1,721,014 research outputs found
EVALUATION OF HIGH-TEMPERATURE TENSILE PROPERTIES OF HEAT-TREATED ALSI10MG ALLOY PRODUCED BY LASER-BASED POWDER BED FUSION
Full text linkThe AlSi10Mg alloy is widely used to produce complex-shaped components by Laser-based Powder Bed Fusion (L-PBF); these parts, characterized by light structures and high specific strength, are currently employed in high-performance room temperature applications in the automotive and aerospace industries. However, it is important to increase the data concerning the high-temperature mechanical properties of the L-PBF AlSi10Mg alloy to spread its use. This study aims to fulfill the lack of knowledge by investigating the mechanical behavior at 200 °C, a representative condition of the average temperature of engine heads, of the L-PBF AlSi10Mg alloy subjected to a T5 heat treatment (artificial aging at 160 °C for 4 h) and an innovative T6 heat treatment (solubilization at 510 °C for 10 min and artificial aging at 160 °C for 6 h). The influence of high temperatures on the mechanical behavior of the L-PBF AlSi10Mg alloy was assessed by tensile tests, while microstructural and fractographic analyses were carried out to correlate the mechanical behavior of the alloy to its microstructure, and consequently explain the failure mechanisms. The ultrafine cellular microstructure, characterizing the T5 alloy, led to higher tensile strength than the homogeneous composite-like microstructure of the T6 alloy, which makes it very interesting for future application in the automotive and aerospace industries
Effetto del trattamento termico T6 su microstruttura e comportamento meccanico della lega AlSi10Mg prodotta mediante Selective Laser Melting: stato dell’arte
No full textLa lega AlSi10Mg è sicuramente la più utilizzata tra le leghe di alluminio per la realizzazione di componenti con il processo di Selective Laser Melting (SLM), anche noto come Laser Powder Bed Fusion (LPBF). Negli ultimi anni numerosi studi si sono focalizzati in particolare sull’ottimizzazione del trattamento termico T6 di questa lega, al fine di massimizzarne le proprietà meccaniche, in relazione alle specifiche caratteristiche microstrutturali indotte dal processo. Nella presente memoria sono stati confrontati i risultati delle ricerche più recenti riguardanti l’effetto del trattamento termico T6 sulla lega SLM AlSi10Mg, in termini di evoluzione microstrutturale e di proprietà meccaniche. Sono stati evidenziati gli aspetti microstrutturali che maggiormente influenzano la durezza, la resistenza a trazione, la fatica e la tenacità all’impatto. L’analisi dei dati riportati in letteratura ha confermato la necessità di definire parametri di trattamento termico specifici per la lega AlSi10Mg SLM, rispetto a quelli utilizzati per la stessa lega ottenuta con processi fusori convenzionali, al fine di ridurne la variabilità nella risposta alle sollecitazioni esterne
Friction welding of particle reinforced aluminium based composites
No full textThe widespread use of metal matrix composites (MMC) is often limited due to the difficulties related to their joining by means of traditional fusion welding processes. The aim of this work was to evaluate the effect on microstructure and mechanical properties (hardness and tensile strength) of two different friction welding techniques used for joining two Al-based metal matrix composites. In particular, Friction Stir Welding was applied to a 6061 (Al-Mg-Si) alloy matrix,
reinforced with 20vol.% of Al2O3 particles (W6A20A), while Linear Friction Welding was applied to a 2124 (Al-Cu-Mg) alloy matrix reinforced with 25vol.% of SiC particles (AMC225xe). Both the
welding processes permitted to obtain substantially defect-free joints, whose microstructures was found to be dependent on both the initial microstructure of the composites and the welding processes. Hardness decrease was in the order of 40% for the FSW joint and of 10% for the LFW joint, mainly due to overaging of the matrix induced by the frictional heating, while the joint efficiency in respect to the ultimate tensile strength was 72% and 82%, respectively. Elongation to
failure increased in the FSW joint due to coarsening of precipitates, whereas it decreased in the LFW joints due to the fibrosity in the thermomechanically altered zone. Fracture surface analysis
showed good matrix/reinforcement interface for both composites
Microstructural evolution induced by heat treatment in the Co28Cr6Mo alloy produced by Selective Laser Melting - Evoluzione microstrutturale nella lega Co28Cr6Mo prodotta tramite Selective Laser Melting a seguito di trattamento termico
No full textLinear Friction Welding of a 2024 Al Alloy: Microstructural, Tensile and Fatigue Properties
No full textThe possibility of using linear friction welding (LFW) to produce high quality joints on an aerospace grade aluminium alloy (AA2024) was evaluated. In this solid state joining process the bonding of two flat edged components is achieved through frictional heating, induced by their relative reciprocating motion, under an axial compressive force. The Al joints were subjected to microstructural and mechanical characterization, including hardness and tensile tests. S–N probability curves were also computed after preliminary axial fatigue tests. No post-weld heat treatment was performed. The microstructural analyses showed substantially defect-free joints, with a relevant plastic flow in the thermo-mechanically altered zone. Maximum hardness decrease in the joint zone was approximately only 5% in respect to the base material. The joint efficiency was about 90% with respect to the ultimate tensile strength, with a slight reduction in the elongation to failure. Good fatigue performances were also detected
Failure analysis in tribology: two case histories involving contact fatigue of metal components
No full textThis paper deals with two case studies of failure analysis in sliding/rolling contacts between metallic components. The investigated tribosystems belong to two different fields and involve different contact conditions, but in both of them contact fatigue plays a main role. The first case history comes from earth moving equipment, where the non-conformal contact between a rotating pin and its bearing leads to evidence of large surface damage of the cylindrical pin, with spalling, typical of contact fatigue. However, failure analysis highlighted a dominant role of the first crack nucleation by torsion fatigue. The second case history comes from packaging devices, where the non-conformal contact between a rotating compression roll and the punches for powder pressing led to the formation of macro- and micro-pitting on the surface of both the punches and the roll, indicating that the main damage mechanism is surface-origin contact fatigue
Dry sliding behaviour of the A357 aluminium alloy processed by Selective Laser Melting and anodized by Electrochemical Oxidation (ECO)
No full textSelective Laser Melting (SLM) is increasingly employed for producing complex, customised aluminium alloys parts for engineering applications in automotive, aerospace and aircraft. However, an important limitation of these alloys is their poor tribological properties in sliding conditions, which can be improved by surface treatments such as anodizing. Processing conditions during SLM strongly affect both surface roughness and microstructure (leading to hierarchical microstructure and very fine distribution of eutectic Si network in Al-Si alloys), hence influencing the growth of the anodic oxide.
In this study, Electro-Chemical Oxidation (ECO) at high voltage was applied to the A357 (AlSi7Mg) alloy produced by SLM, in order to improve its tribological behaviour. Sand cast A357, heat-treated to T6 condition was investigated as a reference for comparison. Dry sliding tests were carried out in block-on-ring configuration against a quenched and tempered SAE52100 (100Cr6) bearing steel rotating cylinder, using the anodized alloys as stationary blocks. The results of this study allowed the comparison of microstructural features and dry sliding behaviour of the oxide layers grown on both the conventional sand cast and SLM A357 alloy
Relationship between microstructure, mechanical and magnetic properties of pure iron produced by laser powder bed fusion (L-PBF) in the as-built and stress relieved conditions
Full text linkIn the present work, the mechanical and magnetic properties of pure iron manufactured by laser-powder bed fusion (L-PBF) were investigated both in the as-built (AB) and stress relieved (HT) conditions, with the aim of elucidating their relationship with the microstructure and evaluating whether and to what extent it can be suitable for industrial applications. The L-PBF process was optimized to obtain high density, crack-free components. Specimens for microstructural analyses, tensile and magnetic tests were manufactured under the optimized conditions and tested both in the as-built and annealed (850 degrees C for 1 h, to relieve the residual stresses) conditions. Tensile tests showed high tensile strength in both AB and HT conditions (larger than those of conventionally produced pure iron), with higher ductility and lower strength after stress relieving. The magnetic study indicated a not optimal magnetic softness although the heat treatment enhanced the permeability and reduced the coercivity with respect to the as-built condition. The high mechanical strength and low magnetic softness came from the very fine grain size (about 5 mu m) of L-PBF pure iron. Instead, the improvement of magnetic softness and ductility after heat treatment was attributed to the possible reduction of dislocation density and consequent stress relief. The results indicated the possibility to achieve a considerably high mechanical strength, in pure iron manufactured by L-PBF, although the fine grain size limits its magnetic softness
DRY SLIDING BEHAVIOUR OF PEO (PLASMA ELECTROLYTIC OXIDATION) TREATED AA 2618/20 % Al2O3P COMPOSITE
No full textThe present study focuses on the influence of the PEO (Plasma Electrolytic Oxidation) treatment on the tribological behaviour of the AA2618/20 % vol. Al2O3p composite, dry sliding against induction hardened UNI C55 steel. Particle-reinforced Al based composites offer a higher wear resistance by comparison with the corresponding unreinforced alloys, however, the presence of critical loads and/or velocities which lead to transition towards severe wear regime, was often observed. In such conditions, the composite can show higher wear rates than those of unreinforced alloys. For this reason, surface modifications, such as PEO, might contribute to improve wear resistance. In this paper, topography, microstructure, phase constitution and surface hardness of the PEO-treated composite were investigated and its tribological behaviour was studied by dry sliding tests using a block-on-ring tribometer. The results were compared with those from the uncoated composite, demonstrating a very positive effect of the PEO treatment, which moved transitions from mild to severe wear towards more severe test conditions, in terms of both load and velocity
Effect of Fe content and microstructural features on the tensile and fatigue properties of the Al–Si10–Cu2 alloy
No full textAs the automotive industry has to meet the requirements of fuel efficiency and environmental concerns, the use of aluminium alloys is steadily increasing. A number of papers have been published about the correlation between microstructure and mechanical properties of the widely used A356/A357 aluminium alloys, while relatively few data are available on others hypoeutectic Al–Si alloys, such as Al–Si–Cu alloys
with higher Si content. In this work the effect of different amounts of Fe and Mn on the tensile and fatigue behaviour of the Al–Si10–Cu2 casting alloy was studied. The reason of this study comes from the fact that cast components are mostly made by secondary Al alloys that inevitably contain Fe, which in turn forms intermetallic compounds, negatively affecting the mechanical behaviour of the alloy. Fatigue specimens were subjected to hot isostatic pressing (HIP) before tests, in order to eliminate the internal pores (gas pores and interdendritic shrinkages) and therefore to solely investigate the effect of microstructural features, rather than solidification defects, on the fatigue propagation stage. The microstructural characterisation
of the alloy was carried out by optical and scanning electron microscopy. Proof and ultimate tensile strength, as well as fatigue life of the investigated alloy were greatly enhanced by high Fe and
Mn content, which reduced the micro-crack propagation rate; on the contrary Fe, without Mn, negatively affected the elongation to failure
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