Hongwei Yan

Effect of Various Retrogression Regimes on Aging Behavior and Precipitates Characterization of a High Zn-Containing Al–Zn–Mg–Cu Alloy

In the present work, the influence of various retrogression treatments on hardness, electrical conductivity and mechanical properties of a high Zn-containing Al–Zn–Mg–Cu alloy is investigated and several retrogression regimes subjected to a same strength level are proposed. The precipitates are qualitatively investigated by means of transmission electron microscopy (TEM) and high-resolution transmission electron microscopy techniques. Based on the matrix precipitate observations, the distributions of precipitate size and nearest inter-precipitate distance are extracted from bright-field TEM images projected along 〈110〉Al orientation with the aid of an imaging analysis and an arithmetic method. The results show that GP zones and η′ precipitates are the major precipitates and the precipitate size and its distribution range continuously enlarge with the retrogression regime expands to an extent of high temperature. The nearest inter-precipitate distance ranges obtained are quite the same and the average distance of nearest inter-precipitates show a slight increase. The influence of precipitates on mechanical properties is discussed through the interaction relationship between precipitates and dislocations.

Single-stage aging behaviour and precipitate evolution in a high Zn-containing Al–9.78Zn–2.02Mg–1.76Cu alloy

ABSTRACT Property evolution in a high Zn-containing Al–9.78Zn–2.02Mg–1.76Cu alloy treated at 120°C, with the microstructure subjected to under-aging (UA), peak-aging (PA) and over-aging (OA), is investigated. Precipitate size distributions and distances between neighbouring precipitates are determined. Results indicate that a certain time is required to reach peak hardness and yield strength, and that peak values can be sustained for a relatively long time. As the aging time increases, the conductivities increase persistently. As the alloy temper varies from UA to PA to OA, the main matrix precipitates change from ‘GPI zone and GPII zone and η′ phase’ to ‘GPII zone and η′ phase’ and then to η′ phase. Meanwhile, the precipitate size distribution becomes broader, and the average precipitate size increases.

Microstructure and Properties of an Al-Zn-Mg-Cu Alloy Plate

The inhomogeneous microstructure and properties at typical position of an Al-7.7Zn -1.7Mg-1.4Cu-0.11Zr alloy plate in T7651 condition have been investigated using OM, TEM and EBSD analysis, tensile properties testing, conductivity measurement and fracture toughness testing. The results indicate that there are obvious differences in grain morphology, quench-introduced precipitation and recrystallization degree in the two typical positions of near the surface layer (T/8 plane) and in the center (T/2 plane) along the thickness direction of the plate. There appear some amount of quench-introduced precipitates at the T/2 plane of the alloy plate, which improves the electrical conductivity. And there is a higher proportion of the recrystallization organization at the T/2 plane of the alloy plate, seriously affecting its elongation and fracture toughness. Due to without marked characteristic of rolling flow line, the strength at the T/8 plane of the alloy plate is lower. The properties at T/8 plane and at T/2 plane of the alloy plate exhibit a difference of 3~18%. Microstructure inhomogeneity of the alloy plate determines the uniformity of its properties.

Classification and Evolution of Porous Defects in Spray-Formed Al–Zn–Mg–Cu Alloy

The porous defects classification in spray-formed Al–Zn–Mg–Cu alloy was investigated in this paper during spray forming, hot isostatic pressing (HIP) and homogenization. Metallographic microscopy and scanning electron microscopy (SEM) were used to study the microstructure and porous defects. The results showed that, there were four kinds of porous defects in spray-formed alloy, which were distinguish by the reasons of formation and shape. The first kind, the second kind and the third kind porous defects contain gas, while the forth kind porous defect did not contain gas. The forth kind porous defects can be eliminated by HIP, but the other three only can be compressed to be smaller. After homogenization, the porous defects with gas grew up and was observed easily again, unless some porous defects connected with ingot surface through the other porous defects which could exhaust gas during HIP. The second phase in the ingot restored back mostly after the homogenization treatment of 440 °C/12 h + 474 °C/48 h.

Microstructure and Properties of Spray-Formed Si–30Al Alloy Used for Electronic Packaging

The microstructure and properties of spray-formed Si–30Al alloy was studied in this paper, which was used for electronic packaging. Hot isostatic pressing was used to compact the ingot, and then electroplating and brazing was carried out. The results showed that, (1) the Si–30Al alloy comprised α-Al phase, pseudo eutectic phase and primary silicon phase; (2) the flow deformation of α-Al phase and pseudo eutectic phase filled pore defect making the alloy compacting by HIP; (3) the alloy could be electroplated and brazed easily, and no pore defect was observed in electroplated coating and weld.

Measurement of Residual Stress in As-Quenched 7055 Aluminum Plate by Various Methods

The accuracy of different residual stress measurement methods has always been the research focus from the beginning of research on residual stress. In this study, both conventional and newly-developed methods were applied to measure the residual stress in as-quenched 7055 aluminum plate. Methods such as hole drilling, X-ray diffraction based on sin2Ψ and cos α approaches, crack compliance method and neutron diffraction method were used. In the meanwhile, finite element simulation was used to obtain the residual stress distribution as a comparison. The results showed that among the methods studied, X-ray diffraction method has the greatest test error due to its shallow test depth. However, if the measurement condition was well controlled, the error could be acceptable. The absolute values of residual stress obtained by X-ray diffraction method were slightly greater than hole drilling method. If calculated with the reasonably chosen crack compliance function, the test result was similar to neutron diffraction method. Under different quenching conditions, all the studied methods showed that the greater the quenching cooling rate, the greater the absolute value of residual stress.

Flow Behaviors and Corresponding Constitutive Equation of the Al–9.4Zn–1.9Mg–2.0Cu Alloy

Isothermal compression tests of the Al–9.4Zn–1.9Mg–2.0Cu alloy were carried out at the temperature ranging from 300 to 460 °C and the strain rate from 0.001 to 10 s−1, and the deformation degree was 70%. Flow stress curves show that the flow stress decreases with the increasing deformation temperature and the decreasing strain rate. The measured flow stress was corrected because of the effect of friction. The corresponding corrected stress values are lower than measured stress values. The effect of friction is far greater when hot-deformations occurred at lower temperatures or higher strain rates. A constitutive equation considering the effect of strain on material constants (i.e. α, n, Q and A) are established based on the Arrhenius-type equation. Compared with the experimental results, the flow stresses calculated by the constitutive equation have a high precision with the correlation coefficient of 0.95. Results show that higher deformation temperatures and lower strain rates are beneficial for hot deformation of the Al–9.39Zn–1.92Mg–1.98Cu alloy.

Quantitative Investigation of Precipitates in a High-Zinc Al–9.54Zn–2.10Mg–1.69Cu Alloy with Various Typical Tempers

In order to analyze single stage ageing behavior of a high-zinc Al–9.54Zn–2.10Mg–1.69Cu alloy, the microstructure of the alloy subjected to T6, T76 and T77 states are investigated via transmission electron microscopy (TEM) combined with high-resolution transmission electron microscopy (HRTEM) attached to it. Under the premise in precipitate observations, diameter distributions and average diameter size of precipitates are deduced from Bright-Field TEM (BF TEM) images projected along \( \left\langle {110} \right\rangle_{\text{Al}} \) orientation with the help of an image processing. The results indicate that the main precipitates are GPII zone and η′ phase in the T6 and T77 alloys while η′ and η phase in the T74 alloy. The Bright field TEM observations reveal that the matrix precipitates for the T6 and T77 alloys have small size and dispersive distribution while that for the T74 alloy has big size and sparse distribution. Quantitative precipitate characteristics including diameter distribution and average diameter size have been gained by an image processing relying on BF TEM images projected along \( \left\langle {110} \right\rangle_{\text{Al}} \) orientation. The results reveal that the T6 and T77 alloys have more than a half percentage of precipitates with a size less than 2 nm while the T77 and T74 alloys have broad precipitate distribution range till 14 and 16 nm, respectively. The grain boundary precipitates (GBPs) for the T6 alloy have continuous distribution with small size while that for the T74 and T77 alloys distribute intermittently with big size.

Modeling and Simulation of Dynamic Recrystallization Behaviors of 7085 Aluminum Alloy During Hot Deformation Using Cellular Automata Method

Cellular Automata (CA) method can be used to simulate the microstructure evolution. The parameters of the CA model and thermal deformation parameters are input to the CA model as important data. The hot deformation behavior was studied by means of a hot simulating test on Geleeble-1500 experiment machine. The range of thermal deformation temperature is 623–723 K, the range of strain rate is 0.001–1 s−1 and the maximum true strain is 0.91. Analysis of microstructure of average grain size and recrystallization fraction by optical microscope (OM) and electron backscatter diffraction (EBSD). CA model was used to study the effects of strain, strain rate and deformation temperature on the deformed microstructure. The simulation results are validated by a great deal of experimental data, the simulation results are in good agreement with the experimental data that shows the feasibility and predictability of the CA method.

Effect of Solution Treatment and Aging Treatment on Microstructure and Properties of 1953 Aluminum Alloy Pipe

Aluminum drill pipes have low density, high specific strength and good stress corrosion resistance, possessing a huge application potential in the oil drilling. The 1953 alloy belongs to the Al–Zn–Mg–Cu alloy, and it is one of the most promising aluminum alloy materials for petroleum drill pipe. In this paper, the 1953 aluminum alloy were studied by hardness tests, conductivity tests, tensile tests, optical microscope and scanning electron microscopy. The results show that there are a large number of AlZnMgCu phases and a small amount of Fe and Si impurity phases after extrusion. After the solution treatment, the AlZnMgCu phases have been dissolved, and the residual phases in the alloy are mainly impurity phases with Fe and Si. The comprehensive performance is excellent after solution treatment at 440 °C/1 h + 470 °C/1 h and aging treatment at 120 °C/24 h. The hardness, electrical conductivity, yield strength, tensile strength and elongation can reach 191.2 HV, 18.9 MS/m, 578 MPa, 620 MPa, and 11.2%, respectively.