Effect of Homogenization Treatment on the Microstructure and Mechanical Property Evolutions of As-Cast Al-Cu Alloy during High-Pressure Torsion

As-cast and homogenization treated as-cast Al-Cu (3 mass% Cu) alloy samples were processed via high-pressure torsion (HPT) under an applied pressure of 8 GPa with 5 revolutions at room temperature. Microstructure, mechanical properties, and fracture surface morphology of the HPT-processed Al-Cu were investigated, demonstrating that the HPT process successfully resulted in distinct grain refinements in both samples. Significant improvements in the microhardness, tensile properties, and deformation homogeneity due to fine grains, high grain boundary misorientation angle, and homogeneous distribution of the theta phase were achieved after the HPT process of the homogenized sample. The homogenization treatment of the as-cast Al-Cu has a significant effect on the fracture surface morphology and fracture mode of the HPT-processed samples.X1110Ysciescopu

Systematic Review of Potential Health Risks Posed by Pharmaceutical, Occupational and Consumer Exposures to Metallic and Nanoscale Aluminum, Aluminum Oxides, Aluminum Hydroxide and Its Soluble Salts

Aluminum (Al) is a ubiquitous substance encountered both naturally (as the third most abundant element) and intentionally (used in water, foods, pharmaceuticals, and vaccines); it is also present in ambient and occupational airborne particulates. Existing data underscore the importance of Al physical and chemical forms in relation to its uptake, accumulation, and systemic bioavailability. The present review represents a systematic examination of the peer-reviewed literature on the adverse health effects of Al materials published since a previous critical evaluation compiled by Krewski et al. (2007). Challenges encountered in carrying out the present review reflected the experimental use of different physical and chemical Al forms, different routes of administration, and different target organs in relation to the magnitude, frequency, and duration of exposure. Wide variations in diet can result in Al intakes that are often higher than the World Health Organization provisional tolerable weekly intake (PTWI), which is based on studies with Al citrate. Comparing daily dietary Al exposures on the basis of “total Al”assumes that gastrointestinal bioavailability for all dietary Al forms is equivalent to that for Al citrate, an approach that requires validation. Current occupational exposure limits (OELs) for identical Al substances vary as much as 15-fold. The toxicity of different Al forms depends in large measure on their physical behavior and relative solubility in water. The toxicity of soluble Al forms depends upon the delivered dose of Al+ 3 to target tissues. Trivalent Al reacts with water to produce bidentate superoxide coordination spheres [Al(O2)(H2O4)+ 2 and Al(H2O)6 + 3] that after complexation with O2•−, generate Al superoxides [Al(O2•)](H2O5)]+ 2. Semireduced AlO2• radicals deplete mitochondrial Fe and promote generation of H2O2, O2 • − and OH•. Thus, it is the Al+ 3-induced formation of oxygen radicals that accounts for the oxidative damage that leads to intrinsic apoptosis. In contrast, the toxicity of the insoluble Al oxides depends primarily on their behavior as particulates. Aluminum has been held responsible for human morbidity and mortality, but there is no consistent and convincing evidence to associate the Al found in food and drinking water at the doses and chemical forms presently consumed by people living in North America and Western Europe with increased risk for Alzheimer\u27s disease (AD). Neither is there clear evidence to show use of Al-containing underarm antiperspirants or cosmetics increases the risk of AD or breast cancer. Metallic Al, its oxides, and common Al salts have not been shown to be either genotoxic or carcinogenic. Aluminum exposures during neonatal and pediatric parenteral nutrition (PN) can impair bone mineralization and delay neurological development. Adverse effects to vaccines with Al adjuvants have occurred; however, recent controlled trials found that the immunologic response to certain vaccines with Al adjuvants was no greater, and in some cases less than, that after identical vaccination without Al adjuvants. The scientific literature on the adverse health effects of Al is extensive. Health risk assessments for Al must take into account individual co-factors (e.g., age, renal function, diet, gastric pH). Conclusions from the current review point to the need for refinement of the PTWI, reduction of Al contamination in PN solutions, justification for routine addition of Al to vaccines, and harmonization of OELs for Al substances

Pan-cancer analysis of whole genomes

Cancer is driven by genetic change, and the advent of massively parallel sequencing has enabled systematic documentation of this variation at the whole-genome scale(1-3). Here we report the integrative analysis of 2,658 whole-cancer genomes and their matching normal tissues across 38 tumour types from the Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium of the International Cancer Genome Consortium (ICGC) and The Cancer Genome Atlas (TCGA). We describe the generation of the PCAWG resource, facilitated by international data sharing using compute clouds. On average, cancer genomes contained 4-5 driver mutations when combining coding and non-coding genomic elements; however, in around 5% of cases no drivers were identified, suggesting that cancer driver discovery is not yet complete. Chromothripsis, in which many clustered structural variants arise in a single catastrophic event, is frequently an early event in tumour evolution; in acral melanoma, for example, these events precede most somatic point mutations and affect several cancer-associated genes simultaneously. Cancers with abnormal telomere maintenance often originate from tissues with low replicative activity and show several mechanisms of preventing telomere attrition to critical levels. Common and rare germline variants affect patterns of somatic mutation, including point mutations, structural variants and somatic retrotransposition. A collection of papers from the PCAWG Consortium describes non-coding mutations that drive cancer beyond those in the TERT promoter(4); identifies new signatures of mutational processes that cause base substitutions, small insertions and deletions and structural variation(5,6); analyses timings and patterns of tumour evolution(7); describes the diverse transcriptional consequences of somatic mutation on splicing, expression levels, fusion genes and promoter activity(8,9); and evaluates a range of more-specialized features of cancer genomes(8,10-18).Peer reviewe

Wear properties of high pressure torsion processed ultrafine grained Al-7%Si alloy

In this paper, Al-7 wt% Si alloy was processed via high pressure torsion (HPT) at an applied pressure 8 GPa for 10 revolutions at room temperature. The microstructure and hardness of the HPT samples were investigated and compared with those of the as-cast samples. The wear properties of as-cast and the HPT samples under dry sliding conditions using different sliding distances and loads were investigated by reciprocated sliding wear tests. The HPT process successfully resulted in nanostructure Al-7 wt% Si samples with a higher microhardness due to the finer Al matrix grains and Si particles sizes with more homogeneous distribution of the Si particles than those in the as-cast samples. The wear mass loss and coefficient of friction values were decreased after the HPT process. The wear mechanism was observed to be adhesive, delamination, plastic deformation bands and oxidization in the case of the as-cast alloy. Then, the wear mechanism was transformed into a combination of abrasive and adhesive wear after the HPT process. The oxidization cannot be considered as a mechanism that contributes to wear in the case of HPT samples, because O-2 was not detected in all conditions. (C) 2013 Elsevier Ltd. All rights reserved.X112634sciescopu

Microstructure Evolution and Mechanical Properties of Al-1080 Processed by a Combination of Equal Channel Angular Pressing and High Pressure Torsion

Equal channel angular pressing (ECAP) and high pressure torsion (HPT) are the most promising severe plastic deformation (SPD) methods. Both methods impose very high strains, leading to extreme work hardening and microstructural refinement. In this paper, billets of Al-1080 were successfully processed by ECAP conducted for up to 10 passes, HPT at an applied pressure of 8 GPa for 5 revolutions, and a combination of ECAP and HPT (ECAP + HPT) at room temperature. The effects of the different SPD processes (ECAP, HPT, and ECAP + HPT) on the evolution of the microstructure and mechanical properties of Al-1080 were investigated. The HPT and ECAP + HPT processes were observed to produce finer grain sizes with greater fractions of high angle grain boundaries (HAGBs) than the ECAP alone. Although the grain sizes after HPT and ECAP + HPT were similar, the ECAP + HPT sample had more dislocations than the HPT sample. HPT after ECAP enhanced the mechanical properties (hardness, tensile strength, and ductility) of the ECAP-processed Al-1080, showing larger dimple size in the tensile fracture surfaces. DOI: 10.1007/s11661-013-1629-7 (C) The Minerals, Metals & Materials Society and ASM International 2013open1167sciescopu

Recycling of AlSi8Cu3 alloy chips via high pressure torsion

In this paper, AlSi8Cu3 alloy chips were consolidated via HPT at an applied pressure 8 GPa for 10 revolutions at room temperature. The microstructure and hardness of the HPT consolidated chips were investigated and compared with those of the HPT processed solid AlSi8Cu3 alloy samples and cold compacted chip samples. The HPT process successfully resulted in fully densified bulk samples with a higher microhardness due to the finer Al matrix grains and Si particles sizes with more grain boundaries with high angles and more homogeneous deformation than those in the HPT processed solid AlSi8Cu3 alloy samples due to the higher imposed total strain. (C) 2012 Elsevier B.V. All rights reserved.X1168sciescopu

3D FEM simulations for the homogeneity of plastic deformation in Al-Cu alloys during ECAP

Equal channel angular pressing (ECAP) is a material processing method that allows very high strains to be imposed, leading to extreme work hardening and microstructural refinement. To investigate the deformation homogeneity in the transverse direction, rigid-viscoplastic 3D finite element simulations were conducted for the different numbers of ECAP passes of Al with Cu contents 0-5%. The simulation results indicated that the material on the outer side of the die channel undergoes less deformation than that in the inner side due to the formation of a corner gap. It was also found that the homogeneity increased with increasing the number of ECAP passes and the copper content due to the decrease in the size of the corner gap. To verify the 3D finite element simulation results, the microhardness homogeneity across the transverse direction of the billet was measured. The same trend was observed: the homogeneity in hardness increased with increasing the number of ECAP passes and Cu contents from 0% to 5%. The homogeneity of deformation indicated by microhardness and by FEM results was higher for route A compared with route Bc and increases with the number of ECAP passes. The homogeneity in route A was higher than that in route Bc by 10% after 2 passes up to 8 passes. (C) 2009 Elsevier B.V. All rights reserved.X111740sciescopu

Microstructure evolution and mechanical properties of pure aluminum deformed by equal channel angular pressing and direct extrusion in one step through an integrated die

In this paper, billets of Al-1080 were successfully processed by ECAP up to 1 pass, and a combination of ECAP + extrusion with extrusion ratios of 2 and 8 through a newly designed integrated die at room temperature. The combination of ECAP + extrusion processes was observed to produce finer grain sizes with greater fractions of high angle grain boundaries (HAGBs) than the ECAP. The average grain size was further decreased and the fraction of high angle grain boundaries (HAGBs) was increased with the increase of the extrusion ratio. Direct extrusion after ECAP enhanced the mechanical properties (tensile strength and hardness) with conserving reasonable degree of ductility (elongation %). ECAP and ECAP + extrusion processed samples, showed large dimple size in the tensile fracture surfaces with clear ductile fracture mode. (C) 2014 Elsevier B.V. All rights reserved.X1188sciescopu

Wear properties of ECAP-processed ultrafine grained Al-Cu alloys

The wear properties of equal channel angular pressing (ECAP) Al-2, 3 and 5%Cu alloys under dry sliding conditions using different sliding distances and loads were investigated by pin-on-disc dry sliding wear tests. The wear mass loss decreased remarkably as the number of ECAP passes and Cu content increased, being affected more by the sliding distance than by the applied load under the experimental conditions. The wear mechanism was observed to be adhesive and delamination initially, and an abrasive mechanism also appeared as the sliding distance increased. The analysis of the wear surface indicates a transfer of Fe from the rotating disc to the Al-Cu alloy pin with increases in the sliding distance, the applied load, the number of passes and the copper content. (C) 2010 Elsevier By. All rights reserved.X113042sciescopu