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The special wettability of superhydrophobic aluminum alloys has a broad applied foreground in important industrial fields, such as aviation, automobiles, and ships. However, the microstructures of superhydrophobic surfaces are easily destroyed, causing them to lose superhydrophobicity, which seriously restricts the application of superhydrophobic surfaces. To solve this problem, we developed a simple and low-cost fabrication method by the blasting and chemical deposition of Ni and P to process robust micro/nano-composite structures on an aluminum alloy material and then obtained a superhydrophobic nickel–phosphorus–aluminum surface (SHP-NiP-Al) with a water contact angle of 163° and a water rolling angle of 3° through low surface energy modification. The prepared SHP-NiP-Al had an excellent self-cleaning performance and antifouling property. In addition, it showed great mechanical robustness and chemical stability performance in the sand impact, blade scratch, and acid/base solution tests. It also demonstrated good corrosion resistance performance. Electrochemical corrosion tests indicated that the corrosion resistance of SHP-NiP-Al was better than that of the original aluminum. Moreover, SHP-NiP-Al could collect the water from the fog environment. This method is helpful for the practical use of superhydrophobic aluminum alloy surfaces. [ABSTRACT FROM AUTHOR]

Abstract: The effects of the pre-stretching and ageing on the microstructure, strength and fracture toughness of the 7050 aluminum alloy were investigated by means of optical microscopy, scanning electron microscopy, transmission electron microscopy, tensile test and the plane-strain fracture toughness test. The results indicate that the peak aged 7050 aluminum alloy possesses a higher strength, but its fracture toughness is poor. The high temperature and a subsequent low temperature ageing improve the fracture toughness by 8% while the strength is decreased by 3.5%. The fracture toughness of the over aged 7050 aluminum alloy is enhanced by 29% with a decrease in the strength of 7%. The retrogression and reaging provides an optimum combination of the strength and fracture toughness, which improves the fracture toughness by 17% without sacrificing the strength. After the pre-stretching, the precipitates within grains become coarse for all the ageing tempers which results in a lower strength. While the strength difference between the matrix and the grain boundary become lower and the area fraction of the grain boundary precipitates become smaller, leading to the higher fracture toughness. [Copyright &y& Elsevier]

The influence of high strain rate on the precipitate microstructure in impacted aluminum alloy was revealed by transmission electron microscopy. The estimated aspect ratio and the area fraction of θ′ precipitate in impacted aluminum alloy specimens were not dramatically changed until impact testing at 5730s−1 or higher at ambient temperature although the hardness of specimens impacted at 667–7050s−1 was decreased. High strain rates are thus a simple way to lower the transformation temperature of θ′ phase in impacted aluminum alloy. [Copyright &y& Elsevier]

The effect of different precipitate microstructures obtained by different heat treatments on fatigue behavior of 7020 aluminum alloy was investigated. The fine Guinier Preston I (GPI) zones in the under-aged alloy can be repeatedly sheared by dislocations produced in cyclic loading, making the fatigue crack initiate difficultly and fatigue crack path propagate tortuously. Fatigue strength and fatigue crack propagation resistance of the alloy with shearable precipitates are much higher than those of the alloy with unshearable precipitates. The peak-aged alloy with continuous grain boundary precipitate (GBP) and narrow precipitate free zone (PFZ) is prone to initiate fatigue cracks and reduce fatigue strength. With the growth of unshearable precipitates, the fatigue strength of the alloy firstly increases and then decreases. Precipitates with moderate size in the over-aged alloy improve the roughness-induced crack closure (RICC) effect. Soft matrix with appropriate width between the precipitates can promote the slip reversibility and relax the crack tip stress. The fatigue strength of the moderately over-aged alloy reaches to 122.1 MPa at 107 cycles of loading, and the fatigue crack growth rate (FCGR) is 35.6% slower than that of the peak-aged alloy at ΔK of 10 MPa·m1/2. [ABSTRACT FROM AUTHOR]

Abstract: Dynamic properties of 2519A aluminum alloy processed by interrupted aging are assessed in this work. At strain rate of 6900s−1, the dynamic yield strength and absorption energy of this material are up to 690.9MPa and 335.5MJ/m3, respectively. Denser and finer θ′ precipitates contribute to these enhancements. [Copyright &y& Elsevier]

Abstract: According to recent researches on the strengthening response of aged aluminum alloys, a unified constitutive model has been developed for creep age forming of heat-treatable strengthening aluminum alloys containing plate or rod shaped precipitates. The description of the microstructure evolution has been introduced into this model, including the dislocation density, the size, volume fraction and aspect ratio of precipitates, which correlate with the strengthening response in the creep aging process. Then the yield strength, which could reflect the comprehensive strengthening response of the material, the applied stress and the creep strain constitute the constitutive relation. The introduction of the temperature variable renders this model suitable for different aging temperature. The static aging part of this model was proved to be in good agreement with the evolving character of precipitation and strengthening response. Furthermore, a multi-step fitting process has been applied to determine the material constants in the constitutive equations for an aluminum alloy by experimental results, meanwhile, the computed results tally well with the experimental data. [Copyright &y& Elsevier]

Abstract: The influence of cooling rate after homogenization on the flow behavior of aluminum alloy 7050 was investigated by hot compression testing over a range of temperatures, 300–450°C, with strain rates of 0.001–1s−1. It was found that water-quenched alloy exhibited higher flow stresses than furnace-cooled alloy, and the difference in the peak stress decreased with temperature increasing. The strain-hardening rate during the initial stage of hot deformation was higher for water-quenched alloy than furnace-cooled alloy. During deformation at low temperatures with the lowest strain rate, flow softening was observed for both alloys, but this effect was more significant for the water-quenched alloy. The activation energy of the water-quenched alloy was more than twice higher than that of the furnace-cooled alloy. With strain increasing, the activation energy decreased for both alloys. These phenomena were explained based on dynamic precipitation and coarsening during hot deformation according to microstructure examination. [Copyright &y& Elsevier]

Abstract Some specific corrosion environments require Al-Mg-Si aluminum alloy extrusions to have superior corrosion resistance. In order to clarify its corrosion mechanism and enhance its corrosion resistance, the corrosion occurrence, propagation path and corrosion morphology of the alloy was characterized by scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). It was found that the corrosion of the alloy first occurred at the grain boundary. Then the grain boundary becomes the origin of the crystallographic pitting after being attacked, and Mg in the Mg 5 Si 6 phase inside the grain is preferentially corroded by precipitate free zone (PFZ), so that the corrosion propagates into the interior of the grain. The morphology of crystallographic pitting presents a regular step-like planes and is always propagated parallel to the direction of {100} Al in the grain. Further, the corroded Mg 5 Si 6 precipitates becomes cathodes in the local area at a later stage, leading to the regular step-like planes has been transformed into dimple-like appearances. Highlights • The grain boundary is the origin of the crystallographic pitting after being attacked. • The morphology of crystallographic pitting presents a regular step-like planes. • The crystallographic pitting is always propagated parallel to the direction of {100} Al in the grain. [ABSTRACT FROM AUTHOR]

The effect of Zener-Hollomon (Z) parameter on quench sensitivity of 7085 aluminum alloy was investigated. With the increase of Z parameter from 2.67E10 to 4.79E16, quench sensitivity relative to hardness tends to decrease first and then increase, and it may be minimised in the range from 2.67E12 to 2.24E13. The reason was discussed mainly on the effect of Z parameter on recrystallization fraction, which changes the amount of nucleation sites of heterogeneous precipitation during slow quenching. Quench-induced η phase with little strengthening effect tends to form preferentially at grain boundaries and on the Al 3 Zr dispersoids with a size larger than about 23 nm in the recrystallized grains. The increase in the number of recrystallized grains can increase the amount of such grain boundaries and Al 3 Zr dispersoids, and therefore a larger amount of quench-induced phase; consequently, quench sensitivity increases. [ABSTRACT FROM AUTHOR]

The flow behavior and microstructure evolution of 7055 aluminum alloy impacted at the strain rates from 1000 s −1 to 6000 s −1 were investigated by a compressive split-Hopkinson pressure bar, optical microscopy, transmission electron microscopy and scanning transmission electron microscopy. The maximum stress tends to increase first with the increase of strain rate from 1000 s −1 to 4000 s −1 , and then decrease at higher strain rate. The strain rate sensitivity is positive in the strain rate range of 1000–4000 s −1 , but became negative above 4000 s −1 because of the presence of shear bands and shear band induced cracks due to intensive strain localization. Impact deformation prompts transformation of η′ phase into η 2 phase, and changes the morphology of precipitates from a platelet-like shape to a globe-like shape. [ABSTRACT FROM AUTHOR]

The deformation degree of many integrated stiffened panels expected to adopt the creep age forming process, exceeds the linear elastic range. However, there is no research report on the possible results therefrom. And it is significant for the structural design and process optimization to systematically study the effect of deformation degree on the property and microstructure of the creep aging formed parts and ascertain the suitable deformation range. For this purpose, a series of creep age forming experiments of AA7475 sheet specimens with different curvature radiuses were conducted employing a radius-adjustable forming tool. Results indicated that the strength property varies by a low-to-peak-to-low manner as the increase of the deformation degree, and the radius-thickness ratio of the peak strength maintains a constant. Moreover, the measured range of the property fluctuation amplitude is 3.5–5.8%, which means a certain property difference may exist on different local regions of an integrated component with various curvature radiuses. In order to reduce the possible negative effect, it shall be necessary to pre-consider this factor and design a reasonable deformation range before the practical manufacturing process. [ABSTRACT FROM AUTHOR]

The influence of grain structure on quench sensitivity relative to localized corrosion of high strength aluminum alloy 7055 was investigated by electrochemical test, accelerated exfoliation corrosion test, optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The decrease of quench rate led to lower corrosion resistance of both the homogenized and solution heat treated (HS) alloy with equiaxed grains and the hot-rolled and solution heat treated (HRS) alloy with elongated grains, but there was a higher increment in corrosion depth and corrosion current density and a higher decrement in corrosion potential for the latter alloy, which therefore exhibited higher quench sensitivity. It is because in this alloy the larger amount of (sub) grain boundaries led to a higher increment in the amount of quench-induced η phase and precipitates free zone at (sub) grain boundaries with the decrease of quench rate, and there was a larger increment in the content of Zn, Mg and Cu in the η phase at grain boundaries due to slow quenching. The presence of subgrain boundaries in the HRS alloy tended to increase corrosion resistance at high quench rates higher than about 630 °C/min but decrease it at lower quench rates. [ABSTRACT FROM AUTHOR]

The effect of natural aging on quench-induced inhomogeneity of microstructure and hardness in high strength 7055 aluminum alloy was investigated by means of end quenching technique, transmission electron microscopy and differential scanning calorimetry thermal analysis. The hardness inhomogeneity in the end-quenched specimens after artificial aging decreases with the increase of natural aging time prior to artificial aging. The quench-induced differences in the amount and size of η′ phase are large in the end-quenched specimen after artificial aging at 120 °C for 24 h, leading to high hardness inhomogeneity. Natural aging for a long time results in a larger amount of stable GPI zones in the slowly-quenched sample, and thus decreases such differences in the end-quenched specimens after subsequent artificial aging, leading to lower hardness inhomogeneity. The hardness inhomogeneity can be reduced from 14% to be 4% by natural aging for 17,280 h prior to artificial aging. [ABSTRACT FROM AUTHOR]

Highlights: [•] Single-stage quenching tests were conducted based on the end quenching equipment. [•] Multi-stage quenching tests are reasonably designed from the experimental results. [•] Coupling control of the cooling rate and the residual stress has been achieved. [Copyright &y& Elsevier]

Abstract: Dynamic impact testing of 2519A aluminum alloy with additions of 0, 0.2 and 0.4wt% Ce was carried out by a split Hopkinson pressure bar (SHPB) equipment performed at temperatures (293K and 573K) and different nominal strain rates (1200, 3100 and 5100s−1). The influences of Ce contents on impact mechanical properties and microstructures of 2519A aluminum alloy were investigated. The results show that the addition of 0.2wt% Ce leads to an increased precipitation phase volume fraction, as well as a more dispersive and homogeneous distribution of θ′ precipitates, which improves the ability of absorbing impact energy. Adiabatic shear lines, fibrous structure and dynamic recrystallizied grains were observed in the impacted specimens and could be attributed to stress concentration and adiabatic temperature rise. [Copyright &y& Elsevier]

Abstract: An Al–7.81Zn–1.81Mg–1.62Cu alloy was subjected to a kind of thermomechanical processing involving solution annealing, quenching, pre-precipitation and warm rolling, with the aim of finding a new efficient way to prevent recrystallization in Al–Zn–Mg–Cu (7XXX) series alloys. On the basis of information on the microstructures from optical metallography (OM) and transmission electron microscopy (TEM), and on the textures from orientation distribution functions (ODFs), we learn that during subsequent solution treatment, appropriate nano/submicron-scale MgZn2 particles, which are precipitated in the thermomechanical processing, inhibit the migration of grain/sub-grain boundaries, and do not induce particle stimulated nucleation (PSN), thus leading to a remarkable decrease in the recrystallized fraction. Suitable thermomechanical processing produced an ultimate tensile strength of 528MPa and yield strength of 459MPa, as well as good intergranular corrosion (IGC) resistance. [Copyright &y& Elsevier]

Abstract: The effect of microstructure on the quench sensitivity of 7055 type aluminum alloys was investigated by hardness testing, optical microscopy and transmission electron microscopy. The results showed that the homogenized and hot-rolled alloys without Zr and the homogenized alloy with Zr were not quench sensitive, while the hot-rolled alloy with Zr was quite quench sensitive. The reason was analyzed according to the difference in the microstructure in these alloys, i.e. type of nucleation sites including dispersoids, (sub)grain boundaries and constituent particles for heterogeneous precipitation during slow quenching. Quench-induced η phase was observed mainly on large dispersoids and (sub)grain boundaries. In the homogenized and hot-rolled alloys without Zr, grain boundaries, which were the main heterogeneous precipitation nucleation sites, resulted in low quench sensitivity. In the homogenized alloy with Zr, grain boundaries and fine and coherent Al3Zr dispersoids led to low quench sensitivity. In the hot-rolled alloy with Zr, the large number of coarse Al3Zr dispersoids and subgrain boundaries were mainly responsible for high quench sensitivity. Constituent particles seemed to have little effect on quench sensitivity. [Copyright &y& Elsevier]