Materials Science Forum Vols. 519-521

Abstract: This paper describes some aspects of reconstruction of microstructures in three dimensions. A distinction is drawn between tomographic approaches that seek to characterize specific volumes of material, either with or without diffraction, and statistical approaches that focus on particular aspects of microstructure. A specific example of the application of the statistical approach is given for an aerospace aluminum alloy in which the distributions of coarse constituent particles are modeled. Such distributions are useful for modeling fatigue crack initiation and propagation.

Abstract: Recently, average automobile weight has shown the tendency of increasing, due, in part, to the the addition of equipment to improve convenience, comfort and safety. At the same time, to help reduce CO2 emissions in the global environment, vast improvment to automobile fuel consumtion is needed. More and more, vehicle weight reduction is being pursued in order to improve fuel economy, but always with a consideration not to sacrifice performance. A design that includes aluminum can be very effective for reducing vehicle weight, however, it is also true that with aluminum there is a concern for increased cost. The use of aluminium alloys in Japan for vehicles started with castings for engines and transmissions. It continues to rival steel for applications in body and chassis components, especially now with the development of higher tensile strength steels. For the expanded use of aluminum, cost effective strategies, such as that of complex part integration, are necessary, to say nothing of the need for a reduction in raw material cost.

Abstract: 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.

Abstract: This paper sets out the needs for and recent advances in microscopy in Al alloys, using solutesolute and solute-vacancy clustering as examples. Cluster-assisted nucleation and cluster strengthening are discussed and this is followed by a discussion of the local electrode atom probe. Heuristic and algorithmic tools for assessing the nanoscale microstructure or nanostructure of Al alloys acquired from atom probe tomography experiments are then presented.

Abstract: For aerospace structural applications of age-hardenable aluminum at temperatures above 100°C, a primary alloy-design criterion is creep resistance which depends on the strengthening effect and thermal stability of the second phases.. First principle calculations can be used to study fundamental properties of these phases and, therefore, help to identify the desired ones and their precipitate structures. In order to produce the desired phases, which are usually thermodynamically metastable, and to suppress the undesired phases, computational analysis (combining first principle calculations, cluster variation methods and CALPHAD) can assist in identifying beneficial trace additions and deleterious impurities that must be eliminated. This paper, using Al-Cu-Mg as an example, illustrates this approach, which if successful, should shorten the normal alloy development period.

Abstract: Processing through the application of severe plastic deformation (SPD) has become important over the last decade because it is now recognized that it provides a simple procedure for producing fully-dense bulk metals with grain sizes lying typically in the submicrometer range. There are two major procedures for SPD processing. First, equal-channel angular pressing (ECAP) refers to the repetitive pressing of a metal bar or rod through a die where the sample is constrained within a channel bent through an abrupt angle at, or close to, 90 degrees. Second, high-pressure torsion (HPT) refers to the procedure in which the sample, generally in the form of a thin disk, is subjected to a very high pressure and concurrent torsional straining. Both of these processes are capable of producing metallic alloys with ultrafine grain sizes and with a reasonable degree of homogeneity. Furthermore, the samples produced in this way may exhibit exceptional mechanical properties including high strength at ambient temperature through the Hall-Petch relationship and a potential superplastic forming capability at elevated temperatures. This paper reviews these two procedures and gives examples of the properties of aluminum alloys after SPD processing.

Abstract: The work hardening of Al alloys is very important in regards to their formability and their deformation behavior in service. The majority of the work in the literature has considered relatively pure materials, and has tended to concentrate on room temperature and elevated temperature behavior. In Al alloys there is interest in work hardening at lower temperatures since they are quite restricted in terms of the elevated temperatures at which they can be used. In this paper the work hardening of commercial 1000, 3000 and 5000 alloys have been investigated from room temperature down to 85°K. The work hardening has been analyzed using the Voce approach, and it is shown that this enables the work hardening of the different alloys to be related to their basic physical metallurgy.

Abstract: The microstructure in heavily deformed metals can be characterized as a complex “mixture” of low and high angle boundaries. By careful annealing of such cold deformed conditions, ultra-fine grained materials can be obtained. This phenomenon has been known for long and utilised in the production of special aluminium sheet qualities, and has received new interest with the emergence of the equal channel angular pressing (ECAP) technique. This work reviews the mechanical properties resulting from plastic deformation and annealing of aluminium, looking at alloys which prior to annealing was subjected to both severe plastic deformation (ECAP) and more conventional deformation by cold rolling. The effect of the resulting microstructures on the subsequent work hardening properties are model, applying the new microstructural metal plasticity model (MMP-model) developed in Trondheim over the last decade.