The Corrosion Behaviour of Additively Manufactured AlSi10Mg Parts Compared to Traditional Al Alloys

Additive manufacturing of metal parts in the motorsport industry is becoming a decisive technology for producing lightweight and rigid parts, with increasing applications as the costs decrease. Among the available metal alloys, AlSi10Mg is one of the most widely used. In this paper, the corrosion resistance of additively manufactured AlSi10Mg is compared with that of other traditionally manufactured aluminium alloys widespread in the automotive industry. Several potentially corrosive agents, typical of vehicle applications, were used: salty water, motor oil, suspension oil, cooling fluid and gasoline. Corrosion tests were conducted at both room temperature and 90 C. The effects of heat and surface treatments were evaluated separately. The samples were visually inspected and weighed to evaluate the corrosion rate with the aid of SEM and EDS analysis. Additively manufactured AlSi10Mg generally showed better corrosion resistance in the stress-relieved condition as compared to the T6-treated state, with slightly better results for the polished samples. Motor oil, suspension oil, cooling fluid and gasoline did not significantly corrode the specimens, except for the T6-treated AlSi10Mg samples at 90 C. However, the corrosion rate was always higher than traditionally manufactured aluminium alloys tested for comparison

Effective Mechanical Properties of AlSi7Mg Additively Manufactured Cubic Lattice Structures

Lattice structures, whose manufacturing has been enabled by additive technologies, are gaining growing popularity in all the fields where lightweighting is imperative. Since the complexity of the lattice geometries stretches the technological boundaries even of additive processes, the manufactured structures can be significantly different from the nominal ones, in terms of expected dimensions but also of defects. Therefore, the successful use of lattices needs the combined optimization of their design, structural modeling, build orientation, and setup. The article reports the results of quasi-static compression tests performed on BCCxyz lattices manufactured in a AlSi7Mg alloy using additive manufacturing. The results are compared with numerical simulations using two different approaches. The findings show the influence of the relative density on stiffness, strength, and on the energy absorption properties of the lattice. The correlation with the technological feasibility points out credible improvements in the choice of a unit cell with fewer manufacturing issues, lower density, and possibly equal mechanical properties

Cross-contamination quantification in powders for additive manufacturing: A study on Ti-6Al-4V and maraging steel

Metal additive manufacturing is now taking the lead over traditional manufacturing techniques in applications such as aerospace and biomedicine, which are characterized by low production volumes and high levels of customization. While fulfilling these requirements is the strength of metal additive manufacturing, respecting the tight tolerances typical of the mentioned applications is a harder task to accomplish. Powder bed fusion (PBF) is a class of additive manufacturing in which layers of metal powder are fused on top of each other by a high-energy beam (laser or electron beam) according to a computer-aided design (CAD) model. The quality of raw powders for PBF affects the mechanical properties of additively manufactured parts strongly, and therefore it is crucial to avoid the presence of any source of contamination, particularly cross-contamination. In this study, the identification and quantification of cross-contamination in powders of Ti-6Al-4V and maraging steel was performed using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) techniques. Experimental results showed an overall good reliability of the developed method, opening the way for applications in machine learning environments

Caratterizzazione a fatica delle leghe AlSi7Mg, Ti6Al4V e X3NiCoMoTi prodotte mediante Laser Powder Bed Fusion

Negli ultimi anni, la tecnologia di Laser Powder Bed Fusion (L-PBF) è diventata la principale tecnica utilizzata per produrre componenti in metallo mediante Additive Manufacturing (AM). Questa tecnica beneficia dei vantaggi dell’Additive Manufacturing insieme alle alte prestazioni offerte dalle leghe metalliche, permettendo di produrre componenti meccanici pronti per l’utilizzo finale. Occasionalmente, a causa del processo di costruzione a strati, all’interno delle parti possono essere presenti dei difetti che, senza alterare sensibilmente le proprietà statiche, provocano un rapido degrado delle proprietà a fatica. Questo aspetto ha indirizzato la ricerca verso lo studio delle reali proprietà meccaniche dei componenti prodotti per AM rispetto a quelli prodotti con tecnologie tradizionali e successivamente verso l’ottimizzazione dell’intero processo con l’obiettivo di limitare i difetti e migliorare l’affidabilità del processo. Mentre sono state ampiamente confermate la elevate proprietà meccaniche statiche, il comportamento a fatica deve ancora essere studiato approfonditamente. In questo studio sono state investigate le proprietà a trazione e a fatica di 3 leghe metalliche realizzate mediante L-PBF, considerando l’applicazione finale nei seguenti settori produttivi: • Ambito automotive: è stata considerata la lega AlSi7Mg per la produzione di un componente telaio ottimizzato topologicamente, per l’applicazione su un’automobile ad alte prestazioni. In particolare, sono stati valutati gli effetti di: - Trattamento termico: nessun trattamento vs. T6 vs. trattamento termico per la verniciatura del telaio; - Finitura superficiale: as-built vs. lucidatura; - Orientazione sulla tavola di costruzione. • Ambito biomedicale: per la costruzione di uno stelo femorale con osteointegrazione migliorata è stata scelta la lega di titanio Ti6Al4V. Per la suddetta applicazione ci si è concentrati sull’effetto delle seguenti variabili: - Contaminazione della polvere; - Diversi set di parametri di processo e polvere; - Finitura superficiale: as-built vs. lucidatura; - Orientazione sulla tavola di costruzione. • Settore stampi per stampaggio a iniezione: per la costruzione di un inserto con canali conformati è stata scelta la lega X3NiCoMoTi. In questo caso è stato studiato l’effetto di: - Fori nel materiale, agenti come concentratori di sforzi; - Finitura superficiale dei fori; - Diversi set di parametri di processo e polvere. Questo lavoro ha lo scopo di fornire una migliore conoscenza delle variabili critiche del processo di costruzione additiva e delle operazioni di post-processo. Questo studio è stato realizzato nel contesto del progetto europeo DREAM (Driving Up Reliability of Additive Manufacturing)In the last years, Laser Powder Bed Fusion (L-PBF) has become the main technology to produce metal parts by Additive Manufacturing (AM). This manufacturing technique comprises the advantages of additive manufacturing and the high performance offered by metal alloys in order to produce mechanical components ready for the final application. Occasionally, due to the layer-wise process, some defects can be produced inside the parts, leading to mechanical properties that are well above the requirements for static loads but rapidly decay under fatigue conditions. This concern leads the researchers to investigate the actual mechanical properties of parts, as compared to those of traditionally manufactured components, and to optimize the whole process in order to limit defects and increase the reliability of the process. While extensive static tests confirmed high mechanical properties of the main metal alloys produced by AM, the fatigue behavior of additive metal parts still needs to be deeply investigated. In this study, the fatigue and tensile properties of 3 metal alloys were analyzed, in view of 3 final applications, listed as follows. • Automotive field: Aluminum alloy AlSi7Mg was studied for the final production of a topologically optimized frame part of a sports car. In particular, the interest was focused on the effect of: - Heat treatment: no heat treatment vs. T6 vs. the heating cycle required for painting the body-in-white frame; - Surface finish: as-built vs. polished; - Orientation on the building platform. • Medical field: Titanium alloy Ti6Al4V was investigated for the production of femoral stems with improved osseointegration. The study on this material was focused on the effect of: - Powder contamination; - Different parameters/powder sets; - Surface finish: as-built vs. polished; - Orientation on the building platform. • Mold manufacturing field: the Maraging steel alloy X3NiCoMoTi was studied for the application in a mold insert with internal cooling channels. The main concern related to this application led to the study of the effect of: - Holes in the material, acting as stress concentrators; - Surface finish of the holes; - Different parameters/powder sets. This work aims to provide better understanding of the critical variables of the manufacturing process and the post-processing operations. This study was accomplished within the European Project DREAM (Driving Up Reliability of Additive Manufacturing

Additive Manufacturing of Locally Weakened Parts to Obtain a Designed Fracture

Today, the additive manufacturing (AM) approach has led to profound changes in part and process design, enabling previously impossible material properties. With the freedom to create the material as components are built layer by layer, AM has permitted precise spatial control of the material properties in manufactured parts. In this work, an original approach is proposed to locally control component and process design and create intentionally weakened regions with designed fracture, which paves the way to tuneable mechanical properties. Tensile tests of specimens with embedded weakened area of various geometries are used to verify the feasibility of a-priori-designed fracture modes and to characterise the variation in material behaviour. The results show that an ad hoc design of the artificially weakened areas is effective for predictable breakage, with load and strain being the precursor for active control of the mechanical behaviour. The attainability of a quantitative relationship between the defect and the mechanical response is exemplified by the fact that, e.g. for a flat geometry, the maximum stress and strain are reduced by half when the thickness of the weak region is doubled

Surface roughness prediction model for Electron Beam Melting ({EBM}) processing Ti6Al4V

Electron Beam Melting (EBM) is an Additive Manufacturing technique to produce functional components. Because of the high temperature during the EBM process, the surface texture of the as-built parts is extremely complex and unique. This distinctiveness of the surface depends on many factors and needs to be well understood to predict final surface properties accurately. Chief among these factors is the surface design. A proper surface design makes it possible to tailor a surface with specific properties such as biomimetics. However, predictive models are difficult to determine especially for downskin surfaces. To properly tailor a surface, a full factorial Design Of Experiment (DOE) was designed, and 2D and 3D roughness profiles were collected on an ad-hoc artefact using a profilometer and a confocal profilometer. This reference part comprises several surfaces to investigate the effect on surface roughness of different sloping angles, including upskin and downskin surfaces and cavities. The data are analysed using descriptive and inferential statistical tools, also by distinguishing the role of roughness and waviness in the overall surface texture. A deep investigation of the causes of surface roughness made it possible to obtain analytical predictive models. These models are robust and consistent with respect to the experimental observations. Finally, the accurate design of the artefact allows highlighting the relationship between the roughness and the surface slope

On the Technological Feasibility of additively manufactured self-supporting AlSi10Mg lattice structures

The capability to design and manufacture metal lattice structures is today one of the most promising targets of Powder Bed Fusion technologies. Not only additively manufactured lattices offer great lightweighting possibilities, but they open the way to tailored and graded mechanical response. To best capitalize on this opportunity, research effort is first needed to assess the feasibility of reticular structures and to quantify the expected deviations from the nominal geometry, as a function of the cell topology and dimensions. Notwithstanding the inherent suitability of additive processes to complex shapes, this paper proposes a more exact definition of the technological boundaries for body-centred cubic lattices, showing to what extent specific dimensional ratios, as well as a self-supporting cell structure, can be favourable to minimize thedeviation from the nominal reticulum in terms of dimensions, density and presence of defects

Design for Additive Manufacturing and for Machining in the Automotive Field

High cost, unpredictable defects and out-of-tolerance rejections in final parts are preventing the complete deployment of Laser-based Powder Bed Fusion (LPBF) on an industrial scale. Repeatability, speed and right-first-time manufacturing require synergistic design approaches. In addition, post-build finishing operations of LPBF parts are the object of increasing attention to avoid the risk of bottlenecks in the machining step. An aluminum component for automotive application was redesigned through topology optimization and Design for Additive Manufacturing. Simulation of the build process allowed to choose the orientation and the support location for potential lowest deformation and residual stresses. Design for Finishing was adopted in order to facilitate the machining operations after additive construction. The optical dimensional check proved a good correspondence with the tolerances predicted by process simulation and confirmed part acceptability. A cost and time comparison versus CNC alone attested to the convenience of LPBF unless single parts had to be produced