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

Sta Cast : Linee guida per la progettazione di getti in lega di alluminio

StaCast (New Quality and Design Standards for Aluminium Alloys Cast Products) è un progetto europeo dedicato allefonderie dell’alluminio con l’obiettivo di sviluppare una nuova classificazione dei difetti strutturali nei getti e di definiredei limiti di accettabilità di questi difetti a seconda della destinazione finale prevista. Il raggiungimento di questo obiettivoaiuterà significativamente le fonderie a ridurre il costo della non-qualità, migliorando nel contempo il loro margine dicompetitività grazie al conseguimento di importanti vantaggi, per esempio nei costi dell’energia. StaCast ha condotto unavasta indagine tra le fonderie europee per conoscere le caratteristiche principali della loro produzione, in quale misuraesse utilizzano gli Standard CEN, il bisogno di nuovi strumenti normativi riferiti ai difetti, alle proprietà meccaniche e allaprogettazione meccanica di getti in lega d’alluminio. Questo articolo presenta i principali risultati di tale indagine, che hacoinvolto circa 80 aziende, e l’impostazione dei documenti normativi che sono stati elaborati sulla Classificazione deiDifetti e sul Potenziale Meccanico di getti in lega d’alluminio

PROPOSAL OF A CLASSIFICATION OF DEFECTS OF HIGH-PRESSURE DIECAST PRODUCTS

The paper gives an introduction to the one of the current actions of the WG “Quality of High Pressure DieCast (HPDC) products” within the TC “High pressure diecasting” of the Italian Association of Metallurgy, The preparation and dissemination of common tools to allow foundries to define a proper, comparable, quality standard is in fact one of the current targets of this WG. The basic tool, to which this paper refers, is a common terminology and classification of defects of HPDC products. An initial survey of literature and industrially adopted classifications of defect in components cast in metallic dies, revealed that the geometry and origin-based approaches are often mixed giving rise to a wide range of hybrid classifications. The proposed classification of defects of HPDC products, discussed within the WG with the contribution of several foundries, is a multi-level, hybrid-type classification. In the first level defects are grouped on the basis of their position (surface/internal and geometry defects) according to the typical control operations during which they can be detected and to the effects of defects on the functionality of the parts. The second level of the classification groups defect in classes according to their general metallurgical origin. The proposed classification doss not specify defect/cause correlations, but gives starting points to the identification of their specific causes. In order to better specify these features the analogies between the origin of internal/surface defects are highlighted by corresponding names for Level II classes: gas-related, shrinkagerelated, filling-related, thermal contraction defects and undesired phases. In addition the class of metal/die interaction defects is proposed for surface defects. The specific defects identified are those included in the third level of the classification. In the present paper an introduction to the general classes of defects defined in Level II is proposed. The action of the WG concerning defect classification of HPDC parts will be completed with the compilation of the official document including the proposed classification and multi-language terminology equivalences

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)

CORRELATION BETWEEN MICROSTRUCTURE AND MECHANICAL PROPERTIES OF Al-Si CAST ALLOYS

The influence of microstructure and process history on mechanical behaviour of cast Al-Si alloys is reported.In the present work, the EN-AC 46000 and 46100 aluminium alloys have been gravity cast using a stepbarpermanent mould, with a range of thickness going from 5 to 20 mm. Metallographic and image analysistechniques have been used to quantitatively examine the microstructural parameters of the ?-Al phaseand eutectic Silicon. Microstructure has been also correlated with the results coming from the numericalsimulation of the casting process. The results show that SDAS and length of eutectic silicon particles increasewith section thickness, and consequently mechanical properties decrease

Systemic importance of financial institutions: regulations, research, open issues, proposals

In the field of risk management, scholars began to bring together the quantitative methodologies with the banking management issues about 30 years ago, with a special focus on market, credit and operational risks. After the systemic effects of banks defaults during the recent financial crisis, and despite a huge amount of literature in the last years concerning the systemic risk, no standard methodologies have been set up to now. Even the new Basel 3 regulation has adopted a heuristic indicator-based approach, quite far from an effective quantitative tool. In this paper, we refer to the different pieces of the puzzle: definition of systemic risk, a set of coherent and useful measures, the computability of these measures, the data set structure. In this challenging field, we aim to build a comprehensive picture of the state of the art, to illustrate the open issues, and to outline some paths for a more successful future research. This work appropriately integrates other useful surveys and it is directed to both academic researchers and practitioners

Combined deformation and solidification-driven porosity formation in aluminum alloys

In die-casting processes, the high cooling rates and pressures affect the alloy solidification and deformation behavior, and thereby impact the final mechanical properties of cast components. In this study, isothermal semi-solid compression and subsequent cooling of aluminum die-cast alloy specimens were characterized using fast synchrotron tomography. This enabled the investigation and quantification of gas and shrinkage porosity evolution during deformation and solidification. The analysis of the 4D images (3D plus time) revealed two distinct mechanisms by which porosity formed; (i) deformation-induced growth due to the enrichment of local hydrogen content by the advective hydrogen transport, as well as a pressure drop in the dilatant shear bands, and (ii) diffusion-controlled growth during the solidification. The rates of pore growth were quantified throughout the process, and a Gaussian distribution function was found to represent the variation in the pore growth rate in both regimes. Using a one-dimensional diffusion model for hydrogen pore growth, the hydrogen flux required for driving pore growth during these regimes was estimated, providing a new insight into the role of advective transport associated with the deformation in the mushy region