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Laser powder bed fusion (LPBF) is a rapid prototyping technology with high forming accuracy, which can print complex metallic components applied in the aerospace field. The aluminum alloy parts manufactured by LPBF can better achieve lightweight structures than other metallic materials due to the combination of materials and structure. However, many metallurgical defects such as spherification, porosity, coarse grain, and crack are more likely formed inside the printed components during the LPBF process, resulting in the decline of properties of the aluminum alloy. In order to solve the above-mentioned problems, researchers have conducted in-depth exploration to improve the mechanical properties of LPBF fabricated Al parts. In this paper, the methods to improve the forming quality of aluminum alloy are explored from the direction of regulation strategies for microstructure and properties. The current research status of LPBF-processed aluminum alloy is discussed from the aspects of process parameter optimization, alloying element modification, reinforcing phase addition, and post-treatment. Furthermore, the microstructure and properties of LPBF-processed aluminum alloy are systematically reviewed. [ABSTRACT FROM AUTHOR]

This study explores the impact of different pre-temper conditions of the base metal (BM) on the microstructure and strength-ductility performance of AA7075 welded joints, aiming to identify effective processing approaches for aluminum alloy forming. The findings reveal that in comparison to the average grain size (AGS) in the weld nugget zone (NZ) of the AA7075-T6 joint (approximately 2.85 µm), the grain refinement is more pronounced in the NZ of the AA7075-O joint (approximately 2.09 µm). Concerning mechanical performance, the AA7075-T6 joint experiences softening in the welding region, demonstrating significantly lower tensile properties than the BM, with an ultimate tensile strength of 416 MPa and an elongation of 4.4 %. Conversely, the AA7075-O joint undergoes hardening in the welding region, displaying higher tensile strength than the BM, with an elongation of 8.7 %. Three-point bending destructive experiments results indicate that the AA7075-O joint can withstand larger bending angles, displaying more thorough plastic deformation and superior forming performance. [ABSTRACT FROM AUTHOR]

Al-Cu-Fe-Ce quasicrystalline-reinforced 6061 aluminum matrix composites were prepared through hot press sintering and treated with a solid solution and aging treatments. The influence of the solid solution and aging treatments on the microstructure and mechanical properties of the composites was investigated by XRD, EDS, SEM, and TEM. The results show that using Al-Cu-Fe-Ce quasicrystalline intermediate alloy as the reinforcing phase increases the interfacial areas of the composites and enhances the grain boundary strengthening effect, which is conducive to the improvement of the mechanical properties of the composites. And through the solid solution and aging treatment, the β phase and the Al2CuMg phase belonging to the orthorhombic crystal system, as well as the β″ phase and a small amount of the β′ precipitated phase, were formed in aluminum matrix composites, and these precipitated phases all existed in the composites in a fine and uniform distribution, which ensured the consistency of the mechanical properties of the materials and improved the mechanical properties of the composites. Meanwhile, the deficiency of quasicrystalline particle-reinforced 6061 aluminum matrix composites in age-hardening was solved and the age-hardening capability of the composites was further developed. This method provides a feasible process route for the preparation of high-performance aluminum matrix composites. The application of this process is expected to improve the mechanical properties and durability of this composite and offer a more reliable option for the application of aluminum matrix composites in aerospace, transportation, and other fields. [ABSTRACT FROM AUTHOR]

The present study employed the ABAQUS numerical simulation method to analyze the forward flow forming of 7075 aluminum alloy tubes using power staggered spinning compression materials. Subsequently, a power staggered spinning experiment was conducted to analyze the microstructure and mechanical properties. The simulation results revealed that increasing the spinning temperature led to a decrease in the limit thickness reduction per pass while increasing range, as well as enhanced deformation along the wall thickness direction. At 400 ℃, favorable forming properties were observed with minimal plastic strain occurring in the inner layer when thickness reduction is below 10%. These findings indicate that an escalation in total thickness reduction resulted in refined and uniform grain distribution along the wall thickness direction, accompanied by improved hardness (up to 178.6 HV) due to synergistic effects from fine grain strengthening, strain strengthening, and dispersion strengthening induced by second particles. [ABSTRACT FROM AUTHOR]

Gradient ultra-low temperature forming is a novel process for improving the forming limit of thin-walled aluminum alloy components. However, it is critical to prevent wrinkling defects through blank holding. It is not clear whether the gradient temperature can meet the deformation requirements for preventing wrinkling defects with draw beads and blank holding. The effects of a draw bead and the blank-holder force on the wrinkling behavior in gradient ultra-low temperature forming of a 7075 aluminum alloy hemispherical shell were investigated experimentally in this study. The wrinkle control mechanism was revealed through stress and strain analyses. The blank-holder force required to prevent wrinkling could be reduced significantly by setting a draw bead. A blank-holder force of 120 kN could be used to form a sound hemispherical specimen with a diameter of 200 mm, which was 31.5% of the force without the draw bead. This benefited from the reduced hoop compressive stress in the unsupported region, which decreased to 165 MPa from 516 MPa. The hemispherical shell formed using gradient ultra-low temperature forming was twice as high as that at room temperature. The deviation in thickness was only 7.2%. Moreover, microstructural observations revealed the reason for this enhanced formability. The uniformly distributed high-density dislocations at ultra-low temperatures significantly improved the strain-hardening ability, thus allowing the deformation to be withstood and transferred. This could prevent splitting of the unsupported region when using a draw bead to prevent wrinkling. This is beneficial for significantly reducing the tonnage requirements, particularly for large-sized thin-walled components, which can expand the application range of gradient ultra-low temperature forming. [ABSTRACT FROM AUTHOR]

An economical Al – Cu powder with high conductivity has been synthesized by a chemical substitution reaction. The powder particles have the form of an aluminium core, on which a copper shell is deposited. The deposition reaction occurs in a copper sulphate solution at a temperature of 45°C. At higher temperatures, copper diffusion proceeds faster, but the aluminium core may crack. The process of aluminium substitution with copper on the particle surface develops at different values of the standard potential of each metal. The minimum resistivity of 1.01 × 10 – 7 Ω ∙ m is obtained in a composite sintered at 550°C from the Al-core Cu-shell powder with addition of 3 wt.% glass frit. This material can find wide application, for example, as a substitute for silver in electronic devices to reduce production costs. [ABSTRACT FROM AUTHOR]

With the development and widespread application of high tech, complex industrial production increases the requirements for the performance and structure of metal materials. In order to improve the performance of metal materials and reduce industrial production costs, a laser selective melting forming method for carbon nanotubes (CNTs)/ aluminum (Al) composite materials was proposed. The composite material powder was prepared by wet mixing followed by ball milling method. CNTs and N-methylpyrrolidone (NMP) were mixed and dispersed using an ultrasonic cleaning machine for 40 minutes to reduce the compactness of CNTs clusters. Then, a finite element model for laser selective melting forming of CNTs/Al composite materials was constructed, and its application effect was tested and analyzed. The results showed that the density of aluminum based composite materials could reach up to 95%. The wear coefficient remained around 0.3, which was reduced by 0.35 compared to aluminum alloy materials. The highest strength and conductivity were 410 MPa and 68%, respectively, which were 240 MPa and 50% International Annealed Copper Standard (IACS) higher than that of aluminum alloy materials. The coefficient of thermal expansion remained at stable levels above 7×10-6 /K. Therefore, the addition of CNTs in laser selective melting forming of aluminum matrix composites had optimized the mechanical properties of aluminum matrix composites, improved conductivity, thermal stability, and wear resistance, and broadened the application range of aluminum matrix composites. [ABSTRACT FROM AUTHOR]

The aim of this work was to determine the effect of the duration and temperature of the Al-Fin process for casting the bimetallic joint on the formation of the metallurgical bond between the AlSi9 aluminium alloy piston and the cast iron insert. Knowledge about the formation of individual bonding layers has a direct impact on the bonding strength between the aluminium alloy and the EN-GJLA-XNiCuCr15-6-2 austenitic cast iron ring. In the performed tests, the Al-Fin casting process was carried out for different temperatures of the liquid AlSi9 alloy. The temperature of the AlSi9 aluminium alloy varied in the range 700–950 °C in steps of 50 °C. The duration of the Al-Fin process ranged from 1 to 10 min. An optical microscope and a scanning electron microscope were used to study the microstructure of the bimetallic joints. The analysis of the microstructure of the bimetallic bond showed that characteristic layers are formed between the aluminium alloy piston and the cast iron insert: a transition layer, in which iron and aluminium atoms from both joined materials are mixed, and a diffusion layer, in which aluminium and silicon atoms penetrate the surface layer of the joined metals. The thickness of the intermetallic diffusion layer formed between the aluminium alloy and the cast iron insert is thinner and does not depend on the heating time of the aluminium insert in the bath. However, there is a significant effect of both the annealing time and the temperature of the AlSi9 aluminium alloy on the thickness of the transition zone. [ABSTRACT FROM AUTHOR]

In this paper, 6061-T6 aluminum alloy and 30CrMnSiA steel are bonded by inertia radial friction welding (IRFW). The formation mechanism of the aluminum/steel friction welded joints and the effect of the welding parameters on the mechanical properties are investigated through the microstructure, microzone composition, and mechanical property analysis. The results show that no visible intermetallic compound layers (IMCs) are detected on the aluminum/steel welding interface, which may be due to Si element aggregating in the welding interface and then forming a Al−Fe−Si phase, preventing the formation and growth of an Al−Fe IMCs. Eventually, a micron ultrathin interface reaction layer composed of Al0.7Fe3Si0.3, FeAl, and Fe3Al phases is formed at the aluminum/steel welding interface. The maximum average shear strength of the joint is 176 MPa. The shear fracture is a typical ductile fracture. Properly reducing the friction speed and increasing the upsetting pressure can improve the bonding strength of aluminum/steel joints. [ABSTRACT FROM AUTHOR]

In this study, extrusion experiments were carried out on Al-Mg-Si-Cu-Mn alloys with different extrusion ratios (ERs), extrusion temperatures (ETs), and extrusion speeds (ESs). By using electron backscatter diffraction (EBSD) analysis, tensile testing, and other analytical means, the evolution of microstructure, texture, and properties of the extruded alloys was systematically investigated, and the strengthening-toughening mechanism induced by the extrusion parameters was revealed. It was found that the strength of the extruded alloy shows a tendency to first increase and then decrease with the increase of the ER and ES, and the 'critical ER' and 'critical ES' are 29.5 and 2.5 mm/s, respectively; the strength of the extruded alloy gradually increases with the increase of the ET. The alloy achieved excellent strength-toughness matching at the ER of 29.5, ET of 480 °C, and ES of 2.5 mm/s. The yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) of the extruded alloy at this condition were ∼169.58 MPa, ∼314.36 MPa, and ∼16.57 %, respectively. This excellent strength-toughness matching is mainly related to the following aspects: 1) grain refinement provides high grain boundary strengthening effect and appropriate work hardening ability; 2) <111>//ED texture has a strong preferential orientation; 3) the variation trend of dislocation density is importantly related to <111>//ED and EX a {011}<111> textures; 4) Cube{001}<100> and Goss{011}<100> textures have a softening effect. The above findings provide new insights into the potential mechanisms of hot extrusion forming of aluminum alloys, which are of important guiding for the design and development of aluminum alloys with excellent strength-toughness combinations. [Display omitted] • <100>//ED texture is related to Cube{001}<100> and Goss{011}<100> textures. • Cube{001}<100> and Goss{011}<100> textures have a softening effect. • <111>//ED texture has a strong preferential orientation. • Dislocation density is importantly linked to <111>//ED and EX a {011}<111> textures. • Excellent strength-toughness matching of Al-Mg-Si-Cu-Mn extrusion alloys can be realized under specific extrusion parameters. [ABSTRACT FROM AUTHOR]

In this study, the joining experiment of SiCp/Al composites with 4 mm thickness was carried out, and the effects of different tool rotational speeds (600, 1000 and 1400 rpm) on the microstructure evolution and mechanical properties of joint were studied. The results show that the rotation speed has a significant impact on the microstructure of the weld nugget (WN). The aluminium matrix forms a fine equiaxed crystal structure in WN. As the rise of the rotational speed from 600 to 1400 rpm, the grain size of WN decreased from 6.9 to 2.3 μm. Compared with the base material, the microhardness of the nugget zone was higher. As the rise of rotational speed, the maximum microhardness value increased. The ultimate tensile strength (UTS) of joints decreased with the increase of rotational speed and can reach 95.9% of the base material at 600 rpm. The failure modes of friction stir welding (FSW) joints are mainly ductile failure and SiC particle fracture. [ABSTRACT FROM AUTHOR]

Copyright of Electroplating & Finishing is the property of Electroplating & Finishing Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Nitriding of Al alloys leads to the formation of a thin, hard nitride layer (AlN) on the surface. A subsequent EBR can both eliminate the nitriding-related cavities under the nitride layer and increase the hardness of the substrate without melting or destroying the nitride layer. This paper deals with investigations regarding the influence of the energy/heat input on the microstructure within both the AlN layer and the remelted Al substrate. Of particular interest was the interface between the AlN and the Al substrate, which changed to a transition zone with a depth of approximately 80 µm. A range of high-resolution imaging and analytical tools for both scanning and transmission electron microscopy were used for these investigations. Based on the findings from the microstructural investigations, a schematic model was developed of the processes occurring within the nitride layer and at the interface as a result of remelting. [ABSTRACT FROM AUTHOR]

A 2A12 aluminum alloy component with uniform high-strength and ductility was developed via predeformation (one-pass repetitive upsetting extrusion) and annular channel angular extrusion (ACAE). Moreover, the microstructure evolution and age-hardening behavior were investigated. The results show that the upsetting-extrusion predeformation improved the cumulative strain of the component and refined the grain size, and that the second Al–Cu–Mg phases were obviously broken and refined, and that, especially, the distribution of the second phases along the extrusion direction was weakened. Thus, compared with directly ACAE-formed components, after the T6 heat treatment, the axial ultimate tensile strength (UTS) of the cabin increased from 476 to 484 MPa, and the elongation (EL) increased from 12.9% to 17.5%. The circumferential UTS increased from 426 to 482 MPa, and the EL increased from 9.24% to 16.8%. A large number of dislocations were introduced into the upsetting extrusion (UE) + ACAE method, which resulted in strain hardening and higher precipitation strengthening in the late artificial aging process. The finer and denser grains and s precipitates significantly enhanced the strength and ensured the good ductility of the alloy. It is suggested that the combination of predeformation and annular channel angular extrusion is an effective method for forming aluminum alloy cabin components with higher and more uniform mechanical properties. [ABSTRACT FROM AUTHOR]

Stir casting has been taken as a low cost and effective way to disperse ceramic particles in molten alloys and obtain the high‐performance metal matrix composites. However, the reinforcement precursors with a similar density to the molten aluminum are difficult to be uniformly dispersed in the melts. Herein, the particulate quartz, which can react with the aluminum melts and form the Al2O3/SiO2 reinforcement, is used as the reinforcement precursor. Effect of the stirring speeds of the melts and the feeding rates of precursor particles on the reinforcement distribution in aluminum matrix are investigated. The numerical simulation is carried out to analyze the particles dispersion course in the melts. Results show that the precursor particles in molten aluminum achieve a relatively uniform dispersion at the modest stirring rate of 400 rpm. Meanwhile, numerical simulation results also prove that precursor particles will distribute homogenously in the Al matrix while exerting the stirring rate at 400 rpm. From the microstructure of the composites, it is evident that extremely high stirring rate and particles feeding rate will lead to the agglomeration of particles, which is not favorable to the composites performance. [ABSTRACT FROM AUTHOR]

In the current work, micro-arc oxidized coatings were fabricated on 2A12 aluminum alloy with different concentrations of Na2WO4. The microstructure, mechanical properties and wear properties of the micro-arc oxidation (MAO) coatings formed on 2A12 aluminum alloy were investigated. The results show that the thickness and the surface roughness of the coating increased with the increase in Na2WO4 concentration. The thickness increased from 21 μm without sodium tungstate to 43.5 μm with 16 g·L−1 sodium tungstate, and the roughness from 3.2 to 5.5 μm. The hardness and wear resistance of the MAO coatings were also significantly influenced by the Na2WO4 concentration. During MAO, Na2WO4 as a passivator and WO4 ions participated in the coating reaction, which can promote the phase transition from amorphous alumina to γ-Al2O3 phase. The mechanism of action of sodium tungstate in the oxidation process was also elucidated. [ABSTRACT FROM AUTHOR]

Friction stir welding (FSW) represents a conceptually simple technique that consists of joining either similar or dissimilar solid-state materials through higher plastic deformation rates. FSW is an important technique in the aeronautical and aerospace industries, and its development is vital because of the significant difficulty in joining higher resistance AA 2000 and AA 7000 aluminum alloys with conventional techniques, like fusion welding, due to porosity and mechanical property losses. Thin sheets with a 1.6-mm nominal thickness of AA2024, heat treated to condition T3, and thin sheets with a 1.6-mm nominal thickness of AA7475, heat treated to condition T761, were used to investigate the influence of welding parameters under superficial residual stress and the efficiency of joints by FSW of AA2024-T3 and AA7475-T761 aluminum alloys. A central composite design (CCD) was used as a statistical model in this study (23 factorial points, six stellar points, two central points, and two replicas). Micrographic analysis showed that in the nugget zone of the AA7475-T761 alloy, there was hardness recovery. The fractography images showed that failures occurred mainly due to the joint line remnant defect, evidenced by the presence of cracks. The superficial residual stresses show a maximum value of 81 MPa at the advancing side in run 27 (hot welding) of AA2024-T3, whereas in AA7475-T761, a value of 57 MPa was found in the same run. Finally, tensile strength represents an efficiency of ~92% of the AA2024-T3 base metal value, while for AA7475-T761, this value was ~85%. From a component design perspective, the parameter window of this study is identified as interesting for its evaluation in the possible application in component manufacturing, due to the low values of superficial residual stresses found compared to those in previous work. [ABSTRACT FROM AUTHOR]

In this paper, the Plasma electrolytic oxidation (PEO) coatings were formed in K2ZrF6-containing electrolyte with the addition of glycerin on aluminum alloy. PEO coating increased the tribological and mechanical properties of the aluminum alloy. The effect of frequency on the properties of PEO coatings was studied. AFM observation showed that the micropores number increased with the increasing frequency. XRD results showed that the content of α -Al2O3 ranged with the frequency increase. The coating formed in the electrolyte with the frequency of 800 Hz was of the lowest friction coefficient and stablest curve. The glycerin is not only of ability to lower the defect of PEO coatings, but can also increase the wear resistance ability of the coatings. [ABSTRACT FROM AUTHOR]

The effect of azelaic acid on microstructure evolution and electrical properties of anodic aluminum foil for electrolytic capacitor is studied quantitatively. The azelaic acid is selected as formation solution in the multi-step anodization process, and boric acid is applied for comparison. The field-emission scanning electron microscopy and X-ray diffractometer technologies are used for observation of microstructure and detection of crystallinity, respectively. The electrical properties are tested by LCR meter and T–V tester. The microstructure observation shows that the 'corn-flake' structures are taken place by 'cotton-ball' ones gradually along with the preparation process, and such phenomenon is more obvious when azelaic acid is used. The pores area of anodic aluminum foil formed in azelaic acid is larger because of the stronger acidity. The formation with azelaic acid induces smaller thickness of oxide film, promotes the formation of crystalline oxide, therefore, a barrier film with higher crystallinity and larger grain size is obtained. The barrier film formed in azelaic acid shows larger specific capacitance, lower withstand voltage and larger leakage current, which needs the multi-step anodization for performance improvement. [ABSTRACT FROM AUTHOR]

In this study, a laser remelting process was applied to the FeCrCoNiTiAl0.6 high entropy alloy coating in order to improve the density and the surface quality of the coating. The coating was fabricated by high-velocity-oxygen-fuel (HVOF) technology. The microstructure and phase composition of the coating were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), X-ray diffractometer (XRD) and confocal scanning laser microscope (CSLM). Moreover, the wear behavior of the coating was evaluated by use of a ball-on-disc test. The coating was denser after laser remelting treatment by eliminating the previous lamellar structure. The microstructure of the laser-remelted coating exhibits two body-centered cubic (BCC) phases, which is different from the HVOF coating. In addition, aluminum oxide formed during laser remelting. Different from the wear mechanism of the HVOF coating, which comprised abrasion and fatigue, the major wear of the laser remelted coating was abrasion. [ABSTRACT FROM AUTHOR]

This paper discusses the influence of Vietnam rare earth (RE) with the composition of 69.4% Ce and 30.5% La (modification content of 4% and 6%) on the microstructure and mechanical properties of Al–5Zn–3.5Mg–1.2Cu alloy when the temperature modification is changed at 7 5 0 ∘ C in 150, 200, 250 s. By optical microscopy, the results showed that the microstructure of the modified sample is finer than the nonmodified sample. By the SEM and EDS analysis, at the grain boundaries of this alloy, MgZn 2 and/or Mg 3 Zn 3 Al 2 intermetallic phases appeared. The modified elements (La, Ce) in RE and aluminum were formed in the intermetallic Al 1 1 RE 3 and Al 2 RE phases, which prevents the development of the dendritic α phase. The result showed Al–5Zn–3.5Mg–1.2Cu alloy modified with 4% RE in 150 s which is the most optimal result, the grain size is 6. 6 7 μ m and the hardness is 107 HB. [ABSTRACT FROM AUTHOR]

• A finite strain elasto-viscoplastic model of aluminum alloys under hot working conditions is established. • The model considers microstructure changes in terms of dislocation density and (sub)grain size evolution. • An efficient numerical implementation of the constitutive model is demonstrated. • Calibration of the model is demonstrated, using AA6099 as an example alloy. A constitutive model for aluminum alloys under hot working conditions is proposed. The elastic-viscoplastic model is implemented in a finite strain continuum mechanical framework. The model accounts for the interplay between dynamic recovery and recrystallization during hot working of aluminum alloys and central aspects of microstructure evolution such as grain/subgrain size and dislocation density. The proposed model is generic in the sense that it can be used for arbitrary aluminum alloys, but in order to demonstrate its capabilities, the model is calibrated to a newly developed AA6099 alloy in the present study. The model is thoroughly discussed and details on the numerical implementation as well as on the calibration of the model against experimental data are provided. [ABSTRACT FROM AUTHOR]

Sheet blanks from copper (M1) and aluminium alloys (AD1, AD32) with a thickness of 3 mm are joined in butt joints and overlap, butt joints - overlap joints by friction stir welding (FSW). The microstructure, mechanical properties and phase components of the welded joints obtained by the FSW are studied by using various methods of metal physics analysis, including X-ray diffraction, mechanical tensile and bending tests, etc. The test results showed that high quality of the welded joint can be achieved when tool rotation is 900 min-1 and the welding speed is 25 mm/min when the angle of tool inclination angle is 3°. The maximum value of the tensile strength is about 66 MPa. Copper and aluminium alloys are formed due to solid-phase mixing in the superplastic state (SPS), forming a characteristic shear-strip-layered structure with alternating layers in zone of weld seam cores (WSC). A mixed structure with characteristic fragments of Cu and Al is formed on the aluminium side on the side of the WSC. New intermetallic phases were not detected in the WSC centre. [ABSTRACT FROM AUTHOR]

• W-temper cryogenic forming was proposed. • Excellent formability and post-form strength were simultaneously obtained. • Large temperature gradient is more suitable for W-temper cryogenic forming. • The deformation and strengthening mechanisms were revealed. Simultaneously obtaining excellent formability and post-form strength in the traditional sheet metal forming of heat-treatable aluminum alloy is challenging, owing to the coexistence of wrinkling and splitting defects during forming and the control problem of microstructure. To solve these problems, W-temper cryogenic forming was proposed based on the cryogenic 'dual-enhancement effect' of an as-quenched (W-temper) aluminum alloy. The effects of the cryogenic temperature gradient and blank-holder force on the drawing behaviors were studied by analyzing the forming defects and thickness distribution. Strength distributions were reflected through Vickers hardness measurements under different aging conditions. The related strengthening mechanism was revealed through microstructure characterization. The drawability can be significantly improved at small or large cryogenic temperature gradients. An Al-Cu alloy semispherical shell component was fabricated via W-temper cryogenic forming. The depth of the formed hemispherical specimens increased by more than 106.4%. Uniform thickness can be also obtained at the temperature gradient of 216 °C, with an average thickness deviation rate of 6.5%, benefiting from the cryogenic dual enhancement effect and enlargement of the stress gradient. The hardness in all regions was higher than 146.5 HV of traditional T8-temper because of the enough accelerating precipitation of θʺ and θʹ phases by prior cryogenic deformation. Strain and precipitation strengthening were the main strengthening mechanisms under post-forming and post-aging conditions, respectively. The peak-aging time can be shortened to 6 h, which is one-third that of the traditional process. Enhanced formability and post-form strength can be simultaneously obtained by W-temper cryogenic forming, which has great potential for the fabrication of thin shells made from heat-treatable aluminum alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

This work evaluated the microstructure, mechanical, and electrochemical properties of Si/DLC coatings deposited using ‎ the plasma-enhanced chemical vapor deposition (PECVD) technique. Tetramethylsilane and acetylene were used as precursor gases in the deposition process. The characteristics of the coating were estimated using different techniques. The corrosion performance was evaluated using various electrochemical methods in 3.5 wt% NaCl solution. The XPS analysis revealed that the film consists of Si and (a-C: H). The results revealed that as the deposition time increased, the hardness and Young's modulus decreased from 15.83 to 14.21 GPa and 125.8–114.9 GPa, respectively, while the thickness and adhesion strength increased. Moreover, the anti-corrosion ability of the DLC has been improved. It was found the corrosion potential moved to more noble direction (−618 to −562 mV Ag/AgCl) while the corrosion rate decreased from 0.012 to 0.001 mmy−1. This trend can be attributed to growing coating thickness and fewer film defects which operated as a protective barrier against the corrosive solution. A failure mechanism of Si/DLC film has been suggested. • Si/DLC films were successfully formed on the 2024 aluminum alloy. • Increasing the deposition time condense the microstructure and decreases the porosities. • The hardness and Young's modulus decrease with increasing deposition time. • Corrosion and passive current densities decreased with the increment of deposition time. [ABSTRACT FROM AUTHOR]

The short carbon fiber reinforced 2024 Al composites were fabricated through powder metallurgy. The effect of short carbon fiber content on the interfacial microstructure and fracture behavior of the composites at different temperatures were investigated. The results showed that the dislocation accumulation was formed in the aluminum matrix due to the thermal expansion mismatch between carbon fiber and aluminum matrix. With the testing temperature increasing, the size of interfacial product Al4C3 and precipitates Al2Cu became larger, and the segregation of Al2Cu was found coarsening around Al4C3. The addition of short carbon fiber improved the hardness and modulus of the aluminum matrix in the vicinity of the interface between carbon fiber and aluminum matrix. Compared to the matrix 2024 Al, the yield strength and ultimate tensile strength of the composites first increased and then decreased with increasing short carbon fiber content at room temperature 423 Kand 523 K. The fracture surface of the composites at room temperature was characterized by shear failure of fiber, while the interface debonding and fiber pulled-out became predominant fracture morphologies for the fracture surface at increased temperatures. [ABSTRACT FROM AUTHOR]

A new four-stage aging treatment, which is composed of pre-aging, retrogression, natural aging (NA) and re-aging, is designed to increase the tensile properties and the fatigue life of forged 7050 aluminum alloy in this work. As compared to traditional T74 and RRA treatments, the four-stage aging-treated sample exhibits the highest tensile properties and ductility. The tensile strength and yield strength are 627 and 608 MPa, respectively, and the elongation is 11.3%. The results of TEM and DSC show that an increased G.P zones and fine η′ phase distributed in the matrix of the alloy are subjected by this new aging processing as compared with T74 and RRA treatments. The natural aging in four-stage aging treatment accelerates the diffusion of Mg vacancies, and promotes the precipitation of G.P zones in grain interior during re-aging stage. On the basis of dislocation shearing mechanism, more dense and fine G.P zones of four-stage aging temper result in the superior tensile strength as compared to T74 and RRA temper. In addition, a combination of shearable precipitates, fine GBPs and narrow PFZs is beneficial to the slip reversibility in the plastic zone at the crack tip, thereby reducing fatigue damage accumulation and increasing the fatigue life. [ABSTRACT FROM AUTHOR]

Abstract Self-lubricating polytetrafluoroethylene-containing PEO (PEO-PTFE) composite coatings were prepared by vacuum impregnation on plasma electrolytic oxidized aluminum alloy with different cathodic voltages. The topography, microstructure and composition of the composite coatings were investigated by FESEM equipped with EDX and XRD. The friction and wear properties were evaluated in the load range of 5–20 N using a reciprocating tribometer. The results show that the tribological properties of PEO-PTFE composite coatings are greatly influenced by the surface microstructure of PEO coating. The PEO coating fabricated at 150 V cathodic voltage shows coarser microstructure, while the corresponding PEO-PTFE composite coating registers superior self-lubricated property with lowest friction coefficient of 0.1 and 0.09 under the applied loads of 5 N and 10 N, respectively. In term of wear resistance ability, the 90 V composite coating possesses relatively low wear rate about 7.47 × 10−6 mm3·(N·m)−1 with the coefficient of 0.13 under the test load of 10 N. The increased microcracks and diameter of micropores, like "grooves" and "ridges" on PEO coating, is beneficial for providing the scope for low-lubricating PTFE material, which can form smooth lubricating film during the friction process. Highlights • Self-lubricating PEO-PTFE coating was successfully prepared on aluminum alloy. • The cathodic voltages have great influence on the microstructure of the coatings. • The PEO-PTFE coating exhibits low coefficient of friction. • PTFE lubricating film formed on the worn surface during the friction process. [ABSTRACT FROM AUTHOR]

Using methods of physical material studies (scanning electron microscopy and micro X-ray spectral analysis), a study was carried out with focus on alteration of structure and phase composition in surface layers of Al-Si alloy (silumin AK10M2N) treated in electroexplosive alloying with a multiphase plasma jet formed in the process of aluminum foil explosion and carrying particles of Y2O3 weighted powder portion. It was revealed that a porous surface layer with non-homogeneously distributed alloying elements (silicon, yttrium) in it is formed in any conditions of electroexplosive alloying of silumin. Thickness of the modified layer is different, varying 50 to 160 μm, depending on the zone to be examined. The modified surface consists basically of Al, Si and Y. Yttrium in the modified layer is thought to be an indirect evidence of better physical and mechanical properties of the surface layer in comparison with the base material. [ABSTRACT FROM AUTHOR]

In this study, the microstructural variations, mechanical properties and forming limit diagrams (FLD) of Al 2024 aluminum alloy sheet with the thickness of 0.81mm are investigated during natural ageing (T4) treatment. The most formability in Al 2024 can be achieved just after solution treatment, and it is better to perform the forming process, on this aluminum alloy sheet, in this condition. However, in industrial applications, there is usually a postponement for some hours after solution treatment to begin the forming process that it means the forming process should be done at the natural ageing condition. This condition decreases the formability of Al 2024 sheets. To monitor the properties variations in natural ageing condition, FLDs were determinedafter specific times (e.g., 0.5. 1.5. 4 and 24 hours). The variations in micro-hardness, yield strength, ultimate tensile strength and elongation at break were observed with changing the ageing time. The scanning electron microscope (SEM) investigations illustrated that density and size of precipitates were changed with ageing time. Moreover, the Nakazima test was utilized to study the forming limits considering the natural ageing condition. Results showed by increasing the ageing time, up to 4h, the majority of properties variations could be seen, and from 4h to 24h, the variations were changed slower. [ABSTRACT FROM AUTHOR]

Good stress relaxation stability enables heat-resistant aluminum alloys to serve well at high temperatures. From the viewpoint of simultaneous regulation of microstructure and precipitates, a deliberate pre-annealing (200–400 ℃) followed by solution-aging (T6) treatment was proposed to improve the stress relaxation stability of an Al-Cu-Mg-Ag heat-resistant aluminum alloy in this work. A peak effect on the stress relaxation stability was found with a pre-annealing temperature of 325 ℃, which is associated with larger-sized grains and finer-sized precipitates of the alloy. This interesting peak phenomenon is attributed to a good balance of recrystallization and precipitation. Moreover, the regulated microstructure surprisingly assisted the 325 ℃ pre-annealing+T6 treated alloy with good tensile properties. The proposed heat treatment method provides a route for developing high-performance heat-resistant aluminum alloys. [Display omitted] • A heat-resistance Al alloy was prepared via pre-annealing/solution-aging treatment. • Regulation of grains and precipitates improved stress relaxation stability. • The alloy showed higher tensile properties than the alloy without pre-annealing. [ABSTRACT FROM AUTHOR]

[Display omitted] • Proposed the preparation of Al-5Ti-1B-1Ce using Al and TC4 machining chips as the main raw materials. • Exploring the effect of reaction temperature and time on the microstructure of Al-5Ti-1B-1Ce. • Presented the idea that Ce transforms the microstructure from needle-like to block-like. The recycling of aluminum and titanium machining chips has always been a challenge. Here, a new recycling method is proposed. Al-5Ti-1B-1Ce alloy was prepared by the melt reaction method by using Al and TC4 machining chips as the main raw materials. The effects of reaction temperature and time on the phase structure were investigated. Al-5Ti-1B-1Ce prepared from remelted chips has effect refinement to pure aluminum. The addition of 0.3 wt% Al-5Ti-1B-1Ce to the aluminum melt refines the pure aluminum grains form 3000 μm to 185.2 μm and keep 60 min without growing. Besides, the addition of Ce optimizes the morphology and distribution of the second phase, which improve the refine ability of Al-5Ti-1B-1Ce. [ABSTRACT FROM AUTHOR]

Surface microstructural modifications of 2A12 aluminum alloy exposed to 60 keV Ar ion bombardment with the dose of 1 × 1017 ions/cm2 under vacuum were studied in detail. The amorphous layer with the thickness of ∼130 nm accompanied with polycrystalline aluminum was formed at the surface after Ar ion bombardment. Beneath the amorphous layer, Al 2 CuMg precipitates were observed. Dynamic recrystallization(DRX)and grain growth were observed with the increment of texture intensity. Surface residual compressive stress and strain were enhanced characterized by electron back-scattered diffraction. After ion bombardment, the contact angles of diiodomethane and DI water on aluminum alloy were increased, and a notable decrement of surface energy of aluminum alloy was measured from 32.5 mJ/m2 to 23.4 mJ/m2. The diffusion experiments indicated that the mutual diffusion of Cu and Al was inhibited due to the bombardment-induced amorphous layer at aluminum alloy surface, which is beneficial to its application as a structure material in aerospace field. • Ar ion bombardment induced surface microstructure modification on aluminum alloy. • An amorphous layer was formed at the aluminum alloy surface after Ar ion bombardment. • Beneath the amorphous layer, DRX, high-density dislocation and grain boundary were induced by ion bombardment. • Surface energy of aluminum alloy was decreased after ion bombardment. [ABSTRACT FROM AUTHOR]

• Several aluminum alloys were 'strip' tested at 298 K and 573 K. However, macroscopic shear bands (MSBs) predominated only in al-6mg deformed at 573 K. • The MSB regions contained higher misorientation, grain elongation and fragmentation. MSBs both improved ductility, and were the sites of eventual fracture. • Though classical criteria predict flow instability at lower strains, our plasticity modeling clearly established MSB inception only at a strain of 0.20. • The 'delay' in MSB inception corresponded to the development of a percolating network of deforming grains. • Strain percolation, in particular, were triggered by differential dynamic recovery between the soft- and hard-oriented grains. Macroscopic shear bands (MSB) may develop during hot working of metallic materials. They are well-understood as a physical manifestation of flow instability, and the processing regimes wherein they form are well-charted. However, the microstructural transitions that occur between the onset of flow instability and MSB inception are not fully understood. In order to elucidate them, several aluminum alloy specimens were subjected to strip testing in a thermomechanical simulator (Gleeble™) at 298 K and 573 K. Prominent MSB were observed along the diagonals of the strip volume of only Aluminum-6 wt% Magnesium alloy specimen deformed at 573 K. Comparing the experimental grain morphology and crystallographic textures with those from plastic flow models revealed that MSB inception occurred only after ∼0.20 homogeneous plane strain deformation. However, classical flow instability was predicted at much smaller strain. This 'delay' was explained experimentally by showing that clusters of neighbouring severely deforming, fragmenting, mostly soft-oriented grains gradually developed due to lattice rotations along the specimen diagonals, and that MSB inception corresponded to the formation of a percolating network of such grains spanning the specimen. Further, clear experimental evidence revealed that differential dynamic recovery between hard- and soft-oriented grains was essential for MSB formation. [Display omitted] [ABSTRACT FROM AUTHOR]

Tube flow forming followed by flattening is an effective way to make ultra-wide sheet for plastic forming of large thin-walled components. However, the work hardening and poor plasticity of flow formed sheet seriously restrict the subsequent plastic formability. To tailor the plastic formability, two types of heat treatments (recrystallization annealing and solution quenching) were conducted on the flow formed 2219 aluminum alloy sheet, and their microstructure evolution and mechanical properties were comparatively studied to obtain a suitable heat treatment scheme. It is found that the deformation in flow forming produces quantities of deformed substructures and the rotating cubic texture. In the recrystallization annealing, recrystallization occurs with the co-existence of two nucleation mechanisms, i.e., subgrain nucleation and particle stimulated nucleation, which produce a weak {100}//RD-CD texture and higher plasticity than that of the flow formed sheet. In addition, it is found that the annealing temperature and holding time have complex interactive effects on the average grain size, the uniformity of grain size and the resultant plasticity. In contrast, the solution quenching obtains weak {100}∥RD-CD texture at lower solution temperature and cube texture at higher solution temperature, respectively; meanwhile, it produces larger average grain size and better grain size uniformity than the recrystallization annealing. Because the uniform grain size can suppress the heterogeneous deformation and the dissolution of second phase particles can delay the generation of crack, the solution quenched sheet presents better plasticity than the recrystallization annealed sheet. Moreover, increasing the solution temperature can improve the plasticity. Therefore, it is suggested to take a solution quenching scheme with higher temperature (535 °C for 30 min) to tailor the flow formed sheet, which can get a similar elongation as that of the initial tube blank. • Two heat treatment types are conducted to tailor the flow formed Al-alloy sheet for better subsequent plastic formability. • Recrystallization annealing cause recrystallization with two coexisting nucleation mechanisms and obtain a weak texture. • Solution quenching obtains larger average grain size and better grain size uniformity than the recrystallization annealing. • Effects of temperature and holding time on the microstructure and properties are investigated for twoheat treatment types. • A solution quenching scheme is determined by comparison to get better plastic formability for flow formed Al-alloy sheet. [ABSTRACT FROM AUTHOR]

[Display omitted] • Microstructure of Ti-based conversion coatings was clarified using FIB/SEM and STEM. • Discontinuous coatings on Al matrix change to continuous layer during deposition. • Further thickening of the conversion layer leads to degradation of adhesion property. • Increasing in the coverage ratio of specimen surface improves corrosion resistance. • Depositing dense particulate coatings provides optimal adhesion/corrosion properties. Chemical conversion coatings are widely used as a surface treatment for aluminum alloys to improve the adhesion of organic coatings and corrosion resistance. Because hexavalent chromium in chromate conversion coatings is toxic and carcinogenic, much effort has been made to replace them with chromium-free coatings. In this study, we searched for conditions to obtain impact adhesion and salt spray corrosion resistance equivalent to those of chromate conversion coatings on extruded A6063 alloy, and observed the microstructure of titanium-based conversion coatings. Discontinuous fine particulate titanium-oxide formed on the aluminum matrix at the initial stage of immersion treatment. A continuous titanium-oxide layer of 50 nm thick formed on the matrix after 5 min of immersion, whereas the titanium-oxide above 1 µm in thickness formed on the Al–Fe–Si intermetallic particles. Controlling the thickness of titanium-oxide layer in sub-50-nm improves the adhesion, while the thick conversion coatings on the intermetallic particles did not affect the adhesion. However, the thin discontinuous conversion coatings have poor corrosion resistance due to insufficient barrier effect. Therefore, we succeeded in achieving impact adhesion and salt spray corrosion resistance equivalent to those of chromate conversion coatings by densely dispersing titanium-oxide particles 20–50 nm thick on the matrix. [ABSTRACT FROM AUTHOR]

Three TA2/AA7005 composite plates were manufactured by horizontal twin-roll casting (HTRC) under various external fields, and the formation mechanism of segregation in the cast-rolling clad process as well as the effect of external fields on the segregation behavior, microstructure and properties of the composite plates were studied. In the non-field (NF) plate, due to the high cooling rate and asymmetric heat transfer in the cast-rolling clad process, a central macro-segregation band and an interface segregation band were formed in the aluminum matrix. After applying the electromagnetic oscillation field (EMOF), the electromagnetic oscillation stirring effect was induced in the melt of the cast-rolling zone. The dendrites grown at the solidification front were broken by a shearing force and re-entered the melt. In addition, the temperature gradient at the solidification front decreased, which inhibited the growth of dendrites and avoided blocking the equilibrium distribution of solute elements due to the "bridging" of dendrite arms. After applying the EMOF, the central and interface segregation bands of the composite plate were nearly eliminated and the microstructure became more homogeneous. As a results, under the action of the EMOF, the tensile strength, yield strength, effective elongation, and interfacial bonding strength of the TA2/AA7005 cast-rolling composite plate were 303.8 MPa, 204.7 MPa, 21.6%, and 25.3 N/mm respectively, which were significantly improved in comparation with the NF plate. [ABSTRACT FROM AUTHOR]

An Correction to this paper has been published: https://doi.org/10.1007/s00170-021-07449-w [ABSTRACT FROM AUTHOR]

• Oxide layer forms in the aluminum matrix near the metallurgically bonded interface. • The fraction of Si and AlFeSi phase evolves complementarily near the interface. • Low age hardening ability near the interface was found with its origin analyzed. Al-7Si-0.6Mg/Fe bimetal was prepared by compound casting; it was heat-treated to investigate the age-hardening behavior of the aluminum matrix near the interface. Metallurgical bonding of the interface is accompanied by the formation of an oxide layer in the aluminum matrix near the interface. The intermetallic layer grows at the expense of the Si and Mg 2 Si particles within the diffusion reach during the solution heat treatment. The fraction of both AlFeSi and Si is low near the interface, the fraction of the AlFeSi phase is the highest just outside the oxide layer and decreases with increasing distance from the interface, which is accompanied by the increase in the fraction of the Si phase. The presence of the continuous oxide layer decreases the age-hardening ability and bonding strength of the aluminum matrix near the bimetal interface; such a negative effect is mitigated by the broken oxide layer. The lower age-hardening ability is resulted from the segregation of the Mg element to the oxide layer. [ABSTRACT FROM AUTHOR]

The direct thermal method is used for the creation of globular microstructures suitable for semi-solid metal forming. In this paper, both simulation and experimental results using direct thermal method are presented. ProCAST® software was used to estimate temperature distribution inside the aluminum billet. In validation work, molten aluminum A356 was poured into metallic copper tube molds and cooled down to the semi-solid temperature before being quenched in water at room temperature. The effect of pouring temperatures of 630°C, 650°C, 665°C, 680°C and holding times of 45s and 60s on the microstructure of aluminum A356 alloy were investigated. The simulation results showed that the average temperature rate within the copper mold, from initial pouring temperature to just before quenching, was approximately 1°C/s. Examination of the solidified microstructures showed that the microstructure was more spherical when lower pouring temperatures and holding periods were used. From the micrographs it was found that the most globular and smallest structures were achieved at processing parameters of 630°C and 45s. [ABSTRACT FROM PUBLISHER]

• Hot gas free bulging test was proposed to evaluate the biaxial formability post solution heat treatment in HFQ process. • The temperature and pressurizing rate dependences of limiting bulging and uniform deformation abilities were clarified. • Excellent formability and thickness uniformity can be obtained simultaneously under rapid pressurizing conditions. • The deformation mechanism under biaxial tension state was revealed by microstructure observation. [Display omitted] Hot forming-quenching integrated process was developed to fabricate aluminum alloy complex-shaped components by taking advantage of the enhanced formability at the temperature close to solution temperature. But, it is very difficult to evaluate the formability under biaxial tension state and continuous cooling conditions. A measuring method was proposed to evaluate the biaxial formability by combining solution heat treatment and hot gas free bulging test. The effects of temperature and pressurizing rate on the bulging ability and thickness uniformity of an Al-Mg-Si alloy sheet were clarified. The deformation mechanism was revealed by microstructure observation. It is found that excellent formability can be obtained under the high temperature with less heat loss and rapid pressurizing conditions. The limiting strain under rapid pressurizing condition decreases from 1.13 at 500 ℃ to 0.81 at 400 ℃, being at a high strain level. Thickness uniformity can be obviously improved at a higher deformation temperature accompanied by rapid loading due to the remarkable strain-rate hardening effect. Dynamic recovery is the main restoration mechanism, resulting in numerous substructures and unchanged grain size. The obtained biaxial formability closer to actual forming condition can provide fundamental guidance for forming aluminum alloy complex-shaped component by hot forming-quenching integrated process. [ABSTRACT FROM AUTHOR]

The need to produce grain-coarsening resistant, micron-grained (< ∼ 10–20 µm) material, which is also not prone to cavitation, for superplastic forming increases the cost of the starting material. Friction stir processing is an evolving technique, which refines the microstructure of materials and thereby improves their mechanical properties and formability characteristics. In this article, aluminum alloy AA6063-T6 temper was subjected to multiple-single-stir friction stir processing (5 passes) and was subjected to different gas pressures and forming temperatures to form a hemispherical dome. The friction stir-processed sheets could be formed successfully whereas the parent material could not be. Theoretical modeling using Matlab v 7.0 and finite element modeling using Abaqus v 6.4.8 led to results which were in good agreement with the experimental findings. [ABSTRACT FROM PUBLISHER]

The nature of newly forming lamellar band boundaries was investigated in accumulative roll bonded aluminum. These boundaries initiate as low angle interfaces parallel to the existing lamellar band boundaries irrespective of the crystallographic orientation of the parent lamellar band. The transverse directions of the divided segments were found to rotate at an angle equal to the degree of misorientation between segments. Such a phenomenon is not sustained when the boundaries become high angle. [Copyright &y& Elsevier]

Abstract: A new model on the evolution of dislocation structure of cell forming metals and alloys through severe plastic deformation is presented. Following previous approaches, the model considers a cellular dislocation structure consisted of two phases: cell interiors and cell walls. The model distinguishes edge and screw dislocations in terms of three categories: mobile dislocations, immobile dislocations in cell interiors and immobile dislocations in cell walls. Then considering physical and geometrical assumptions for each dislocation category, an evolutional law is derived, based on some dislocation interaction mechanisms such as dislocation generation, annihilation, locking and migration. The model is applied on a severe plastic deformation process of aluminum called constrained groove pressing. The outputs of model are detailed description about dislocation densities (densities of edge and screw dislocations of all three mentioned categories) and cell size evolutions during deformation. To verify the results of modeling, X-ray diffraction patterns of deformed samples are analyzed. The achieved dislocation densities and cell sizes from the X-ray tests are compared with that achieved from the model and a good agreement is obtained. [ABSTRACT FROM AUTHOR]

Abstract: By using spray forming technique Fe-contained hypereutectic Al–Si alloys were prepared with different Mn/Cr additions for the study of their effects on the microstructures. The results show that adding 2wt.% Mn/Cr separately can strikingly refine the Fe-bearing phase in spray-formed Al–25Si–5Fe–3Cu (wt.%) alloy into quantities of fine, uniformly distributed granular α-Al(Fe,Mn/Cr)Si phase, and Cr is more effective. But some short-plate Fe-bearing phases still exist in the spray-formed Al–Si alloys. Then, combined addition of Mn and Cr transforms these short-plate Fe-bearing phases into fine, granular α-Al(Fe,Mn,Cr)Si phase, promoting the appearance of almost single α-Al(Fe,Mn,Cr)Si phase in the spray-formed Al–Si alloys. Two mechanisms are proposed to elucidate the formation of α-Al(Fe,TM)Si phase (TM=Mn/Cr/(Mn+Cr)) during the solidification process: (1) transformed from metastable δ-Al(Fe,TM)Si phase in Mn/(Mn+Cr)-added alloys or (2) precipitated from liquids directly in Cr-containing alloys. Because the strong interactions and isomorphic substitution among different TM elements, the metastable δ-Al(Fe,TM)Si phase (clusters) can be precipitated from the liquids and transformed into stable α-Al(Fe,Mn,Cr)Si phase in Mn- or (Mn+Cr)-added alloys. The stable α-Al(Fe,Cr)Si phase can precipitate directly from the liquids because no metastable ternary intermetallics exist in Al–Cr–Si system and can be transformed into stable α-AlCrSi phase. Also the high segregation temperature of Cr in liquid Al melts promotes the microsegregation of Cr and formation of (AlCrSi) clusters/intermetallics in Cr-added alloys. As a result, both metastable δ-Al(Fe,TM)Si phase (clusters) and stable α-Al(Fe,TM)Si phase (clusters) can be present in (Mn+Cr)-added alloys. With further solidification, these clusters become the nucleation sites and grow up unceasingly. The coexistence of the nucleus of δ-Al(Fe,TM)Si and α-Al(Fe,TM)Si phases in the liquid alloys can induce the simultaneous presence of these two phases in atomized droplets or particles. With continuous deposition of atomized droplets or particles, the appearance of mushy zone on the surface of preforms promotes the transformation of metastable δ-Al(Fe,TM)Si phase into stable α-Al(Fe,TM)Si phase, especially inducing the ideal case featured by single α-Al(Fe,TM)Si phase. It is concluded that the improvements of the thermal stability of present hypereutectic Al–Si alloys are attributed to the increment of solidus temperatures and the presence of the granular α-Al(Fe,TM)Si phase with high dissolution temperature induced by TM addition. [Copyright &y& Elsevier]

Abstract: In the present study, a novel thixoforming process for semi-solid deformation of A356 aluminum alloy is introduced using a continuous hot deformation process to the temperature being lower than the eutectic temperature of the alloy. A new hypothesis was introduced and the deformation mechanism of the alloy was investigated using the presented hypothesis. Microstructure and fracture surfaces of thixoformed samples were investigated using image analyzing technique and scanning electron microscopy. Obtained results indicated that this novel thixoforming process produces fine and compact silicon particles, dispersed uniformly in the microstructure of the alloy, compared to those produced by conventional thixoforming and gravity-cast processes with large and integrated morphology for silicon particles. The production stages of these silicon particles in this process were well documented by mentioned hypothesis. In order to investigate the effect of this novel process on mechanical properties of A356 alloy, tensile tests were conducted on produced samples. It was found that morphological changes of silicon particles as well as increasing the density ratio of samples in this process have a remarkable effect on enhancing the mechanical properties of produced alloy in comparison with other production routes. A new combination parameter, i.e. silicon density ratio (SDR) index was introduced. This parameter correlates the mechanical properties of samples to morphological properties of silicon particles and density ratio of them. Results of the study also indicated that samples with low SDR index have superior mechanical properties and consequently intergranular fracture mode. [Copyright &y& Elsevier]

Abstract: In this paper laser beam welding (LBW) was used to join Ti–6Al–4V alloy as a pre-forming operation before superplastic deformation (SPF) process. Superplastic deformation behavior of laser welded Ti–6Al–4V alloy was investigated. The results indicated that the welded Ti–6Al–4V alloy had good superplasticity when deformed at temperature range of 870–920°C and strain rate range of 10−3–10−2 s−1, and the elongation was 233–397%. The microstructure observation indicated that dynamic recrystallization happened in the weld bead, and the acicular structure of weld bead was transforming into equiaxed grains during tensile process. [Copyright &y& Elsevier]

Abstract: Single-point incremental forming of thin aluminum foils, which did not require any die and any backing plate, was developed for fabricating customized parts of thin shell miniature objects. Thin aluminum foils were deformed incrementally using a round-tip single point tool on a desktop type of milling machine controlled with a personal computer. It was found that an aluminum foil 12μm thick was much smaller in forming limit than an aluminum foil 50μm thick when a single point tool with a tip radius of 0.5mm was not rotated, but its forming limit was improved greatly by rotating the tool up to 20,000rpm. Measured forming forces revealed that the tool rotation decreases the in-plane forces by approximately 50%. Hydrodynamic lubrication at the interface between a rotating tool and aluminum foil must have had a direct and favorable influence on the forming process, while increasing the forming limit of the thinner foil. It was also found that the optimum stepwise axial feed was found to be around the value of foil thickness. Then, incremental forming of arrays of dots 0.1mm in diameter, miniature pyramids, a miniature car and miniature letters was performed successfully under the optimized conditions at arbitrary positions of 12-μm-thick foils. [Copyright &y& Elsevier]