Aging Profiles of AlSi7Mg0.6 and AlSi10Mg0.3 Alloys Manufactured via Laser-Powder Bed Fusion: Direct Aging versus T6

The artificial aging heat treatments performed directly on as-built and solubilized AlSi7Mg0.6 and AlSi10Mg0.3 samples were characterized and discussed. The analysed bars and billets (height of 300 mm) were manufactured via the Laser Powder-Bed Fusion process on a build platform heated at 150 °C. Therefore, its influence on the as-built samples was studied in terms of mechanical performance variations between the bottom and top regions. Vickers microhardness measurements were performed to obtain aging profiles after direct aging (175–225 °C) and T6 heat treatments and to highlight better time and temperature parameters to optimize the mechanical properties of both alloys. SEM observations were used to characterize the microstructure before and after the heat treatments and its influence on the fracture mechanisms. Generally, the direct aging heat treatments show the same effects on both aluminium alloys, unlike the solubilization at 505 °C followed by artificial aging at 175 °C. The strengths vs. elongation values obtained after the direct aging treatments are better than those exhibited by T6 as highlighted by the quality index

Defect-Correlated Vickers Microhardness of Al-Si-Mg Alloy Manufactured by Laser Powder Bed Fusion with Post-process Heat Treatments

Laser powder bed fusion is an additive manufacturing process characterized by different advantages like the manufacture of samples with complex geometry without the use of tools and/or molds. Generally, the manufactured samples are characterized by high tensile strengths which, however, can be affected by the presence of defects due to the unoptimized process parameters. In a large applications field, a low density of the as-built AlSi10Mg samples is a very important parameter to considered, e.g., due to both the loss of the tensile strengths correlated with a premature failure of the samples and the increase in time and costs associated with the manufacturing process. In addition, different post-process heat treatments can increase these effects leading to an ineffective manufacturing process. In this scenario, the present work shows the analysis of spherical and lack-of-fusion pores induced by the laser powder bed fusion process on the AlSi10Mg samples and their variations after different heat treatments (direct aging and T6). At the same time, the influence of pores on the Vickers microhardness and the tensile properties has been studied in the same AlSi10Mg samples (bars and billets) that were printed with single- and double-laser machine setup. Different process parameters were also analyzed and compared. The study was supported by the microstructural and pore analysis performed by optical microscopy along the XZ plane (build direction) and the XY plane. Finally, the greatest effects of pores were observed on the Vickers microhardness values; in fact, two different relationships between microhardness and density variation are discussed. The T6 heat treatment leads to a rounding of the pores already formed in the as-built samples and to a formation of new small pores. Graphical Abstract: [Figure not available: see fulltext.

Static and dynamic precipitation phenomena in laser powder bed-fused Ti6Al4V alloy

The present paper investigates static and dynamic precipitation phenomena in the Ti6Al4V alloy produced via laser-powder bed fusion, solubilized at 1050 degrees C and aged in the range of 450-650 degrees C. In relation to the distance from the platform on which the samples are disposed during the solution heat treatment, the microstructure varies from alpha-laths to alpha-colonies arranged in a Widmanstatten structure. The aging heat treatment at 450 degrees C promotes the formation of stacking faults into alpha-laths and the precipitation of alpha(2)-Ti3Al phases. SEM and TEM observations reveal that the density of precipitates increases after aging at 500 degrees C, while coarsening of the alpha-phase occurs only after aging heat treatment at 600 degrees C. Vickers microhardness measurements reveal different peak-aging conditions and show that the alloy is unstable at high temperatures (T > 450 degrees C), both in the case of static and dynamic precipitation phenomena. Only the aging profile at 450 degrees C shows a constant trend of Vickers microhardness after 4 h of treatment

Separate and overlapping functional roles for efference copies in the human thalamus

How the perception of space is generated from the multiple maps in the brain is still an unsolved mystery in neuroscience. A neural pathway ascending from the superior colliculus through the medio-dorsal (MD) nucleus of thalamus to the frontal eye field has been identified in monkeys that conveys efference copy information about the metrics of upcoming eye movements. Information sent through this pathway stabilizes vision across saccades. We investigated whether this motor plan information might also shape spatial perception even when no saccades are performed. We studied patients with medial or lateral thalamic lesions (likely involving either the MD or the ventrolateral (VL) nuclei). Patients performed a double-step task testing motor updating, a trans-saccadic localization task testing visual updating, and a localization task during fixation testing a general role of motor signals for visual space in the absence of eye movements. Single patients with medial or lateral thalamic lesions showed deficits in the double-step task, reflecting insufficient transfer of efference copy. However, only a patient with a medial lesion showed impaired performance in the trans-saccadic localization task, suggesting that different types of efference copies contribute to motor and visual updating. During fixation, the MD patient localized stationary stimuli more accurately than healthy controls, suggesting that patients compensate the deficit in visual prediction of saccades - induced by the thalamic lesion - by relying on stationary visual references. We conclude that partially separable efference copy signals contribute to motor and visual stability in company of purely visual signals that are equally effective in supporting trans-saccadic perception

Associations of short-term particle and noise exposures with markers of cardiovascular and respiratory health among highway maintenance workers

BACKGROUND: Highway maintenance workers are constantly and simultaneously exposed to traffic-related particle and noise emissions, and both have been linked to increased cardiovascular morbidity and mortality in population-based epidemiology studies. OBJECTIVES: We aimed to investigate short-term health effects related to particle and noise exposure. METHODS: We monitored 18 maintenance workers, during as many as five 24-hour periods from a total of 50 observation days. We measured their exposure to fine particulate matter (PM2.5), ultrafine particles, noise, and the cardiopulmonary health endpoints: blood pressure, pro-inflammatory and pro-thrombotic markers in the blood, lung function and fractional exhaled nitric oxide (FeNO) measured approximately 15 hours post-work. Heart rate variability was assessed during a sleep period approximately 10 hours post-work. RESULTS: PM2.5 exposure was significantly associated with C-reactive protein and serum amyloid A, and negatively associated with tumor necrosis factor α. None of the particle metrics were significantly associated with von Willebrand factor or tissue factor expression. PM2.5 and work noise were associated with markers of increased heart rate variability, and with increased HF and LF power. Systolic and diastolic blood pressure on the following morning were significantly associated with noise exposure after work, and non-significantly associated with PM2.5. We observed no significant associations between any of the exposures and lung function or FeNO. CONCLUSIONS: Our findings suggest that exposure to particles and noise during highway maintenance work might pose a cardiovascular health risk. Actions to reduce these exposures could lead to better health for this population of workers