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In this paper, the effect of deep cryogenic treatment (DCT) on the microstructure and properties of automotive 6063 aluminum alloy at different times was investigated with automotive 6063 aluminum alloy as the research object. The results show that under the conditions of deep cryogenic treatment, the lattice distortion occurs in the alloy matrix microstructure, and the resulting internal stress promotes the large proliferation of dislocations within the alloy and the increase of dislocation density; meanwhile, after the deep cryogenic treatment, the deformed grains are transformed into recrystallized and sub-crystals structural grains, the grains are refined, and the size of the grains is refined from the original 25.2 μm to 20.3 μm, with fine equiaxed crystals. Among them, the mechanical properties of the DCT36h specimen were the best, and its hardness, tensile strength, yield strength and elongation reached 142.44 HV, 328.32 MPa, 177.42 MPa, and 29.29%, which were 34.17%, 5.62%, 11.10%, and 32.77% higher than the original sample, respectively. We believe that the main mechanism for the increase in toughness is multiple reinforcement such as dislocation strengthening, grain refinement strengthening, precipitated phase strengthening and texture strengthening. [ABSTRACT FROM AUTHOR]

AA6101 Al alloy is widely used as a high-strength conductive aluminum alloy, and the contents and existence of Mg and Si can influence its electrical conductivity and mechanical properties obviously. In this paper, experiments were conducted to find the optimal Mg, Si additions and Mg/Si ratio and then combined with heat treatment to improve the EC and mechanical properties at the same time. Firstly, considering the proper Mg/Si ratio, two optimal Mg and Si additions were determined: Al–0.7Mg–0.5Si and Al–0.4Mg–0.7Si with EC of 51.5%IACS and 51.4%IACS, and through homogenization treatment, their EC improved to 57.0%IACS and 55.7%IACS, respectively. Then, appropriate Fe was added to further control Si to achieve the balance of EC and mechanical properties. Results showed that for AA6101 Al alloy the ideal Mg/Si mass ratio was 1.4 and high Mg and low Si can obtain good EC and mechanical properties. Besides, it can be found that at low Mg/Si ratio, the alloy conductivity takes longer to reach its peak hardness. So the best performance Al–0.7Mg–0.5Si–0.2Fe alloy was obtained within the range of AA6101 national standard. The EC of Al–0.7Mg–0.5Si–0.2Fe can reach 56.3%IACS, and hardness is 91.3 Hv. Based on the study, a schematic diagram was drawn to analyze the influence mechanisms of Mg, Si and Fe on EC and hardness of AA6101 Al alloy. [ABSTRACT FROM AUTHOR]

Aluminum (Al) alloys are of great importance and interest because of their extensive applications in various engineering fields. Lightweighting of our infrastructure has been a driver for more than the last two decades as our need to reduce carbon footprint on a global scale has become an inevitable reality. As a result, we have witnessed much progress in alloy development in Al alloys, especially with the advent of Integrated Computational Materials Engineering (ICME) and other computational tools. However, the limitations of the properties one may attain through alloy development to date have relied on the traditional solvent/solute model, where the matrix is Al with additions of elements (solute) to the matrix. Despite making much progress, we are still locked-in to the strength-ductility curve without any appreciable increase in modulus (stiffness) of the alloy. High Entropy Alloys (HEAs) provide a new paradigm as they differ from conventional alloys in entropy-based mixing logic of various elements, which is different from the solvent/solute model. HEAs offer the opportunity to move out of the strength-ductility curve as well as the opportunity to increase the alloy's modulus. In this paper, we present a retrospective view of Al alloys, followed with an understanding of the principles of HEAs, and lastly, with the idea of applying high entropy concept to conventional Al alloys to develop a novel Al alloy category, which we have coined HEAl. Preliminary results with a commentary on potential future opportunities are also given. [ABSTRACT FROM AUTHOR]

Knowledge of the fracture and fatigue behaviour of metallic alloys at extreme environmental temperature conditions is required to assess the safety of structural components operating in particular fields: aero-spatial, off-shore structures, power plants superconductors, polar Antarctic facilities, etc. Among the structural metallic alloys for civil, mechanical engineering and plant applications, steel S275 J2 is widely used, whereas aluminium alloys such as Al7075 T6 are significant especially for aero-spatial and polar Antarctic applications. In this paper, the main experimental mechanical characteristics of such metallic materials at room temperature as well as at low temperatures are examined. Three temperatures are considered: 293 K (+20 °C, room temperature RT), 243 K (−30 °C) and 193 K (−80 °C). The corresponding values of fracture toughness and endurance limit available in the literature are reported herein. Further, experimental tests have been performed to determine the unavailable mechanical properties. Then, the values of such fracture and fatigue parameters at various temperatures are critically discussed. [ABSTRACT FROM AUTHOR]

The effect of Friction Stir Processing (FSP) on the mechanical properties of a Sc, Zr modified 2024 aluminium alloy was investigated in the present paper. The room temperature tensile properties of the material were obtained in longitudinal direction respect to the processing one and compared with those of the unstirred material and unmodified alloy. Tensile tests were also performed at higher temperatures and different strain rates in the nugget zone. The superplastic properties of the recrystallized material were evaluated and the differences with the parent material as a function of the strong grain refinement due to the Friction Stir Process were put in evidence. The high temperature behavior of the material was studied, in longitudinal direction, by means of tensile tests in the temperature and strain rate ranges of 450–525°C and 10−1–10−3 s−1 respectively. [ABSTRACT FROM AUTHOR]

The development of cast TiAl-based components for the automotive industry and the possibility of wrought components for applications in gas turbines are clear indications that these alloys are maturing as materials for engineering components. There are however problems in the cost of manufacture and in the properties of these alloys. In this paper it is argued that recent developments, which have resulted in a totally new microstructure, taken together with improved casting technology, open the way for wider application of these alloys. The new microstructure has been obtained by tempering massively transformed TiAl alloys so that a highly convoluted fine scale microstructure is obtained by simply heat treating cast samples. This fine microstructure can thus be obtained in cast components, without the need to add boron and problems associated with the extreme plastic anisotropy of fully lamellar samples are also eliminated. [ABSTRACT FROM AUTHOR]

Cold rolling the CC AA 5754 aluminum alloy to different reductions was followed by an hour of annealing at 537 °C under varied pressures. The changes in microstructure and texture were studied. According to the findings, high-pressure heat treatment restricts recrystallization, and the restriction effect is stronger as pressure rises. The refining impact of high-pressure heat treatment can refine recrystallized grains, and it becomes stronger as the rolling reduction gets higher. The variation of recrystallization texture is significantly affected by high-pressure heat treatment. The sheet with a 19.6% reduction is found to have a weak cube texture at atmospheric pressure and 2 GPa, but the sheet that has been annealed at 4 GPa and 6 GPa has a strong cube texture and a weak β fiber rolling texture. High-pressure heat treatment improves the intensities of the cube and R textures in the fully recrystallized sheets with the same reduction. The strengthening impact of R texture from high-pressure heat treatment improves with increasing rolling reduction. [ABSTRACT FROM AUTHOR]

Aluminum alloy is the optimum material for weight reduction and widely used in a lot of industries including automobile, rail transportation, aerospace, and so on. Ternary Ti3AlC2 powder was adopted in this study to improve the laser welding quality of 6061 Al alloy. Addition of the Ti3AlC2 powder could increase the width and stability of the molten pool, which was beneficial to inhibit the formation of defects such as pore, spatter, rugged surface, sagging, and undercut. Reaction products of Ti3AlC2 powders including Ti3AlxC2, TiAl3, and TiC impeded the growth of dendrites and could serve as nucleating agent, resulting in the formation of massive isometric crystals and dispersed precipitates. The refinement strengthening and dispersion strengthening could impede the extension of deformation and made up the influences of uneven melting loss of alloying elements, leading to the increase and uniformity of weld hardness from 53.1 HV0.2 to 74.9 HV0.2. Both of the welded joints with and without assistant powder fractured at the welds. Elimination of pores increased the loading area of weld while generation of precipitates impeded the extension and connection of dimples, leading to the improvement of tensile strengths from 191.0 to 232.5 MPa and displacements from 0.95 to 1.59 mm. [ABSTRACT FROM AUTHOR]

Al-Mg alloys are normally prone to lose part of their yield and tensile strength at high temperatures due to insufficient thermal stability of the microstructure. Here, we present a Ca-modified Al–Mg–Sc alloy demonstrating high strength at elevated temperatures. The microstructure contains Al4Ca phases distributed as a network along the grain boundary and Al3(Sc,Zr) nano-particles dispersed within the grains. The microstructure evolution and age-hardening analysis indicate that the combination of an Al4Ca network and Sc-rich nano-particles leads to excellent thermal stability even upon aging at 300 °C. The tensile strength of the alloy for temperatures up to 250 °C is significantly improved by an aging treatment and is comparable with the commercial heat-resistant aluminum alloys, i.e., A356 and A319. At a high temperature of 300 °C, the tensile strength is superior to the above-mentioned commercial alloys, even more so when expressed as the specific strength due to the low density of Ca-modified Al–Mg–Sc alloy. The excellent high-temperature strength results from a synergistic effect of solid solution strengthening, grain boundary strengthening and nanoparticle order strengthening. [ABSTRACT FROM AUTHOR]

In this study, the microstructure, tensile properties, and the fracture behavior of hypereutectic A390 aluminum alloy produced by route BC of equal channel angular pressing (ECAP) were investigated. Microstructural observations showed that the microstructure of the A390 alloy was considerably improved by the ECAP. After the fourth pass, most of the primary silicon particles (PSPs) and coarse acicular eutectic silicon particles (ESPs) were broken, and the α-Al was refined. The ultimate tensile strength (UTS) of ECAPed specimens after 1 pass, 2 passes, 3 passes, and 4 passes was increased by 28%, 59%, 30%, and 61%, and the fracture strain was improved by 52%, 54%, 106%, and 93%, respectively. The fractography results revealed that the fracture mechanism turned to mixed rupture which is characterized by cleavage in the PSPs and dimples in the Al matrix. Finally, results showed that route A on modifying of microstructure and improvement of the tensile properties is more effective than route BC. This difference could be explained by the redundant strain between each pass and cyclic restoration in every 4 passes of route BC. [ABSTRACT FROM AUTHOR]

The natural passivity, or induced by anodizing process, does not always result in an effective corrosion barrier for aluminium when exposed to environments containing specific chemicals that can cause material degradation phenomena with localized corrosion morphology. The present work investigates the effects of ethyl bromide (EtBr), a neutral organic molecule, sometimes used as a fumigant in packaging containers, that has been recently indicated as a possible cause of corrosion in aluminium alloy components. The study was conducted on Al 1050 alloy samples in aqueous solutions of sodium sulphate at increasing EtBr concentrations, ranging from 500 to 8600 ppm. Long-term exposure tests (936 h) and electrochemical experiments (potentiodynamic and potentiostatic polarizations, as well as time-dependent corrosion potential monitoring) were carried out, together with SEM and EDS examinations of the morphology and nature of the corrosion products. The results showed that the alloy undergoes different corrosion behaviours depending on the concentration of EtBr, spanning from passivity at the lowest concentrations to pitting at the highest, passing through the initiation and propagation of crevice at intermediate EtBr contents. A crucial role of the exposure time was detected, tentatively attributed to ethyl bromide hydrolysis in aqueous solution that liberates the bromide anion that is aggressive towards the passive state of aluminium alloys. [ABSTRACT FROM AUTHOR]

In terms of aluminum alloy matrix composites, the effect of reinforcement on precipitation is worth investigating. In this work, the silicon carbide nanoparticles-reinforced 7075Al (SiCnp/7075Al) composite was fabricated through a series of powder metallurgy procedures, shift-speed ball milling, hot pressing, and hot extrusion, and the precipitation behavior of SiCnp/7075Al composite was compared with that of 7075Al alloy after T6 treatment. The results show that only a small addition (1 vol%) of SiCnp modifies the morphology and dispersion of precipitates. The uniformly dispersed small precipitates (η′ phase) and increased dislocation density have a positive influence on the mechanical properties of composites. Based on the fracture surface and element composition, a fracture mode dominated by precipitated phase-induced crack initiation was proposed. This study suggests a promising approach to design the alloy matrix composites through controlling the behavior of precipitated phases with nano-reinforcement. [ABSTRACT FROM AUTHOR]

A new concept of fragility of superheated melt is used to analyze the viscosity of eutectic Al–12 wt%Si melts modified with phosphorus (P). The influence of P on the melt is investigated on the basis of Arrhenius law and fragility concept. The value of generalized fragility M named here is determined and available for evaluating the stability of modified eutectic Al–12 wt%Si melts and predicting the modifying effect of P. [ABSTRACT FROM AUTHOR]

The age hardening behavior of solid Al-alloy–SiCp composite and closed cell Al-alloy–SiCp composite cellular materials has been examined and compared. The peak aging period of these materials were also compared with that of the solid unreinforced alloy. The effect of SiCp content on the peak aging time has been examined. It was found that the composite aged faster than the alloy irrespective of SiCp content, wherein peak aging time was invariant to SiCp content. On the other hand, while the closed cell composite foam reached a peak aged condition faster than the alloy when SiCp content was less than 10 wt%, further increases in SiCp content delayed the age-hardening kinetics. [ABSTRACT FROM AUTHOR]

A multi-scaled model for the fracture toughness of an aluminum alloy has been developed that agrees well with the experimental data. It has been shown that fracture toughness decreases as the volume fraction of the first-class (related to microconstituents/inclusions) and second-class (related to second phase precipitates) microcracks increase, with the first-class microcracks have greater and more obvious effects. Thus, decreasing the volume fraction of the microconstituents (normally Fe and Si impurities) can decrease the volume fraction of the first-class microcracks and help improve the fracture toughness. At the same time, decreasing the volume fraction of the precipitates along the grain boundaries can also improve the fracture toughness by decreasing the volume fraction of the second-class microcracks. [ABSTRACT FROM AUTHOR]

Thixocast samples of an Al-Si-Cu alloy were solution treated at 500°C for 4 h, aged at 170°C for different times and tensile tested at room temperature. Statistical analysis on the fractured Si particles has pointed out how the fraction of damaged particles is influenced by the ageing treatments performed before deformation. The damage accumulation per unit of strain decreases with increasing ductility of the samples. The Considére criterion for plastic instability shows no significative necking. [ABSTRACT FROM AUTHOR]

The joint properties of dissimilar formed Al alloys, cast Al alloy and wrought Al alloy, were examined with various welding conditions. Friction stir welding method could be applied to join dissimilar formed Al alloys which had different mechanical properties without weld zone defects under wide range of welding condition. The weld zone of dissimilar formed Al alloy exhibited the complex structure of the two materials and mainly composed of the retreating side material. The mechanical properties also depended on the dominant microstructure of the weld zone with welding conditions. The different mechanical properties of the weld zone with welding conditions were related to the behavior of the precipitates of wrought Al alloy and Si particles of cast Al alloy. The higher mechanical properties of the weld zone were acquired when a relatively harder material, wrought Al alloy, was fixed at the retreating side. [ABSTRACT FROM AUTHOR]

It is well known that the spatial distribution and the spatial density of the particles oα-AlFeSi and β-AlFeSi in the billets of Al-Mg-Si alloys, such as AA6063 alloys affect the quality of anodizing performance of their extrusions. For this reason it is very important to control the spatial distribution and the spatial density of both AlFeSi particles at extrusion plants. The X-ray diffraction method (XRD) has been used for discrimination between α-AlFeSi and β-ALFeSi particles. However it is not an appropriate method for determining the spatial distributions of particles in the alloys. As an alternative method an electron probe microanalyzer (EPMA) has been used for determining the spatial distributions of each element in the microstructures. However, unfortunately it is difficult to discriminate between the particles composed of the same elements like α-AlFeSi and β-AlFeSi particles. Thus, we tried to develop a convenient method to discriminate between α-AlFeSi and β-AlFeSi particles in the microstructure of AA6063 alloys and developed the EPMA mapping of α-AlFeSi and β-AlFeSi particles. First, in order to discriminate between the two particles, we tried to use the relative X-ray intensity ratio, the IFe/ISi ratio instead of the Fe/Si mass ratio. Then, we calculated the value of the IFe/ISi ratio from α-AlFeSi and β-AlFeSi by using Monte Carlo calculations and obtained the critical value of the IFe/ISi ratio, to distinguish between α-AlFeSi and β-AlFeSi. After that, using the discrimination value, we developed the EPMA mapping program (EPMA method) to observe the distributions of α-AlFeSi and β-AlFeSi, and to calculate the areas (%) of α-AlFeSi and β-AlFeSi. Finally, we checked the correlation between the EPMA and the XRD methods. Consequently, the two methods were in good agreement. Today, this EPMA method instead of the XRD method is successfully used in the quality control of 6063 aluminum alloy billets after heat treatment at our aluminum extrusion works. [ABSTRACT FROM AUTHOR]

The thermal expansion behavior of two aluminum alloys (Al-4%Cu and Al-12%Si) reinforced with alumina planar random short fibers has been studied, both experimentally and theoretically. The metal matrix composites (MMCs) were manufactured by pressure infiltration of molten metal into short fiber preforms with a planar random distribution of fibers. Dilatometric testing was used to investigate the influence of fiber volume fraction and architecture, and the effects of thermal cycling between 25 °C to ∼560 °C. Thermal expansion measurements showed that, by increasing the fiber content in the composites, both the thermal strains and the effective coefficient of thermal expansion (CTE) were reduced in the whole temperature range. Furthermore, the thermal strains of MMCs increased almost linearly up to a critical temperature, Tcr, where the metallic matrix began to yield macroscopically due to internal thermal stresses. For temperatures higher than Tcr the thermal strains of MMCs showed a marked hysteresis during heating/cooling cycles due to the elasto-plastic response of the metallic matrix. In this temperature range, the thermal expansion curves deviated appreciably from linearity and the planar (in the plane of fibers) and transverse (normal to the plane of fibers) responses were very different: while the planar CTE was strongly reduced, the transverse CTE increased sharply with temperature, being even larger than the CTE of the unreinforced alloy. Thermal cycling produced a net dimensional change of composites during the first 2-3 cycles but, on the subsequent cycles, the permanent deformation disappeared almost completely and the successive thermal expansion curves were identical. Experimental results were compared to the theoretical predictions of an analytical model based on the Eshelby's equivalent inclusion method, and an excellent agreement was obtained. [ABSTRACT FROM AUTHOR]