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Dissimilar friction stir welding joints are widely employed in the industrial field due to the excellent microstructural and mechanical properties of the resulting joints. Nevertheless, to further enhance the weld properties, the addition of reinforcement particles on the joint-line during the process has been proven effective for increasing its mechanical performance. In the present investigation, the microstructure and the impact behaviour of FSWed joints between AA2024-T351 and AA7075-T651 aluminium plates were investigated, considering the effect of different process parameters selected through a full factorial 2k design of experiments: both the rotational and translational speed of the tool, as well as the addition of Al2O3-SiC microparticles, were considered as input parameters. Unnotched 10 x 5 x 55 mm impact specimens were tested through an instrumented 50 J Charpy pendulum: total impact energy, the two complementary initiation and propagation energies as well as the peak force were correlated to the adopted process parameters. From the performed analyses, it was found that joints with reinforcing particles are prone to form wormhole defects across the stir zone that not only affect the microstructural development, but also the impact behaviour since they require less energy at break in comparison with joints fabricated without particles addition.

The present work deals with the anisotropic high-strain rate behavior of laser-powder bed fusion (L-PBF) produced AlSi10Mg alloy in different heat treatment conditions. Impact specimens were produced with different orientations towards building platform and U-notch positions to assess the anisotropic properties. Besides the as-built material, several heat treatments were considered, including annealing, standard T6, hot isostatic pressing (HIP), HIP plus T6, and a recently proposed T6 at high pressure. The high-strain rate behavior was investigated by conducting Charpy impact tests, while material characterization was performed by scanning electron microscopy and x-ray diffraction. Results show that as-built and annealed alloys display significant anisotropic impact properties, whereas samples heat-treated at high temperatures generally have more consistent behavior. A coupled microstructural and fractographic investigation highlights that mitigation of anisotropy descends from the recovery of microstructural heterogeneity of the Si phase after heat treatment at high temperatures. This does not happen for both grain morphology or crystallographic structure, which are not significantly altered after the heat treatment. The present study aims to fill the gap in the literature regarding the anisotropic high-strain rate behavior of additively manufactured Al alloys and provide useful insights for mitigation of anisotropy by heat treatment.

In the context of developing an innovative seismic dissipation system, which aims to compromise on the steadiness of friction and processes costs, this work deals with the tribological characterization of an S355JR structural steel, whose surface has been preliminarily treated by different mechanical and galvanic processes. Tribological tests were performed in a pin-on-disk configuration and in reciprocating motion, using values of 1 Hz and 2 Hz as the motion inversion frequency, a constant normal load of 50 N, and variable test duration, according to the most frequent seismic events. The tribological system was composed of S355JR structural steel pins and disks of the same steel, which were alternatively treated by electrolytic nickel plating, electrolytic zinc plating, and two different shot peening processes. The results highlight that while electrolytic nickel increments the overall steadiness of the coefficient of friction (COF), electrolytic zinc plating guarantees the longest first steady-state stage and a COF lower than the one guaranteed by the coupling of untreated pins and disk.

The last two decades have seen a growing trend toward the use of inorganic binders in core making for the metalcasting field. Despite the health and environmental benefits of the inorganic binders, wider commercial use requires ongoing technical improvements to address some potential inherent limitations of this technology. Considering that inorganic cores can suffer from storage stability, this study sets out to check whether inorganic core binders are fit to replace organic ones in producing a gravity diecasting Al alloy component. First, the humidity resistance of both organic and inorganic sand cores, within a typical time-frame storage in the foundry, was evaluated by moisture absorption tests. Then, 3D optical measurements were performed to assess the relative dimensional changes of inorganic cores. Last, the influence of the core system was analyzed through microstructural and mechanical investigations on castings manufactured by using organic and inorganic binders. The experimental findings have shown that the moisture absorption during storage in the foundry warehouse, which lasted up to 14 days, was not enough to jeopardize the functionality of the cores. Furthermore, the tensile and microstructural outcomes revealed that inorganic cores could comply with both high component design requirements and even more stringent environmental regulations of foundries.

The present work focuses on the evolution of hardness and impact toughness after thermal exposure at high temperatures of the AlSi10Mg alloy produced by selective laser melting. The thermal exposure simulated the vapor deposition of coatings on aluminum alloys. The aim is to assess the possibility of combining the ageing step of heat treatments and the deposition treatment. The alloy was aged at 160 and 180 °C for up to 4 hours, both directly and after an innovative rapid solution treatment. Direct ageing had no significant effects on the microstructure, showing an almost constant hardness trend. These results accord with the impact properties, which showed a negligible difference in the impact toughness of the direct aged and the as-built samples. The same ageing treatments performed after rapid solution treatment induced age hardening in the alloy. The hardness values were lower by 38% than those of the directly aged samples. The innovative solution treatment positively affected impact toughness, which increased by 185% compared to the directly aged material. These results highlight that the ageing step can be integrated with the vapor deposition process. Moreover, the heat treatment is suitable for components requiring high impact strength after coating.

The performance improvement in engineering components during operation is a challenging issue and surface engineering methods have been attracting considerable interest in both research and industrial fields [...]

Surface material loss due to erosive wear is responsible for the increased cost of maintenance and downtime in industries. Hence, hardfacing is one of the most valuable and effective techniques employed to improve the wear resistance of heavy-duty components. The present paper investigates the microstructural and erosive wear characteristics of a hypereutectic high-chromium cast iron, considering the erosion resistance, resulting from the impact of micro-sized particles, of both as-received and heat-treated conditions. Micro-sized particles involve the erosion-resistant characteristics of carbide and matrix, contemporary. Due to this, the enhancement of the matrix strength could improve the mechanical support to withstand cracking deformation and spalling. Accordingly, the effect of a destabilization heat treatment on the microstructure was firstly investigated by hardness tests, X-ray diffraction analyses, optical and scanning electron microscopy. Specifically designed erosive tests were carried out using a raw meal powder at an impingement angle of 90°. The resulting superior wear resistance of the heat-treated samples was relayed on the improved matrix microstructure: consistent with the observed eroded surfaces, the reduced matrix/carbides hardness difference of the heat-treated material is pivotal in enhancing the erosion resistance of the hardfacing. The present results contribute to a better understanding of the microstructure–property relationships concerning the erosive wear resistance.

Due to the high complexity of the Additive Manufacturing processes, the effect of individual deposition parameters on integrity and mechanical performance of the 3D-printed part is not easily assessable. An energy density-based approach is often adopted to overcome such complexity, being the Volumetric Energy Density (VED) one of the widely used parameters. However, previous works on the AlSi10Mg alloy suggest that fully dense parts could be achieved with a well defined VED range. This study investigates different combinations of deposition parameters to reproduce part of this range and assess its effect on porosity, microstructure and tensile properties of the AlSi10Mg alloy. It was found that different combinations of deposition parameters in the employed VED range did not alter the microstructural features significantly. Conversely, they severely affected porosity, showing that VED is not a reliable parameter to predict the final density of the additively manufactured components. Moreover, specimens produced with a similar VED but different hatch spacing exhibit significantly different tensile properties. This fact suggests that the effect of deposition parameters should not be solely related to the amount of energy imparted to the material. Finally, systematically higher tensile properties characterise our specimens compared to results available in the literature, due to the microstructure obtained with the adopted combination of deposition parameters. The energy density-based approach lacks in considering the effect of process parameters on the microstructural features other than porosity, which could identify their actual proper combination misleadingly. Our results suggest that new approaches to define the optimum choice of process parameters need to be evaluated to maximise the final performance of AM components.

The evolution of microstructure in relation to dating and nationality of origin was investigated in twenty-four cast iron objects of street furniture produced between XIX and XX centuries in United Kingdom, France, and Italy. Chemical composition of the metalworks was evaluated by glow-discharge optical emission spectrometry. Fragments from the cast irons were analyzed by optical microscopy and scanning electron microscopy with energy-dispersive spectroscopy. Form, distribution, and size of graphite were evaluated in the microstructure according to standard EN ISO 945-1:2008. An image analysis software was employed to quantify the area fraction of graphite in the matrix, major axis, and shape factor of graphite lamellae, area fraction of manganese sulfides (ψ S), area fraction of steadite, and number of eutectic cells per area unit. All data were grouped and linear discrimination analysis (LDA) was applied to assess the group assignment and the probability of correct classification for each metalwork. The results showed that the microstructural features were compatible with those of cast irons produced in the XIX and XX centuries. Values of ψ S also suggested re-melting of cast irons, associated with recycling of cast iron and/or steel scraps. The high values of steadite found in the metalworks are probably due to the excellent castability required for complex shape castings in these centuries. The LDA multivariate analysis allowed to discriminate cast irons based on the year of manufacturing and the nationality of origin.

The purpose of the study is to assess the influence of SiC particles and heat treatment on the wear behaviour of Ni–P coatings when in contact with a 100Cr6 steel. Addition of reinforcing particles and heat treatment are two common methods to increase Ni–P hardness. Ball-on-disc wear tests coupled with SEM investigations were used to compare as-plated and heat-treated coatings, both pure and composite ones, and to evaluate the wear mechanisms. In the as-plated coatings, the presence of SiC particles determined higher friction coefficient and wear rate than the pure Ni–P coatings, despite the limited increase in hardness, of about 15%. The effect of SiC particles was shown in combination with heat treatment. The maximum hardness in pure Ni–P coating was achieved by heating at 400 °C for 1 h while for composite coatings heating for 2 h at 360 °C was sufficient to obtain the maximum hardness. The difference between the friction coefficient of composite and pure coatings was disclosed by heating at 300 °C for 2 h. In other cases, the coefficient of friction (COF) stabilised at similar values. The wear mechanisms involved were mainly abrasion and tribo-oxidation, with the formation of lubricant Fe oxides produced at the counterpart.

Thermal analysis is widely used as a prediction tool for the quality of Al alloys before casting. In the present work, the effects of different grain refiners on the characteristic temperatures and on the grain size of α-Al phase were studied by thermal analysis and metallographic investigations. The response of an AlSiMg alloy towards grain refiners, added in form of rods and tabs, was investigated. In foundry practice, the fading phenomenon of grain refiners is well-known but not completely understood. For these reasons, the fading effect of each refiner at 60 minutes and 120 minutes holding times was also studied. Cooling curves and their derivatives were obtained during solidification of the alloys in a metallic crucible. Experimental data indicated the increase of the temperature associated with the nucleation of α-Al dendrites for the grain-refined alloys in comparison to the untreated ones. Simultaneously, a decrease in primary Al growth temperature, that led to the disappearance of the minimum temperature, were observed. Microstructural features revealed that an increase of 6 ÷ 7 °C of the nucleation temperature, compared to the not refined alloy, corresponds to a significant decrease in average grain size.

This work investigates the causes of excessive wear occurring at the rocker arm/pushrod and rocker arm/valve interfaces of a diesel engine for industrial cleaning machines, after only 1000 h of engine operation. In this engine, the recent replacement of tappets by hydraulic valve lifters not only reduced the running time but also required supplementary maintenance. The chemical composition of the worn components was verified by optical emission spectroscopy. The microstructures, mechanical properties and surface textures were determined by optical microscopy, Vickers hardness and non-contact 3D profilometry. To evaluate the wear mechanisms, the worn surfaces were analyzed by scanning electron microscopy with energy dispersive spectroscopy. The results indicated non-uniform wear damage at the rocker arm/valve interface, probably due to a misalignment of valves with respect to valve seat inserts. For rocker arms and pushrods, improper austenitization parameters and/or unsuitable design of the inductor left some free ferrite, responsible for non-compliance with required specifications for the induction hardening treatment. All worn surfaces were characterized by material removal by scuffing; initiation of fatigue cracks was also observed at the rocker arm/valve interface, and probably erosive cutting occurred at the rocker arm/pushrod interface.

This work evaluates the effects of heavy loadings on a Cr2O3 ceramic coating/steel couple under dry sliding and in conditions similar to those occurring in heavy-duty diesel engines. Two types of wear tests were performed by a standard pin-on-disc tribometer under high constant and variable loads. Before wear tests, microstructure and mechanical properties of coating and steel were determined by optical emission spectrometry, optical microscopy, roughness, microhardness and x-ray diffractometry (XRD). The friction coefficient was directly calculated by the tribometer. The wear rate of Cr2O3 ceramic coating was evaluated by the wear volume and that of pins by weighing them before and after tests. The wear tracks on pins and coating surfaces were analyzed by XRD and by scanning electron microscopy with energy-dispersive spectroscopy. For all loads except the lowest constant one, the results indicated high friction and wear involving material removal from the coating surface, through a severe-oxidational wear associated with extensive cracking of the surface of the coating, softening of the carburizing steel and removal of the carburized layer of pins. The wear mechanism was mild-oxidational under the lowest constant load, which was therefore suggested as the limit for acceptable performance of the sliding couple under study.

The study aimed to investigate crack initiation and propagation at the micro-scale in heat-treated Al–7Si–Mg cast alloys with different copper (Cu) contents. In-situ cyclic testing in a scanning electron microscope coupled with electron back-scattered diffraction and digital image correlation was used to evaluate the complex interaction between the crack path and the microstructural features. The three-nearest-neighbour distance of secondary particles was a new tool to describe the crack propagation in the alloys. The amount of Cu retained in the α-Al matrix after heat treatment increased with the Cu content in the alloy and enhanced the strength with a slight decrease in elongation. During cyclic testing, the two-dimensional (2D) crack path appeared with a mixed propagation, both trans- and inter-granular, regardless of the Cu content of the alloy. On fracture surfaces, multiple crack initiation points were detected along the thickness of the samples. The debonding of silicon (Si) particles took place during crack propagation in the Cu-free alloy, while cracking of Si particles and intermetallic phases occurred in the alloy with 3.2 wt% Cu. Three-dimensional tomography using focused ion beam revealed that the improved strength of the α-Al matrix changes the number of cracked particles ahead of the propagating crack with Cu concentration above 1.5 wt%.

In the present paper, microstructural and mechanical properties of an innovative AlSi3Mg alloy were studied. Particularly, the effect of the addition of Cr and Mn on tensile strength and impact toughness was evaluated. In fact, the presence of these elements leads to the formation of an intermetallic phase with a globular or polyhedral morphology. It was therefore investigated the role played by Cr-Mn containing particles in the failure mechanism and the influence of the heat treatment parameters. Moreover, tensile and impact tests were performed on A356 samples in T6 condition, whose results were compared with the performance of the innovative alloy. Considering the static properties, the innovative alloy showed remarkable values of tensile strength, while ductility was improved only after heat treatment optimization. Poor impact toughness values were measured and the microstructural analysis confirmed the presence of coarse intermetallics, acting as crack initiation and propagation particles, on the fracture surfaces.

Two metal plaques and a cock statuette belonging to a private collection and stylistically consistent with the Royal Art of Benin (Nigeria) were investigated in order to verify their authenticity. The characterization of alloys and patinas were carried out by inductively coupled plasma mass spectrometry, optical microscopy, scanning electron microscopy and energy dispersion spectroscopy, and X-Ray diffraction spectrometry. Furthermore, thermal ionization mass spectrometry was used to assess the abundances of lead isotopes and to attempt a dating by the measurement of 210 Pb/ 204 Pb ratio. The results showed that all three artefacts were mainly composed of low lead-brass alloys, with relatively high concentrations of zinc, antimony, cadmium and aluminum in the solid copper solution. Microstructures were mostly dendritic, typical of as-cast brasses, and characterized by recrystallized non-homogeneous twinned grains in areas corresponding to surface decorations, probably due to multiple hammering steps followed by partial annealing treatments. The matrix was composed of a cored α-Cu solid solution together with non-metallic inclusions, lead globules and Sn-rich precipitates in interdendritic spaces. On the surface of all metalworks, both copper and zinc oxides, a non-continuous layer of sulphur-containing contaminants and chloride-containing compounds, were identified. The lead isotope results were consistent with brasses produced shortly before or after 1900 CE. Overall, the data obtained by different techniques supported the hypothesis that the three artefacts were not authentic.

The effect of copper (Cu) addition up to 3.2 wt.% on crack initiation and propagation in an Al-Si-Mg cast alloy was investigated using in-situ cyclic testing in the as-cast condition. A novel combination of digital image correlation, electron backscatter diffraction, and scanning electron microscopy was used to investigate crack initiation and propagation behaviour during in-situ cyclic testing. The results showed that Cu-rich intermetallic compounds with the addition of Cu up to 1.5 wt.% do not affect the fatigue behaviour of these alloys, and that crack propagation in these cases is trans-granular and trans-dendritic. However, increasing the concentration of the Cu retained in the primary α-Al matrix in solid solution and Cu-containing precipitates delayed crack propagation during cyclic testing. The results showed that strain accumulation was highest at the grain boundaries; however, the crack preferred to propagate along or across primary α-Al dendrites due to the relatively lower mechanical strength of the matrix compared to the eutectic and intermetallic phases. Moreover, the addition of Cu of more than 3.0 wt.% to Al-Si-Mg alloys changes the fatigue behaviour such that an almost static failure occurs, with limited crack propagation.

The request of even more stringent restrictions, regarding efficiency and environmental impact of industrial components, determines an optimized use of primary energy but also entails the design of more lightweight, smart and flexible devices, able to adapt their operation as a function of several different inputs. In this framework, the use of a fascinating class of metallic materials, called Shape Memory Alloys (SMAs), could represent a valid support for the designers. The capability of these materials to react to an external stimulus, without continuing to supply energy to external actuators, represents, especially in the aerospace engineering field, a technological breakthrough. The present paper reports the basic ideas and summarizes the important aspects related to the development of SMA-based actuators in relation to the present state of the art. A case study of morphing blades, equipped with embedded SMA strips, for an automotive cooling fan is reported. Finally, some hints, regarding the design process of SMA-based actuators, are proposed.

Towards the end of the last century, vacuum heat treatment of high speed steels was increasingly used in the fabrication of precision cutting tools. This study investigates the influence of vacuum heat treatments at different pressures of quenching gas on the microstructure and mechanical properties of taps made of M35 high speed steel. Taps were characterized by optical microscopy, scanning electron microscopy with energy dispersive spectroscopy, X-ray diffraction, apparent grain size and Vickers hardness measurements, and scratch tests. Failure analysis after tapping tests was also performed to determine the main fracture mechanisms. For all taps, the results showed that microstructures and the values of characteristics of secondary carbides, retained austenite, apparent grain size and Vickers hardness were comparable to previously reported ones for vacuum heat treated high speed steels. For taps vacuum heat treated at six bar, the highest plane strain fracture toughness was due to a higher content of finer small secondary carbides. In contrast, the lowest plane strain fracture toughness of taps vacuum heat treated at eight bar may be due to an excessive amount of finer small secondary carbides, which may provide a preferential path for crack propagation. Finally, the predominant fracture mechanism of taps was quasi-cleavage.

In this study, the effect of aging on the mechanical properties of unmodified A356 aluminium casting alloy with trace additions of Ni or V was investigated. Trace elements were added in concentrations of 600 and 1000 ppm of Ni and V, respectively. Samples from sand and permanent mould castings in as cast and T6 heat-treated conditions were tested. Tensile tests were performed at both room and high temperature (235 °C). Taking into account the results from both testing conditions, Vickers hardness was measured in order to endorse the hypothesis of artificial aging occurring during high temperature tensile tests. In order to study this effect, a series of specimens was aged at 235 °C for different aging times, and aging curves were plotted. The occurrence of static and dynamic aging was evaluated by comparing hardness values of tensile specimens and aged samples, particularly in the range of 5-20 min, as this range corresponds to the time necessary for pre-heating and testing of the tensile samples. A basic correlation between tensile strength and hardness is also given.

Micro-sized solid particle adhesion affects several industrial processes and machines. Particle adhesion is responsible for reducing reliability and efficiency. A great example is represented by gas turbines and heat exchangers. These machines collect a huge amount of contaminants during their common operation. These deposits determine operability issues and efficiency losses. In this work, the particle deposition phenomenon and its development over time are studied in-depth through an experimental campaign. A high-speed airflow laden with micro-sized sand particles has impinged onto a flat surface. The particle mass flow, after being carefully dosed by an aerosol generator (contaminant concertation equal to 50 mg/m3), is injected into the main airflow using an aerodynamic eductor. The tests were conducted with different impact velocities ranging from 22 m/s to 48 m/s, and considering different exposure periods. For each test, different roughness levels were tested to define the influence of the surface quality on the particle sticking capability. The deposits amount was evaluated in quantitative and qualitative ways. Weighing measurement was used for extracting quantitative information about particle sticking, while the video and stereomicroscope image analyses were used to gain insight into the morphology of the surface and its modification over the exposure time. The results show a strong dependence of particle sticking on both flow/particle velocity and the roughness of the substrate, characterized by non-linear correlations due to the action of the detachment process.

This work aims at investigating the impact behavior of an additively manufactured AlSi10Mg alloy subjected to different heat-treatment conditions. The commonly used heat-treatment routes were compared with a novel route (HPT6), which combines hot isostatic pressing (HIP), gas quenching, and ageing at high pressures. The as-built and treated alloy was characterized by Charpy impact testing and several microstructural and fractographic techniques, such as scanning electron microscopy, transmission electron microscopy (TEM), and X-ray diffraction. The as-built material displayed a very fine non-equilibrium microstructure, which led to a high impact strength but limited absorbed energy. Low-temperature annealing severely modified the starting microstructure of the alloy and restored its equilibrium condition. Even though this alloy did not suffer from strength loss, its absorbed energy increased significantly, resulting in an excellent impact performance. HIP application inhibited the growth of gas-hosting pores in the alloy when treated at high temperatures, yielding a material with a final relative density higher than 99%. TEM demonstrated that the novel HPT6 route induced precipitation strengthening in the alloy, thus increasing its impact strength when compared to the HIP route. Moreover, the HPT6 alloy and the alloy subjected to standard heat-treatment exhibited comparable impact performance. This suggests that the novel route proposed in this study can possibly replace the standard heat-treatment protocol, which would reduce the processing duration and cost of production of the additively manufactured AlSi10Mg alloy.

The effect of copper (Cu) addition up to 3.2 wt% on crack initiation and propagation in an Al–Si–Mg cast alloy was investigated using in-situ cyclic testing in the as-cast condition. A combination ...

Several production processes involve the use of turbomachinery for the transport of gases with high concentrations of solid particles. Centrifugal fans employed in clinker production operate under severe erosive conditions. To limit the erosive wear of specific fan zones, wear-resistant plates are used. This paper presents a numerical investigation of the erosion behavior of a large-sized centrifugal fan operating in a cement factory. A contaminant characterization is carried out to define particle shape, size distribution and physical characteristics (i.e. density) on which the particle model is based. In addition, the surface analysis and microstructural characterization of the weld-deposited hardfacing alloy provide the wear-resistant coating features. Particles are tracked with a Lagrangian approach on the instantaneous flow fields corresponding to different relative impeller-to-volute positions. The particle impact angle is found to have a significant influence on the erosion of fan surfaces. CFD predictions are in close agreement with on-field erosion detections.

In the present study, instrumented impact strength tests were carried out on Charpy AlSi10Mg samples produced using laser additive manufacturing in order to accurately investigate the influence of building directions, heat treatment parameters and also the effect of Hot Isostatic Pressing (HIP) on their impact properties. AlSi10Mg cast samples were also tested for comparison. In addition to metallographic inspections, a deep characterization of the fracture surfaces in all the analysed conditions was performed. Microstructural features were also correlated to the impact properties: absorbed energy, peak force, crack nucleation and propagation energies. It was found that additive manufactured samples in as-produced condition exhibit the best performance due to their peculiar microstructure. HIP, followed by T6 heat treatment, is positive for the alloy properties since it effectively reduces porosities, which are a favourable path for crack propagation. Building direction has a clear effect on the fracture propagation. Samples in as-produced condition display greater unevenness of the fracture surface in the horizontal direction than in the vertical direction. This trend is less evident after heat treatment, but still detectable. The fractal dimension of the fracture surfaces is a quantitative parameter sensitive to the building orientation of samples and to the performed heat treatments.

In recent years, the influence of Ni on high-temperature mechanical properties of casting Al alloys has been extensively examined in the literature. In the present study, room temperature mechanical properties of an A356 alloy with Ni additions from 0.5 to 2 wt % were investigated. The role of Ni-based compounds and eutectic Si particles in reinforcing the Al matrix was studied with image analysis and was then related to tensile properties and microhardness. In the as-cast condition, the formation of the 3D network is not sufficient to determine an increase of mechanical properties of the alloys since fracture propagates by cleavage through eutectic Si particles and Ni aluminides or by the debonding of brittle phases from the aluminum matrix. After T6 heat treatment the increasing amount of Ni aluminides, due to further addition of Ni to the alloy, together with their brittle behavior, leads to a decrease of yield strength, ultimate tensile strength, and Vickers microhardness. Despite the fact that Ni addition up to 2 wt % hinders spheroidization of eutectic Si particles during T6 heat treatment, it also promotes the formation of a higher number of brittle Ni-based compounds that easily promote fracture propagation. © 2018 by the authors. Submitted for possible open access publication under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

High-temperature tensile properties of unmodified A356 alloy with and without the addition of Ni or V in traces (600 and 1000 ppm of Ni and V, respectively) were investigated by analyzing samples obtained from sand and permanent mold castings in the as-cast and T6 heat-treated conditions. Tensile tests were performed at 508 K (235 °C) at a crosshead speed of 1 mm/min. In addition, samples were subjected to artificial aging at 508 K (235 °C) for different times, and corresponding hardness curves were plotted. Microstructures and fracture surfaces, analyzed by FEG-SEM equipped with energy dispersive X-ray spectroscopy, showed that neither Ni nor V addition had a detrimental effect on high-temperature tensile properties. Aging curves showed a strong loss of hardness affecting the T6 class between 30-min and 1-h exposure time. After 6-h aging, no evidence of aging treatment persisted on hardness of the tested material. Hardness values did not reveal any significant difference between the reference alloy and the Ni- and V-containing alloys in both casting conditions, in complete analogy with the tensile properties. Unmodified eutectic silicon particles provided inhomogeneity in the α-Al matrix and acted as the principal source of stress concentration leading to fracture.

In Al-Si alloys, Fe is present as an inevitable impurity element, which mainly precipitates in the form of β-Fe or α-Fe crystals. While the latter usually has polyhedral or Chinese script morphology, the platelet-like shape of the β-Fe phases acts as a stress raiser and can also increase the amount of porosity. To inhibit the formation of this detrimental phase, several elements act as neutralizers of the embrittling effects of Fe and, among them, Mn is the most widely used. Mg strongly affects the mechanical properties and the formation of Fe-bearing phases. In the present work, a series of A356 aluminum foundry alloys with several combinations of Mn/Fe ratios and Mg contents were studied. To investigate the effect of Mn additions, five alloys with constant Fe and Mg content and increasing Mn/Fe ratios, from 0.37 wt. % to 1.11 wt. %, were considered. Moreover, four alloys with reduced Mg amounts up to 0.25 wt. % were evaluated. Tensile samples were machined from permanent mold castings and T6 heat-treated. The influence of the alloying elements on the mechanical properties were compared to microstructural observations. The results indicate that increasing the Mn/Fe ratios does not result in a significant increase of the tensile properties of the alloys. Conversely, the reduction of the Mg amounts leads to the decrease of yield stress, ultimate tensile strength and hardness combined with an increase in the elongation to fracture. Finally, the quality index approach was used to express the quality of the castings as a function of their ductility, yield strength and strain hardening ability.

In a traditional automotive cooling system, energy optimization could be achieved by controlling the engine temperature by means of several sensors placed inside the cooling circuit. Nevertheless, in some cases the increasing use of a great number of sensor devices makes the control system too bulky, expensive and not sufficiently robust for the intended application. This paper presents the development of a heavy-duty automotive cooling axial fan with morphing blades activated by Shape Memory Alloy (SMA) strips that work as actuator elements in the polymeric blade structure. The blade was designed to achieve the activation of the strips (thermo-mechanically treated on purpose) by means of an air stream flow. With the aimof studying the morphing capability of the adaptive structure together with the recovery behavior of the NiTi strips, four different polymeric compounds have been compared in a specifically-designed wind tunnel. As the airstream flow increases its temperature, the strips recover the memorized bent shape, leading to a camber variation. To study the possibility of employing SMA strips as actuator elements, a comparison with common viscous clutchbehavior is proposed. The time range actuator response indicates that the SMA strips provide a lower frequency control that fits well with the engine coolant thermal requirement. The experimental results demonstrate the capability of SMA materials to accommodate the lower power actuators in the automotive field. This innovative passive control system results from the selection of (i) the memorized shape of the SMA strips and (ii) the polymeric compound used for the blade structure.

This paper focuses on the development and experimental testing of a composite blade for an automotive axial fan. A novel concept of morphing blade is proposed with the aim of replacing the conventional actuator systems. The structure is made up of a polymeric matrix equipped with NiTi shape memory alloy strips as active elements. The morphing blade changes its shape as the phase transformations of the strips are thermally activated by airflow. To study the morphing capability of the blade, together with the recovery behavior of the NiTi strips, four different polymeric compounds have been compared. Digital image analysis techniques have been performed to quantitatively analyze the blade deflections and to evaluate the most suitable polymeric matrix for the intended application. Finally, the blade shape modifications, which occur along the blade span during the activation cycles, have been reconstructed by three-dimensional non-contact surface detection. Results from the comparison between these two reverse engineering methods could provide a powerful support for the assessment of the aerodynamic performance of the morphing blade. Keywords: NiTi shape memory alloy, Polymeric matrix, Adaptive deformable structure, Digital image analysis, Reverse engineering

Two constitutive models representative of two well-known modeling techniques for superelastic shape-memory wires are reviewed. The first model has been proposed by Kim and Aberayatne in the framework of finite thermo-elasticity with non-convex energy [1]. In the present article this model has been modified in order to take into account the difference between elastic moduli of austenite and martensite and to introduce the isothermal approximation proposed in [1]. The second model has been developed by Auricchio et al. within the theory of irreversible thermodynamics with internal variables [2]. Both models are temperature and strain rate dependent and they take into account thermal effects. The focus in this article is on investigating how the two models compare with experimental data obtained from testing superelastic NiTi wires used in the design of a prototypal anti-seismic device [3, 4]. After model calibration and numerical implementation, numerical simulations based on the two models are compared wit...

One way to improve the mechanical properties of Al–Si alloys is to add chemical modifiers that affect the microstructure of the cast components. Small amounts of Sr cause the modification of the eutectic Si particles from a coarse plate-like morphology into a fine fibrous one. This study sets out to analyse the effects of chemical modification on an Al–7%Si–0.3%Mg foundry alloy treated with Sr, ranging from 62 to 820 ppm. Assessment of modification level was evaluated by both thermal analysis technique and quantitative microstructural investigations. Up to now, little attention has been paid to the role played by microstructural characteristics in evaluating the modification level, which is commonly performed by comparison with standard images. In the present investigation, numerical methods proposed in the literature have been considered in an attempt to understand their effectiveness. The correlation between thermal analysis results and geometrical parameters of eutectic Si particles highlighted the impact of microstructural homogeneity on modification-level evaluation. In addition, the presence of Ca in Sr-based intermetallics has been further investigated by means of scanning electron microscopy combined with energy-dispersive X-ray spectroscopy.