Stefan Pogatscher

Influence of trace impurities on the in vitro and in vivo degradation of biodegradable Mg-5Zn-0.3Ca alloys

The hydrogen evolution method and animal experiments were deployed to investigate the effect of trace impurity elements on the degradation behavior of high-strength Mg alloys of type ZX50 (Mg-5Zn-0.3Ca). It is shown that trace impurity elements increase the degradation rate, predominantly in the initial period of the tests, and also increase the materials susceptibility to localized corrosion attack. These effects are explained on the basis of the corrosion potential of the intermetallic phases present in the alloys. The Zn-rich phases present in ZX50 are nobler than the Mg matrix, and thus act as cathodic sites. The impurity elements Fe and Mn in the alloy of conventional purity are incorporated in these Zn-rich intermetallic phases and therefore increase their cathodic efficiency. A design rule for circumventing the formation of noble intermetallic particles and thus avoiding galvanically accelerated dissolution of the Mg matrix is proposed.

In-situ probing of metallic glass formation and crystallization upon heating and cooling via fast differential scanning calorimetry

The crystallization of small-scale Au-based metallic glass samples was investigated by fast differential scanning calorimetry. Rapid cooling and heating makes possible in-situ probing of glass formation from the supercooled liquid state or direct transition from the glassy state to the equilibrium liquid and, thereby, the determination of a critical cooling (Φc ∼ 600 Ks−1) and heating rate (Φh ∼ 6 × 103 Ks−1) for crystallization. Crystallization kinetics was studied in the whole supercooled liquid region by linear heating and isothermal calorimetry. We show that the temperature dependence of crystal growth is reflected in a “Kissinger plot” for Au49Ag5.5Pd2.3Cu26.9Si16.3 and compares well with a model for crystal growth in a glassy system. Linear heating and isothermal measurements after heating the glass show that its crystallization is always growth-controlled up to its temperature of melting. In contrast, for a low degree of direct undercooling from the equilibrium liquid isothermal crystallization is ...

Compositional dependence of shear-band dynamics in the Zr-Cu-Al bulk metallic glass system

Shear-band velocities of individual shear bands in ZrxCu90−xAl10 (x = 45–65) metallic glasses were investigated as a function of temperature and Zr-content. The apparent activation energy of the shear-band propagation dynamics increases with Zr-content, giving evidence for the sensitivity of inhomogeneous plastic flow and related time scales to chemical composition. The shear-band viscosities derived display a Zr-content trend which contrasts with equilibrium viscosities in the supercooled liquid regime. These findings are discussed in terms of effective temperature and short-range order.

Property Criteria for Automotive Al-Mg-Si Sheet Alloys

In this study, property criteria for automotive Al-Mg-Si sheet alloys are outlined and investigated in the context of commercial alloys AA6016, AA6005A, AA6063 and AA6013. The parameters crucial to predicting forming behavior were determined by tensile tests, bending tests, cross-die tests, hole-expansion tests and forming limit curve analysis in the pre-aged temper after various storage periods following sheet production. Roping tests were performed to evaluate surface quality, for the deployment of these alloys as an outer panel material. Strength in service was also tested after a simulated paint bake cycle of 20 min at 185 °C, and the corrosion behavior was analyzed. The study showed that forming behavior is strongly dependent on the type of alloy and that it is influenced by the storage period after sheet production. Alloy AA6016 achieves the highest surface quality, and pre-ageing of alloy AA6013 facilitates superior strength in service. Corrosion behavior is good in AA6005A, AA6063 and AA6016, and only AA6013 shows a strong susceptibility to intergranular corrosion. The results are discussed below with respect to the chemical composition, microstructure and texture of the Al-Mg-Si alloys studied, and decision-making criteria for appropriate automotive sheet alloys for specific applications are presented.

Correlation between Supersaturation of Solid Solution and Mechanical Behaviour of Two Binary Al-Si-Alloys

Cooling of age-hardening Al-alloys after solution annealing is a critical step with respect to distortion and residual stresses. In order to predict their extent by simulation models, the mechanical behaviour must be known in a wide range of conditions and compositions. Therefore, experimental data is needed both for calibration and validation of the mechanical model. It is known for Al-Mg-Si alloys that supersaturation of the solid solution leads to a significant increase of strength during cooling. In order to understand the influence of single alloying elements on the strengthening effect, the mechanical properties of different binary alloys are investigated experimentally. The precipitation behaviour during cooling was investigated by Differential Scanning Calorimetry in a wide cooling rate range. A methodology to determine the degree of supersaturation of the solid solution based on the calorimetric results is presented. This approach is compared to atom probe tomography data. The mechanical behaviour of the alloys after various heat treatments was analysed by mechanical tests performed in a quenching and deformation dilatometer. Flow curves with high resolution at small strains (< 3 %) were measured at different temperatures. The results of the different experimental techniques are discussed in comparison and with respect to their testing limitations.

THE ROLE OF CO-CLUSTERS IN THE ARTIFICIAL AGING OF AA6061 AND AA6060

In this study the role of Mg, Si-co-clusters formed during long-term natural aging on the artificial aging behavior was investigated by hardness measurements for the alloys AA6061 and AA6060. It was found that kinetics and age hardening response of artificial aging at common temperatures (e.g. 170 °C) are lowered by a strong presence of co-clusters, but enhanced at high temperatures (e.g. 250 °C) for AA6061. Co-cluster formation in the alloy AA6060 increases the age hardening response at 170 °C, but barely influences kinetics in both temperature regions. The co-cluster dissolution was analyzed by a model based on temperature dependent reversion of the hardness, which showed similar activation energies for both alloys. It is supposed that the different behavior of the alloys AA6061 and AA6060 can be explained by solute-vacancy interactions.

The Role of Vacancies in the Aging of Al-Mg-Si Alloys

In this paper the role of vacancies in the aging of Al-Mg-Si alloys is examined and novel concepts to improve their aging behavior are presented. It has been proposed that the technologically favored fast nucleation of the major hardening phase during artificial aging requires quenched-in vacancy assisted diffusion. The well-known interdependence of natural aging and subsequent artificial in Al-Mg-Si alloys can be understood in terms of quenched-in vacancy trapping in Mg/Si-clusters formed during natural aging. Diffusion during artificial aging is then determined by the dissolution of these vacancy-containing Mg/Si-clusters. This simple concept can guide the development of strategies to avoid the negative effect of natural aging. It is shown that the aging behavior of Al-Mg-Si alloys can be improved not only by processing related measures, but also by compositional interventions, which apply the following recipe: (i) avoid the trapping of vacancies in Mg/Si-clusters, (ii) prevent the vacancy annihilation during RT, and (iii) make them available for diffusion during artificial aging. It is shown that this strategy can be executed in Al-Mg-Si alloys by adding defined trace amounts of elements with an attractive binding energy to vacancies and sufficient solubility in the aluminum matrix.

Effect of Interrupted Quenching on Al–Zn–Mg–Cu Alloys

Al–Zn–Mg–Cu alloys are widely used in aged-hardened condition for aircraft applications because of their high strength, adequate fracture toughness, stress corrosion cracking resistance and good machinability. In this study the effect of interrupted quenching (I.Q.) from solution temperature to 25–225 °C on subsequent artificial ageing was studied. Hardness measurements, tensile tests and instrumented impact tests were used to characterize the mechanical properties of Al–Zn–Mg–Cu plates. The results indicate that a high hardness can be reached directly after I.Q. for medium I.Q. temperatures. Compared to standard water quenching, the results showed that hardening kinetics and the age hardening response during artificial ageing can be enhanced for I.Q. at medium artificial ageing temperatures, but are reduced at high temperatures. I.Q. at high temperatures affects subsequent artificial ageing via the formation of precipitates, which contribute less to hardening but consume a significant amount of solute.

Aktuelle Entwicklungstrends und zukünftige Herausforderungen im Bereich der Nichteisenmetallurgie

ZusammenfassungDer Umgang mit Rohstoffen und Energie ist für die industrielle Entwicklung Europas von großer Wichtigkeit. Dem Recycling kommt daher eine immer größere Bedeutung zu, wobei jedoch der gesamte Produktlebenszyklus betrachtet werden muss, sodass eine intensive Vernetzung von Rohstofftechnik, Metallurgie und Werkstoffwissenschaften in Zukunft einen wesentlichen Punkt darstellen wird. Darüber hinaus spielen Entwicklungstrends wie Industrie 4.0, Energiewende, E-Mobility, Wasserstofftechnologie usw. für die gesamte Nichteisenmetallurgie im Bereich der Prozesse und Produkte in den nächsten Jahren eine entscheidende Rolle.AbstractResources and energy have an essential importance for the industrial development in Europe. Especially the relevance of recycling processes will increase, which means that the life cycle of a product has to be considered. Therefore an intensive interaction of raw material technology, metallurgy, and material science will be necessary in the future. Furthermore, development trends, like “Industry 4.0”, alternative energy production, E-mobility, hydrogen technology, and more, will influence the nonferrous metallurgy in the field of processes and products within the next few years.

Influence of Chemical Composition and Process Parameters on Mechanical Properties and Formability of AlMgSi-Sheets for Automotive Application

The heat treatable AlMgSi-alloys of the 6xxx-series are widely used for automotive sheet applications due to their good combination of strength and formability. Magnesium and silicon are the main alloying elements in this group forming the agehardening phase Mg2Si. Moreover intentional addition of copper, manganese and also impurities (for example iron) can have a significant influence on the mechanical properties and on the forming behavior of automotive body sheets. Beside the chemical composition also thermo-mechanical process parameters can lead to changes in material properties. The purpose of this work is to investigate the influence of alloying elements and process parameters on (I) strength and (II) ductility in temper T4 and after the typical paint bake cycle at 185°C/20min. Furthermore (III) the formability of different AlMgSi-alloys is studied with bending tests, cross-die tests, hole expansion tests and FLC-analysis.