Luca Tomesani

Microstructure analysis of aluminum extrusion: grain size distribution in AA6060, AA6082 and AA7075 alloys

Microstructure and material flow of aluminum alloys have a significant influence on the mechanical properties and surface quality. In extrusion of aluminum billets at high temperatures the microstructure is dependent on the alloy and the forming and temperature history. A prediction of grain size and precipitation is of increasing importance in order to design the process by adjustment of parameters such as punch speed, temperatures, and quenching. To give references for microstructure prediction based on material flow, and with it strain and strain rate history, this paper deals with the microstructure during the extrusion process of AA6060, AA6082, and AA7075 alloys. Billets have been partly extruded to axisymmetric round profiles and the microstructure of the press rests consisting of the billet rests in container and die has been considered. Furthermore, these rests have been analyzed to show the material flow, dynamic and static recrystallization based on macro etchings and visible microstructure under different conditions, e.g. as in the area of high strain rate near the container wall, or in dead zones [1]. To allow an accurate simulation of the extrusion process, punch force and temperature conditions during the tests have been measured and are presented in this paper, too.

Seam Welds in Hollow Profile Extrusion: Process Mechanics and Product Properties

In this paper a review of several papers published on seam weld formation also by the authors is presented and discussed: the process mechanics is deeply investigated and several experimental results are related to process parameters by means of FEM simulations. The relation between die design and local welding parameters, such as contact pressure, temperature, time of contact, strain and strain rate paths is analyzed. In particular, by testing profiles extruded in different conditions, it was found that it is possible to find optimum processing conditions for a welded profile to behave like a not welded one. The possibility to adopt criteria for assessing the welding quality is finally discussed, together with its implementation directly inside process FEM codes.

Seam Welds Modeling and Mechanical Properties Prediction in the Extrusion of AA6082 Alloy

This work summarizes the outcome of recent research by the authors on modeling the formation of seam welds in aluminum extrusion and on evaluating the related mechanical properties on the final products. A profile with a seam weld in the middle section was produced with different die designs in order to investigate the relation between die design and local welding parameters, such as contact pressure, temperature, time of contact, strain and strain rate paths. The local welding conditions were evaluated by complete thermo-mechanical 3D FEM simulation of the processes. Specimens were extracted from the profiles and tensile tested, the resulting mechanical properties being discussed with respect to the local welding conditions. The possibility to adopt criteria for assessing the welding quality is discussed, together with the effect of high speed damage cracking.

Extrusion Benchmark 2007 – Benchmark Experiments: Study on Material Flow Extrusion of a Flat Die

The experimental conditions chosen as a reference for the 2007 edition of the extrusion benchmark and the corresponding main results are summarized in this work. The die design stage is first explained in order to address the main features of the experiment and its objectives. The die is a flat one with multiple holes; four angular profiles were produced with different pocket geometries, the experimental plan being entirely described. The initial temperatures for the billet and the die set, together with the temperature development during the process strokes are also reported. The results are shown, for each profile, in terms of final profile length, mean exit speed, global process load, profile exit temperature.

Microstructure Prediction of Hot-Deformed Aluminium Alloys

In this paper, a deformation test method to reproduce, on a laboratory scale, the microstructure evolution of aluminium alloys occurring during industrial forming processes with a limited number of tests is presented. A hot inverse extrusion setup was designed in order to generate, inside one single specimen, a wide range of strains at a given temperature and ram speed. Two commercial aluminium alloys (AA6060 and AA6082) were investigated at different processing conditions (temperatures and forming rates). Detailed optical microstructures were examined and grain sizes were determined at different spots of each specimen. Thermo-mechanical coupled simulations of the deformation tests were performed using the DEFORM 3D FEM code. On the basis of recrystallization equations, the distributions of strains, strain rates and temperatures were correlated to the grain sizes measured through linear regression. Finally, FEM simulations were run again with the established recrystallization model, and the results were compared with the experimental data.

Modelling heat transfer coefficient at cast/chill interface to account for effects of metal head

Abstract The evolution of heat transfer coefficient (HTC) in the sand casting of A357 aluminium alloy against aluminium chills is evaluated with different metal heads to study the effect of pressure on the HTC. Inverse modelling techniques based on Becks analysis were used to determine the experimental evolution of HTC as a function of time, casting temperature and chill temperature. The experiments were reconstructed by means of numerical analyses to determine the best way to fit the experimental data. Two approaches were considered: in the first, a simple thermal analysis of the solidification was carried out with the HTC depending on both the interface casting temperature and the effective metal head as determined from the experiments; in the second, a coupled thermal stress analysis was performed with the HTC dependent on the interface pressure.

Effect Of Die Design On Strength And Deformability Of Hollow Extruded Profiles

In this paper, the behaviour of two different die design concepts in the production of the same industrial profile is described by both experimental tests and numerical FEM analysis. The investigated parameter is the shape of the leg for the extrusion of an AA6060 round tube 80mm in diameter and 1mm in thickness. Press loads and profile temperatures were monitored during the production. The processes are simulated by means of Deform 3D fully coupled simulations. and the results compared with the experimental ones. The profile are characterized by means of tensile tests in order to evaluate strength and deformability of the joints, and the results are related to the welding parameters as they were obtained by FEM. Finally, the die stress is investigated in order to explain tool life behaviour of the dies as it was observed during their whole life.

The Use of Extruded Profiles as Filling Material in Friction Stir Welding (FSW)

In this paper, an innovative approach is presented for joining two sheets with an extruded profile all made by AA6082-T6 aluminum alloy. The tested configuration is the T-joint and the innovation presented in this paper is the use of a specially design appendix of the extruded profile as filler material during the friction welding. In particular three configurations were analyzed: without appendix, with I appendix and with T appendix. In the experiments, several process parameters and PIN shapes were investigated in order to determine optimal processing conditions able to produce an effective sound weld. Specimens were extracted from the joint and tensile tests were performed along the sheet direction thus allowing a comparison of the welded sections respect to the base material. It was found that the appendixes of the extrude profile are able to effectively fill the distance between the sheets and, in particular with the T shape, a gap up to 1,7 mm on the retreating side was successfully welded.

The Influence of the Metal Head on the HTC Evolution in the Sand Casting of A357

The influence of the effective metal head height on the HTC (Heat transfer coefficients) in sand casting of A357 aluminum alloy is analyzed here. Different metal heads were used for the same casting process, evaluating the heat transfer at the metal-chill interface. Thermal analysis and inverse modeling techniques were used, based on the temperature measurements at selected locations in the casting and the chill. The experiments were specifically developed for replicating typical sand casting manufacturing conditions. Aluminum was used as the chill material. Evolutions of HTC and heat flow are reported as a function of time, casting temperature, chill temperature and variation in temperature between casting and chill.

Microstructure Prediction in Aluminium Extrusion by Means of FEM Simulation

An original inverse extrusion test was developed in order to study the microstructural evolution in the plastic deformation of 6060 and 6082 aluminium alloys. Sample billets were extracted from commercial logs and subjected to plastic deformation in an inverse extrusion process, particularly aimed at producing different strain and strain rate conditions at representative positions within the billet section. Different experiments were performed at various temperatures and strain rates. The particular thermo-mechanical history of each point in different experiments was then reconstructed by FEM analysis. The cups were sectioned and the microstructure was analysed at some representative locations, to relate it to the FEM simulation results.