Staff

Abstract:
In this work, significant strength and ductility variations are reported for AlSi10Mg parts fabricated at different orientations using laser powder bed fusion (LPBF). Hardness and surface roughness of the specimens at different orientations were measured. Tensile testing together with digital image correlation technique were conducted on the specimens. XY specimens showed the highest yield stress and ultimate tensile strength while XZ specimens showed the highest ductility. Hardness measurements for different specimens were in accordance with the tensile test results, following the same order as the UTS values, XY specimens being the highest and XY-45° (out-of-plane) specimens being the lowest. Fractography of the broken surfaces of the specimens under tensile testing revealed the microstructural features and various defects in the tensile fracture. The anisotropy in mechanical properties is attributed to the microstructural anisotropy as well as presence of various types of defects induced by the AM process, which affects the deformation and failure mechanism of the parts. Linear relationships between experimental Vickers hardness versus yield stress and UTS measurements were developed. In case of material selection for different applications, these relationships can be used as a simple tool for converting hardness and yield stress (or UTS) values to each other. An equivalent strain-hardness relationship was also proposed which can be used for health monitoring of parts subject to tensile loading.

Keywords:
Laser powder bed fusion, Hardness, Mechanical properties, Defects, Microstructure

Abstract:
The paper is related to the material behaviour of additively manufactured samples obtained by the direct metal laser sintering (DMLS) method from the AlSi10Mg powder. The specimens are subjected to a quasi-static and dynamic compressive loading in a wide range of strain rates and temperatures to investigate the influence of the manufacturing process conditions on the material mechanical properties. For completeness, an analysis of their deformed microstructure is also performed. The obtained results prove the complexity of the material behaviour; therefore, a phenomenological model based on the modified Johnson–Cook approach is proposed. The developed model describes the material behaviour with much better accuracy than the classical constitutive function. The resulted experimental testing and its modelling present the potential of the discussed material and the manufacturing technology.

Keywords:
AlSi10Mg aluminium alloy, additive manufacturing, DMLS method, compression, SHPB experiment, constitutive model

Abstract:
Plasma Electrolytic Oxidation (PEO) is the most advanced of the anodizing methods. In comparison to traditional anodizing PEO provides coatings with higher wear- and corrosion- resistance and hardness. Moreover, PEO is carried out in an alkalic bath, instead of strong acids, which makes this method more environmentally friendly. PEO is an excellent surface treatment for light metals, like magnesium or aluminium. More often light metals are produced by additive technologies (3d printing). The microstructure of additively manufactured alloys strongly differs from casting alloys. Characteristic melting pools are observed. AlSi10Mg alloy presents eutectic structure surrounded by Si-net. The microstructure is strongly connected to laser paths. Fine-grain microstructure results in higher strength than cast alloy. In this study, traditional anodizing, hard anodizing (HA) and PEO were carried out on AlSi10Mg manufactured by Direct Metal Laser Sintering (DMLS). Moreover, PEO was also performed on cast AlSi10Mg alloy. Thin, conversion coatings were obtained (thickness under 10 μm). A microstructure of oxide coatings was observed. Scratch resistance was tested and allowed to describe the films' adhesion. PEO coatings are vastly porous and include more SiO2 oxides than traditional and HA coatings. SiO2 oxides are more difficult to obtain as silicon has higher resistance than aluminium. Moreover, PEO guarantees more phase-mixed surface microstructure, including amorphous, ceramic phases, which cannot be formed in low-voltage processes. In comparison to traditional and HA oxide coatings, PEO coatings exhibit better adhesion and scratch resistance. Traditional anodizing and hard anodizing on additively manufactured AlSi10Mg provide the critical load LC1 at which coating begins to be broken of 8.5N and 10N respectively. A similar LC1 value can be obtained for PEO performed on cast alloy (7.8N), while in the case of additively manufactured AlSi10Mg this LC1 is increased four times to 42.1N.

Keywords:
Additive manufacturing, Plasma Electrolytic Oxidation, Aluminium alloys AlSi10Mg

Abstract:
Direct Metal Laser Sintering is a powder bed fusion process, which allows direct production of elements with complex shapes and very good mechanical properties. However, regardless of manufacturing technology elimination of some materials’ weaknesses is definitely tough to eliminate. These weaknesses might be excluded by surface engineering.This poster presents results of producing oxidized films on AlSi10Mg alloy manufactured by Direct Metal Laser Sintering using EOSM280 system equipped with 400W Yb fiber laser and standard EOS AlSi10Mg powder. AlSi10Mg is a near-eutectic die casting alloy which is applied to automotive and aviation industries. The density of printed samples was under 99%. We used 3 different methods of oxidation: traditional electrochemical oxidation, electrochemical oxidation in lower temperature (hard anodizing) and plasma electrochemical oxidation. Processes lasted 20 or 25 minutes. Traditional and hard anodizing was carried out in H2SO4 with the voltage in the range of 18.5-32.5 V. Plasma oxidation was carried out in 2 g/l KOH + 4 g/l Na2SiO3 and the applied voltage was between 190 and 225 V. Metallography, SEM and EDS proved that we received Al2O3 oxides on the AlSi10Mg surfaces. All produced films were thin (2-5 um), providing slightly increased microhardness and roughness of the surface. Roughness depends especially on electric current parameters applied in the oxidation process. Therefore the structure of layers manufactured by plasma electrochemical oxidation was more irregular and porous. All films had high adhesion which was confirmed by scratch tests.

Keywords:
DMLS, electrochemical oxidation, anodizing, aluminum alloy, AlSi10Mg