Microstructural, texture, plastic anisotropy and superplasticity development of ZK60 alloy during equal channel angular extrusion processing

In this study, equal channel angular pressing (ECAP) was exploited to refine the grain size of a ZK60 magnesium alloy in multi-processing steps, namely at temperatures of 250˚C, 200˚C and 150˚C, producing an ultrafine-grained (UFG) structure. The microstructural development and texture evolution during ECAP were systemically investigated by electron backscattered diffraction (EBSD) analysis. The microstructure of the ECAP processed alloy was remarkably refined to an average grain size of 600 nm. During ECAP process the original fiber texture of the as-extruded alloy was gradually weakened and eventually replaced by a stronger texture component coinciding with ECAP shear plane. The ECAP processed material showed a proper balance of tensile as well as compression strength and tensile ductility at room temperature. Yield strength of 273 and 253 MPa in tension and compression, respectively, ultimate tensile strength of 298 MPa and fracture elongation of about 30% were obtained in the UFG alloy. A transition from ductile–brittle to ductile fracture consisting of very fine and equiaxed dimples was also found in the ECAP processed material. Compared to the as-received alloy, a combination of grain refinement and texture development in the UFG alloy gave rise to a notable reduction in mechanical asymmetric behavior at room temperature. The superplastic behavior of the as-extruded and ECAP processed alloy was also investigated at 200˚C with strain rate of 1.0×10-3 s-1. The concurrent effect of grain boundary sliding and favorable basal texture in the UFG alloy led to an achievement of elongation value of about 300% while, under similar testing conditions, the elongation of about 140% was obtained in the as-extruded alloy

Adjustment of Numerical Simulation Model to the Investment Casting Process

This paper presents the adjustment process of a simulation model to improve the correlation between simulation results and parts industrially manufactured. It includes the data registration at foundry plant, the preliminary set-up of the model and the later adjustment process to reach a correlation level according to the industrial necessities. The adjustment has been performed by means of inverse modelling. This technique uses thermal histories experimentally registered as base, and modifies the material properties and boundary conditions used in simulation until reaching a good correlation between numerical simulated cooling curves and they registered experimentally. The adjustment has been also focused on the shrinkage defects. The simulation model is a FEM model developed in commercial software specifically focused on metal casting simulation. The case of study is an investment casting process, vacuum poured, of a nickel base superalloy designated Hastelloy X. Usual in the manufacture of components for aeronautical turbines.GALDATEK project, funded by the INNOTEK program of the Basque Government (Department of Industry and Innovation)

L’analisi termica di Fourier applicata alla modifica eutettica di una lega AlSi7

La “Fourier Thermal Analysis” (FTA) è una tecnica avanzata di analisi termica, sviluppata negli anni’80-’90 per determinare il calore latente rilasciato in fase di solidificazione, allo scopo di indagare sullecinetiche di nucleazione ed accrescimento delle varie fasi coinvolte. I risultati delle indagini condotte conquesta metodologia hanno contributo allo sviluppo dei codici di calcolo per la modellazione dei fenomenidi solidificazione di leghe da fonderia come le ghise e le leghe Al-Si. Scopo di questo lavoro è la verificadelle potenzialità della FTA nello studio della modifica eutettica di una lega Al-Si, e più in generale nelladinamica della solidificazione delle leghe Al-Si. La modifica eutettica viene impiegata allo scopo diincrementare le caratteristiche di resilienza e resistenza a fatica delle leghe Al-Si, l’efficacia deltrattamento è vincolata alla presenza di una percentuale minima di elemento modificante. L’analisitermica può essere impiegata per verificare il livello di modifica della lega, e quindi l’efficacia deltrattamento. È stata presa in considerazione una lega della classe A356, modificata con Na metallico, esono state confrontate le curve fs(t) e fs(T) ottenute con diversi livelli di modifica, allo scopo di correlarele caratteristiche delle curve di frazione di fase solida rispetto al tempo ed alla temperatura con lecaratteristiche microstrutturali della lega

Fourier thermal analysis applied to sodium eutectic modification of an ALSI7 alloy

The so-called "Fourier Thermal Analysis" (or FTA) is an evolution of the "integral thermal analysis", which is actually used as a process control in Aluminium and cast iron foundries. It has been developed since late 80´s in order to investigate nucleation and growing kinetics of the various phases in multi-component alloys. FTA is based on the evaluation of the thermal gradient in one-dimensional thermal field that arises in a cylindrical solidifying specimen. During the last twenty years, both the traditional thermal analysis and FTA have been applied to the experimental determination of the solid fraction during solidification, in order to assess results from numerical simulation. Nevertheless, FTA has not been applied to foundry process control or optimisation.Eutectic modification is extensively used in low-pressure permanent mould processes, in order to improve tensile properties and toughness of Al-Si alloys. The effectiveness of the treatment is subjected to the presence a minimum amount of modifying elements, such as Sr, Na or other elements. Traditional thermal analysis is useful in determining modification level of the alloy, then to control the modification treatment. Aim of this work is to verify the potentiality of gradient-based thermal analysis method, such as FTA, in eutectic modification investigation. An A356-type hypoeutectic Al-Si alloy has been modified with metallic sodium at four different modification levels. Two-thermocouple thermal analysis curves have been recorded, in order to perform FTA analysis. Fraction solid versus time (fs(t)) and temperature (fs(T)) have been determined at different modification levels. Microstructural characterization has been made using automatic image analysis. Average values of dimension and roundness of eutectic Si have been compared to thermal analysis results.A significant correlation between the so-called "eutectic depression" and silicon morphology has been observed. More relevant is the behaviour of the fraction solid curves, from which it is possible to note a significant delay in the start of eutectic reaction. This delay has been observed not only in time but also in temperature and fraction solid domain

Design and realization of an experimental cold crucible levitation melting system for light alloys

Thanks to their properties of ultra-lightness and high strength/weight ratio, Mg and Al alloys find increasingemploy in aerospace, automotive and biomedical applications. These alloys can be formed using all theconventional technologies used for other materials, like casting and forming. However, the mechanicalproperties of the final components are significantly influenced by the quality of the starting liquid metal.In fact, the quality of the starting liquid metal has been substantially increased in recent years, thanks to theimprovement of cleaning technologies. To this purpose, electromagnetic processing of materials has evolved asan important experimental technique in the fields of material processing, associated with applications such asshape controlling, flow driving, online detecting, controlled heat generation, inclusion removing, magneticlevitation. In particular, electromagnetic levitation, as a promising technique, can be helpful to create somenew phenomena and discoveries, especially in melting process. This work describes the design, optimizationand realization of a cold crucible levitation melting (CCLM) system for light alloys. Electromagnetic models areused and applied in FEM codes to numerical simulate the working range of the CCLM.The simulation results show good agreement with experimental data

Evaluation HPDC Lubricant Spraying for Improved Cooling and Die Protection

This study tries to find out a better cooling and temperature homogenization as well as better die protection on high-pressure die-casting (HPDC) spray lubrication. Test procedures have been set up to study the Leidenfrost point (LFP), contact angle (CA), film thickness and protection from die soldering of lubricants typically applied into the die surfaces during HPDC process. Five different lubricants have been studied as well as the influence in different controllable process parameters (type of die material, oxidation of the surface, temperature, roughness, droplet diameter, water hardness and lubricant concentration). The increase of the LFP, avoiding film boiling regime, and a reduced CA, improve the cooling and film ability of die surface during spraying. The best chemistry exhibits high LFP, shows an increased thickness of the formed film and is more effective preventing the sticking of the aluminum part to the die surface. Thermogravimetric analysis shows better thermal properties for lubricants with anti-sticking performance. The study performed and the test protocols set up result in a better insight of the involved phenomena and allow selecting the most favorable operating window for HPDC lubrication

Solubilizzazione isoterma della fase sigma in un acciaio superduplex UNS S32760

In questo lavoro si riportano i risultati delle prove di solubilizzazione isoterma della fase sigma eseguite su unacciaio inossidabile superduplex UNS S32760. Il materiale base è stato dapprima sottoposto a trattamentiisotermi a 1173 K e poi solubilizzato a 1323 K e a 1353 K. La cinetica di solubilizzazione è stata valutataprelevando i campioni dal forno a diversi intervalli di tempo e misurando la percentuale rimanente di precipitatomediante analisi di immagine. I risultati, riportati in termini di curve, mostrano, per le diverse temperature ditrattamento, la variazione di fase sigma in funzione del tempo e della percentuale iniziale di precipitato. Infine,è stato sviluppato un modello semiempirico che descrive con buona accuratezza i dati sperimentali

Evidence of a hormetic effect in growth inhibition algal test.

Elutriation process was applied on sediments of Guanabara Bay (Rio de Janeiro, Brazil), a very polluted coastal ecosystem, in order to determine their potential toxicity. Elutriates were tested using Skeletonema costatum, an eurialin Diatom. Several ratios of elutriate/growth medium (v/v) were assayed (1:10, 1:4, and undiluted) as cultural medium for exponentially growing algae, carrying out a blank control for each replicate. Tests were performed for five days, controlling algal growth by manual cell counting by microscope, in order to verify the status of the organisms every assay’s day. This experimental design was proved able to highlight a particular phenomenon, i.e. hormesis. Regarding some sites in the southern part of the Guanabara Bay growth curves, relative to lower sediment elutriate dilutions, showed, in fact, a so called toxic stimulation typical of hormetic event. On the contrary undiluted elutriates never permitted algal growth. Obtained results could help furthermore to explain the particular eutrophic situation of the water body, in which there is a high superficial eutrophization and absolute life deficiency in the deeper water column