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Additive Manufacturing (AM), applied to metal industry, is a family of processes that allow complex shape components to be realized from raw materials in the form of powders. The compaction of the powders is achieved by local melting of bed. Electron Beam Melting (EBM) is an additive manufacturing process in which a focalized electron beam is the heat source that allows the powders to be compacted. By EBM it is possible to realize complex shape components; this feature is of particular interest in titanium industry where numerous efforts are done to develop near net shape processes. One of the limits of EBM based AM process is the difficulty to realize large dimension parts. Due to this limit the study of joining processes of different parts is of great interest. In the present work the microstructure evolution of sheets of TI6Al4V made by EBM and joined by Linear Friction Welding (LFW) is analyzed in details. The bulk microstructure of the specimen is fine lamellar; lamellae are enclosed in alpha colonies. Different types of porosities are observed. In the joint a Thermo Mechanical Affected Zone (TMAZ) and Weld Bead (WB) are evident. In TMAZ a partial recrystallization occurs and the parent microstructure is deformed. Complete recrystallization occurs in WB whose structure is martensitic.

The incremental forming of titanium alloy sheets combines the advantages of this advanced flexible manufacturing process, that allows to produce complex components without using dedicated tools, with the interesting properties of the material under consideration. In this study, thin sheets of grade 1 titanium were incrementally formed to evaluate their formability and surface quality by varying the tool-sheet contact conditions. Experimental tests and surface analyses highlight dependence on the contact conditions of the surface quality rather than of the formability. Moreover, they emphasize that the tool-sheet contact conditions mainly affect the repeatability of the process due to the occurrence of galling.

Metal foams are an interesting class of materials with very low specific weight and unusual physical, mechanical and acoustic properties due to the porous structure. In recent years several manufacturing techniques were developed. The limit of these techniques is that it is difficult, even if impossible, to manufacture precursors and then foams able to reinforce complex shaped components; this drawback, to date, limits the application of metal foams. This proof of concept paper is focused on the study of an innovative manufacturing technique able to produce complex shaped precursors. The key idea is to spray a powder mixture (made of both aluminum alloy powders as metal matrix and titanium hydride particles as foaming agent) through the cold gas dynamic spray on a free shape metallic substrate and then carry out the foaming process. A preliminary granulometric analysis was carried out to estimate the particles mean size and then sound assisted (140dB–80 Hz) fluidization process was used to achieve a homogenous and deep mixing between the fine metal powders and the blowing agent ones. In particular, two different types of mixtures with 1 wt% and 2.5 wt% of TiH 2 were investigated; moreover, air compressed as well as helium were used as CGDS carrier gas in order to ensure a higher impact velocity and a better compacting of the powders. Finally, the cross sections of manufactured solid foams were observed by means of a SEM microscope for having information about internal metallurgical phenomena as well as the distribution and morphology of foam cells. Macrographs of created porous structures showed the effectiveness of the developed innovative manufacturing process.

Cemented carbides, also known as Widia, are hard metals produced by sintering process and widely used in mechanical machining. They show high cutting capacity and good wear resistance; consequently, they result to be excellent materials for manufacturing cutting tools and sandblast nozzles. In this work, the wear resistance of WC-Co carbides containing Eta-phase, a secondary phase present in the hard metals when a carbon content deficiency occurs, is analyzed. Different mixtures of carbide are prepared and sintered, with different weight percentages of carbon, in order to form Eta-phase and then analyze how the carbon content influences the wear resistance of the material. This characterization is carried out by abrasive wear tests. The test parameters are chosen considering the working conditions of sandblast nozzles. Additional information is gathered through microscopic observations and the evaluation of hardness and microhardness of the different mixtures. The analyses highlight that there is a limit of carbon content below which bad sintering occurs. Considering the mixtures without these sintering problems, they show a wear resistance depending on the size and distribution of the Eta-phase; moreover, the one with high carbon content deficiency shows the best performance.

Nowadays, the need of developing high flexible forming processes matches with the need of weight reduction. In this light, the incremental forming of titanium alloys sheets can guarantee both these aspects by combining the flexibility of the process, particularly suggested for small batches and customized parts, with the good properties of titanium alloys, in particular for aerospace applications.The aim of this work was to obtain information useful to enhance the general knowledge of the hot incremental forming processes of grade 1 titanium sheets at different temperatures.First, both tensile and straight groove tests were carried out by varying the test temperature; in this phase, information regarding both the forming forces and the wear phenomena due to the tool-sheet contact was acquired.Successively, on the basis of the mechanical characterization of the sheets previously carried out, explicit analyses, effectuated by a non-linear FE code, allowed to determine the formability curves of the sheets for the different temperatures.

Ti–6Al–4V is an alloy increasingly used for structural applications in aeronautics due to its characteristics of high mechanical properties, lightness, and corrosion resistance. This alloy is conventionally forged below the beta transus temperature in order to control the microstructure evolution, to obtain a component with the desired properties. In this paper, some experiences of an innovative beta forging process of the Ti–6Al–4V alloy are reported. A preliminary campaign of forging tests in the beta field on cylindrical coupons was carried out in order to study the microstructural evolution in different forging conditions, in terms of both temperature and strain rate. Moreover, in order to study the microstructural evolution due to the beta forging in a complex shaped component, a case study is presented. The forged component showed a microstructure coherent with the forging process experienced; moreover, the hardness values measured were similar to the ones of the Ti–6Al–4V alloy in mill-annealed conditions.

Magnesium alloys are attractive for lightweight structural applications in the transportation industry because of their low density and high specific strength and stiffness [1]. With an ultrafine-grained microstructure, they exhibit superplasticity at relatively low temperatures and high strain rates [2]. Friction stir processing (FSP) was used to obtain a microstructure with ultrafine grains in the magnesium alloy AZ31. In this project, microstructures obtained using different rotational speeds are studied. Free bulge forming of the FSP processed AZ31 sheets are carried out to evaluate the superplastic behaviour [3]. The model and the evolution equations have been implemented into a commercial finite element modeling (FEM) code and different simulations are conducted to correlate the experimental and numerical results for the model validation [4]. The purpose of this study is to investigate the effect of the microstructure on the superplastic forming behaviour using free bulge forming and FE simulations.

Superplastic forming and diffusion bonding (SPF/DB) is a near-net-shape forming and joining process used with alloys having superplastic properties in order to make manufact which should have light weight and high stiffness. The aerospace is one of those sectors in which such technology is mainly used. This process allows to reduce the buy-to-fly ratio and consequently the production costs thanks to the possibility to produce complex shape components in a single shot. The material widely used for this application is the Ti-6Al-4V alloy for its high strength vs weight ratio, excellent mechanical proprieties, corrosion resistance and galvanic compatibility with carbon fiber reinforced composite materials. In this study, finite element analysis of the SPF/DB process has been carried out in order to investigate the thickness prediction, the optimization of the tooling’s geometry and the definition of the sheets initial thickness in the blow forming process of a multi-sheets configuration.

2024 aluminium alloy is used for parts and structures which demand high-strength/weight ratio. In particular, Al2024 is, for its high specific strength and good chemical stability, a suitable material for aerospace application. Aluminium alloys are involved in corrosive phenomena when they are used in critical applications, such as the aeronautic ones. The solution commonly adopted to solve corrosive problems is to paint aluminium alloy surface including 2024 aluminium alloy which is the subject of this study. The applied paint film protects the aluminium alloy from corrosion. In order to improve the adhesion of the paint film it is necessary to pre-treat the manufactured surface. The objective of the pre-treatment is to develop a cleaned, uniform, wettable surface. Cold plasma is an efficient, economic and environmentally attractive alternative to the use of the traditional pre-treatment. This work aims to study the relationship between cold plasma and 2024 aluminium alloy wettability and cleaning. Surface samples have been analysed by: (i) standard procedure to measure the quantitative wettability; (ii) Energy Dispersive X-ray Spectroscopy or EDS to determine a quantitative measure of organic contaminant. This work demonstrates that air cold plasma treatment improves significantly wettability and cleaning of 2024 aluminium alloy surfaces both associated with pre-cleaning by MEK® and without pre-cleaning by MEK®: the wettability reducing has been greater than 70% and the contaminants reducing greater than 65%.

A serious number of critical aspects have to be considered when aluminium and its alloys, especially if heat treated, are welded. These drawbacks, to date, limit the application of the welded joints in the aeronautical sector. The possibility of overcoming these limitations is focused in current paper by studying the mechanical performance of two types of dissimilar laser beam welds in T-joint configuration. The dissimilar joints, planned for aeronautical applications, combine the same skin, made of AA 6156 alloy, with two different base materials for the stringers, namely the AA 2139 and the non-standard alloy PA765. The alloys under investigation are characterized by enhanced weldability if compared to the standard AA 2024, widely used in aeronautic. Due to the contemporary presence of dissimilar heat treatable aluminium alloys, both joints have been subjected to dedicated multi-step heat treatments. Metallurgical and microstructural analysis were carried out in order to highlight the influence of both chemical composition and thermal cycles experienced on the final microstructures of different zones of the joints, governing the mechanical properties of the joint itself. Vickers micro-hardness measurements were performed to fully characterize the heterogeneity in mechanical properties across the different zones of the dissimilar welds. Strain data acquisition by Digital Image Correlation (DIC) allowed to assess the influence of local weld properties on joints strength in tensile loading. The important role of the temper conditions of the parent materials, resulting from the different joint pre and post-welding heat treatment options, on the tensile behaviour of the skin and, in this way, on the global strength of the connection was showed. The dramatic role played by the Heat Affected Zone and the influence of the distribution of the strengthening elements on examined joints mechanical properties has been put in evidence, according to mechanical test results.

The subject of this study, 2024 aluminium alloy, is widely used in the aeronautic field for its high mechanical properties. In order to solve corrosive problems, where Al2024 is involved in critical applications such as aeronautic ones, it is necessary to paint aluminium alloy: the applied paint film protects the aluminium alloy from corrosion. To improve the adhesion of the paint film it is necessary to pretreat the manufactured surface: pretreatments develop a cleaned, uniform and wettable surface. Cold plasma is an efficient, economic and environmentally attractive alternative to the traditional pretreatment. An air cold plasma treatment improves the wettability of aluminium alloy and also cleans organic contaminants from the surface. This work aims to value the possible correlations between: (1) the wettability and the cold plasma treatment time, (2) the superficial cleaning and the cold plasma treatment time and (3) the superficial cleaning and the wettability.

Superplastic materials show a very high ductility, i.e. maximum elongation of about 5000%, even if they are lowly stressed. This is due to both peculiar process conditions and material intrinsic characteristics. The aerospace industry has shown that, in order to produce complex parts requiring large tensile elongations that cannot be formed by conventional processes, superplastic forming can be used. A detailed design of technological process is necessary so as to exploit at best the peculiar potentialities of superplastic forming. The aim of the present work is to show a method to characterise superplastic materials. This method is based on the approximate analysis of a superplastic forming process in a triangular indefinite prismatic-shaped die. It has been experimentally validated through laboratory samples on material formed by room temperature; moreover, it has been compared to several methods proposed by other authors.

Superficial coatings are widely used in industrial applications in order to improve the superficial properties of metallic components. In particular, in the aeronautic field, all the components are coated in order to prevent both corrosion and wear. In this field, heat treatable aluminum alloys, in age hardened condition, are used; consequently, superficial coatings must be carried out through “cold” processes, i.e. coating processes in which the component to be coated remains at low temperatures, below 100°C. Cold gas dynamic spray technique (CGDS) is a process of deposition that consists in the realization of surface coatings with high-velocity metal particles sprayed on the substrate at temperature significantly lower than the melting one of the substrate itself and at relatively low temperatures if compared to other spray techniques. When processing conditions are optimized, the process can produce near fully dense coatings. This technique could be particularly useful in the coating of rolled sheets, needing of successive cold plastic deformations. One of the cold plastic processes is incremental forming, a high flexible process for rapid manufacturing of complex sheet metal part shapes; it presents the potential to be easy to automate and particularly attractive for small batches and customized parts. In this process, a simple tool describes a path that allows to locally deform the sheet clamped along its periphery. The aim of this paper is to study the evolution and behaviour of aluminum coating deposed by CGDS on AA 2024-T3 sheets carried out by an incremental forming process. This evaluation is carried out by characterizing the cold sprayed coating after the forming process for different wall angles of simples geometries.

The forming limit diagram of superplastic PbSn60 alloy was investigated in this paper. The superplastic sheet was bulged using dies with aspect ratios of 1:1, 15:11, 5:3 and 5:2, at the constant gas pressure and at the temperature of 293 K. Square sheets of dimensions 80 × 80 mm were machined and printed with grid circles of 3 mm diameter. In the test, the specimen is fixed on an elliptical shape die by the action of a blank holder; the sheet is stressed mechanically by a pressure gas, inducing on the pole a biaxial strain state. It was found that the forming limit diagram is not sensitive to die aspect ratio and it is different from a typical cold forming limit diagram.

2024 aluminium alloy is widely used in aeronautical applications because it provides a high mechanical strength and low weight. Aeronautical critical environmental conditions cause corrosion on the surface in part, due to the Cu present in Al2024. To solve problems associated with corrosion, the aluminium alloy surface is commonly covered by paint; it is important to guarantee the adhesion of the paint coating to the aluminium alloy and the stability of the coating in the course of time. To achieve this aim the surface must be prepared before applying a protective coating. Cold plasma treatment represents an efficient, non-polluting and economical alternative to clean and activate aluminium surfaces. In particular, it has been demonstrated that an oxygen cold plasma treatment improves wettability and adhesion of the Al2024 surface. The aim of this work has been to value the wettability ageing time of Al2024 surfaces treated with oxygen cold plasma. The evaluation of the ageing time represents a fundamental step to plan the insertion of the plasma process inside an industrial process. In fact, once the ageing time has been determined, it is possible to establish how much time has to pass between the surface activation of a body, obtained by cold plasma treatment, and the following paint process.

Publisher Summary The dieless incremental forming process is an innovative sheet metal working technology where a considerable amount of knowledge and intelligence is required, in order to obtain accurate and efficient operations. In conventional forming process, the final shape is mostly determined by the die shape. In dieless incremental forming, however, the final shape must be predicted and controlled only by means of a proper process design. For this reason, several issues of this process must still be investigated on a scientific base. This chapter discusses the dieless forming process as an aid towards an intelligent process planning. In most sheet metal incremental forming processes (shear spinning, flow forming, and dieless forming), the deformation occurs by pure shear. The main process parameters are the feed rate, the part conicity, and the punch radius r. Formability in incremental forming has been often investigated and it is well recognized that severe strain may occur before fracture. Thinning and fracture largely depend on the part conicity. Besides, decreasing the feed rate has a positive effect. On the contrary, the effect of the punch radius r has been seldom explored in quantitative terms. The chapter investigates the effect of r on the formability of thin sheet metals, when plastically deformed by incremental forming.

The need to contrast the severe use conditions developing in the aeronautical field requires surface protection of 2024 aluminium alloy structures by a paint coating. Therefore the aluminium alloy, to be suitable for painting, has to be subjected to complex and critical processes involving a cleaning by acid solvent, a chromate plating, a primer and a protective paint application. Oxygen cold plasma treatment represents an efficient, not-polluting and economic alternative to clean and activate aluminium alloy surfaces. It allows simplification of the anticorrosive protection process of aluminium alloy surfaces and, therefore, reduction of their manufacturing costs. The aim of this work has been to improve the wettability and its ageing time of an aluminium alloy surface treated with oxygen cold plasma. A set of process variables has been identified and used to carry out some experimental tests on the basis of design of experiment techniques.

A number of materials is subject to the cavitation during superplastic deformation. The cavities nucleate at sites such as grain boundaries, second phase particles, and triple points; subsequently, they grow and interlink with the neighbouring cavities. Cavitation usually leads either to the undesirable post-forming characteristics or to the premature tensile failure. It is also apparent that the cavities can pre-exist in the form of cracks and decohered interfaces, which develop during thermomechanical processing necessary to produce the superplastic microstructures. Evidently, extensive cavitation imposes significant limitations on their commercial application. The effect of material properties such as the cavity growth rate of intentionally pre-machined voids on specimens subject to the tensile deformation and to the biaxial deformation has been determined. The tensile tests have been conducted at constant crosshead velocity, using a fine-grained Pb–Sn alloy that presents superplastic properties at room temperature. The results of the experiments are in agreement with the numerical predictions obtained using a code based on the finite element method (FEM).

Because of cavities nucleation at the grain boundaries and their subsequent growth and coalescence large number of alloys show premature failure during superplastic flow. In this paper, the authors will introduce the study of the growth of void intentionally premachined on specimen subject to tensile test: in particular the effects of the material parameters on the void growth will be analysed. Tensile tests were conducted at constant crosshead velocity using a fine-grained Pb–Sn alloy that presents superplastic properties at room temperature. The results of the experiments are in good accordance with the numerical predictions obtained by using a code based on the finite element method.

In the paste, different authors [1,2,3,4,5,6,7,8] have developed analytical process models of superplastic sheets bulged into dies of simple shapes such as cylindrical cavities, parallel walls, conical and prismatic dies. An important data for any type of process model is the constitutive equation of superplastic material. In general, the most common method of characterising a material consists in submitting a specimen, with standardised geometry, to a uniaxial tensile test. For superplastic materials the tests were carried out at different strain-rate in order to determine the flow stress as a function of strain-rate. In alternative, to determine the constitutive equation of superplastic materials, biaxial tests was derived from analytical process models [1,4,5,8]. In this study, the method to determine the strain-rate sensitivity coefficient of superplastic materials, based on the analysis of forming process in a prismatic die, was experimentally validated in the laboratory on specimen of material formed at room temperature. The authors have confirmed, by finite element method, the validity of the material characterisation carried out using a prismatic die.

A series of experiments regarding the deposition of Ti powders on an aluminum substrate with different inlet temperatures, stand-off distance, and gun speed allowed to study the relation between these factors and the morphology of the coating. A suitable geometrical approximation of the coating profile was then found and used, together with the mass balance of the deposition process, to write a relationship between the coating cross section and the process parameters. The proposed equations are expected to be useful in a manufacturing environment for predicting the coating parameters from the process conditions and ultimately to optimize the deposition.