Search

The microstructure, age-hardening behavior, mechanical properties and texture of extruded Mg-6Gd-2.5Y-0.5Zr alloys with various additions of Nd have been investigated through optical microscopy, x-ray diffraction, scanning electron microscopy, transmission electron microscopy, electron back-scattered diffraction, hardness and tensile tests. The results indicate that the number of second-phase particles in the as-extruded alloys increases (especially with the addition of 1.5 wt.% Nd), and the amount of the strengthening β′ phase in the peak-aged sample initially increases, and then decreases when the content of Nd increases above 1.0 wt.%. The precipitation of second-phase particles in the extrusion process weakens the age strengthening. The peak-aged Mg-6Gd-2.5Y-1Nd-0.5Zr alloy shows a maximum yield strength of 259 MPa and an ultimate tensile strength of 350 MPa, which can be attributed to the finely dispersed strengthening β′ phase. All as-extruded alloys exhibit that (0001) planes are aligned perpendicular to the extrusion direction, and the maximum intensity of the texture increases gradually with Nd addition. [ABSTRACT FROM AUTHOR]

To fabricate components with high performance, the compression behavior and microstructure evolution of a differential pressure casting Mg-8Gd-4Y-Nd-Zr alloy were investigated. The cylindrical samples were compressed at temperatures ranging from 350 °C to 525 °C and strain rates ranging from 0.001 s to 2 s. For the compression at 350 °C, dynamic precipitation occurs and consumes much of the solutes in the matrix, which should be avoided. The recrystallized grain size (d) decreases when the proposed deformation parameter (Z) increases, and the resulting Z-d relationship is established. Finally, a superior deformation process of 500 °C/0.01 s is determined based on the experimental results. Moreover, a plate with an ultimate tensile strength of 413 MPa was fabricated. [ABSTRACT FROM AUTHOR]

Compared with the traditional anodization of aged aluminum alloy, a novel process was carried out by anodic oxidation of solid solution aluminum alloy, followed by aging treatment to optimize the interface's composition and microstructure, under which the thickness, hardness and modulus of the oxidation film wouldn't be influenced and the strength of base materials kept the same. As β" precipitates cannot be formed in the subsequent aging process due to the consumption of Mg on the film-base interface, line defects caused by lattice distortion were avoided. Therefore, the stress concentration point in the fatigue process was reduced, and the fatigue property of the anodized material was improved from 89 MPa to 125 MPa. The anodizing of solid solution aluminum alloy helps the dispersion of Mg in the oxide film, which increases the self-corrosion potential of the oxide film from −0.97 V to −0.32 V and delays the occurrence of pitting corrosion during long-term immersion in 5 wt% NaCl solution. • A novel sequence of anodizing and aging was presented to improve the properties. • Interface characteristics of anodic oxide film under various state were revealed. • Both the fatigue and corrosion properties were improved after the novel treatment. • The reduction of line defects at the interface increases the fatigue limit. [ABSTRACT FROM AUTHOR]

In order to confirm whether the Zener—Hollomon parameter (Z)—recrystallized grain size (d) model obtained from hot compression tests is suitable for the commercial production, the microstructure and mechanical properties of the extruded Mg-8Gd-3Y-0.6Zr alloy plate were investigated. The grain size of the plate has been predicted based on this model. The results indicated that the predicted grain sizes disagree with the measured ones. The static recrystallization should be considered for the center area samples, and the recrystallization mechanism of particle stimulated nucleation (PSN) together with the inhibiting effects caused by precipitated particles should be taken into account for the edge area samples. Precipitation of β phases during extrusion lowered the driving force during ageing, which resulted in the yield strength and ultimate strength of the samples cut from the edge area lower than that of the samples cut from the center area. [ABSTRACT FROM PUBLISHER]

• The effect of twinning and texture on the fatigue properties was studied. • The law of crack propagation during fatigue was studied. • The relationship between grain structure and fatigue resistance was built. • Non-basal planes have better resistance to crack propagation. The fatigue crack propagation behavior of rolled magnesium alloys was studied and compared with as-cast alloys to unravel a relation between the early crack propagation and the fatigue resistance at the microstructural level. Grain structures results indicated that the geometric compatibility of grains and stress component on basal slip planes determine the propagation path of cracks. Twins are usually unfavorable for crack propagation, and the texture changes the stress component distribution in grains under the condition of unchanged loading. Both twins and textures increase the difficulty of crack propagation and improve the fatigue resistance at higher stress level. [ABSTRACT FROM AUTHOR]

An amorphous SiO 2 ceramic coating with a thickness of ∼72 μm is prepared within 13 min in organo-silicon electrolyte, which is stable in strong acid solutions, reducing corrosion current density of 6061 aluminum alloy by 3 orders of magnitude. With the aim to reveal influence of the electrolyte concentration, NaOH content and additive (NaPO 3) 6 on microstructure and corrosion resistance of the coatings, SEM/EDS, XRD, electrochemical tests were used to characterize their thickness, surface and cross-sectional morphology and structure, and corrosion performance prepared by using different electrolytes under the same electric control parameters. The results show that they significantly affect the surface morphology, structure and corrosion resistance of the coatings. Dilution of the electrolyte results in a significant decrease in coating thickness and surface porosity, reduction of NaOH content leads to coating thinning, increased porosity but reduced pore size. Coatings with lower porosity or smaller pore sizes are more effective in resisting corrosive media penetration for long term immersion. Whereas, the additive (NaPO 3) 6 promotes coating thickening, widening of the transition layer, which helpfully improves the corrosion resistance of the coating. [Display omitted] [ABSTRACT FROM AUTHOR]

Low-cost Si was added to Mg-8Gd-4Y-1Nd alloys to improve their ductility. With the Si increased from 0 to 1.0 wt %, the elongation increased from 8.7% to 17.1% for as-extruded Mg-8Gd-4Y-1Nd alloys. Microstructures results indicated that the formation of GdSi and Y 5 Si 3 intermetallic phases increased significantly with the Si addition, which was shown to promote the random orientation of grain structures. As Si works as substitutional atoms in Mg alloys can decrease the first intrinsic stacking faults (I 1 SF) energy, the pyramidal dislocation was activated during deformation, thus the {0001} Mg basal plane deviate from the extrusion direction and alter to random textures. Activating both the pyramidal and basal slip provided more independent slip systems during deformation and caused more stress accumulation, which exceeded the critical shear stress (CRSS) for tensile twinning. The simultaneous activation of the pyramidal slip and tensile induced twinning improved the ductility of the Mg-8Gd-4Y-1Nd-1.0Si alloy. [ABSTRACT FROM AUTHOR]

In this paper, two high Fe containing Al–Mg–Si–Mn–Fe alloys with Mg, Si and Mn modified were prepared, and their microstructures and mechanical properties were comparatively studied with a common applied alloy. Furthermore, the effects of alloying elements on their microstructures and the corresponding strengthening mechanisms were analyzed. It was found that the two Al–Mg–Si–Mn–Fe alloys exhibited good combination of strength and elongation in spite of their high Fe content. When compared with the common applied alloy, the yield strength of the two alloys was increased by 28 MPa and 50 MPa respectively, whereas the elongation was only slightly decreased. The higher strength of the two Al–Mg–Si–Mn–Fe alloys was mainly attributed to precipitation and solid solution strengthening which were substantially caused by the appropriated proportion of Mg and Si. Owing to the appropriate addition of Mn, no β–AlFeSi phases were found in the alloys, and the detriments of Fe were fully eliminated. The submicron scaled α–Al(FeMn)Si phases slightly improved the yield strength because of their contribution to grain refinement and dispersion strengthening. The results of this paper provide a valuable insight into the strengthening and industrial manufacturing of Al–Mg–Si alloys. [ABSTRACT FROM AUTHOR]

Crushing performance is being widely investigated because it is the key performance indicator of the thin-walled beam structure in automobile safety components. In this study, five kinds of ageing state with different yield strengths were prefabricated with a self-developed KHC63 alloy. Using a rectangular tube profile, the physical relationship between crushing properties and mechanical properties, and the structure of the profile, were studied. According to variation characteristics, the crushing curve was divided into four typical stages: elastic stage, bending stage, compaction stage and folding stage. In the elastic stage, the peak load of the component is related to material elasticity and structure elasticity, and the relationship is approximately linear. In the bending stage, the driving factor of plastic hinge deformation is the bending moment, and it is always constant. In the compaction stage, the crushing curve correlates well with the cosine function. In the folding stage, the crushing process begins to lose stability and is hard to predict. The mathematical relationships between force and displacement were established according to the characteristics of each stage, and the calculated results were close to the measured results except for the folding stage. The deviation of the calculated energy absorption from the measured data in the first three stages is only 4.3%, but it is 10.6% in the folding stage. The calculation method used for the first three stages is, therefore, suitable. [ABSTRACT FROM AUTHOR]

Large number density of coarse precipitates were introduced into the Al–Zn–Mg–Cu alloy by interrupted aging and then over-aging at 300 °C. Both the overaged and homogenized samples were isothermal MDFed at 5 × 10−3 s−1 with temperatures ranging from 300 °C to 450 °C to investigate the effect of high number density of precipitates on the microstructural evolutions. The results showed that the precipitates decreased gradually during MDF of overaged samples at 300 °C and 350 °C while they were almost dissolved at 400 °C and 450 °C. And as the result of that the precipitates could pin dislocations during deformation, and much greater grain refinement was achieved during MDF of overaged samples at 300 °C and 350 °C. • Large number of η precipitates were introduced in the Al–Zn–Mg–Cu alloy by interrupt aging and over-aging. • The introduced high density precipitates expanded the temperature range with significant grain refinement. • The introduced high density precipitates accelerated the grain refinement effect during MDF. • The number density of precipitates decreased gradually during isothermal MDF. [ABSTRACT FROM AUTHOR]

The Al 3 Zr particles formed in the Al–Cu–Li–Zr alloy during single and double-step homogenization treatments contributed to various microstructures and mechanical properties during the subsequent thermomechanical treatment. Compared with the single-step homogenization treatment (ST), the double-step homogenization treatment (DT) generated higher density and more uniform distribution of β′ (Al 3 Zr) phases, which makes the alloy retain more substructures and improve the initial strength of solid solution. During the ageing process, Al 3 Zr particles induced the T 1 precipitation in grain interior and the width of PFZ get narrowed. Therefore, the strength and toughness of the DT sample improved in peak aged state compared with that of the ST sample. The peak hardness value of DT sample is 167.8 HV, which is higher than that of ST sample with 153.1 HV. Furthermore, the tensile strength and elongation of the DT sample at peak aged state (521 MPa, 556 MPa and 8.8 %, respectively) are higher than those of the STA sample (492 MPa, 535 MPa and 6.7 %, respectively), and the impact toughness of the DTA sample (13.2 J cm−2) is also higher than those of STA sample (9.1 J cm−2). Strength model showed that more uniform distribution of Al 3 Zr phases and substructures improve the initial strength of solid solution state, which increased by 16 MPa in the DT sample compared with the ST sample. The promotion of T 1 precipitation inducing the strength increased by 18 MPa in the DT sample at the peak aged state compared with that of the ST sample. The increase of elongation and toughness contributed from the oriented grains with finer distribution and higher Schmid factor, less grain boundaries precipitates and narrower PFZ width. [ABSTRACT FROM AUTHOR]

Butt joining of Al-Mg-Si alloys with 6.0 mm in thickness was made with conventional rotational shoulder friction stir welding (RSFSW) and non-rotational shoulder friction stir welding (NRS-FSW) process, respectively, and the resultant mechanism of different shoulders affecting the microstructure and mechanical properties of joint was discussed. A new zone named "triangle zone" (TZ) in the RSFSWed joint was first clearly defined, while the shoulder and pin affected zone (SPAZ) did not exist in the NRS-FSWed joint. The distribution of average grain sizes in each zone of the joints ("M" shape) and the changes in the proportion of high angle grain boundaries (HAGBs) ("W" shape) are unified with the typical "W" shape distribution of microhardness in the joints. Compared to rotational shoulder, the non-rotational shoulder significantly reduced the width of softened area. In particular, the microstructure of the joints by NRS-FSW with triple facets on the pin surface is finer, denser and more homogeneous. The tensile strength coefficient of the joint welded by NRS-FSW and NRS-FSW with the pin of triple facets increased by 2.3% and 11.6%, respectively, compared to the joint welded by RSFSW. Accordingly, the fatigue performances increased by 1.72 times and 3.19 times, respectively. Unlabelled Image • A new zone "triangle zone" in rotational shoulder FSWed joint was first defined. • The characteristic of microhardness and grain size in joint were first unified. • Dynamic recrystallization process in different stages during welding was explained. • A mechanism of material flow of the "upturned phenomenon" in FSW was proposed. [ABSTRACT FROM AUTHOR]

The mechanical properties of Al-Zn-Mg alloys via multi-stage aging treatments were studied to explore the strength-toughness trade-off. The microstructures of aged alloys were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). The results indicated that large numbers of GP zones and some part of η′ phases were formed during the low-temperature (90 °C) aging at the third-stage aging, which consumed considerable solid solubility. This prevents fast growth and coarsening of precipitates at the fourth-stage aging (150 °C). Finally, the mixed precipitation state of mainly η′ phases and some η phases formed. The grain boundary phase grew insignificantly, which is beneficial to decrease the strength gap between intragranular and grain-boundary. The intragranular equilibrium η phase is beneficial to pin the movement of dislocation, which avoids fracture caused by accumulation of dislocations around the large second-phase and on the grain boundaries. Although the strength of materials decreased slightly, the impact toughness of materials significantly increased due to the positive effect of the intragranular equilibrium η phase. Compared with the conventional retrogression and re-aging (RRA) treatment (120 °C/24 h + 185 °C/105min + 120 °C/12 h), the designed four-stage ageing treatment (FSA) (120 °C/24 h + 185 °C/105min + 90 °C/12 h + 150 °C/12 h) resulted in the decrease of tensile strength and yield strength by only 3% and 4%, respectively, but contributed to the increases of elongation and impact toughness by 15% and 17%, respectively. [ABSTRACT FROM AUTHOR]

• The direct observation of corrosion process is performed by EBSD. • The small grains corrode easily. • There is almost no corrosion attack suffered by the largest grain with (10-10) non-basal orientation. • Under the similar grain size condition, the non-basal plane is more vulnerable to corrosion than the basal plane. The influence of grain size and crystal orientation on the corrosion behavior of as-extruded Mg-6Gd-2Y-0.2Zr alloy is investigated by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD). The EBSD system is used to characterize the grain size, crystal orientation and corroded surface. By investigating the corrosion process of as-extruded Mg-6Gd-2Y-0.2 Zr alloy, we can observe that the smaller grains and (10-10)/(11-20) non-basal planes are more susceptible to corrosion in the aggressive corrosion environment. Furthermore, the relationship between the corrosion rate and grain size is connected with the crystal orientation and whether the passivation occurs. [ABSTRACT FROM AUTHOR]

A new ageing treatment method was developed in this work to improve the strength and ductility of Al–Cu–Li alloy. Al–Cu–Li alloy treated via pre-deformation followed by double ageing process (PDA) exhibited excellent yield strength and ultimate tensile strength of 609 and 629 MPa, respectively, while maintaining higher elongation (11.5%). The precipitates in matrix and sub-grains regions indicated that both the PCA (pre-deformation followed by creep ageing) and PDA treatments increased the precipitation number density and yielded refined precipitates (i.e., T 1 and θ′ precipitates) in the matrix due to the dislocations produced by pre-strain. Uniform and fine strengthening precipitates in the matrix are beneficial to increase the strength of the alloy. In addition, eliminating precipitation free zones, reducing the δ′ precipitation and regulating the T 1 precipitates at sub-grain boundaries further promote the plasticity of aged alloys. When this excellent structure is obtained simultaneously, the alloy can obtain high strength while maintaining high elongation. [ABSTRACT FROM AUTHOR]

In this study, the microstructure and corrosion resistance of Mg-6Gd-2Y-χNd-0.2Zr (χ = 0, 0.5, 1 and 1.5 wt%) alloys in extrusion condition are investigated using the correlative microscopic observations, immersion tests and electrochemical measurements. Results show that the addition of Nd can affect the grain size, crystal orientation and secondary phase of the alloys. The corrosion resistance of Mg-6Gd-2Y-χNd-0.2Zr alloys increases with the increase of Nd content from 0% to 0.5 wt%, and then decreases from 0.5 wt% to 1.5 wt%. A minor 0.5 wt% addition of Nd can improve the corrosion resistance of Mg-6Gd-2Y-0.2Zr alloy. The grain size of the four alloys is in a range from 4 μm to 7 μm and the 1.5Nd alloy with the smallest grain has the highest corrosion rate. The highest corrosion resistance of 0.5Nd alloy is attributed to the highest intensity of (0001) basal texture and the less amount of secondary phases. However, the higher fraction of secondary phase is the main reason for the highest corrosion rate of 1.5Nd alloy. Image 1 • A minor addition of Nd can improve the corrosion resistance of Mg-6Gd-2Y-0.2Zr alloys. • The highest corrosion resistance of Mg-6Gd-2Y-0.5Nd-0.2Zr alloy is attributed to the highest (0001) basal texture. • The highest corrosion rate of Mg-6Gd-2Y-1.5Nd-0.2Zr alloy is due to the highest fraction of secondary phase. • The filiform corrosion features are observed in the Mg-6Gd-2Y-1.5Nd-0.2Zr alloy. [ABSTRACT FROM AUTHOR]

An Al-Zn-Mg-Cu alloy was isothermal compressed at temperatures ranging from 300 °C to 450 °C with strain rates ranging from 10−5 s−1 to 10 s−1 to study its deformation and recrystallization behaviors. The evolution of grain structure during the isothermal compression demonstrated that sub-grains found in grain interiors of those deformed with high strain rates from 10−2 s−1 to 10 s−1, were mainly the results of continuous dynamic recrystallization (CDRX), while many recrystallized grains formed at grain boundaries of those deformed with low strain rates from 10−5s−1 to 10−3s−1, were largely believed to be the result of discontinuous dynamic recrystallization (DDRX). Furthermore, two totally different constitutive equations as the result of different dynamic recrystallization mechanisms were proposed. • Two different dynamic recrystallization mechanisms (CDRX and DDRX) occur at different strain rates. • The formation of recrystallized grains at the lower strain rates leads to a rapider decreasing of flow stress. • The activation energy increases when the dynamic recrystallization mechanism changes from CDRX to DDRX. • Two different constitutive equations are constructed at the two different strain rate ranges. [ABSTRACT FROM AUTHOR]

An Al–Zn–Mg–Cu support bracket forging was isothermal precision forged at 400 °C with speeds of 0.1 mm/s, 0.01 mm/s and transient speed changing from 1 mm/s to 0.01 mm/s by finite element simulation and experiment. The stress concentration at high ribs of the simulated forging corresponded to the defects of under-filling and folding of the experimental forging at the speed of 0.1 mm/s while none defects appeared at the speeds of 0.01 mm/s and transient speed. Besides, not only less time was used to finish forging but also much more fine grains and sub-grains were formed in the forging that precision forged at the transient speed as compared with that at the speed of 0.01 mm/s, which leaded to the higher mechanical properties. Furthermore, the resistance to IGC was much better in the forging that precision forged at the transient speed for the particles η distributed along the grain boundaries was much wider. [ABSTRACT FROM AUTHOR]

In this study, the tensile deformation of the AA5083 aluminum alloy at elevated temperatures was elucidated via thermo–mechanical tests conducted at various temperatures (553–793 K) and strain rates (0.01–10 s−1). Furthermore, the effects of the deformation parameter on the flow stress, microstructure evolution, fracture characteristics, and underlying mechanisms were discussed, and a new phenomenological fracture damage model was proposed to predicate the fracture strain. The results were as follows. Increasing the temperature or decreasing the strain rate reduced the flow stress, increased the elongation, and accentuated the intergranular fracture characteristic of the alloy. Under the tested conditions, dislocation movement and ductile fracture were observed to be the primary deformation mechanism and fracture mechanism, respectively. Dynamic recrystallization was enhanced by increasing the temperature or the strain rate. Under the smallest strain rate (0.01 s−1), the elongation of the material drastically decreased at a deformation temperature of 793 K owing to grain-boundary weakening. The fracture damage predicted using the fracture damage model agreed well with the experimental results, with a maximum relative error of only 5.23%. [ABSTRACT FROM AUTHOR]

An amorphous silica ceramic coating with thicknesses exceeding 100 μm (adjustable thickness) was prepared on 6061 aluminum alloy by plasma electrolytic oxidation in organosilicon electrolyte. To investigate its formation process and structural characteristics, the digital microscope system, SEM, X-ray diffractometer and microhardness tester were used to characterize morphology, structure and hardness at different voltages and times. The results show that it thickens rapidly after the voltage is raised to 480–500 V, and its surface begins to roughen and the micropores appear to enlarge. In organosilicon electrolyte, unlike conventional electrolytes, the coarse Al–Fe–Si second phase particles in the matrix do not negatively affect the PEO treatment. The produced coatings increase the surface hardness of 6061 aluminum alloy by more than 6 times and are stable in common acid solutions such as HCl and HNO 3. Furthermore, the energy consumption rate of PEO treatment can be significantly reduced to 0.24–0.31 kJ cm−2 μm−1. The potentiodynamic polarization curves measured in 1 mol L−1 HCl solution show that the ceramic coating can reduce the corrosion current density of 6061 aluminum alloy from 3.74 × 10−2 A cm−2 to 2.24 × 10−6 A cm−2. And its corrosion resistance can be further improved by adding a 2nd low-voltage PEO treatment. [Display omitted] • Thickness of coating can be adjusted over a wide range. • Amorphous silica ceramic coating increase surface hardness more than 6 times. • Coarse Al–Fe–Si second phase particles won't bring extra void, hole or crack at the interface. • A lower energy consumption rate of PEO coating is 0.24–0.31 kJ cm−2 μm−1. • Corrosion current density reduced from 3.74 × 10−2 to 2.24 × 10−6 A cm−2 in 1 mol L−1 HCl solution. [ABSTRACT FROM AUTHOR]

This study investigates the impact of hard coatings on the fatigue properties of pure titanium. A specialized fatigue test which ensured machine equivalence was conducted to compare the fatigue behavior of coated and uncoated metals. The findings reveal that the application of coatings adversely affects the fatigue properties of pure titanium due to stress concentration from the coating, which accelerates fatigue crack propagation within the substrate material. Notably, zigzag fatigue cracks at the interface between the coating and substrate and multiple micro-cracks initiated within the coating are found. [ABSTRACT FROM AUTHOR]

Plasma electrolytic oxidation (PEO) was performed on 6061 aluminum alloy in organosilicon electrolyte using a stepwise constant potential control method for 23 min. The resulting coating was a sponge-like structured amorphous silica ceramic with a thickness of about 130 μm. Its exceptional wear resistance was attributed to the high hardness of the silica ceramic and the low elastic modulus of the sponge-like structure. The corrosion resistance was enhanced by a dense layer of approximately 2 μm between the coating and the substrate. Impressively, the indentation depth of the PEO coating during nano-indentation tests was only 50–60% of that of 6061 aluminium alloy under varying loads, while the recovery depth of the PEO coating after unloading was 2.5–3.1 times greater than that of 6061 aluminium alloy. Due to its special composition and structure, the PEO coating caused serious wear to the high hardness Si 3 N 4 friction balls during the friction and wear test. In the electrochemical tests, the coating reduced the corrosion current density from 1.056 × 10−5A·cm−2 to 1.239 × 10−7A·cm−2, while extending the passivation region from 0.322 V to 1.032 V. [Display omitted] • The TEOS solution used as the PEO electrolyte. • A sponge-like structured amorphous silica ceramic coating with high hardness and low elastic modulus. • High energy field activates O and Si to diffuse into the matrix to form a dense layer. • Stepwise increasing potentiostatic method achieves continuous and rapid thickening of coating. [ABSTRACT FROM AUTHOR]

To elucidate the effect of solution temperature on microstructures and mechanical properties of the Al-Cu-Li-Sc alloy, the evolution of the second phase and precipitates were analyzed to reveal the strength contribution by dissolving Cu-enriched second phases. It is demonstrated that the diffusion rate of the Cu atom in Cu-enriched second phases, mainly Sc-containing θ (Al 2 Cu) phases, increased with solution treatment temperature, which induced more T 1 (Al 2 CuLi) precipitates formed during the aging process. More 10 at. % Cu atoms in second phases could dissolve into the Al matrix with the solution temperature increased from 490 °C to 520 °C, and these Cu-enriched second phases transformed into near equilibrium Sc-containing θ phases. Increasing the Cu atomic concentration in Al solid solution reduced GPB zones and inhibited δ′ (Al 3 Li) phases, thus improving the precipitation kinetics of the T 1 phase. Less δ′ phase was observed in the sample at peak aging with a solution treatment at 520 °C, and the T 1 phase was dominant. A clear improvement in the peak-aging hardness by 15.5% and yield strength by 19.1% of the sample after solution-treated at 520 °C compared with 490 °C. • The effect of solution temperature on subsequent aging behaviors has been studied. • The diffusion behavior of Cu atoms in the second phase is discussed. • Increasing of Cu atomic concentration in the Al solid solution promotes the precipitation kinetics of the T 1 phase. • Reducing GPB zones and inhibiting δ′ phases, significantly increasing the strength contribution of T 1 phases. [ABSTRACT FROM AUTHOR]

The anisotropic of microstructure for additively manufactured Al alloys is attributed to sharp temperature gradient during laser melting, resulting in anisotropy of mechanical properties. The correlation of grain orientation, size and aspect ratio on mechanical properties were investigated using in-situ EBSD tensile method on selective laser melting Al–Mn-Sc alloys in longitudinal section and cross section. The lattice rotation behavior and the effects of grain orientation, grain size and aspect ratio on mechanical anisotropy were explored. The predominant <001> orientation of the columnar crystals in the longitudinal section and the <102 > and <101> orientation that dominates the equiaxed crystals in the cross-section had a certain influence on the anisotropy of mechanical properties. The grains with different shapes and sizes exhibited different rotation behavior, and lattice rotation of equiaxed crystals with smaller grain sizes was more complex. By introducing anisotropy coefficients (K a), the anisotropy sensitivity to grain orientations was revealed. Based on the anisotropy coefficient, grain size and aspect ratio, the mechanical anisotropy in both directions was accurately predicted. [ABSTRACT FROM AUTHOR]

Al-air batteries have become one of the most potential candidates in industrial application. In this study, the influence of Mg, Sn and Ga on the electrochemical behavior and anode property of the Al-Sb alloy is investigated in detail. The single addition of Mg increases the discharge activity and suppresses the hydrogen evolution corrosion, improving the anode property of the Al-Sb alloy. The Al-0.3Mg-0.05Sb alloy presents high specific capacity of 2881.8 mAh∙g−1, outstanding anode utilization of 96.71 % and energy density of 2356.5 mWh∙g−1 at 80 mA∙cm−2. This is because Sb-rich phases enhance the uniform dissolution of the grain boundary and improve the corrosion resistance. Simultaneously adding Mg and Sn improves the energy density of the Al-Sb alloy at high current density. The Al-Sb alloy presents the highest energy density at 80 mA∙cm−2 by simultaneous addition of Mg, Sn and Ga. But the aggravating hydrogen evolution corrosion and serious intergranular corrosion lead to obvious decrease of the specific capacity and anode utilization of the Al-Sb alloy, which is attributed to excessive precipitates and segregation of Ga along the grain boundary. [Display omitted] • Adding Mg, Sn and Ga promotes the precipitation of the phases of the Al-Sb alloy. • Adding Mg reduces the hydrogen evolution reaction rate of the Al-Sb alloy. • Simultaneous addition of Mg and Sn (and Ga) decreases the corrosion resistance. • The Al-Mg-Sb alloy shows high anode performance at 80∙mA cm−2. [ABSTRACT FROM AUTHOR]

An austenite aging steel coating was prepared by laser cladding on H13 steel in order to overcome the poor thermal stability and high-temperature wear resistance of the latter. The microstructure, element and phase distribution of the austenite aging steel coating were investigated by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM), and recrystallization were determined by quasi-in-situ EBSD. High temperature wear tests for the austenite aging steel coating and H13 steel were performed on a high temperature pin-on-disk friction and wear tester, and their wear resistance was comparatively evaluated. The austenite aging steel coating was dominated by γ-Fe as matrix phase, while micrometer-grade NiAl and nano-scale Ni 3 Ti existed as strengthening phases. These fine particles existing in the grain boundary of the coating could effectively improve the recrystallization resistance and thermal stability, which was confirmed by quasi-in-situ EBSD and thermal stability tests. Owing to such superior thermal stability, oxidative mild wear prevailed for the austenite aging steel coating in most of sliding conditions except for 600 °C and 150 N, where a mild-to-severe wear transition of oxidative wear occurred. In particular, the plastic extrusion wear of H13 steel at 600 °C and 150 N was impeded due to the existence of laser-cladded austenite aging steel coating. • An austenite aging steel coating was deposited on H13 steel by laser cladding to improve high temperature wear resistance. • The superior thermal stability of the coating played a positive role in hightemperature wear resistance. • The microstructure stability and wear mechanisms of the coating were exploredat elevated-temperature. [ABSTRACT FROM AUTHOR]

Precipitation strengthening and strain hardening after pre-deformation in low Mg Al–Cu–Li alloys dominated by T 1 phases have been widely studied in recent years due to their excellent mechanical properties. In this study, the aging precipitation behavior and the associated strengthening mechanisms caused by the increasing dislocation density in high Mg Al–Cu–Li alloys were systematically studied. The results showed that the dislocation density change along with the degree of the pre-stretching as well as the precipitation behavior, that is the pre-stretched methods inhibit the development of GPB zones and reduce the total precipitation of T 1 phases to promote the development of S phases. Finally, the fraction of recrystallized zones decreases from 59.3% to 2.8% while the average KAM value increases from 0.62 to 1.40, and the yield strength increases from 500 MPa to 620 MPa. The overall precipitation strengthening increment in the case of multi-phase coexistence is essentially independent of dislocation density, which is mainly a result of the decrease in the strengthening increment for T 1 phases is compensated by the strengthening increment for S phases. Our study is expected to provide theoretical contributions to the development of high-strength and high-toughness Al–Cu–Li alloys. [ABSTRACT FROM AUTHOR]

Al-Cu-Li alloys are used extensively in the aerospace manufacturing industry for their outstanding properties, however, the addition of trace Sc elements will form high-temperature insoluble (Cu, Sc)-containing phases during homogenization leads to a decrease in age-strengthening, and there is a limited investigation on how to overcome this unfavorable factor. In this work, the effects of plastic deformation coupled with heat treatment on the microstructure and mechanical properties of Sc-containing Al-Cu-Li alloy were systematically investigated by using age-hardening curves and room-temperature tensile tests combined with characterization by TEM, EBSD, and SEM/EDS. The results show that plastic deformation before high-temperature treatment fragments and promotes the dissolution of coarse phases, reduces the development of (Cu, Sc)-containing enriched phases, and simultaneously increases the content of Cu atoms within the Al matrix. Among all precipitates (GPB zones, S phases, T 1 phases) after T6 aging, T 1 phases act as the dominant strengthening phase of the alloy. At the same time, we found that the decrease in the Cu-containing residual phase after solid solution treatment will result in a remarkably increasing number density and volume fraction of T 1 phases at the peak aging. In a word, we obtain a good strength-ductility trade-off (the yield strength is ∼500 MPa while maintaining ∼10% elongation) Al-Cu-Li alloy with Sc element by optimizing the distribution of Cu elements and modulating the aging precipitation behavior. Our proposed process is expected to provide an experimental and theoretical guide toward the development of Al-Cu-Li alloys with superior properties. • The effect of homogenization treatment on the subsequent precipitation behavior of Sc-containing Al-Cu-Li alloys is studied. • A new strategy to improve the mechanical properties of Sc-containing Al-Cu-Li alloys is evaluated. • Plastic deformation before high-temperature treatment reduces the formation of (Cu, Sc)-containing enriched phases. • Reducing the formation of (Cu, Sc)-containing enriched phases, significantly increasing the precipitation strengthening. [ABSTRACT FROM AUTHOR]

The intergranular corrosion (IGC) behavior of an extruded 6005A alloy profile with the coexisting of peripheral coarse grain (PCG) structure and partial recrystallized grain (PRG) structure was investigated by using an accelerated corrosion test, electrochemical impedance spectroscopy and a quasi in situ examination of IGC process. PCG structure was found to have a unique IGC behavior that pitting corrosion and subsequent IGC are less severe and will not be transformed into intragranular corrosion as they were found in PRG structure. Microstructure characterization reveals that the microstructural differences in grain boundary precipitates, primary α-AlFeMnSi intermetallic particles and grain characteristic between PCG structure and PRG structure are the reason for these phenomena. Further analysis indicates that the grain boundaries decorated with more AlFeMnSi particles and Q phase precipitates are more sensitive to corrosion, where Q phase precipitates are the primary cathodes and the most important factor affecting IGC; AlFeMnSi particles are supposed to initiate pitting corrosion since they are dissolved as anodes in the early stage of corrosion. With the development of corrosion, they are transformed into cathodes and become the bridges of IGC propagation by connecting the Q phase precipitates at grain boundary. In addition, grain characteristic was also found to have great effects on IGC. With the decrease in grain size and the increase in the frequency of high-angle grain boundaries and the dislocation density, corrosion becomes more severe and more likely to be transformed into intragranular corrosion. [ABSTRACT FROM AUTHOR]

In the present study, the influence of Zn content on the microstructure and mechanical properties of the Al-Mg-Si alloy is systematically investigated. The results show that the precipitation sequence within the grains of the alloy does not change when Zn content does not exceed 2.0 wt%. The intragranular precipitates are mainly composed of β" precipitates with a small amount of η' precipitates when Zn content reaches 4.0 wt.%. Zn addition does not affect the precipitation sequence along the grain boundaries of the alloy when Zn content does not exceed 1.0 wt.%. But the grain boundary precipitates (GBPs) transform into Zn-rich phases when Zn content increases to 2.0 wt.%. The strength of the alloy firstly gradually improves and then reduces when Zn content increases to 2.0 wt.%. This is mainly due to the effect of Zn content on the distribution of the intragranular precipitates. The strength of the alloy significantly enhances again as a result of the increase of the number density of β" precipitates and the formation of η' precipitates when Zn content reaches 4.0 wt%. [Display omitted] • Zn addition promotes the precipitation behavior of the intragranular precipitates. • The size and type of the GBPs change with the variation of Zn content in the alloy. • Zn content has great effect on the PFZ width. • Zn addition improves the strength mainly due to the high number density of the intragranular precipitates. [ABSTRACT FROM AUTHOR]

Different ageing treatment process was conducted to improve the mechanical properties of 6082 Al alloy. Tensile results show that as compared to the T6 sample, the ultimate tensile strength, yield strength and elongation of the T6I6 sample increase by 3.2 %, 3.5 %, and 47.3 %, respectively, the ultimate tensile strength, yield strength and elongation of the RD+T6I6 sample increase by 12.9 %, 11.8 % and 12.5 %, respectively. Microstructural results reveal that holding at 65 ºC for 336 h after pre-ageing promotes the formation of GP zones and stimulates the transformation of GP zones into β" precipitates during subsequent ageing at higher temperature. The introducing of the asymmetric rolling deformation after pre-ageing can reduce the average grain size, induce high-density dislocations and increase the average Taylor factor (M) due to the increasing of S and Brass texture. The dislocations have a good effect on the formation of fine β" precipitates during subsequent ageing. This microstructure is responsible for the improvement of the mechanical properties. [Display omitted] ● The T6I6 significantly increases the El and the RD+T6I6 obviously enhances the strength. ● The holding aging promotes the formation of GP zones. ● The asymmetric rolling deformation can reduce the average grain size. ● The asymmetric rolling deformation can increase deformation texture. [ABSTRACT FROM AUTHOR]

Abstract: The modification effect of gadolinium (Gd) on Mg2Si in the hypereutectic Mg–3wt.% Si alloy has been investigated using optical microscope, scanning electron microscope, X-ray diffraction and hardness measurements. The results indicate that the morphology of the primary Mg2Si is changed from coarse dendrite into fine polygon with the increasing Gd content. The average size of the primary Mg2Si significantly decreases with increasing Gd content up to 1.0wt.%, and then slowly increases. Interestingly, when the Gd content is increased to 4.0 and 8.0wt.%, the primary and eutectic Mg2Si evidently decrease and even disappear. The modification and refinement of the primary Mg2Si is mainly attributed to the poisoning effect. The GdMg2 phase in the primary Mg2Si is obviously coarsened as the Gd content exceeds 2.0wt.%. While the decrease and disappearance of the primary and eutectic Mg2Si are ascribed to the formation of vast GdSi compound. Therefore, it is reasonable to conclude that proper Gd (1.0wt.%) addition can effectively modify and refine the primary Mg2Si. [Copyright &y& Elsevier]

The effect of dislocation in stress aged Al–Cu alloys has barely been discussed as less observation results were reported. In this work, Al–4Cu single crystal was applied 40 MPa compressive stress along [3, 2, 25] direction during ageing to study the precipitates distribution. Scanning transmission electron microscopy (STEM) and high-resolution transition electron microscopy (HRTEM) images from [010] and [100] axes were conducted to characterize the distribution and size of θ precipitates. The results indicated that oversize θ′ precipitates grew preferentially along four edge dislocations b1 (1, −1 1)[0 1 1], b2 (1 1 1)[0,-1,1], b3 (1 1 1)[-1,0,1] and b4 (−1 1 1)[1 0 1]. As dislocations induced the precipitation of (0 1 0) θ′ and (1 0 0) θ′ , the stress orienting effect degree of three θ′ variants is not the calculated result 12.5 : 1: 1.5 but the observation result 3.6 : 1: 1.1. The low stress (40 MPa) induced dislocations during stress ageing inhibited the stress induced preferentially oriented (0 0 1) θ′ , providing new idea to decrease the anisotropy of metal products manufactured by creep age forming. Image 1 • Al–4Cu alloy single crystal was used to study the effect of stress ageing on precipitation. • The orienting degree of three θ′ variants was described quantitatively. • The large θ′ variants distributed densely in dislocation tubes. • The stress orienting effect degree of three θ′ variants were calculated. • The stress orienting effect on (0 0 1) θ′ were partially inhibited by edge dislocations. [ABSTRACT FROM AUTHOR]