Jürgen Hirsch

Texture control by thermomechanical processing of AA6xxx Al–Mg–Si sheet alloys for automotive applications—a review

Abstract The properties of Al-alloys for car body applications are largely controlled by microstructure and crystallographic texture of the final sheets. In this paper, the impact of texture on formability and, in particular, on surface appearance of the sheets is reviewed. The paper summarizes the principles of microstructure and texture evolution during the main steps of the thermomechanical processing of age-hardenable Al–Mg–Si sheets (6 xxx series alloys). The most important parameters that may be used to modify the textures and hence to improve the resulting properties are outlined.

Textures in Industrial Processes and Products

Textures and related anisotropy effects which occur in certain industrial processes are presented for as-cast, deformed and annealed (recrystallized) Aluminium alloys and products. They are analyzed in detail and discussed based on their formation mechanisms, which are growth selection during solidification and the formation of new grains during casting and recrystallization, glide on selected slip planes during plastic deformation and oriented nucleation and oriented growth of new grains during recrystallization. Alloy composition and constitution that control microstructure evolution during processing (e.g. casting, extrusion, hot and cold rolling, annealing) determine the material quality and product performance.In these cases industrial processing of Aluminium alloys is specifically designed to control textures to achieve superior anisotropic properties and so better meet special product requirements. Examples are given for resulting properties, like strength and formability / anisotropy effects in packaging and automotive sheet applications. Other examples are given for the etching behaviour of high purity Aluminium capacitor foil and strength anisotropy of age hardened extrusions for aerospace applications.

Through Process Modelling

A new approach to improve existing and develop new simulation models and apply them in a sequence to simulate the complete production processes of Aluminium semi-finished products is described. The development has been a joint effort of academic and industrial partners developed in the frame of the VIR* European projects. It integrated advanced material models with industrial fabrication process models to predict the microstructures and properties in the complete production chain processes of Al sheet and profiles, i.e. by DC ingot casting, rolling and extrusion and analyze complex interactions of critical process parameters with the corresponding metallurgical mechanisms and predict the related material response and properties. The principles are discussed and examples are given for their successful application to simulate industrial fabrication processes.

Texture Evolution and Earing in Aluminium Can Sheet

The texture evolution during hot and cold rolling of AlMg1Mn1 can body sheet is described and the related anisotropy effects during deep drawing are analysed quantitatively. The typical textures of rolled aluminium show the transition between ß-fibre orientations and cube recrystallization texture, depending on rolling temperature and strain. These correlate with transitions between 45° and 0°/90° ear heights in deep drawn cups which are described by a new method of Fourier series expansion. Processing parameters to achieve low anisotropy are discussed.

Hot Formability and Texture Formation in Al Alloys

The effect of plastic deformation of Aluminium alloys at elevated temperatures is described and its effects on texture evolution in Aluminium and its alloys. The softening mechanisms involved are recovery, recrystallization and grain boundary sliding which reduce strain hardening and affect plastic deformation also in industrial fabrication and forming processes of Aluminium alloys, like (hot) forming, rolling, extrusion and superplastic forming. These effects that control high temperature formability and the resulting textures and final properties are described.

Effect of Dispersoids on Long-Term Stable Electrical Aluminium Connections

In electrical power systems bolted joints with bus bars made of aluminium are common, whereby the tendency towards higher operating temperatures can be observed. At higher temperatures a reduction of the joint force can occur due to creep and/or stress relaxation processes, which leads to an increasing electrical resistance and, in the worst case, to failed joints. The aim of this project is to increase the creep resistance (and to minimise the stress relaxation) of aluminium conductors for electrical applications without a significant reduction in their electrical conductivity – even after long-term exposure to elevated temperatures. The effect of dispersoids in different aluminium alloys on the longterm behaviour of currentcarrying joints at high temperatures (i.e. 140 °C) was investigated. Longterm tests on bolted joints with force measuring devices were performed to monitor the joint forces and to measure the joint resistances, both with and without current supply.

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.