Hans Erik Vatne

The roles of oriented nucleation and oriented growth on recrystallization textures in commercial purity aluminium

The development of the recrystallization texture in commercial purity Al (AA1145) containing large Al3Fe precipitates was investigated to determine the dependence on the degree of deformation and recrystallization temperature by means of X-ray macrotexture analysis. The amount of Fe in solid solution was varied by applying different heat treatments. The recrystallization textures develop from the competition between the Cube-orientation, the R-orientation (similar to the rolling texture S-orientation) and randomly oriented grains due to particle stimulated nucleation (PSN). The formation of these orientations is discussed in terms of their nucleation and subsequent growth behaviour. Particular attention is focused on the influence of the process parameters, i.e. strain, temperature and heating rate, on the ratio between the individual orientations in the recrystallization textures.

Modeling recrystallization kinetics, grain sizes, and textures during multipass hot rolling

A physically based model for the evolution of recrystallization microstructures and textures during hot rolling of aluminum is presented. The approach taken differs from similar models developed for steels. The present model is based on recent experimental investigations directed toward identifying the nature of the nucleation sites for recrystallized grains of different crystallographic orientations. Particle stimulated nucleation (PSN) and nucleation from cube bands and grain boundary regions have been incorporated in the model. The multipass aspect complicates the modeling due to partial recrystallization between the rolling passes. Two different approaches have been suggested to handle this. The model has been applied to predictions of recrystallization kinetics, recrystallized grain sizes, and recrystallization textures during multipass hot rolling of aluminum. The predictions are reasonable compared to experimental results.

The Effect of Particles on Recrystallisation Textures and Microstructures

The way in which large and small particles influence on recrystallised grain size and texture is considered with special emphasis on the processing of aluminium. It is well known that large particles might induce nucleation of recrystallised grains, while finely dispersed small particles will exert a pinning force on boundary movement. It the present paper, these two effects of particles will be discussed in detail. The discussion will to some extent be in an overview form, but also new ideas and recent experimental results will be presented. These include cases where strong effects are caused by small precipitated particles.

Texture evolution during extrusion of flat AA6060 and AA6082 aluminium profiles

Extrusion trials have been carried out in a laboratory extrusion press on the two important industrial aluminium alloys AA6060 and AA6082 The cooling devices positioned just below the outlet of the die in this laboratory press give the possibility to freeze the entire deformed structure developed during the extrusion process in such a way that the recrystallization process can be avoided. Textures were measured through the profile thickness for both alloys in the as-deformed state and after recrystallization annealing. The deformation textures in the two investigated alloys follow the same pattern In both cases the textures are dominated by a β-fibre in the centre section where the Bs orientation is the sharpest, while the β-fiber is rotated/degenerated towards the surface. The strengths of the fibres are comparable in both alloys, but alloy AA6082 has a somewhat weaker Cu component. There is, however, a difference for the starting point where the fibres begin to rotate and degenerate. This indicates that the shear deformation penetrates deeper into the material in the softer AA6060 alloy. Both alloys display a significant cube component in the deformation texture with comparable strength and similar scatterings around ED and ND. The recrystallization textures are in both materials dominated by the cube orientation with scatterings as observed in the deformation texture The strength of the cube orientation is very high in the centre, especially for 6060, but decreases towards the surface as the cube transforms into a fibre and is gone for the outer 75μm. The outer surface zone is dominated by a weak texture (close to random) with some goss and 45° ND-rotated cube.

Texture and Structure Evolution During Indirect Extrusion of an AlSiMgMn Aluminium Alloy

Texture evolution during indirect extrusion of cylindrical profiles of an AlSiMgMn aluminium alloy was investigated in the present work. The effect of extrusion temperature on texture development, through-thickness texture variations and texture variations along the length of the extruded profiles were investigated. In all cases a combined 〈100〉 and 〈111〉 fibre texture developed. Generally, the 〈111〉 fibre was sharper than the 〈100〉 fibre. The texture evolution was rather similar along the length of the profile, while the variations through the thickness were considerable. In a region midways between the centre and the surface of the profiles, the 〈100〉 fibre was weakened, and in the surface regions the two fibres were significantly rotated. The texture measurements showed a strong dependence on extrusion temperature, in the sense that the higher the temperature, the sharper the 〈100〉 fibre texture. The influence of texture variations on formability were also investigated.

A model for recrystallisation kinetics, texture and grain size applied to multipass hot rolling of an AlMgMn aluminium alloy

Abstract A physically based model for primary recrystallisation, including recrystallisation kinetics, grain size and texture evolution, during hot rolling of aluminium is presented. The model is based on extensive experimental investigations that have been directed towards identifying the nature of the nucleation sites for recrystallised grains of different crystallographic orientations. Particle stimulated nucleation and nucleation from cube bands and grain boundary regions have been incorporated in the model. The model has been applied to the hot rolling of an AlMgMn alloy processed in 13 passes. Reasonable model predictions have been obtained for cases of reversing rolling and a 3-stand tandem mill, including variations in the exit gauge temperature.

Experimental Investigation of Particle Break-up during Cold Deformation of Non Heat Treatable Aluminium Alloys

In the present work, image analysis has been used for a quantitative description of particle size distributions in NHT-aluminium alloys. The influence of magnification on the experimental results has been investigated. The results demonstrate that more large particles are detected when the magnification is reduced. For the present investigation this is probably due to that a larger sample area is measured at the lowest magnification, thereby increasing the probability of finding large particles. The particle break-up during processing of NHT-alloys has been investigated after cold rolling and hot plane strain deformation. For cold rolling, there is an increased tendency for particle break-up with increasing strain for 1050 and 3003, with the 3003-alloy showing the strongest tendency for such a break-up. The 5005-alloy did not show any sign of break-up with increasing strain.

Substructure Characteristics of Grain Boundary Regions and Nucleation of Recrystallisation at Grain Boundaries in High Purity Aluminium

Boundaries existing prior to deformation are well known nucleation sites for recrystallisation. Several mechanisms have been suggested, e.g. strain induced boundary migration (SIBM) and ordinary nucleation of recrystallisation by growth of highly misoriented subgrains. The objective of the present work was to give some insight on the formation and characteristics of such boundary zones Substructure evolution nearby pre-exsisting grain boundaries was studied as a function of orientation differences or Taylor factor differences between neighbouring grains and of pre-deformation grain size, i.e., amount of shear deformation (grain boundary sliding) occuring in grain boundary areas. Slabs of high purity aluminium with different initial grain sizes were cold rolled to strains of 0.5, 1 0 and 2.0. The substructure, i.e., subgrain size and sub-boundary misorientation, were measured along grain boundaries with different orientation relationships and in the interior of the neighbouring grains. It was observed that the misorientations between subgrains were larger in the grain boundary regions than in the interior of the grains The high misorientations and high stored energy in the grain boundary regions makes them preferential as nucleation sites for recrystallised grains This was also shown indirectly by the fact that smaller initial grain size leads to smaller recrystallised grains in samples deformed to identical deformation strains.