Jurij J. Sidor

Controlling the plastic anisotropy in asymmetrically rolled aluminium sheets

The formability of metals depends on the crystallographic texture produced during thermo-mechanical processing. The crystallographic orientation of the deformed grains results from the applied deformation path. Asymmetric rolling is a new process that is expected to improve the formability of rolled aluminium sheets by introducing an intense shear deformation and an associated shear texture. Asymmetric rolling was applied to aluminium alloy AA6016 with roll diameters ratio of 1.5. Both full constraints and grain interaction models are employed to investigate the evolution of texture during conventional and asymmetric rolling processes. The superior planar and normal anisotropy values of asymmetrically rolled and annealed sheet over the conventionally produced one are interpreted in terms of differences in the deformed microstructures and the ensuing rolling and recrystallization textures.

Grain Refinement of a Cold Rolled TRIP Assisted Steel after Ultra Short Annealing

Recrystallization and austenite formation in a TRIP-assisted steel during conventional and ultra fast reheating for intercritical annealing are studied with the purpose to clarify the possibility for grain refinement. Partially recrystallized (or transformed) samples were prepared by reheating and water quenching to temperatures between 650 and 1050°C at reheating rates of 10, 50, and 3000 °C/s, respectively, without isothermal soaking from 95% cold rolled steel sheet with ferrite-pearlite microstructure. By monitoring the hardness and microstructure, it was shown that the increase of the reheating rate from 10 to 3000°C/s causes grain refinement from 5µm to 1µm in diameter and the final ferrite grain size depends significantly on both reheating temperature and reheating rate. It was observed that after an extreme reheating rate of 3000°C/s the α-γ phase transformation starts before the completion of the recrystallization. This opens up possibilities for further structural refinement and alternative texture control.

Texture Formation in High Strength Low Alloy Steel Reheated with Ultrafast Heating Rates

Texture formation during annealing of a 95% cold rolled HSLA steel with 10°C/s and ~3000°C/s was studied with the purpose to investigate the interaction between the recrystallization and the austenite formation as well as the possibility of grain refinement. The recrystallization and austenite formation were monitored by means of optical microscopy (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). It was found that at extreme reheating rates of 1000°C/s and higher, the α-γ phase transformation starts before the completion of recrystallization and the deformation texture is partially retained in the samples after annealing. The crystallographic texture observed in the martensitic phase which is the product of intercritical austenite transformation in as-quenched samples, i.e. after the double α-γ-α’ transformation, is the same as the initial cold rolling texture, which is an indication for the texture memory effect. After ultra fast reheating with average reheating rates of 1000°C/s and higher a significant grain refinement was observed with an average ferrite grain size of ~1µm. The obtained final ferrite grain size depends significantly on both the reheating temperature and the reheating rate.

Texture Evolution during Asymmetrical Warm Rolling and Subsequent Annealing of Electrical Steel

The core loss and magnetic induction of electrical steels are dependent on the microstructure and texture of the material, which are produced by the thermo-mechanical processing. After a conventional rolling process, crystal orientations of the α-(//RD) and γ-(//ND) fibers are strongly present in the final texture. These fibers have a drastically negative effect on the magnetic properties of electrical steels. By applying asymmetric rolling, significant shear strains could be introduced across the thickness of the sheet and thus a deformation texture with more magnetically favorable components is expected. In this study, an electrical steel of 1.23 wt.% Si was subjected to asymmetric warm rolling in a rolling mill with different roll diameters. The evolutions of both deformed and annealed textures were investigated. The texture evolution during asymmetric warm rolling was analyzed by crystal plasticity simulations using the ALAMEL model. A good fit between measured and calculated textures was obtained. The annealing texture could be understood in terms of an oriented nucleation model that selects crystal orientations with a lower than average stored energy of plastic deformation.

Validation of the Texture-Based ALAMEL and VPSC Models by Measured Anisotropy of Plastic Yielding

Several multilevel plasticity models that make use of the crystallographic texture have been developed in the past for the prediction of deformation textures. State-of-the-art models that consider grain interaction, such as Alamel and VPSC, are known to give superior deformation texture predictions compared to the well-known (full constraint) Taylor model. In this paper, these models are assessed on a different basis, namely their ability to predict plastic anisotropy in single-phase steel sheet. A wide range of mechanical tests is considered: uniaxial tension, plane strain tension, simple shear and sheet normal compression. Furthermore, the sensitivity of the anisotropy predictions is analyzed, considering the variability in textures measured by routine XRD. The considered grain interaction models clearly produce improved predictions of plastic anisotropy over the Taylor model.

Texture Control in Aluminum Sheets by Conventional and Asymmetric Rolling

The evolution of microstructure and crystallographic texture during conventional and asymmetric rolling processes in Al alloys are discussed based on both experimental data and results of various modeling approaches. The effects of roll geometry and heat treatment parameters on microstructure and texture evolution were analyzed. The texture evolution during cold rolling was modeled with a vast variety of crystal plasticity models. Annealing textures and microstructures are interpreted by comparing experimental results with simulated results obtained with recrystallization models. It is concluded that the strain mode of both hot and cold rolling processes significantly affects the anisotropy of recrystallized material.

Texture Control in Steel and Aluminium Alloys by Rolling and Recrystallization in Non-Conventional Sheet Manufacturing

The sheet manufacturing process, which involves various solid-state transformations such as phase transformations, plastic deformation and thermally activated recovery processes, determines the texture of steel and aluminium sheet. The conventional process of flat rolling and annealing only offers limited degrees of freedom to modify the texture of the final product. After annealing a {111} recrystallization fibre in BCC alloys and a cube dominated recrystallization texture in FCC metals is commonly obtained. Many applications, however, require other texture components than the ones achievable by conventional processing. In the present paper it is shown that by asymmetric rolling of a Si-alloyed ultra-low carbon steel a texture can be obtained with increased intensity on the {001} fibre, which is of interest for magnetic applications. Also in aluminium alloys the strong cube annealing texture can be drastically modified by the process of asymmetric rolling. It is argued that by observing the proper rolling and annealing conditions a recrystallization texture with improved normal and planar anisotropy of the mechanical properties may be produced.

Particle Stimulated Nucleation in Severely Deformed Aluminum Alloys

The microstructural changes were investigated in severely deformed 5182 alloy. The as-cast block was cold rolled with different reduction levels up to 98%. The deformation textures appearing after various rolling reductions account for minor qualitative changes (i.e. new texture components emerging with increasing rolling reductions) whereas significant quantitative differences were observed (i.e. changing intensity of rolling components). The presence of large non-deformable constituents affects both deformation and recrystallization textures. During rolling, large particles induce strain path changes in their vicinity, which produces microstructural heterogeneities. In recrystallization, the highly strained field around the particle induces particle stimulated nucleation (PSN). The current contribution tries to clarify the effect of different strain modes involved in severe plastic deformation on the development of recrystallization textures.

Recrystallization in Severely Deformed Aluminum

Qualitative and quantitative texture changes are investigated in a severely deformed 5xxx series aluminum alloy. Unusual recrystallization textures are observed after a rolling strain of more than 97% in thickness reduction. The influence of both strain amplitude and strain mode on the development of the deformation and recrystallization textures is discussed based on experimental data and results of crystal plasticity calculations.

Improved Plastic Anisotropy in Asymmetrically Rolled 6xxx Alloy

Formability, which is the property that characterizes the ability of a material to be deformed without fracture or necking, is strongly correlated to the crystallographic texture. Al alloys from the 6xxx series with non-conventional textures were produced by hot and cold asymmetric rolling processes. The plastic responses i.e. the formability of differently textured samples are characterized based on crystal plasticity modeling.