1,721,071 research outputs found
A study of a non-conventional evaluation of results from salt spray test of aluminum High Pressure Die Casting alloys for automotive components
No full textAim of the present work was to investigate in a non-conventional way the results of aluminum castings salt spray tests. These experiments were engineered in order to obtain a quantitative measurement of the corrosion rate, instead of the qualitative visual analysis usually employed in the traditional salt spray test. These tests were performed on aluminum EN AC-46000, EN AC-44400, and EN AC-43500 samples. A comparison was made with electrochemical tests on specimens and the traditional salt spray testing on a real dimension component. The results showed a good reliability of the new method that gave outputs in agreement with the electrochemical technique. The new concept of salt spray test data processing was able to detect very small differences in corrosion behavior of tested alloys, demonstrating higher precision and reliability in respect to the polarization technique. Such result was explained considering the adoption of specimen with larger area and longer time of exposure to the selected corrosive environment that reduce respectively the effect of uneven distribution of porosity and intermetallics in the samples, typical of aluminum castings, and the potential local and transient events related to these defects
On some experiments on EAF slags
No full textSome EAF slags sampled from different electric steel works in the northern region of Italy have been analysed by microscopic observations and microanalytical measurements, coupled with X-ray diffraction experiments. Interesting results have been obtained concerning the relationship between structure and thermal history of the slag
Investigations on leaching behaviour of EAF steel slags
No full textChromium release from different types of EAF steel slags cooled in different conditions was assessed by standard leaching test. The aim of this work was to relate these results to the microstructure and phases composition of the samples, that were carefully investigated by X-Ray Diffraction experiments and SEM-EDXS analyses. In particular, EDXS measurements were performed on polished slag samples before and after immersion in the leaching test solution. The results show that larnite and gehlenite are the only phases of the slags to be strongly dissolved. Their content is very high in slowly cooled slags which also gave rise to the largest release of chromiu
Caratterizzazione di scorie di acciaieria e studio del rilascio di cromo
No full textFin da tempi remoti le emissioni e gli scarti dell'industria siderurgica venivano recuperati per differenti applicazioni come, ad esempio, l’utilizzo delle scorie da altoforno per la costruzione di strade. Obbiettivo di questo lavoro di ricerca è lo studio delle scorie prodotte al forno elettrico che, tuttora, pongono alcuni problemi di smaltimento e difficoltà iniziali di riutilizzo, nonostante le loro caratteristiche si prestino per gli stessi campi delle applicazioni proposte per le scorie da altoforno. Il riciclaggio delle scorie nelle costruzioni stradali è sicuramente l’utilizzo più interessante; a questo scopo le scorie devono possedere specifiche proprietà meccaniche, ambientali e di stabilità. La sperimentazione si è dedicata allo studio del rilascio di cromo nelle scorie ottenute da due diversi forni elettrici e raffreddate in diverse condizioni, in particolare si è cercato di trovare una correlazione tra i risultati di rilascio delle prove di lisciviazione, la composizione e la microstruttura delle scorie, accuratamente analizzate mediante diffrazione di raggi X e analisi SEM-EDS. Le analisi sono state effettuate su campioni inglobati in resina e preparati metallograficamente, prima e dopo l’immersione nella soluzione liscivante per 24 ore. I risultati hanno mostrato che la fase Ca2SiO4 (larnite) è l’unico costituente ad essere stato fortemente disciolto. Il suo contenuto è molto elevato nelle scorie raffreddate lentamente, le quali hanno anche prodotto il maggior rilascio di Cr
Fatigue characterization and optimization of the production process of heavy section ductile iron castings
No full textIn heavy section cast iron components, anomalous microstructures can be formed especially at the core, because of low cooling rate, with a consequent decrease in mechanical properties. The matrix microstructure, the presence of surface defects, such as inclusions and porosities, and the size and morphology of graphite nodules are critical issues to ensure the adequate performance of the component in fatigue applications. Proper design of heavy section ductile iron castings requires a database of information about microstructures and mechanical properties that nowadays is missing or is very poor. In this paper, we presented the mechanical characterization of ductile irons with solidification times up to 20 h, carried out to identify the metallurgical and the process parameters that most affect the improvement in fatigue strength. An innovative production line was designed, aimed at reproducing on a small-scale sample the characteristics of heavy walled components. A standard ferritic ductile cast iron compared to a ferritic cast iron with high silicon content and a fully pearlitic ductile cast iron were studied by tensile, Brinell hardness and rotating bending fatigue tests. Optical microscope analysis and scanning electron microscope observations of the most significant fracture surfaces were also performed. It was concluded that the ferritic cast iron is more suitable for the production of large thickness castings undergoing fatigue loads, because the decrease in ductility and its effect on other properties is less pronounced
Comparison of the sliding wear of a novel Zn alloy with that of two commercial Zn alloys against bearing steel and leaded brass
No full textZinc alloys are known for their low melting point, high castability, and useful wear resistance in certain applications, and at a relatively low cost. In the recent years, many attempts have been made to substitute more expensive copper alloys for zinc-based materials in wear-critical parts. In this regard, the most investigated zinc alloy is ZA27, but good wear resistance can be also achieved by using an alloy with lower aluminium content, like Zamak2. In this paper, the sliding wear behavior of a novel zinc alloy ZnAl15Cu1 was compared to that of ZA27 and Zamak2 in order to assess its relative suitability for applications where sliding wear resistance is required. Pin-on-disk tests were carried out using both bearing steel and aleaded brass sliding partners under three loads and various sliding distances. Friction coefficient and wear rates were compared. Analyses of the worn surfaces was done to identify the damage mechanisms and to understand the friction coefficient behaviour. The ZnAl15Cu1 alloy exhibited wear resistance that is comparable to or better than that for ZA27 and Zamak2
Simulation and validation of spray quenching applied to heavy forgings
No full textThe effect of water pressure, water flow rate and cycling spray during spray quenching of a heavy steel forged part were modelled by using numerical simulation, experimental tests and metallographic analyses. Changes in water mass flow produce small variations on cooling rates, while the reduction of water pressure and especially the use of cycling spray allow to induce a relevant slowdown of cooling rate in small sections, decreasing the thermal gradients in complex shaped heavy forgings. The agreement between calculated and experimental results permitted to validate the simulatio
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