Empirical models of mechanical behaviour of Al-Si-Mg cast alloys for high performance engine applications

The main limitation of cast Al-Si-Mg alloys isthe considerable influence of the solidificationand heat treatment conditions on the finalmicrostructure and consequently on themechanical properties, that can thus widelyvary in the same cast component. In this workwe perform a deep microstructural andmechanical characterisation on specimensextracted from some A356 T6 gravity die castcylinder heads. The aim of the work is todevelop empirical models to successfullypredict the local tensile properties of thecasting from the main microstructuralparameters and alloy hardness. As the formerwe considered and measured secondarydendrite arm spacing, shape and size of theeutectic silicon, grain size and percentagearea of defects. The latter instead primarilydepends on the heat treatment conditions. Onthe base of these data we propose a set ofsimple equations to predict the ultimate tensilestrength and the proof strength with a meanerror of 2% and the elongation to failure witha mean error of 20%. The equations allow thedesigner to know the local tensile behaviourwithout any tensile tests. Moreover, in a coengineereddesign approach, the equationscan link the post-processing results of thecasting simulation software to the preprocessingphase of the structural software.This leads to less bench tests and to a greatreduction of validation time of a new product

Heat treatment response and influence of overaging on mechanical properties of C355 cast aluminum alloy

The research activity was focused on the optimization of heat treatment parameters for C355 (Al-Si-Cu-Mg)cast aluminum alloy and on its microstructural and mechanical characterization in T6 condition, also evaluatingthe effect of subsequent high temperature exposure. Differential thermal analyses were carried out to identifythe solution heat treatment optimal temperature. After solution heat treatment and quenching, samples weresubjected to artificial aging, at different times and temperatures, as to obtain the corresponding hardnesscurves. Samples for successive hardness and tensile tests were subjected to hot isostatic pressing (HIP) and T6heat treatment, according to the parameters optimized in the foregoing research phase. Some of the T6 heattreated samples were also characterized after overaging, induced by holding at 210 °C for 41 h. Aiming to carryout a comparative study, tensile properties of C355 alloy, both in T6 and overaged conditions, were comparedto those of A356 alloy (results from a previous study), which is currently more widely employed than C355.Experimental results showed how C355-T6 alloy is characterized by superior mechanical properties as comparedto A356-T6, especially in the overaged condition, due to the higher thermal stability induced by Cu-basedstrengthening precipitates

Unpublished Mediterranean and Black Sea records of marine alien, cryptogenic, and neonative species

To enrich spatio-temporal information on the distribution of alien, cryptogenic, and neonative species in the Mediterranean and the Black Sea, a collective effort by 173 marine scientists was made to provide unpublished records and make them open access to the scientific community. Through this effort, we collected and harmonized a dataset of 12,649 records. It includes 247 taxa, of which 217 are Animalia, 25 Plantae and 5 Chromista, from 23 countries surrounding the Mediterranean and the Black Sea. Chordata was the most abundant taxonomic group, followed by Arthropoda, Mollusca, and Annelida. In terms of species records, Siganus luridus, Siganus rivulatus, Saurida lessepsianus, Pterois miles, Upeneus moluccensis, Charybdis (Archias) longicollis, and Caulerpa cylindracea were the most numerous. The temporal distribution of the records ranges from 1973 to 2022, with 44% of the records in 2020–2021. Lethrinus borbonicus is reported for the first time in the Mediterranean Sea, while Pomatoschistus quagga, Caulerpa cylindracea, Grateloupia turuturu, and Misophria pallida are first records for the Black Sea; Kapraunia schneideri is recorded for the second time in the Mediterranean and for the first time in Israel; Prionospio depauperata and Pseudonereis anomala are reported for the first time from the Sea of Marmara. Many first country records are also included, namely: Amathia verticillata (Montenegro), Ampithoe valida (Italy), Antithamnion amphigeneum (Greece), Clavelina oblonga (Tunisia and Slovenia), Dendostrea cf. folium (Syria), Epinephelus fasciatus (Tunisia), Ganonema farinosum (Montenegro), Macrorhynchia philippina (Tunisia), Marenzelleria neglecta (Romania), Paratapes textilis (Tunisia), and Botrylloides diegensis (Tunisia).Stelios Katsanevakis, Michail Ragkousis, Maria Sini, Markos Digenis and Vasilis Gerovasileiou were supported by the Hellenic Foundation for Research and Innovation (HFRI) under the “First Call for HFRI Research Projects to support Faculty members and Researchers and the procurement of high-cost research equipment grant” (Project ALAS – “ALiens in the Aegean – a Sea under siege” (Katsanevakis et al. 2020b); Project Number: HFRI-FM17-1597). Konstantinos Tsirintanis was co-financed by Greece and the European Union (European Social Fund-ESF) through the Operational Programme “Human Resources Development, Education and Lifelong Learning”, 2014-2020, in the context of the Act “Enhancing Human Resources Research Potential by undertaking a Doctoral Research” Sub-action 2: IKY Scholarship Programme for PhD candidates in the Greek Universities. Maria Zotou was supported by the project “Coastal Environment Observatory and Risk Management in Island Regions AEGIS+” (MIS 5047038), implemented within the Operational Programme “Competitiveness, Entrepreneurship and Innovation” (NSRF 2014-2020), co financed by the Hellenic Government (Ministry of Development and Investments) and the European Union (European Regional Development Fund, Cohesion Fund). Razy Hoffman was supported by Yad-Hanadiv Foundation, through the Israel Society of Ecology and Environmental Sciences and Israel Nature and Parks Authority, an integrated program for establishing biological baselines and monitoring protocols for marine reserves in the Israeli Mediterranean Sea (Grant #10669). Tatiana Begun, Adrian Teaca and Mihaela Muresan were supported by the European Union’s Horizon 2020 BRIDGE-BS project under grant agreement no. 101000240. Fiona Tomas was supported by the project “Invasion of the tropical alga Halimeda incrassata in the Balearic Islands: ecology and invasion dynamics (AAEE119/2017)”, funded by the Vicepresidencia y Consejería de Innovación, Investigación y Turismo del Govern de les Illes Balears, with support from the European Union and FEDER funds, and the project “Una nueva alga invasora en el Mediterráneo: invasibilidad, detección y erradicación del alga tropical Halimeda incrassata (INVHALI)”, funded by the Fundación Biodiversidad, del Ministerio para la Transición Ecológica y el Reto Demográfico. Simonetta Fraschetti, Laura Tamburello, Antonia Chiarore were supported by the project PO FEAMP 2014-2020 - DRD n. 35/2019, “Innovazione, sviluppo e sostenibilità nel settore della pesca e dell'acquacoltura per la Regione Campania” (ISSPA 2.51) and the EU EASME - EMFF (Sustainable Blue Econ-omy) Project AFRIMED (http://afrimed-project.eu/, grant agreement N. 789059). Carlos Jimenez, Louis Hadjioannou, Vasilis Resaikos, Valentina Fossati, Magdalene Papatheodoulou, and Antonis Petrou were supported by MedPan Small Projects, Mava, and LIFE-IP. Louis Hadjioannou, Manos L. Moraitis and Neophytos Agrotis received funding from the European Union’s Horizon 2020 research and innovation program within the framework of the CMMI/MaRITeC-X project under grant agreement No. 857586. Ernesto Azzurro was supported by the project USEIt - Utilizzo di Sinergie operative per la gestione integrata specie aliene Invasive in Italia, funded by the research programme @CNR. Antonietta Rosso and Francesco Sciuto were supported by the University of Catania through “PiaCeRi-Piano Incentivi per la Ricerca di Ateneo 2020–22 linea di intervento 2.” This is the Catania Paleoecological Research Group contribution n. 484. Diego K. Kersting was supported by the Beatriu de Pinós programme funded by the Secretary of Universities and Research (Government of Catalonia) and the Horizon 2020 programme of research and innovation of the European Union under the Marie Sklodowska-Curie grant agreement No 801370. Francesco Tiralongo was supported by the AlienFish project of Ente Fauna Marina Mediterranea (Scientific Organization for Research and Conservation of Marine Biodiversity, 96012 Avola, Italy), a citizen science project for monitoring and studying rare and non-indigenous fish in Italian waters. Adriana Vella, was supported by funds through the BioCon_Innovate Research Excellence Grant from the University of Malta awarded to her. Noel Vella was supported by REACH HIGH Scholars Programme-Post Doctoral Grant for the FINS project. Some of the records provided by Victor Surugiu were obtained during surveys carried out within the framework of the project “Adequate management of invasive species in Romania, in accordance with EU Regulation 1143/2014 on the prevention and management of the introduction and spread of invasive alien species”, SMIS 2014+ 120008, coordinated by the Romanian Ministry of Environment, Water and Forests in partnership with the University of Bucharest (2018–2022). Alan Deidun and Alessio Marrone were supported by the “Spot The Alien” citizen science campaign for the monitoring of the Alien species in the Maltese archipelago and by the Interreg Italia-Malta Harmony project. The authors from the National Institute of Biology (Slovenia) acknowledge the financial support of the Slovenian Research Agency (Research Core Funding No. P1-0237) and of the Ministry of Agriculture, Forestry and Food (project “Survey of the species richness and abundance of alien species in the Slovenian Sea”). Emanuele Mancini and Fabio Collepardo Coccia were supported by the project PO-FEAMP 2014-2020 “BIOBLITZ: research, knowledge and participation for the sustainable management of marine resources (BioBlitz Blu 2020)” coordinated by CURSA for MIPAAF, the Italian Ministry of Agricultural, Food and Forestry Policies, Measure 1.40 - Protection and restoration of biodiversity and marine ecosystems and compensation schemes in the context of sustainable fishing activities. Daniele Grech was supported by the PO-FEAMP 2014-2020 project ECOGESTOCK “Approccio ECOsistemico per la tutela e la GEStione delle risorse biologiche e STOCK ittici nelle acque interne”, the citizen science project Progetto Fucales: chi le ha viste? and the Paralenz Every dive counts sponsor. Jamila Rizgalla was supported by the project Snowball for the monitoring of alien species in Libyan waters له اهتفش له اهتدطصا ؟) have you seen it have you fished it?). Gerasimos Kondylatos and Dimitrios Mavrouleas were supported by the project “EXPLIAS” (MIS (ΟΠΣ): 5049912), design and piloting methods of commercial exploitation of invasive alien species with a view to contributing to their population control, coordinated by the National Technical University of Athens with the collaboration of the Hellenic Centre for Marine Research and the University of the Aegean and co-founded by Greece and the European Union. G. Kondylatos and Savvas Nikolidakis were supported by the project “SAMOS” (ID CODE: 32.2072004/001), a study for a submarine productive park in Marathokampos of Samos. Paraskevi K. Karachle, Aikaterini Dogrammatzi, Giorgos A. Apostolopoulos, Kassiani Konida and Melina Nalmpanti were supported by the project “4ALIEN: Biology and the potential economic exploitation of four alien species in the Hellenic Seas”, funded by NRSF 2017-2020 (MIS (ΟΠΣ): 5049511). Fabio Crocetta and Riccardo Virgili were partially funded by the project PO FEAMP Campania 2014–2020, DRD n. 35 of 15th March 2018, Innovazione, sviluppo e sostenibilità nel settore della pesca e dell’acquacoltura per la regione Campania, Misura 2.51, WP5, Task 5.5 Presenza e distribuzione di specie non indigene del macrozoobenthos e del necton in Campania. Michel Bariche was partially funded by the University Research Board of the American University of Beirut (DDF 103951/2592). Constantinos G. Georgiadis, Dimitra Lida Rammou, Paschalis Papadamakis and Sotiris Orfanidis were supported by the MSFD monitoring program. Sonia Smeraldo was supported by the MPA-Engage project, led by the Institute of Marine Sciences of the Spanish National Research Council and funded by the Interreg MED program. Evgeniia Karpova acknowledge that the publication of this article was in part carried out within the framework of the state assignment of the FRC IBSS “Patterns of Formation and Anthropogenic Transformation of Biodiversity and Bioresources of the Azov– Black Sea Basin and Other Regions of the World Ocean” (No. 121030100028-0). Elena Slynko’s work was carried out within the framework of a State Assignment no. 121051100109-1 of IBIW RAS. Manuela Falautano and Luca Castriota were supported by ISPRA citizen science campaigns for the monitoring of alien species through the dedicated institutional project ([email protected]). María Altamirano was supported by the project RUGULOPTERYX funded by Fundación Biodiversidad-Ministerio para la Transición Ecológica y el reto Demográfico (Spain) and the project UMA20-FEDERJA-006 with support from the European Union and FEDER funds and Junta de Andalucía. Records provided by L. Mangialajo were collected in the framework of projects funded by the Pew Charitable Trust, by the European Commission (AFRIMED, http://afrimed-project.eu/, grant agreement N. 789059) and by the Académie 3 de l’Université Côte d’Azur (projet CONVOST).Peer reviewe

Unpublished Mediterranean and Black Sea records of marine alien, cryptogenic, and neonative species

To enrich spatio-temporal information on the distribution of alien, cryptogenic, and neonative species in the Mediterranean and the Black Sea, a collective effort by 173 marine scientists was made to provide unpublished records and make them open access to the scientific community. Through this effort, we collected and harmonized a dataset of 12,649 records. It includes 247 taxa, of which 217 are Animalia, 25 Plantae and 5 Chromista, from 23 countries surrounding the Mediterranean and the Black Sea. Chordata was the most abundant taxonomic group, followed by Arthropoda, Mollusca, and Annelida. In terms of species records, Siganus luridus, Siganus rivulatus, Saurida lessepsianus, Pterois miles, Upeneus moluccensis, Charybdis (Archias) longicollis, and Caulerpa cylindracea were the most numerous. The temporal distribution of the records ranges from 1973 to 2022, with 44% of the records in 2020–2021. Lethrinus borbonicus is reported for the first time in the Mediterranean Sea, while Pomatoschistus quagga, Caulerpa cylindracea, Grateloupia turuturu, and Misophria pallida are first records for the Black Sea; Kapraunia schneideri is recorded for the second time in the Mediterranean and for the first time in Israel; Prionospio depauperata and Pseudonereis anomala are reported for the first time from the Sea of Marmara. Many first country records are also included, namely: Amathia verticillata (Montenegro), Ampithoe valida (Italy), Antithamnion amphigeneum (Greece), Clavelina oblonga (Tunisia and Slovenia), Dendostrea cf. folium (Syria), Epinephelus fasciatus (Tunisia), Ganonema farinosum (Montenegro), Macrorhynchia philippina (Tunisia), Marenzelleria neglecta (Romania), Paratapes textilis (Tunisia), and Botrylloides diegensis (Tunisia).peer-reviewe

Correlazioni tra microstruttura e proprietà meccaniche ed effetto della permanenza in temperatura in leghe Al-Si-Mg ed Al-Cu trattate termicamente

Ottima attitudine a processi di deformazione plastica e fusori, alta resistenza alla corrosione e soprattutto elevata resistenza specifica, hanno reso le leghe di alluminio da trattamento termico fra le migliori candidate per applicazioni strutturali nel settore dei trasporti. L’esigenza industriale moderna è, infatti, quella di produrre veicoli sempre più leggeri e con motori dalle sempre maggiori potenze specifiche, al fine di garantire contemporaneamente alte prestazioni nel rispetto delle sempre più stringenti normative. Per raggiungere tale obiettivo, la tendenza ormai consolidata è quella di un uso crescente di leghe d’alluminio anche per gli elementi più critici, quali teste, basamenti motore e pistoni. Numerosi studi hanno evidenziato che una criticità, soprattutto per le leghe da fonderia, è costituita dalla forte dipendenza delle proprietà meccaniche locali dalla microstruttura e dai difetti di solidificazione. Porosità da gas, cavità da ritiro e film di ossido, ne riducono infatti drasticamente resistenza a fatica e duttilità. Inoltre, anche quando questi difetti riescano ad essere contenuti a livelli particolarmente ridotti, tramite l’adozione di opportune pratiche di fonderia, altri parametri microstrutturali, come la distanza fra i rami secondari delle dendriti (SDAS), le dimensioni del grano e le caratteristiche degli eutettici e/o intermetallici presenti, influenzano in maniera consistente le proprietà del materiale. Particolarmente nel caso di getti a geometria complessa, le proprietà meccaniche sono dunque una caratteristica puntuale e questo comporta evidenti criticità nella fase di progettazione degli stessi: il materiale non potrà essere sicuramente considerato continuo, omogeneo ed isotropo. Altro aspetto di rilevanza fondamentale, sia per le leghe da fonderia che da deformazione plastica trattate termicamente T6, è che, nel caso di componenti destinati a lavorare a temperature superiori a quelle di invecchiamento, si assiste ad un deterioramento delle proprietà meccaniche funzione del tempo e temperatura di esposizione. Questo, comporta un’ulteriore ed evidente complicazione progettuale. Questo lavoro rientra all’interno di due ampi progetti di ricerca portati avanti, in collaborazione con due note aziende nel campo auto e motociclistico, con l’obiettivo di sviluppare un’innovativa metodologia di progettazione di componenti motore in lega d’alluminio, ottenuti per fusione e sollecitati termomeccanicamente, integrando aspetti progettuali/strutturali, metallurgici e tecnologici attraverso l’implementazione di moderni sistemi di simulazione. Obiettivo di questo lavoro, è stato dunque quello di supportare e legare fra loro le fasi di simulazione di colata e di simulazione strutturale di getti complessi in lega Al-Si-Mg. Nel primo caso, si sono forniti tutti i dati per l’opportuna definizione delle condizioni a contorno del problema, nonché per la verifica dei risultati delle simulazioni, in termini di distribuzione di difettosità e SDAS. Nel secondo caso, si sono forniti dati di caratterizzazione meccanica del materiale (trazione e fatica), che contribuissero a superare le ipotesi semplificative di continuità, omogeneità, isotropia e costanza nel tempo delle proprietà meccaniche. Nel corso del progetto, la parziale trasferibilità dei risultati ottenuti in campo metallurgico su componenti ottenuti per fusione (teste e basamenti motore), a componenti sottoposti a deformazione plastica (pistoni), ha consentito un ampliamento del campo di ricerca. Con maggiore dettaglio, le attività svolte hanno previsto la valutazione dello stato dell’arte, relativo a microstrutture, proprietà meccaniche e trattamento termico, inerenti alcune leghe Al-Si-Mg (Al-Cu). In un secondo momento, si è provveduto all’estrazione del materiale sperimentale da teste motore in lega EN AC-42100 e da pistoni forgiati in lega EN AW-2618 ed EN AW-4032. Tramite tecniche di microscopia ottica, microscopia elettronica in scansione ed analisi di immagine, è stato dunque ampiamente investigato l’effetto del processo produttivo sulle microstrutture di teste motore colate in conchiglia in lega EN AC-42100 T6 [AlSi7Mg0,3]. Sono stati valutati il contenuto di difetti, la distribuzione di SDAS e l’ effetto degli affinanti ed degli agenti modificatori su dimensioni del grano e morfologia del Si eutettico. Analogamente, si è evidenziato come la forgiatura di leghe di alluminio per la produzione pistoni, quali la EN AW-2618[AlCu2MgNi] e la EN AW-4032 [AlSi12MgCuNi], comporti una disomogeneità microstrutturale (e quindi di proprietà) all’interno del componente. Tramite prove di durezza, trazione e fatica, si è indagato l’effetto della microstruttura sulle proprietà meccanica della lega EN AC-42100 T6, quantificando il contributo di ogni caratteristica microstrutturale nella definizione delle proprietà statiche e dinamiche. Sono stati, a riguardo, proposti modelli empirici di previsione della resistenza a trazione (UTS), della resistenza a snervamento (YS) e dell’allungamento a rottura (E%) in funzione di durezza, SDAS, contenuto di difetti e dimensione media del Si eutettico della lega. I risultati hanno evidenziato errori medi del 3% nella previsione di UTS ed YS e del 20% nella previsione di E%. La caratterizzazione a fatica del materiale ha invece evidenziato grandi dispersioni dei dati, per ridotte tensioni di carico, conducendo a risultati significativi solo per tensioni alterne di 70 MPa. In questo caso, è stata rilevata una buona dipendenza tra il numero di cicli a rottura del materiale ed i valori di SDAS e del contenuto medio di difetti (R2∼0,6). E’ stato studiato l’effetto della temperatura sulle proprietà tensili della lega da fonderia EN AC-42100 T6 e sulle leghe da deformazione plastica EN AW-2618 T6 e la EN AW-4032 T6. Nel primo caso, è stato condotto uno studio sia delle diverse fasi del trattamento termico, che della variazione di proprietà del materiale allo stato T6 con l’esposizione ad alta temperatura. Si è così evidenziato come un pre-invecchiamento a temperatura ambiente anche di sole 2 h, potesse ridurre le tensioni di rottura e snervamento di circa il 20% e l’allungamento a rottura di circa il 30%. Inoltre, si è visto come la durezza residua e lo SDAS siano le variabili fondamentali per definire il comportamento meccanico del materiale nel suo stato sottoinvecchiato, di picco e sovrainvecchiato. Anche in questo caso, sono stati proposti modelli empirici di previsione delle proprietà meccaniche tutti caratterizzati da coefficienti di determinazione molto alti (R2>0,8). La previsione dell’allungamento a rottura ha fatto registrare coefficienti leggermente inferiori (R2∼0,7), evidenziando l’importanza dello SDAS nel definire questa proprietà. Nel caso invece delle leghe da deformazione plastica, gli effetti della microstruttura sono risultati minori, con al massimo una variazione del 5% in funzione della zona di estrazione del campione. La durezza residua del materiale, allo stato sovrainvecchiato, è risultata il parametro necessario e sufficiente per definire tutte le proprietà del materiale (UTS, YS, E%, coefficienti di resistenza K ed incrudimento n) con grande precisione (R2∼0,9). Con l’obiettivo di verificare i dati sperimentali ottenuti, si è proceduto, in ultima istanza, con lo sviluppo di un applicativo in ambiente MATLAB®, per il calcolo delle proprietà meccaniche residue delle leghe studiate, dopo un‘esposizione a temperatura variabile. I risultati, ottenuti con cicli di prova a T costante, hanno evidenziato scarti ridotti nella previsione della durezza residua (max 4%), mentre errori maggiori sono stati riscontrati in applicazioni su cicli transitori fra due temperature, ma con grandi margini di ottimizzazione. In conclusione, l’obiettivo di supportare la nuova metodologia di progettazione di componenti sollecitati termo-meccanicamente, che vede integrate le fasi di progettazione meccanica e tecnologica, al fine di ridurre tempi e costi di sviluppo prodotto, è stato pienamente raggiunto. I risultati ottenuti, in termini di quantità e qualità, hanno rappresentato un passo significativo in questa direzione che, per essere totalmente intrapresa in ambito aziendale, ha bisogno di vincere le resistenze di un sistema progettuale con una storia consolidata e ricca di successi quale quella di Ferrari S.p.A. I grandi cambiamenti sono frutto però di piccoli passi successivi, uno dei quali è costituito da questo studio e dal progetto nell’ambito del quale questo è stato realizzato

Estimation of local fatigue behaviour in A356–T6 gravity die cast engine head based on solidification defects content

Al–Si–Mg cast alloys have widespread applications, especially in the aerospace and automotive industries, due to their excellent combination of castability and high specific strength. Among Al– Si alloys, hypoeutectic A356 (Al–7Si–0?3Mg) ranks as one of the most widely used for the production of a variety of components, including engine blocks and engine heads, due to its excellent castability and good mechanical properties. The microstructure of this alloy greatly depends on chemical composition, solidification conditions, metal soundness and heat treatment. Furthermore, its mechanical properties are strongly affected by solidification microstructure and defects, which can vary greatly in complex shaped castings. Among the different microstructural features, only secondary dendrite arm spacing and percentage defect content can currently be predicted with sufficient accuracy by casting simulation software. This makes the prediction of the fatigue life of complex shaped Al–Si castings very difficult, since it is widely accepted that fatigue behaviour mainly depends on the size of solidification defects (gas pores and cavity shrinkages). In this study, the experimental work was carried out on an industrial A356–T6 gravity die cast engine head, with the aim of finding relationships among the main microstructural features and solidification defect parameters. The goal of this analysis was to correlate the defect size, which is the most important variable affecting the fatigue behaviour, to the other microstructural parameters that can be predicted by casting simulation software. Moreover, by applying literature models for fatigue behaviour prediction, based on maximum defect size, the local expected fatigue life/fatigue limit on a section of the casting will be evaluated and compared with those obtained by rotating bending fatigue tests. This study would demonstrate the effectiveness of a new approach of coengineering design, with a strong synergy between the structural finite element method and the casting simulation process, able to estimate the local fatigue strength in complex shaped A356 castings

Effects of Casting Size on Microstructure and Mechanical Properties of Spheroidal and Compacted Graphite Cast Irons: Experimental Results and Comparison with International Standards

The aim of this research was to investigate the effects of casting size (10-210 mm) on the microstructure and mechanical properties of spheroidal (SGI) and compacted (CGI) graphite cast irons. A comparison of the experimental mechanical data with those specified by ISO standards is presented and discussed. The study highlighted that the microstructure and mechanical properties of SGI (also known as ductile or nodular cast iron) are more sensitive to casting size than CGI (also known as vermicular graphite cast irons). In particular, in both types of cast iron, hardness, yield strength and ultimate tensile strength decreased, with increasing casting size, by 27% in SGI and 17% in CGI. Elongation to failure showed, instead, an opposite trend, decreasing from 5 to 3% in CGI, while increasing from 5 to 11% in SGI. These results were related to different microstructures, the ferritic fraction being more sensitive to the casting size in SGI than CGI. Degeneration of spheroidal graphite was observed at casting size above 120 mm. The microstructural similarities between degenerated SGI and CGI suggested the proposal of a unified empirical constitutional law relating the most important microstructural parameters to the ultimate tensile strength. An outstanding result was also the finding that standard specifications underestimated the mechanical properties of both cast irons (in particular SGI) and, moreover, did not take into account their variation with casting size, at thicknesses over 60 mm

Ottimizzazione del trattamento termico di componenti in lega EN AC-46500 pressofusi in vuoto

E\u2019 noto come la maggioranza dei getti pressofusi non possa essere sottoposta a trattamento termico T6, comprendente una fase di solubilizzazione ad alta temperatura, seguita da tempra ed invecchiamento artificiale, a causa dell\u2019alto contenuto di gas intrappolato nel getto. Il gas occluso (aria ed idrogeno) nella fase di solubilizzazione tende, infatti, ad espandersi e, per la diminuita resistenza al flusso plastico del materiale ad alta temperatura, provoca deformazioni plastiche localizzate, che in superficie si manifestano con il fenomeno noto come \u201cblistering\u201d. L\u2019adozione di tecniche di pressocolata in vuoto, riducendo l\u2019entit\ue0 del gas occluso, pu\uf2 limitare questa problematica, ma risultati ottimali possono essere raggiunti solo con un attento controllo dei parametri di trattamento termico. Questo studio ha avuto come obiettivo quello di valutare l\u2019applicabilit\ue0 del trattamento termico T6 a getti in lega EN AC-46500 (AlSi9CuFeZnMg) prodotti tramite pressocolata in vuoto mediante processo Fondarex\uae. Dopo aver effettuato delle analisi termiche differenziali (DTA) \ue8 stato determinato l\u2019intervallo di temperatura all\u2019interno del quale eseguire il trattamento di solubilizzazione. Sono state considerate tre diverse temperature di solubilizzazione a cui sottoporre la lega quindi, fissati i parametri per un preliminare trattamento di invecchiamento, fra tre possibili temperature di solubilizzazione \ue8 stata scelta quella che consentisse il raggiungimento del pi\uf9 alto picco di durezza, senza che si manifestasse blistering. Una volta definito il trattamento di solubilizzazione, si \ue8 poi proceduto all\u2019ottimizzazione del trattamento d\u2019invecchiamento, analizzando temperature nell\u2019intervallo 160\ub0C\uf7200\ub0C e tempi di mantenimento fino ad 8 ore. I risultati sperimentali hanno mostrato come, al fine di evitare la formazione di blistering, sia importante non superare la temperatura di 485\ub0C in fase di solubilizzazione. La durezza finale dei getti pressofusi con tecnologia Fondarex\uae, trattati nelle condizioni ottimizzate, \ue8 risultata del tutto paragonabile a quella di getti prodotti con la stessa lega tramite colata in conchiglia e trattati T6. Le prove di trazione, inoltre, hanno messo in evidenza come la resistenza a rottura di tali getti fosse superiore di circa il 50% rispetto a quella del materiale non trattato e comunque prossima a quella del materiale colato in conchiglia e trattato termicamente T6

A study on the relationship between solidification conditions and microstructural characteristics of a complex shaped A356 gravity die cast cylinder head

Al-Si-Mg cast alloys have widespread applications, especially in the aerospace and automotive industries, due to an excellent combination of castability and high specific strength. Among these alloys, hypoeutectic A356 (Al7Si0.3Mg) is one of the most widely used for the production of a variety of components, including engine blocks and cylinder heads. The microstructure of this alloy greatly depends on chemical composition, solidification conditions, metal soundness, and heat treatment. Most of the literature data about the microstructure of this alloy are generally obtained from laboratory specimens, under highly controlled production conditions, often very different from those of complex shaped industrial components. In the present study, the experimental work was carried out on an industrial A356 gravity die cast cylinder head, with the aim of relating the local microstructural parameters to the different solidification conditions and of finding correlations between the main microstructural features, such as secondary dendrite arm spacing and solidification defects (gas pores and shrinkage cavities) content. Fatigue resistance of Al-Si-Mg castings greatly depends in fact on microstructure and, first of all, on the size of solidification defects. Casting simulation software can nowadays give a good prediction of percentage defect content distribution but cannot predict the defects size. An important finding of this study is indeed the correlation between the equivalent diameter of the maximum pore and the percentage fraction of solidification defects measured in the casting. This finding, added to the predictive potential of casting simulation software, can so lead to an estimation of the local fatigue resistance of Al-Si-Mg castings, already in the design phase of the production

Effects of the Delay Between Quenching and Aging on Hardness and Tensile Properties of A356 Aluminum Alloy

The aim of the study was to evaluate the accuracy of heat treatment guidelines, generally followed in industrial practices, about the T6 heat treatment of A356 aluminum alloy. In particular, the effect of the delay between quenching and artificial aging (pre-aging time) on microstructure, hardness, and tensile behavior was studied using specimens extracted from different locations of a cylinder head, characterized by different cooling rates and, consequently, by different secondary dendrite arm spacing values. Hardness and tensile tests confirmed the detrimental effect of pre-aging with a 20% reduction in hardness and strength after approximately 1 h of pre-aging, both for samples with fine and large SDAS. Differential scanning calorimetry analyses on samples that were solutionized, quenched, and pre-aged between 0 and 96 h, suggested that the nature and composition of the clusters formed during pre-aging, rather than their size, influenced the subsequent precipitation process and the final mechanical properties of the alloy