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The quench sensitivity of the corrosion and mechanical properties of an Al-Zn-Mg-Cu-Cr-Zr alloy was investigated utilizing tensile testing, intergranular corrosion experiments and microstructure characterization. The research results indicated that, with a decrease in quenching rate, quenching precipitates sequentially nucleated non-uniformly at grain boundaries (GBs) (η phase), E phase (η phase) and Al3Zr particles (η and T phases). As the quenching rate decreased, the size and area fraction of quenching precipitates increased within the grains, consuming many solute atoms. This led to a reduction in the precipitation of the η′ strengthening phase during the aging process, resulting in a decrease in mechanical properties. Simultaneously, the decrease in quenching rate resulted in a significant increase in the size of the η phase at the GBs, Zn and Mg content, and the width of the precipitate-free zone at the GBs, making the GBs more susceptible to corrosion. This accelerated the rate of corrosion crack propagation along the GBs, reducing the corrosion resistance of the alloy. [ABSTRACT FROM AUTHOR]

Based on end-quenching experiments combined with conductivity, hardness testing, and microstructural characterization, the quenching sensitivity of the mechanical and corrosion properties of 7475 aluminum alloy was investigated. The study revealed that as the quenching rate decreased, both the mechanical properties and exfoliation corrosion resistance exhibited increased quenching sensitivity. With the quenching rate decreasing from 31.9 °C/s to 2.5 °C/s, the conductivity increased by 4.1%IACS, the hardness decreased by 31%, the exfoliation corrosion grade transitioned from EC to ED, and the maximum exfoliation corrosion depth increased from 237 μm to 508 μm. As the quenching rate decreased, the η phase sequentially precipitated at recrystallized grain boundaries (RGBs), E phase particles, and subgrain boundaries (SGBs), while the T phase primarily precipitated on E phase particles. Furthermore, the significant precipitation of η and T phases led to a notable reduction in the quantity of age-precipitated phases, an increase in their size, and poor coherency with the matrix, resulting in decreased mechanical properties and a higher quenching sensitivity of the mechanical performance. Meanwhile, with the reduction in quenching rate, the size and spacing of grain boundary precipitated phases increased, the Zn and Mg contents of grain boundary precipitated phases increased, and the Precipitation Free Zone (PFZ) widened, leading to decreased exfoliation corrosion resistance and higher quenching sensitivity of the exfoliation corrosion performance. [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]

The effect of hot deformation on microstructure and quenching-induced precipitation behavior of an Al-Zn-Mg-Cu alloy 7055 was investigated by electron backscattered diffraction (EBSD), transmission electron microscope (TEM), high resolution transmission electron microscope (HRTEM) and scanning transmission electron microscope (STEM). In the solution heat treated and slowly-quenched alloy without hot deformation, there are equiaxed grains with low dislocation density, and there is major quenching-induced η (MgZn 2) phase located at grain boundaries and on some Al 3 Zr dispersoids in the interior of grains and minor T(Al 2 Zn 3 Mg 3) phase on Al 3 Zr dispersoids inside grains. While in the solution heat treated and slowly-quenched alloy after hot rolling, there are recrystallized grains and subgrains with higher dislocation density, and there is a larger amount of quenching-induced η and T phase on incoherent Al 3 Zr dispersoids inside recrystallized grains and at (sub) grain boundaries; moreover, quenching-induced S (Al 2 CuMg) phase and Zn-Cu rich Y phase are observed in the interior of subgrains. The precipitation behavior of these quenching-induced phases has been discussed primarily based on their chemical compositions, nucleation sites and different microstructure features in the solution heat treated alloy with and without hot deformation. • Major quenching-induced η and minor T phase appear in the slowly-quenched alloy without hot rolling. • Quenching-induced η, T, S and Y phase appear in the slowly-quenched alloy after hot rolling. • η and T phase tend to form on (sub) grain boundaries and Al 3 Zr dispersoids inside grains. • S and Y phase tend to associate with dislocations inside subgrains. [ABSTRACT FROM AUTHOR]

[Display omitted] • With the increase in Be content, the hot-compressed flow stress decreases. • With the increase in Be content, the grain size increases and becomes more uniform. • With the increase in Be content, DRX occurs in the β phase, leading to the softening of the alloy. The increase in beryllium content in Cu-Be alloys results in an unexpected reduction of hot-compressed flow stress at 780 °C and a strain rate of 1 s−1, accompanied by grain coarsening. This phenomenon can be primarily attributed to the rising volume fraction of the hard and brittle β phase with increasing beryllium content, which enhances dynamic recrystallization and consequently contributes more significantly to softening deformation. [ABSTRACT FROM AUTHOR]

The microstructures, mechanical properties, and thermal conductivity (TC) of Al-2Fe-xCo (x = 0~0.8) alloys in as-cast, homogeneous annealed, and cool rolled states are systematically studied. Results indicate that appropriate Co modification (x ≤ 0.5) simultaneously improves the thermal and mechanical properties of as-cast Al-2Fe alloys. The improvement of TC is attributed to ameliorating the morphology of primary Al3Fe phases from needles to short rods and fine particles, which decreases the scattering probability of free electrons during the electronic transmission. However, further increasing the Co content (x = 0.8) decreases the TC due to the formation of a coarse plate-like Al2FeCo phase. Besides, the thermal conductivity of annealed Al-2Fe-xCo alloys is higher than that of as-cast alloys because of the elimination of lattice defects and spheroidization of Al3Fe phases. After cool rolling with 80 % deformation, thermal conductivity of alloys slightly increases due to the breaking down of Al2FeCo phases. The rolled Al-2Fe-0.3Co alloy exhibits the highest thermal conductivity, which is about 225 W/(m·K), approximately 11 % higher than the as-cast Al-2Fe sample. The ultimate tensile strength (UTS) and elongation (EL) of as-cast Al-2Fe-0.5Co (UTS: 138 MPa; EL: 22.0 %) are increased by 35 % and 69 %, respectively, compared with those of unmodified alloy (UTS: 102 MPa; EL: 13.0 %). [ABSTRACT FROM AUTHOR]