amount of warm rolling on the superplastic forming behavior of a standard grade 7075 aluminum alloy. The thermomechanical treatment process presented for grain refinement includes furnace cooling from the solution treatment temperature to the overaging temperature, warm rolling from 65–85% deformation, recrystallization, and artificial aging treatment. Increasing the amount of warm rolling beyond 80% deformation does not produce material with higher elongation to failure when the thermomechanical treatment process presented is used. The largest value of elongation to failure was 700%, which was obtained for a specimen having a grain size of 8 μm at a strain rate of 6×10⁻³S⁻¹. The fracture surface exhibits a granular appearance indicative of an intergranular fracture mode. Dislocation activities within grains were observed, indicating the occurrence of dislocation slip during grain boundary sliding.     

Development of microstructure and texture of medium carbon steel during heavy warm deformation

The microstructure and texture development of a medium-carbon steel (0.36% C) during heavy warm deformation (HWD) was studied using scanning electron microscopy and electron back scattering diffraction. The spheroidization of pearlite is accelerated due to the HWD, which leads to the formation of completely spheroidized cementite already after the deformation and coiling at 873 K (600 °C). The homogeneity of the cementite distribution depends on the cooling rate and the coiling temperature. The cooling rate of about 10 K/s (ferrite–pearlite prior to HWD) and deformation/coiling at 943–973 K (670–700 °C) lead to a homogeneous cementite distribution with a cementite particle size of less than 1 μm. The ferrite softening can be attributed to continuous recrystallization. Even up to fairly high deformation/coiling temperatures of 983 K (710 °C) the texture consists of typical deformation components. During the continuous recrystallization the amount of high angle grain boundaries can increase up to 70% with a ferrite grain size of 1–3 μm. An increase of the cooling rate up to 20 K/s (ferrite–pearlite–bainite prior to HWD) deteriorates the homogeneity of the cementite distribution and the softening of ferrite in the final microstructure.     

Formation of the Nanocrystalline Structure in an Equiatomic NiTi Shape-Memory Alloy by Thermomechanical Processing

The microstructural evolution during cold rolling followed by annealing of an equiatomic NiTi shape-memory alloy was investigated. The high purity Ni₅₀Ti₅₀ alloy was cast by a copper boat vacuum induction-melting technique. The as-cast ingots were then homogenized, hot rolled, and annealed to prepare the suitable initial microstructure. Thereafter, annealed specimens were cold rolled up to 70 % thickness reduction at room temperature. Post-deformation annealing was conducted at 400 °C for 1 h. The microstructure was characterized using scanning electron microscopy, transmission electron microscopy, x-ray diffraction, and differential scanning calorimetry techniques. The initial microstructure was free from segregation and Ti- or Ni-rich precipitates and was composed of coarse grains with an average size of 50 μm. The cold rolling of NiTi alloy resulted in a partial amorphization and the deformation-induced grain refinement. A nanocrystalline structure with the grain size of about 20-70 nm was formed during the post-deformation annealing.     

Microstructure and temperature monitoring during the hot rolling of AZ31

This study details the microstructural evolution during hot rolling of AZ31 alloy sheet using a pilot-scale rolling mill. The aim is to understand the deformation mechanisms leading to grain refinement under industrial processing conditions and to design and optimize the hot rolling schedule for AZ31 in order to produce sheet with a fine and homogeneous microstructure. The study examined three different hot rolling temperatures, 350, 400, and 450°C, and two rolling speeds, 20 and 50 rpm. A total thickness reduction of 67% was obtained using multiple passes, with reductions of either 15% or 30% per pass. It was found that the microstructure of the AZ31 alloy was sensitive to the rolling temperature, the reduction (i.e., strain) per pass and the rolling speed (i.e., strain rate). The results show that the large cast grain structure is broken down by segmentation of the cast grain through localized deformation in twin bands, where dynamic recrystallization occurs in these bands as well as at the grain boundaries (necklacing).     

形变细化晶粒和润滑轧制对Ni-9.3at.%W合金基带立方织构形成的影响

采用光学显微镜(OM)、X射线四环衍射(XRD)技术、电子背散射衍射(EBSD)技术分析研究了形变细化晶粒、润滑轧制对Ni-9.3at.%W(Ni9.3W)合金基带立方织构形成的影响。结果表明,采用形变细化晶粒的方法能有效提高Ni9.3W合金基带的立方织构含量,并且随着初始形变量的增加,晶粒细化程度越大,立方织构含量越高,采用优化的形变细化晶粒工艺使得Ni9.3W合金基带立方织构含量提高了9.8%。另外,增加形变细化晶粒后的轧制总变形量,立方织构含量进一步提升了24.7%,根据以上结果,确定了初始坯锭制备阶段的参数。在此基础上,研究了轧制变形的润滑与非润滑对立方织构形成的影响,相比非润滑轧制而言,采用润滑轧制,轧制织构中获得了较多的S取向与Copper取向,经再结晶退火后,润滑轧制基带的立方织构含量比非润滑轧制基带的立方织构含量高9.6%,达到了86.7%(<15°),而且孪晶界数量、小角度晶界含量均要优于非润滑轧制,说明润滑轧制对立方织构形成有着积极的影响。     

Superplastic deformation behaviour of friction stir processed 7075Al alloy

Commercial 7075Al rolled plates were subjected to friction stir processing (FSP) with different processing parameters, resulting in two fine-grained 7075Al alloys with a grain size of 3.8 and 7.5 μm. Heat treatment at 490 °C for 1 h showed that the fine grain microstructures were stable at high temperatures. Superplastic investigations in the temperature range of 420–530 °C and strain rate range of 1×10⁻³–1×10⁻¹ s⁻¹ demonstrated that a decrease in grain size resulted in significantly enhanced superplasticity and a shift to higher optimum strain rate and lower optimum deformation temperature. For the 3.8 μm 7075Al alloy, superplastic elongations of >1250% were obtained at 480 °C in the strain rate range of 3×10⁻³–3×10⁻² s⁻¹, whereas the 7.5 μm 7075Al alloy exhibited a maximum ductility of 1042% at 500 °C and 3×10⁻³ s⁻¹. The analyses of the superplastic data for the two alloys revealed a stress exponent of 2, an inverse grain size dependence of 2, and an activation energy close to that for grain boundary self-diffusion. This indicates that grain boundary sliding is the main deformation mechanism for the FSP 7075Al. This was verified by SEM examinations on the surfaces of deformed specimens.     

Improving Toughness of Heavy Steel Plate by Deformation Distribution Under Low Finish Cooling Temperature

The significant role of deformation distribution in toughness improvement of heavy steel plate under low finish cooling temperature was investigated. Deformation distribution was conducted by changing temperature-holding thickness in two-stage control rolling. The results show that the low finish cooling temperature always inhibits the ferrite transformation. However, when heavy deformation was applied at noncrystallization region, extensive ferrite was formed and ferrite was also effectively refined. Hence, homogeneous ferrite microstructure through the thickness with the ferrite volume fraction of 82.4% and grain size refined to 6.7 μm at quarter thickness of 40-mm heavy steel plate was obtained when the deformation at nonrecrystallization region reaches 70%. Thus, high toughness can be achieved, showing that the fully ductile fracture can be maintained at ?60 °C and the ductile-to-brittle transition temperature is lowered to ?91 °C. The improved toughness is ascribed to the high ferrite volume fraction, refinement of ferrite and hard phase colony and the increase in the percent of high-angle grain boundaries and average grain boundary misorientation.     

Effect of Stretch Orientation and Rolling Orientation on the Mechanical Properties of 2195 Al-Cu-Li Alloy

Sheets of 2195 aluminum-lithium alloy were solution-treated at 507 °C for 30 min. One set was stretched to 3-5% in the 0°, 45°, and 90° angle with respect to the original rolling direction. Two other sets were rolled 6% reduction in thickness and 24% reduction in thickness in the 0°, 45°, and 90° angle with respect to the original rolling direction. All specimens were aged at 143 °C for 36 h. A second group of samples was rolled at 24 and 50% reduction in thickness after a solution treatment of 507 °C for 1 h prior to aging at 190 °C for 24 h. Tensile specimens were machined from each sheet at 0°, 45°, and 90° angles to the original grain orientation. Tensile testing was used to determine the mechanical properties and anisotropic behavior of each condition. Rolling 6% reduction in thickness in the 45° orientation yielded anisotropy of 7.6% in the yield strength.     

Effect of the Size of Al<Subscript>3</Subscript>(Sc,Zr) Precipitates on the Structure of Multi-Directionally Isothermally Forged Al-Mg-Sc-Zr Alloy

The effect of Al₃(Sc,Zr) dispersoids on the evolution of the cast Al-Mg-Sc-Zr alloy structure under multi-directional isothermal forging (MIF) has been investigated. The alloy, which has an equiaxed grain structure with a grain size of ~25 μm and contains dispersoids 5–10 and 20–50 nm in size after onestage (at 360°C for 6 h) and two-stage (360°C for 6 h + 520°C for 1 h) annealing, respectively, was deformed at 325°C (~0.65 T_m) up to cumulative strains of e = 8.4. In the initial stages of MIF, new fine (sub)grains surrounded by low-angle and high-angle boundaries (HABs) were formed near the initial grain boundaries. With increasing strain, the volume fraction and misorientation of these crystallites increased, which led to the replacement of a coarse-grained structure with a fine-grained one with a grain size of ~1.5-2.0 μm. Dynamic recrystallization occurred in accordance to a continuous mechanism and was controlled by the interaction of lattice dislocations and/or (sub)grain boundaries with dispersoids that effectively inhibited the migration of boundaries, as well as the rearrangement of lattice dislocations and their annihilation. The particle size and the density of their distribution significantly affected the parameters of the evolved structure; in an alloy with smaller particles, a structure with a smaller grain size and a larger HAB fraction developed.     

Evolution of grain structure in AA2195 A1-Li alloy plate during recrystallization

The evolution of the grain structures in AA2195 Al-Li alloy plate warm-rolled by 80% reduction during recrystallization annealing at 500℃ was investigated by electron backscatter diffraction, scanning electron microscopy and transmission electron microscopy. It is found that the elongated grain structures are caused by the lamellar distribution of recrystaUization nucleation sites, being lack of large second phase particles （〉 1μm）, and dispersive coherent particles （such as δ′ and β′concentrated in planar bands. The recrystallization process may be separated into three stages： firstly, recrystallization nucleation occurs heterogeneously, and the nuclei are concentrated in some planar zones parallel to rolling plane. Secondly, the grain boundaries interacted with small particles concentrate in planar bands, which is able to result in the elongated grain structures. The rate of the grain growth is controlled by the dissolution of these small particles. Thirdly, after most of small particles are dissolved, their hindrance to migration of the grain boundaries fades away, and the unrecrystallized zones are consumed by adjacent recrystallized grains. The migration of high angle grain boundaries along normal direction leads a gradual transformation from the elongated grains to the nearly equiaxed, which is driven by the tension of the grain boundaries.     

Mechanical properties of aluminum-based nanocomposite reinforced with fullerenes

The strengthening effect of fullerenes in aluminum matrix composites was investigated. The composites are produced using a two-step ball-milling technique combined with a hot rolling process. First, fullerene aggregates, where fullerene molecules initially come together to form giant particles (～200 μm in diameter) via van der Waals bonding, are shattered into smaller particles (～1 μm in diameter) by planetary milling. Second, primarily ball-milled fullerenes are dispersed in aluminum powder via attrition milling. Finally, aluminum/fullerene composite powder is consolidated by hot-rolling at 480 °C. For the composite sheet, grain refinement strengthening and dispersion hardening by fullerenes are accomplished at the same time, thereby exhibiting HV ～222 of Vickers hardness (e.g., ～740 MPa of yield strength) with only 2% (volume fraction) of fullerenes.     

On the Issue of the Improvement of Magnesium Plasticity by Cold Severe Plastic Deformation

The paper presents the results of a study of the effect of the texture of a magnesium specimen on the mechanical properties of its plates and foils. Three cylindrical specimens with different columnar structure orientation were used for the experiments. The deformation was carried out in two steps at room temperature. First, long magnesium plates 1 mm thick (true deformation e ~ 3.9) were produced by lateral extrusion. These plates were then deformed by rolling to obtain foils, 120 μm thick (e ~ 6.0) and 10 μm thick (e ~ 7.5). It was seen that the sharpness of the basal texture and mechanical properties depend on the orientation of the initial samples. It has been shown that the deformation leads to a significant grain refinement: from several millimeters to several microns. This is due to the simultaneous development of slip, twinning, and dynamic recrystallization processes.     

Grain refinement of Al-3.5FeNb-1.5C master alloy on pure Al and Al-9.8Si-3.4Cu alloy

The refinement potential of Al-3.5 Fe Nb-1.5 C master alloy on pure aluminium and Al-9.8 Si-3.4 Cu alloy has been investigated. Different amounts of Al-3.5 Fe Nb-1.5 C master alloy were added to estimate the optimal addition level. It was found that the addition of Al-3.5 Fe Nb-1.5 C grain refiner can promote significantly the refinement of grains in the pure aluminium, particularly at 0.1 wt.%, with the mean primary aluminium α-grain size reducing to 187±3 μm from about 1-3 mm. Similarly, the microstructural study of the Al-9.8 Si-3.4 Cu alloy die casting at different weight percentages(viz. 0.0 wt.%, 0.1 wt.% and 1.0 wt.%) of Al-3.5 Fe Nb-1.5 C master alloy shows that the Al-3.5 Fe Nb-1.5 C master alloy as a grain refiner is also acceptable for Al-Si cast alloys when the silicon content is more than 4 wt.%. As a result of inoculation with Al-3.5 Fe Nb-1.5 C master alloy, the average grain size of α-Al is reduced to 22±3 μm from about 71±3 μm and grain refining efficiency is not characterized by any visible poisoning effect, which is the major limitation in the grain refinement of Al-Si cast alloys by applying Al-Ti-B ternary master alloys. Mechanical properties such as ultimate tensile strength and yield strength are significantly improved by 9.6% and 9.7%, respectively.