Matthias Schmidtchen

Effect of Inter-Metallic Phases on the Bonding Strength and Forming Properties of Al/Mg Sandwiched Composite

Composite sheet of Twin Roll Cast (TRC) AZ31-Mg alloy and industrial pure Al-1050 was fabricated as Al/Mg/Al with a hot roll bonding process. As the diffusion zone at the interface between the layers plays a crucial role in the formation of bonding strength and formability of clad sheets. It is important to describe the processes of inter-diffusion layer generation in order to assess the abilities of the laminate composites for further processing. Thus, the aim of this study was to investigate the development of the bonding strength, microstructure and mechanical properties of the bonding interface directly after roll bonding and additionally post-annealing processes. Microstructure characterization techniques such as optical and scanning electron microscopy including energy dispersive X-ray analysis (EDX) were applied to investigate the bonding area. No inter-metallic phases were present directly after the roll bonding process. The creation and growth of Al2Mg3 and Al12Mg17 phases were apparent after annealing at temperatures of 250 to 400 °C at different times ranging from five to 120 minutes. The results prove that the growth rate of inter-metallic phases increases considerably with an increase in the annealing temperature. The micro-hardness of the interface-area was also investigated. It was observed that the two inter-metallic phases were significantly harder than the substrate Mg and Al. In order to examine the influence of the inter-metallic phases on the resulting bonding strength after the annealing process, the shear bonding strength test has been conducted for different samples that were annealed at different heat treatment conditions. The results indicate that the optimum annealing temperature is 200 °C leading to a maximum bonding strength. Moreover, the mechanical properties of the composite after roll bonding and post annealing were determined by means of room temperature tensile test. The fracture mechanism after tensile test was also discussed.Keywords:Rollbonding,Al/Mghotrollbonding,TwinrollcastAZ31,bondingstrength

Simulation of Inhomogeneous Materials Evolution in Hot Rolling Using a Layer Model

A fast simulation of the inhomogeneous materials evolution during the deformation steps and its effect on subsequent processes is demanded for the development of new technologies for materials with a homogeneous microstructure. In the paper a layer model for flat hot and cold rolling is presented. A deepened understanding of the influence of inhomogeneities in material state and material flow on the whole process can be reached due to the introduction of a new computational concept for variable layer thickness distributions in the layer model. The concept will be explained and the additional information obtained concerning the influence of shear, local residual stresses as well as inhomogeneous stress and strain states in the roll gap on the microstructure evolution will be presented and discussed.

Dynamic Recrystallization Behaviour of Twin Roll Cast AZ31 Strips during Hot Deformation

The recrystallization behaviour of a Twin Roll Cast AZ31 alloy, under deformation conditions corresponding to the initial stands of a magnesium hot rolling process, has been investigated. A set of strain levels, beginning at the critical strain for the onset of dynamic recrystallization has been studied. The dynamic recrystallization, taking place during hot deformation of magnesium alloy AZ31 is analyzed with help of plane strain compression tests conducted together with microscopic examination. Dynamically recrystallized volume fraction and size of dynamically recrystallized grains increase with increasing strain. When the strain is constant, the dynamically recrystallized volume fraction is higher at higher deformation temperatures or lower strain rates. Furthermore, it has been found out that deformation temperature plays a major role, rather than strain rates, in activating the dynamic recrystallization process during deformation. The results were used to identify the coefficients for the JMAK-model approach on the dynamic recrystallization of an AZ31 TRC-sheet.

Numerical Simulation of Hot Rolling

In the present paper actual demands for modern simulation strategies for hot rolling are discussed. The main focus of the discussion is on material flow simulation for hot rolling and the computation of material inhomogeneities. An overview on simulation techniques for material flow and microstructure evolution is given. Approaches for new simulation strategies which give fast results with a high modeling depth are discussed. As a result of actual investigations a fast model for material flow is presented.

Extension of the Freiberger Model of Spread for the Calculation of Material Flow during Rolling of Long Products to a New Material Group of Mg Alloys AZ31, AZ81, WE43

This article shows the extension of an empirical model for the numeric calculation of the spread during rolling Freiberg in calibres developed at TU Bergakademie to Mg alloys AZ31, AZ81 und WE43.The material independent foundations were developed at the Institute of Metal Forming at TU Bergakademie Freiberg.The Freiberger spread model has, through numerous rolling trials and examinations of the material flow, been broadened. Furthermore, the results of the calculations were compared with these trials.The Freiberger model for spread takes the geometrical input and output parameters into consideration, as well as the material flow, the deformation rate v, the deformation temperature θ, the chemical composition of the material Cw, longitudinal tension CL, and friction Cμ between the rolling stock and rolls. And it further considers the diagonal ratio CA∗aKNn of the box pass and the filling ratio of the box pass m.

Hot rolling simulation for non-oriented electrical steel

For improving material properties, a fundamental knowledge of all processing steps is necessary. Non-oriented electrical steels are characterized by low losses and a high permeability in the final application. To achieve high grades, every processing step needs to be coordinated with the previous and subsequent one. Simulation tools are useful to harmonize these steps. Experimental investigation had shown, that a heterogeneous material flow and microstructure evolution is a key feature for bcc Iron-Silicon alloys. Therefor hot rolling of non-oriented electrical steel with a silicon content of 2.4 wt.% is simulated by the software LaySimS that allows a fast investigation of heterogeneous deformation stated during rolling. In comparison to experimental rolling trials on a semi-continuous rolling mill the area of validity is predicted and shown. The focus of a comparison between experiment and simulations is put to the microstructure after hot rolling.

Haftfestigkeit und Stofffluss beim Walzplattieren sowie Walzen von Werkstoffverbunden - Theorie und Experiment

Moderne Anwendungsgebiete fur plattiertes Halbzeug erfordern den Einsatz sehr hochwertiger und kostenintensiver Metalllegierungen. Hinzu kommen die begrenzten Vorkommen an Nichteisen- und Edelmetallrohstoffen. Beides erzwingt die Optimierung des Materialeinsatzes. Weiterhin erfolgt der Einsatz von Halbzeugen mit Eigenschaftskombinationen, die mit herkommlichen Legierungen nicht erreichbar sind (z. B. sehr hohe mechanische Festigkeit mit sehr guter elektrischer Leitfahigkeit).

Walzkonzept für die Kalt- und Warmumformung neuer metastabiler Stähle auf der Flachbahn

Die vorgestellten Untersuchungen beschaftigen sich mit der Formgebung metastabiler, hochlegierter CrMnNi Stahle mit TRIP/TWIP-Effekt mittels Kaltund Warmwalzen. Infolge einer Kaltumformung konnen diese Stahle sowohl eine deformationsinduzierte martensitische Phasenumwandlung, als auch eine verformungsinduzierte Zwillingbildung aufweisen. Diese Martensitbildung ist gleichzeitig Ursache eines sehr guten Verfestigungsvermogens. Um die damit einhergehende Dehnungsanomalie ausnutzen zu konnen, sind neue Walzstrategien erforderlich. Wird im elastischen Umformbereich bereits spannungsinduziert Umformmartensit gebildet, so setzt dieser sogar das Umformvermogen herab., Konventionelle Walzstrategien konnen deshalb nur begrenzt angewendet werden. Ziel war es demnach, Walzkonzepte fur die Kalt- und Warmumformung fur diese Werkstoffgruppe zu entwickeln. Unter Beachtung der werkstoffspezifischen Kennwerte, wie Auslosespannung, Stapelfehlerenergie sowie Martensitstart- und -umwandlungstemperatur, konnten sowohl fur die Kalt- als auch fur die Warmumformung mit dem Freiberger Stichplanmodell Stichfolgen entwickelt werden. Die Anwendbarkeit der Walzkonzepte konnte experimentell nachgewiesen werden.

Model Approaches for Simulation of Processes in Rod and Wire Production

Actual improvements in rod or wire production e.g. in relation to power requirements, energy consumption and final material properties demand powerful simulation tools for process optimization, pre-setting calculations or automation. The groove pass design model of TU Bergakademie Freiberg was developed and applied for this purposes. This paper gives a short review of the history of this model approaches and highlights some important stages of development.

Investigation of the influence of the chemical composition of HSLA steel grades on the microstructure homogeneity during hot rolling in continuous rolling mills using a fast layer model

The newly developed LaySiMS simulation tool provides new insight for inhomogeneous material flow and microstructure evolution in an endless strip production (ESP) plant. A deepened understanding of the influence of inhomogeneities in initial material state, temperature profile and material flow and their impact on the finished product can be reached e.g. by allowing for variable layer thickness distributions in the roll gap. Coupling temperature, deformation work and work hardening/recrystallization phenomena accounts for covering important effects in the roll gap. The underlying concept of the LaySiMS approach will be outlined and new insight gained regarding microstructural evolution, shear and inhomogeneous stress and strain states in the roll gap as well as local residual stresses will be presented. For the case of thin slab casting and direct rolling (TSDR) the interrelation of inhomogeneous initial state, micro structure evolution and dissolution state of micro alloying elements within the roughing section of an ESP line will be discussed. Special emphasis is put on the influence of the local chemical composition arising from direct charging on throughthickness homogeneity of the final product. It is concluded that, due to the specific combination of large reductions in the high reduction mills (HRM) and the highly inhomogeneous inverse temperature profile, the ESP-concept provides great opportunities for homogenizing the microstructure across the strip thickness.