C. Schäfer

The origin and development of the P{011} orientation during recrystallization of particle-containing alloys

Abstract During annealing of particle-containing aluminum alloys, very often the development of the so-called P {011}<111>-texture and ND-rotated Cube {001}<310>-texture components are observed. The present paper focuses on the origin of the P-component near particles in an Al-1.1 wt.% Mn alloy and its further evolution during annealing. It is shown that the occurrence of these components depends on the annealing treatment rather than on the absolute annealing temperature.

An Extended Age-Hardening Model for Al-Mg-Si Alloys Incorporating the Room-Temperature Storage and Cold Deformation Process Stages

In this article, a new age-hardening model for Al-Mg-Si alloys is presented (named NaMo-Version 2), which takes into account the combined effect of cold deformation and prolonged room-temperature storage on the subsequent response to artificial aging. As a starting point, the original physical framework of NaMo-Version 1 is revived and used as a basis for the extension. This is permissible, since a more in-depth analysis of the underlying particle-dislocation interactions confirms previous expectations that the simplifying assumption of spherical precipitates is not crucial for the final outcome of the calculations, provided that the yield strength model is calibrated against experimental data. At the same time, the implementation of the Kampmann–Wagner formalism means that the different microstructure models can be linked together in a manner that enforces solute partitioning and competition between the different hardening phases which form during aging (e.g., clusters, β″ and β′). In a calibrated form, NaMo-Version 2 exhibits a high degree of predictive power, as documented by comparison with experiments, using both dedicated nanostructure and yield strength data as a basis for the validation. Hence, the model is deemed to be well-suited for simulation of thermomechanical processing of Al-Mg-Si alloys involving cold-working operations like sheet forming and stretch bending in combination with heat treatment and welding.

Modeling Recrystallization of Aluminum Alloys: A Refined Approach to Particle Stimulated Nucleation

A refined view of particle stimulated nucleation of recrystallization is presented, which utilizes a combination of advanced modeling tools. FEM simulations were carried out in order to model the evolution of the deformation zone around particles for various particle sizes and shapes. The results of these simulations were complemented by EBSD measurements to determine the number and orientation of nuclei. Finally, this information on particle stimulated nucleation was incorporated into a 3D cellular automaton recrystallization model CORe to model microstructure evolution. From these simulations the dependence of grain size and texture on particles size and shape was derived.

Nucleation at Cube Bands during Recrystallisation in Commercial Al Alloy

In the present study, nucleation at Cube bands during annealing of a cold rolled commercial aluminium alloy AA8079 was investigated. The main goal of this work was to provide experimental data for subsequent modelling. By studying the deformed material the geometrical parameters of Cube bands were determined. The Cube band spacing in the deformed state was measured experimentally and accordingly calculated with a simple geometric model, taking the initial Cube fraction in the pre-deformed state and the deformation degree into account. The nucleation frequency during subsequent annealing of the cold deformed material was estimated from the geometry and size of deformed Cube bands prior to deformation. From investigations of the orientation relationship between the Cube oriented nuclei and the adjacent deformed matrix with S orientation, the fraction of 40°<111> grain boundaries having optimum growth conditions, was established.

Modelling the Combined Effect of Room Temperature Storage and Cold Deformation on the Age-Hardening Behaviour of Al-Mg-Si Alloys-Part 1

In the present paper, an extended age hardening model for Al-Mg-Si alloys is presented. In this new approach the combined precipitation, yield strength and work hardening model, known as NaMo Version 1, has been further developed to account for the effects of room temperature storage and cold deformation on the resulting age hardening behaviour. Incorporation of these two new stages in NaMo largely increases the versatility of the model by allowing simulations of complex multi-stage industrial processing involving thermomechanical treatment as well. Part 1 of this work deals with the theoretical background and experimental validation of the extended version of NaMo, while Part 2 focuses on the new applications of the model by showing some numerical examples related to production of automotive body panels.

Methodology for Quantification of the Roping Phenomena in 6xxx Automotive Car Body Sheet Alloys

An important aspect when Al sheets are to be used for visible outer car body panels is surface appearance. Some age-hardenable Al-Mg-Si alloys of the AA 6xxx series can suffer from a phenomenon called roping. Roping appears on a macroscopic scale and manifests itself as the development of ridges and valleys 90° to the original rolling direction with a wavelength ranging from 1 to 10 mm when the sheet is formed to typical parts like doors or hoods. In the past years Al industry has developed means to minimise roping by careful control of alloy composition and through appropriate thermo-mechanical processing schedule. The increasing use of aluminium for outer skin applications gives proof that these efforts were successful. However, the extent of roping, and further the judgment of the quality of the surface appearance has up to now been done on a qualitative basis with comparisons against reference samples, as there are no established experimental techniques and no established analysis procedures for the quantification of this phenomenon. The goal of such a methodology is to be able to quantify the extent of roping in 6xxx automotive car body sheet alloys and to correlate it to a visual appearance ranking of roping. In the present study, a novel combination of a characterisation technique with an evaluation method is used to characterize and evaluate the roping behavior in aluminum alloys. This approach combines these already individually existing methods to a powerful tool: the measurement of a 3D surface topography with a subsequent analysis by means of Fourier analysis. The analysis of various car body sheet grades by means of this technique for uniaxial and biaxial loading conditions is presented in this paper.

Modelling Nucleation of Recrystallisation in Aluminium Alloys

The predictions from a grain cluster deformation texture model, GIA, are utilized to study the nucleation texture of recrystallisation of aluminium alloys. In combination with a dislocation based work hardening model, the propensity of specific grains in their granular environment for select nucleation mechanisms is investigated. Quantitative criteria for the nucleation events can be formulated. The results can be fed into a growth model of recrystallisation to predict recrystallisation textures and lend themselves to through-process modelling.

A Combined TEM and Atom Probe Approach to Analyse the Early Stages of Age Hardening in AA 6016

In this study we aim at combining the results from transmission electron microscopy (TEM) and atom probe tomography (APT) to study the early stages of phase decomposition in the age hardening alloy AA 6016. Samples are subjected to different periods of natural ageing or artificial pre-ageing at elevated temperature in order to produce different types of clusters and early stages of precipitation before age hardening commences. APT is utilized to detect clusters and identify their compositions, whereas TEM is applied to analyse and quantify number density and sizes of the particles during artificial ageing at 185°C. It is shown that the two techniques, TEM and APT, are complementary and a combined approach yields more detailed insight into the early stages of phase decomposition in age hardening 6xxx series alloys than possible by the sole use of either technique individually.

Quantification of roping in aluminium sheet alloys for car body applications by combining 3D surface measurements with Fourier analysis

Abstract The present study introduces a new method to characterise and evaluate the roping behaviour of aluminium sheet alloys of the AA 6xxx series for car body applications. The new approach combines two known methods into a novel powerful tool, (i) the measurement of a 3D surface topography with a white-light interferometer and (ii) the subsequent data analysis by means of Fourier analysis. Use of the white-light interferometer allows analysing roping of deformed samples without the need of additional surface preparation steps, e.g. inking, stoning, etc., which may falsify the surface appearance. The use of data analysis by means of fast Fourier transform allows differentiating between different surface phenomena, e.g. unidirectional component versus isotropic components. It was found that the new approach is capable of giving reliable and reproducible data, which qualifies this method to study roping in aluminium car body sheets in an objective manner.