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The effects of solution temperature and holding time on the microstructure, mechanical properties and surface morphology of 2A12 aluminum alloy sheets were discussed in this paper. The universal tensile tester was used to test the tensile strength and yield strength of aluminum alloy sheets with different treatment systems. The surface morphology of the alloy sheets was characterized by a white light interference profile scanner, and the microstructure of the sheets was characterized by optical microscope (OM), scanning electron microscope (SEM) and electron backscattered diffraction (EBSD). The results showed that the mechanical properties of the sheets could not satisfy GBT228.1-2010 national standard when the holding time was 10 min and the holding temperature was 475 °C. However, under the other heat treatment systems, the alloy could reach the GBT228.1-2010 national standard. Moreover, with the extension of the holding time, the part of the matrix gradually diffused into the aluminum-clad layer. When the holding time was shorter than 25 min, the boundary between the matrix and the aluminum-clad layer was relatively obvious. And the diffusion gradually became obvious when the holding time was over 25 min. Thereby, the boundary became blurry. The further investigation suggested that the solution temperature of 495 °C and the holding time of 35 min showed better mechanical properties and better surface morphology.

The transformation behavior of precipitates in Al–Mg–Si–Cu alloys with and without Zn addition during artificial aging at 170 °C was investigated in this study. For Al–Mg–Si–Cu alloys with and without Zn addition, two types of precipitates, needle-like β″ and lath-like L, are formed with the aging time increasing from 8 to 34 h. The needle-like β″ precipitate exhibits a Mg-to-Si atomic ratio of 1.31 which is in agreement with the theoretical ratio of 1.25 for β″ (Mg5Al2Si4). In addition, the β″ precipitate is supposed to contain Al and Cu. With further partitioning of Mg, Si and Cu and release of Al, the needle-like β″ precipitate can transform to lath-like L phase. The L phase has significantly higher concentrations of Mg, Si and Cu and lower concentration of Al, with a higher Mg-to-Si atomic ratio (1.41) deviated from theoretical ratio of β″. However, the major of Zn has a random distribution in Al matrix and exhibits no significant partitioning into precipitates. Zn remained in matrix can enhance the transformation of β″ precipitates to L precipitates.

The increase in zinc content in Al–Zn–Mg–Cu alloys provides an effective method to enhance the strength. Transmission electron microscopy (TEM) and tensile test were employed to analyze the microstructure and tensile properties, respectively, of Al–9.3Zn–2.0Mg–1.8Cu alloy (9.3Zn alloy) and Al–9.8Zn–2.0Mg–1.8Cu alloy (9.8Zn alloy) with single- and double-stage aging states. The results showed that the two alloys possessed a closed strength under single-stage peak-aging treatment. As for double-stage aging treatment, 9.8Zn alloy had a higher strength values than 9.3Zn alloy under the same aging regimes. With the second step aging time prolonging, the strength gap was extended. The main precipitates for the two alloys with single-stage peak-aging state were GP zones and η′ phase, while there were a majority of η′ phases and η phases for the two alloys under typical double-stage over-aging state. Under double-stage over-aging state, the proportion of precipitate with large size for 9.3Zn alloy was larger than that for 9.8Zn alloy. Besides, a more obvious trend was revealed for the double-stage over-aging state. The gap of strength between the two alloys was explained by the difference of precipitation characteristics via interaction mechanism between precipitates and dislocations.

The microstructure of 2624-T39 aluminum alloy was analyzed by means of metallographic (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The effects of different microstructure characteristics on the tensile properties and fatigue crack growth rate of 2624-T39 aluminum alloy were studied. Results showed that the grain size of the alloy was a typical fiber structure along the rolling direction, and the main second phase was the Al2CuMg phase. The grain size of the alloy had an obvious influence on the fatigue crack growth rate, and the alloy showed a lower fatigue crack growth rate due to the larger grain size. The crack initiation zone on the fracture surface of alloys with lower fatigue crack growth rate was relatively rough, the crack propagation zone had obvious fatigue striations, and the transient fracture zone had a large number of smaller dimples.

It has been reported that the element scandium (Sc) is the most effective modificator which can significantly refine the grain size, prohibit recrystallization process and increase the strength. Adding trace of Sc in 7000 series aluminum alloys is considered to be an effective way to modify its microstructure and promote mechanical properties. In order to study the effect of Sc element on as-cast microstructure of Al–Zn–Mg–Cu–Zr alloy, ingots containing different amounts of Sc were prepared by ferrous-mold cast. Microstructures were characterized by means of differential scanning calorimeter (DSC), X-ray diffraction (XRD), optical microscope (OM) and scanning electrical microscope (SEM). The results indicate that when the Sc level exceeds a critical concentration, Al3(Sc,Zr) primary phase would form in the melt and act as an efficient nucleant, resulting in very refined grain and an equiaxed grain structure. Sc element reduces the number of eutectic phases formed during solidification, coupled with an increase in the concentration of major alloying elements retained in the solute. This behavior suggests possible benefits in improving the integrated properties of terminal products.

Based on the ABAQUS/explicit finite element method, the deep drawing of 6A16 alloy pre-aged and then storaged at room temperature for 1 week with various blank-holder forces (10, 14, 18 kN) was studied. The distribution and variation of stress and strain in deformation zones were investigated to drive the forming property and process of the alloy. Besides, the simulation result was verified combined with the deep drawing experiments. The results show that the stress and strain of the deformation zone have an incremental trend with the blank-holder force increasing while the deformation degree and grain size within a certain deformation zone have an obvious increase and an enlargement, respectively. After the deep drawing, the hardness of products also increases with the enhancement of blank-holder force. The blank-holder force of 18 kN is certified as the preferential one by the analysis of microstructure and simulation results.

The effect of solution treatment on the microstructure and mechanical properties of a novel 7A56 aluminum alloy plate was investigated by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), conductivity, hardness and tensile tests. The results indicate that the coarse second phases in the hot-rolled plate mainly consist of AlZnMgCu quaternary phase and Al7Cu2Fe phase, and no Al2CuMg phase is found. The amount of the second phases gradually reduces with the increase in temperature (450–480 °C) and time (1–8 h) during the solution treatment, and the soluble particles are completely dissolved into the matrix after solution treatment at 470 °C for 4 h, while the residual phases are mainly Fe-rich phase along the grain boundaries. The recrystallization fraction of the alloy gradually increases with the degree of solution treatment deepened. When the temperature exceeds 480 °C, over-burning takes place. The mechanical properties of samples treated at 470 °C for various times were tested. After the solution treated at 470 °C for 4 h, the quenching conductivity and peak-aged hardness of the alloy are 30.8%IACS and HV 204, respectively. The ultimate tensile strength and yield strength of the samples aged at 120 °C for 24 h are 661 and 588 MPa, respectively.

With the aid of scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), differential scanning calorimetry (DSC) analysis and electron backscatter diffraction (EBSD), the microstructure of the alloy in as-extruded state and various solution-treated states was investigated. The results indicate that second phase of the as-extruded 7136 aluminum alloy mainly consists of Mg(Zn, Cu, Al)2 and Fe-rich phases. The Mg(Zn, Cu, Al)2 phase directly dissolves into the matrix during solution treatment with various solution temperatures. After solution treated at 475 °C for 1 h, Mg(Zn, Cu, Al)2 phases are dissolved into the matrix, while Fe-rich phases still exist. Fe-rich phases could not dissolve into the matrix by prolonging solution time. The mechanical property test and EBSD observation show that two-stage solution treatment makes no significant improvement in mechanical properties and recrystallization of the alloy. The optimized solution treatment parameter is chosen as 475 °C/1 h.

The hot deformation behavior of Al–Cu–Li alloy was investigated by hot compression tests in the temperature range of 340–500 °C with strain rate of 0.001–10.000 s−1. Based on the dynamic materials model (DMM), processing maps of the test alloy were developed for optimizing hot processing parameters. The optimum parameters of hot deformation for Al–Cu–Li alloy are at temperature of 400–430 °C and strain rate of about 0.100 s−1, with efficiency of power dissipation of around 30%. The microstructural manifestation of the alloy deformed in instability domains is flow localization, and dynamic softening first occurs in flow localizations structure. In stable domains, dynamic recovery (DRV) and dynamic recrystallization (DRX) are the main microstructural evolution mechanism. DRX is gradually strengthened with the increase in deformation temperature and the decrease in strain rate. During hot deformation, the DRX mechanism of Al–Cu–Li alloy is dominated by continuous DRX (CDRX). A DRX model of Al–Cu–Li alloy is proposed based on the microstructural evolution process of the test alloy.

Finite element method (FEM) simulations were employed to investigate the quenching residual stress distributions of 7085 aluminum alloy plates. The effect of dimensional variation on the quenching residual stress distributions was studied and discussed by using models with different dimensions (length, width, and thickness). The accuracy and efficiency of the models were verified by other numerical examples. The order of the dimension effects on the quenching residual stress distributions is: thickness > width = length. The maximum tensile stress and compressive stress increase from 33 to 190 and 39 to 270 MPa, respectively, as the thickness increases from 30 to 150 mm. The ultimate maximum tensile stress (about 190 MPa) is equivalent to half of the quenching yield strength at 20 °C, while the ultimate maximum compressive stress (about 300 MPa) is equivalent to 80 % of the quenching yield strength at 20 °C. There are stress fluctuations at the edge of the large plate both in rolling and in transverse directions. The ratio of the fluctuation region along the rolling direction and transverse direction increases as the thickness increases, while it decreases as the length or width increases. The actual length of the fluctuation region is almost a constant value for the plates with a thickness of 115 mm (about 500 mm in length and 300 mm in width).

The transformation and dissolution of Mg(Zn, Cu, Al)2 phase during solution treatment of an Al–Zn–Mg–Cu alloy containing high zinc were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDX) and X-ray diffraction (XRD). The results show that solution temperature is the main factor influencing phase dissolution. With solution temperature increasing, the content of residual phases decreases. Phase transformation from Mg(Zn, Cu, Al)2 to S(Al2CuMg) occurs under solution temperature of 450, 460 and 465 °C. Mg(Zn, Cu, Al)2 phase is directly dissolved into the matrix under solution temperature of 470 and 475 °C, and no S(Al2CuMg) phase transformed from Mg(Zn, Cu, Al)2 phase is observed. The formation of S(Al2CuMg) phase is mainly controlled by Zn elemental diffusion. The mechanism of transformation and dissolution of second phases was investigated. At low temperature, the dissolution of Zn is faster than that of Mg and Cu, resulting in an appropriate condition to form S(Al2CuMg) phase. At high temperature, the dissolution of main alloying elements has no significant barrier among them to form S(Al2CuMg) phase.

The multilayered 7XXX series aluminum alloy was impacted by 7.62 mm ogival projectiles at velocities ranging from 787 to 851 m·s−1. The deformed microstructure under various impacting velocities and fracture surfaces of different sections were investigated at different physical scales to determine the process of failure. Optical microscopy (OM), electron back-scattered diffraction (EBSD) and scanning electron microscopy (SEM) were used in the investigation. The results show that crater is constrained in the 7B52 front layer and two types of adiabatic shear bands which are transformed bands and deformed bands and different types of cracks are observed. Spall fracture is the significant failure mode of 7B52 front layer, and the resulting delamination leads to the presence of bending tensile fracture instead of the shear plugging. The ductile 7A01 layer blunts and deflects the spall crack tips, preventing the targets from full spall, and induces a constraint of 7A52 rear layer. The level of the constraint determines different fracture modes of 7A52 layer, accounting for the asymmetry of damage.

The effect of solution heat treatment (SHT) on mechanical properties, microstructure and surface quality of Al-1.2Mg-0.6Si-0.2Cu-0.6Zn alloy was investigated by tensile test, Erichsen test, surface topography, scanning electron microscope (SEM) and electron back-scattered diffraction (EBSD). The results indicate that with the increase in SHT temperature, yield strength and cupping test value (I E) of the sheets increase greatly and reach a peak value, then decrease. Meanwhile, intermetallic compounds dissolve into matrix gradually. The grains grow up as SHT temperature increases, and abnormal grain growth leads to the surface defects after solution-treated above 560 °C. Considering mechanical properties, I E value, residual phases, grain size and surface quality of the sheets, SHT temperature for the alloy should not be higher than 550 °C.

Phases and microstructures of three high Zn-containing Al–Zn–Mg–Cu alloys were investigated by means of thermodynamic calculation method, optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and differential scanning calorimetry (DSC) analysis. The results indicate that similar dendritic network morphologies are found in these three Al–Zn–Mg–Cu alloys. The as-cast 7056 aluminum alloy consists of aluminum solid solution, coarse Al/Mg(Cu, Zn, Al)2 eutectic phases, and fine intermetallic compounds η(MgZn2). Both of as-cast 7095 and 7136 aluminum alloys involve α(Al), eutectic Al/Mg(Cu, Zn, Al)2, intermetallic η(MgZn2), and θ(Al2Cu). During homogenization at 450 °C, fine η(MgZn2) can dissolve into matrix absolutely. After homogenization at 450 °C for 24 h, Mg(Cu, Zn, Al)2 phase in 7136 alloy transforms into S(Al2CuMg) while no change is found in 7056 and 7095 alloys. The thermodynamic calculation can be used to predict the phases in high Zn-containing Al–Zn–Mg–Cu alloys.

The aging behavior of Al-Cu-Mg-Ag alloys with high Cu/Mg was studied by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) using synchrotron radiation. TEM study reveals that the major strengthening phases of the alloy after aging at 160 °C for 10 h are Ω and less θ′. SAXS study shows that the scattering patterns are composed of several concentric circles at the beginning of aging process, which is replaced by the butterfly-wings scattering patterns with the increase of aging time. The butterfly-wings scattering patterns are composed of several branches. The angles between the branches are roughly equal to that between the habit planes of precipitates. The evolution of Guinier radius with aging time indicates the good coarsening resistance of the precipitates. The evolution of integrated intensity is consistent with the classical two-step precipitation process.

The effects of interrupted multi-step aging on the microstructure and properties of Al-Cu-Mg-Ag-Zr alloy were studied by tensile, hardness, electrical conductivity tests and transmission electron microscopy (TEM). Interrupted multi-step aging delayed the peak aging time compared to one-step aging and kept the same levels of hardness, electrical conductivity, ultimate tensile strength (UTS), yield strength (YS) and elongation as those of the T6 temper alloy while increased the fracture toughness notably. Ω phase and a little θ′ phase precipitated and grew simultaneously in the process of one-step aging at 160°C. During the second-step aging at 65°C of interrupted multi-step aging, no TEM characteristic of Ω precipitates could be found. During the third step of interrupted multi-step aging, Ω began to dominate the microstructure like what happened in the process of one-step aging. The difference of properties between the T6 temper and the interrupted multi-step aged alloys might be related to the different precipitation sequences in the process of the two heat treatment technologies.

The elevated temperature performances of 2D70 Al alloy hot extrusion rods after two-stage homogenization and intensive deformation were studied by measuring the elevated temperature enduring strength and the creep ultimate strength. The fracture morphology of some selected samples after testing at different elevated temperatures was observed by scanning electron microscopy (SEM). The results indicate that, as the test temperature increases, the elevated temperature enduring strength of 2D70 Al alloy decreases gradually. In a comparison between 150°C and 240°C, the notch enduring strength drops from 375 to 185 MPa and the smooth enduring strength drops from 337 to 130 MPa. Enduring strength is not sensitive to the notch. The notch sensitivity ratio (NSR) coefficient is in the range of 1.119 to 1.423 from 150°C to 240°C. The creep test results show that, as the test temperature increases from 150°C to 240°C, the creep ultimate strength of 2D70 Al alloy rods drops gradually from 312 to 117 MPa.

High strength Al-Zn-Mg-Cu alloys were prepared by spray deposition and casting techniques. The microstructures of the Al-Zn-Mg-Cu alloys were studied using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. Secondary phases in the microstructures of the alloys prepared by spray deposition and conventional cast were examined. The results indicate that under the conventional casting condition, the microstructure of the alloy revealed the presence of coarse Al/Mg(ZnCu) 2 eutectic phases, and the spray deposited process causes an obvious modification in size, morphology, and distribution of secondary phases in the microstructure as well as reduction of segregation. The superior microstructure of the spray-deposited Al-Zn-Mg-Cu alloy was attributed to the high cooling rate, and associated with the rapid solidification process.

The effects of the two-step ageing parameters (temperature and time) on the mechanical properties and electrical conductivity of 7B04 (Al-Zn-Mg-Cu) pre-stretched thick plates were studied. The results reveal that the initial T1 ageing contributes a major increase of the tensile strength, and the 0.2% proof stress value reaches 482 MPa after ageing for 7 h at 115°C. Behavioral differences in the tensile properties of the alloy after the two-step ageing treatment were less with the first-step ageing at 115°C for different time periods (7, 14, and 21 h). The effects of the second ageing parameters on the properties and microstructure of the 7B04 alloy were remarkable. TEM analysis of the samples aged at Temper I (7 h at 115°C + 12 h at 160°C) and Temper II (7 h at 115°C + 16 h at 165°C) indicates that two kinds of phases, i.e. η' and η phases, precipitate from the matrix and efficiently improve the tensile strength of the alloy, and the grain boundary precipitates are coarse and discrete. There are obvious precipitate free zones (PFZs) along the grain boundary in the microstructure of the alloy after the two-step ageing treatment.

Al-10.8Zn-2.8Mg-1.9Cu alloy was synthesized by spray atomization and deposition technique. GP zones and age-hardening process in the alloy were investigated using high-resolution electron microscopy (HREM), selected area diffraction (SAD), and differential scanning calorimetry (DSC) analysis. The results indicated that spray deposition process accelerated the aging kinetics of the alloy at an aging temperature of 120°C, thereby reducing the peak aging time to 16 h. GPI and GPII are the two types of zones that are major precipitates for the alloy under peak-aged condition. The precipitation sequence for the alloy is also discussed.

The flow stress of spray formed 70Si30Al alloy was studied by hot compression on a Gleeble-1500 test machine. The experimental results indicated that the flow stress depends on the strain rate and the deformation temperature. The flow stress increases with an increase in strain rate at a given deformation temperature. The flow stress decreases with the deformation temperature increasing at a given strain rate. The relational expression among the flow stress, the strain rate, and the deformation temperature satisfies the Arrhenius equation. The deformation activation energy of 70Si30Al alloy during hot deformation is 866.27 kJ/mol from the Arrhenius equation.