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Al-5.8Mg-0.4Mn with minor alloying additions of Sc and Zr was investigated via electrochemical testing and nitric acid mass loss testing (NAMLT) in order to reveal the influence of Sc and Zr upon sensitization and intergranular corrosion. The Al-Mg-Mn alloys were also analysed using an electron probe microanalyzer, indicating that β-phase (Al

Effects of N and Zr on the as-cast microstructure and properties after annealing of high-speed steel (HSS) were investigated by using electronic probe micro-analysis, Rockwell hardness test, X-ray diffractometry and differential scanning calorimetry with combination of microstructure analysis. The results indicate that the addition of N and Zr will refine the eutectic structures and enhance the stability of carbides which are mainly MC, M2C and M7C3. The coarse dendritic structures decrease significantly and most of the carbides are distributed in the microstructure uniformly. Moreover, a kind of Zr–Si compound which only exists in VC is discovered, and this new phase is speculated to be related with the spheroidization of VC. The annealing process is set up to 6 different time periods which are 1, 3, 6, 10, 15 and 20 h, respectively. In different annealing processes at 750 °C which is lower than austenitizing temperature, the addition of N and Zr makes the decrease of hardness more obvious and restrains the precipitation of secondary carbides with the extension of time. Moreover, when the annealing time reaches 20 h, some clusters appear in the matrix of the two samples, and the density of clusters in HSS1 is lower, but the matrix of HSS1 contains more C and alloying elements which indicate more carbides precipitate.

The hot deformation behavior of Al-6.2Zn-0.70Mg-0.30Mn-0.17Zr alloy and its microstructural evolution were investigated by isothermal compression test in the deformation temperature range between 623 and 773 K and the strain rate range between 0.01 and 20 s-1. The results show that the flow stress decreased with decreasing strain rate and increasing deformation temperature. At low deformation temperature (≤673 K) and high strain rate (≥1 s-1), the main flow softening was caused by dynamic recovery; conversely, at higher deformation temperature and lower strain rate, the main flow softening was caused by dynamic recrystallization. Moreover, the slipping mechanism transformed from dislocation glide to grain boundary sliding with increasing the deformation temperature and decreasing the strain rate. According to TEM observation, numerous Al3Zr particles precipitated in matrix, which could effectively inhibit the dynamic recrystallization of the alloy. Based on the processing map, the optimum processing conditions for experimental alloy were in deformation temperature range from 730 K to 773 K and strain rate range from 0.033 s-1 to 0.18 s-1 with the maximum efficiency of 39%.

A refined microstructure of Al-Zn-Mg-Sc-Zr alloy sheet was produced by simple hot and cold rolling to an average grain size of 3 µm. Experiments were completed in electro-fluid servo-fatigue tester and results were investigated by means of optical microscope (OM), scanning electron microscopy (SEM) and transmission electron microscope (TEM). Superplastic deformation was conducted and superplastic ductility of ≥200% was achieved at a testing temperature range from 425 oC to 500 oC and relative high strain rate range of 1×10−3 s−1~1×10−1 s−1. The maximum elongation of 539% was obtained at 500 oC and 1×10−2 s−1. In addition, the scanning electron microscopy (SEM) and transmission electron microscope (TEM) analyses showed that the presence of Al3 (Sc, Zr) particles in pinning grain boundaries and dislocations had a great influence on the superplastic deformation. The analyses of superplastic test data calculated out the coherent strain rates sensitivity parameter of 0.43 and the average activation energy of 143.762 kJ/mol. The data interpreted that the dominant deformation mechanism was grain boundary sliding controlled by lattice self-diffusion.

An extensive study was made of the boundary area microstructure between the matrix and dense inner sublayers of the ceramic coating formed on AZ91 magnesium alloy substrate by micro-arc oxidation(MAO).The coating was prepared in an alkaline electrolytic solution composed of 5-20g/l of NaH2PO4, 1-5g/l of NaOH, 5-8g/l of KF; 0.5-2g/l of Na3C6H5O7, and 0.5-2g/l of EDTA , employing a constant-current controlled AC power supply with a current density of 10-30A/dm2; and the microstructure of the coatings was characterized using transmission electron microscopy(TEM) and scanning electron microscopy(SEM). It was found that (1) the main constituent of the coating adjacent to the boundary was microcrystalline and nanocrystalline; (2) the microhardness of the coating adjacent to the boundary was improved than that of the matrix. It was due to the formation of the intermixing of Mg and MgO and their grains were refined, these leaded to fine-crystal strengthen.

The effects of stress-aging on the microstructure and properties of Al–Cu–Mg–Ag alloy were studied by hardness test, electric resistivity test, optical microscopy and transmission electron microscopy. The results show that the application of external stress during aging did not change the grain morphology of Al–Cu–Mg–Ag alloy, but resulted in great changes of the precipitations. The precipitation of θ′ phases was promoted while that of Ω phases was restrained and the initial hardening rate of the alloy decreased. This might originate from the large amounts of dislocations during stress-aging that provided sites facilitating heterogeneous nucleation of θ′ phases. This was verified by the phenomenon that the density of θ′ phases increased while that of Ω phases decreased and the peak hardness was reduced when Al–Cu–Mg–Ag alloy was cold deformed with 6% stretch prior to aging.

The mechanical property, fracture toughness and fatigue behavior of T7451 Al-Zn-Mg-Cu alloy thick plates in different orientations and with various thicknesses were investigated by means of tensile, fatigue and plain strain fracture toughness testing. And the microstructures and fracture morphologies were analyzed with optical microscopy and scanning electron microscopy. The results showed that the samples in longitudinal (L)-transversal (T) orientation possessed better mechanical property, fracture toughness and fatigue resistance than that in T-L orientation. Fractography and optical microanalysis clearly demonstrated that the feature of recrystallized grains is the decisive factor for this anisotropy. On the other hand, values of strength and fracture toughness decreased with the increase of plate thickness, but their fatigue crack growth rate became slower. Combined with the fractography analysis, the increase of recrystallization degree and the coarser grains in the thicker plate should be the main reason for the detrimental to the strength and toughness properties since the main fracture mechanism changes from ductile transgranular fracture to intergranular failure. However, these coarse recrystallized grains play an advantageous role for fatigue resistance from crack deflection and closure perspectives.

The creep behavior of Al–Cu–Mg–Ag alloy and its microstructural evolution during creep deformation were studied at 100–210 °C with the external stress of 150–300 MPa. The results show that both Ω and θ ׳ precipitate secondarily in the under-aged sample during the creeping process, resulting in the excellent creep-resistant property compared to the peak aged sample. The temperatures between 100 and 150 °C have little affect on the creep curves of the alloy. The larger external stress led to the growth of the creep holes on the grain boundaries and the higher creep temperature led to the growth of the precipitations in the grains inner. They both result in the lower creep resistance of Al–Cu–Mg–Ag alloy. The steady creep rate increased with increasing creep temperature or external stress, which can be described by a constitutive equation with the creep deformation activation energy 102.00 kJ/mol.

Effect of Retrogression and Reaging (RRA) treatment on the microstructure and fatigue crack growth behavior of 7050 aluminum alloy thick plate was investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). The results showed that the RRA microstructure is similar to that for T6 treatment inside the grains, but is slightly denser and coarser and more stable in nature. Also grain boundaries precipitates (GPBs) coarsen obviously, distributing discontinuously and isolated. The precipitation free zones (PFZs) are broadened than that of the T6 sample, and narrower than that of the T7451 sample. And maintaining strength equal to that for the T6 peak-aged treatment and enhanced fatigue crack growth resistance to that for the T7451 overaged treatment can be achieved for RRA treatment.

The hot deformation behavior of Ni-base superalloy Rene'41 has been investigated by isothermal compression in deformation temperature range from 850 to 1050 °C with strain rates of 0.1–50 s−1 on Gleeble-3500 thermal simulation machine. The constitutive equation of the alloy is established, which describes the flow stress as a function of strain rate and deformation temperature. Based on dynamic material model and Prasad's instability criterion, the processing maps for the alloy are constructed at strains of 0.3 and 0.5. The processing map at the strain of 0.5 exhibits a single stable domain of 910–1050 °C at 0.1–1 s−1 with a peak efficiency of about 45% occurring at 0.1 s−1 and 960 °C. The dynamic recrystallization of the alloy can be easily observed at 1000 °C and 0.1 s−1. With increasing deformation temperature and/or decreasing strain rate, the volume fraction of dynamic recrystallization increases. At strains of 0.3 and 0.5, the flow instability domain mainly located at higher strain rate (>1.5 s−1). On the basis of processing map and microstructure evolution, the optimum processing conditions at the strain of 0.5 are in deformation temperature range between 950 and 1050 °C and strain rate range of around 0.1–1 s−1.

The thermal stability of Al–Cu–Mg–Ag alloy was tested by thermal exposure and creep performance. The results show that the under-aged Al–Cu–Mg–Ag alloy possessed better thermal stability compared to the peak-aged one, due to the secondary precipitations of the strengthening phases. The number of the precipitations in the under-aged sample increased and then decreased with increasing the thermal exposure or creep time while that of the peak-aged sample decreased gradually. The tensile strength of the under-aged sample increased and then decreased with increasing the thermal exposure time with a peak value of 524 MPa after exposed for 20 h, which was 19 MPa higher than that of the peak-aged alloy. The steady creep rate of the under-aged sample was much lower and the creep-life was much longer to that of the peak-aged one, indicating that the under-aged sample possessed excellent creep resistance property at elevated temperatures.

The flow behavior of Al-Zn-Mg-Sc-Zr alloy during hot compression deformation was studied by thermal simulation test at strain rate of 0.001 to 10s-1 and deformation temperature of 340 to 500°C on the Gleeble-1500 thermal mechanical simulator. The results show that the flow stress increases with increasing strain rate, and decreases with increasing deformation temperature. The flow stress of the alloy during the elevated temperature deformation can be represented by a Zener-Hollomon parameter with the inclusion of the Arrhenius term. The values of A, n, α in the analytical expression of flow stress are fitted to be 1.49×1010s−1, 7.504 and 0.0114MPa−1, respectively. The hot deformation activation energy of the alloy during hot deformation is 150.25kJ/mol.

The intercrystalline corrosion, exfoliation corrosion (EXCO), and stress corrosion cracking (SCC) of Al–Zn–Mg–Sc–Zr alloy were investigated by means of constant temperature immersion corrosion method, optical microscopy, transmission electron microscopy (TEM), and electrochemical impedance spectroscopy (EIS). The results show that intercrystalline corrosion, and EXCO susceptibility of Al–Zn–Mg–Sc–Zr alloy decrease gradually with increasing of aging time. Corrosion susceptibility order from low to high is as follows: OA > PA > UA > NA. The SCC susceptibility index of PA temper is more than OA temper at the same strain rate. According to TEM observation, with aging time prolonging, a part of η′ phases transform to η equilibrium phases, which become coarse gradually. The distribution discontinuity of the grain boundary precipitates increases. In addition, for Al–Zn–Mg–Sc–Zr alloy without EXCO, the EIS is comprised by a capacitive impedance arc at high frequency and an inductive impedance arc at low frequency. Once EXCO occurs, the EIS is composed of two capacitive impedance arcs at high frequency and at low frequency, respectively.

An Al-5.8Mg-0.4Mn-0.35(Sc+Zr) (mass fraction, %) alloy sheet was prepared using water chilling copper mould ingot metallurgy processing which was protected by active flux. The influence of stabilizing annealing on mechanical properties and microstructure of the cold rolling sheet was studied. The results show that the strength and hardness of the alloy decrease, while the elongation increases with increasing the stabilizing annealing temperature. With the increase of stabilizing annealing time, the strength and hardness of the alloy drop slightly but its ductility exhibits no change. Partial recovery and recrystallization orderly occur with the increase of annealing temperature during stabilizing treatment. Only different degrees of recovery occur in the alloys annealed below 400 °C for 1 h. Partial recrystallization occurs after annealed at 450 °C for 1 h. By annealing at 300 °C for 1 h, the alloy can obtain the optimum application values of σb, σ0.2 and δ, which are 436 MPa, 327 MPa and 16.7%, respectively.

Corrosion behaviour of different tempers (namely NA, UA, PA and OA) of AlZnMgCuZrSc alloy was studied by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), optical microscopy (OM) and transmission electron microscopy (TEM). Over aged (OA) can decrease the susceptibility to exfoliation due to the discontinuous distribution of the η precipitates at the grain boundaries, cause a negative shift of the corrosion potential (Ecorr), and lead to the prolonging of the time of the appearance of two time constants in impedance diagrams. In addition, AlZnMgCuZrSc alloy with over aged treatment has an enhanced resistance to exfoliation corrosion.

The effects of solution treatment on the microstructure and mechanical properties of Al–Cu–Mg–Ag alloy were studied by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), differential scanning calorimeter (DSC), transmission electron microscopy (TEM) and tensile test, respectively. The results show that the mechanical property increases and then decreases with increasing the solution temperature. And the residual phases are dissolved into the matrix gradually, the number fraction of the precipitation and the size of recrystallized grains increase. Compared to the solution temperature, the solution holding time has less effect on the microstructure and the mechanical properties of Al–Cu–Mg–Ag alloy. The overburnt temperature of Al–Cu–Mg–Ag alloy is 525 °C. The yield strength and the elongation get the best when the alloy is solution treated at 515 °C for 1.5 h, is 504 MPa and 12.2% respectively. The fracture mechanism of the samples is ductile fracture.

The thermal stability of Al-Cu-Mg-Ag alloys under-aged and peak-aged was analyzed by tensile testing and transmission electron microscopy (TEM). And the microstructural evolution and mechanical properties of Al-Cu-Mg-Ag alloy during thermal exposed at elevated temperature were also studied. The results show that the under-aged Al-Cu-Mg-Ag alloy possessed better thermal stability compared with the peak-aged alloy when exposed at 150 . The tensile strength of the peak-aged alloy decreased with prolonging the holding time. While that of the under-aged alloy increased and then decreased with a peak of 524 MPa after exposed for 20 h, which was 19 MPa higher than that of the peak-aged alloy. Meanwhile the precipitations were distributed dispersively and amount of fine phases were observed. The tensile strength of the under-aged alloy was 434 MPa after exposed for 1000 h at 150 . When exposed at 200 , the tensile strength of the under-aged sample decreased and the prolongation increased with prolonging the thermal exposure time. The tensile strength of the sample decreased dramatically when exposed at 250 and 300 and the strengthening phases coarsened dramatically and evolved to the equilibrium phases . The width of the precipitation free zone (PFZ) increased with increasing the thermal exposure temperature and the distribution of the precipitations on the boundaries became discontinuous.

The hot compression behavior of ZK60 magnesium alloy was investigated at the temperatures from 523 to 673K and strain rates from 0.001 to 1s-1 on Gleeble-1500 thermal simulator. The results show that flow stress of ZK60 magnesium alloy decreases with the increase of deformation temperature and the decrease of strain rate. The flow stress curves obtained from experiments can be described in four different stages, i.e., work hardening stage, transition stage, softening stage and steady stage. For higher temperature and lower strain rate, the transition and softening stage are less obvious. The onset of dynamic recrystallization (DRX) occurred before the stress peak in true stress-true strain curves. The critical stress characterizing the onset of DRX rises with the increase of strain rate and/or the decrease of deformation temperature. The constitutive equation of ZK60 magnesium alloy during hot compression was constructed allowing for the effect of true strain on materials constants. The predicted stress-strain curves according to the constitutive equation are in good agreement with experimental results.

The exfoliation corrosion behavior of an Al–Zn–Mg–Cu–Zr alloy containing Sc artificially aged at 120 °C for 24 h is studied by macroscopic observation techniques and electrochemical impedance spectroscopy (EIS) measurements. After 48 h immersion, the blisters start bursting and delamination initiates, along with the appearance of two time constants in the impedance diagrams. According to the simulation by equivalent circuit, the corrosion rate decreases sharply and then reaches a steady state, which is due to the change of the solution pH and oxide layer thickness, as well as the accumulation of corrosion products.

The microstructure and mechanical properties of Al–Cu–Mg–(Ag)–Mn–Zr alloys were studied by means of tensile testing, optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that small additions of Ag to Al–Cu–Mg–Mn–Zr alloy can accelerate the hardening effect of the aged alloy and reduce the time to peak-aged. The mechanical properties can be improved both at room temperature and at elevated temperatures, which is attributed to the fine and uniform plate-like Ω precipitates. Meanwhile the ductility of the studied alloys remains at relatively high level. The major strengthening phases of the Ag-free alloy are θ ′ and less S ′, while that of Al–Cu–Mg–Mn–Zr alloy containing trace amounts of Ag are Ω and less θ ′.

The microstructure evolution in an Al–Cu–Mg–Ag heat-resisted alloy during homogenization was studied by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and differential scanning calorimeter (DSC). The results show that severe dendritic segregation exists in Al–Cu–Mg–Ag alloy ingot. There are many eutectic phases in grain boundary and the distribution of the main elements along interdendritic region varies periodically. The main secondary phase is θ-Al 2 Cu. By increasing the homogenization temperature or prolonging the holding time, the residual phases are dissolved into the matrix gradually, grain boundaries becomes sparse and all elements become more homogenized, which can be described by a constitutive equation in exponential function. The overburnt temperature of Al–Cu–Mg–Ag alloy is 510 °C. And the proper homogenizing process is 500 °C × 16 h, which is consistent with the results of homogenization kinetic analysis.

The flow behavior of Al–Cu–Mg–Ag alloy and its microstructural evolution during hot compression deformation were studied by thermal simulation test. The flow stress increased with increasing the strain rate, and decreased with increasing the deforming temperature, which can be described by a constitutive equation in hyperbolic sine function with the hot deformation activation energy 196.27 kJ/mol, and can also be described by a Zener–Hollomon parameter. The dynamic recrystallization only occurred at low Z values, which must be below or equal to a constant of 5.31 × 10 13 s −1 . With decreasing Z value, the elongated grains coarsed and the tendency of dynamic recrystallization enhanced. Correspondingly, the subgrain size increased and the dislocation density decreased. And the main soften mechanism of the alloy transformed from dynamic recovery to dynamic recrystallization.

The flow stress behavior of Al-3.5Cu-1.5Li-0.25(Sc+Zr) alloy during hot compression deformation was studied by isothermal compression test using Gleeble-1500 thermal-mechanical simulator. Compression tests were preformed in the temperature range of 653–773 K and in the strain rate range of 0.001–10 s−1 up to a true plastic strain of 0.7. The results indicate that the flow stress of the alloy increases with increasing strain rate at a given temperature, and decreases with increasing temperature at a given imposed strain rate. The relationship between the flow stress and the strain rate and the temperature was derived by analyzing the experimental data. The flow stress is in a hyperbolic sine relationship with the strain rate, and in an Arrhenius relationship with the temperature, which imply that the process of plastic deformation at an elevated temperature for this material is thermally activated. The flow stress of the alloy during the elevated temperature deformation can be represented by a Zener-Hollomon parameter with the inclusion of the Arrhenius term. The values of n, α and A in the analytical expressions of flow stress σ are fitted to be 5.62, 0.019 MPa−1 and 1.51×1016 s−1, respectively. The hot deformation activation energy is 240.85 kJ/mol.

The effects of aging on the microstructure, mechanical properties, intergranular corrosion, and exfoliation corrosion of an Al-3.5Cu-1.5Li-0.22(Sc+Zr) alloy have been investigated. The results show that the alloy has the character of age hardening, and the major phase of precipitation and strengthening is the T1 phase. The aging temperature and aging time have a significant effect on the amount and distribution of the T1 phase. The proper artificial single-aging treatment of the alloy is at 160r°C for 40 h. The intergranular corrosion and exfoliation corrosion of the alloy are caused by the anodic dissolution of the T1 phase and the precipitate-free zone (PFZ). With increasing the aging time to overaged, the T1 phase coarsens, and the PFZ widens, leading to an increase in the susceptibility to intergranular corrosion and exfoliation corrosion.

Three kinds of Al-Zn-Mg-Cu based alloys with 0.22%, 0.36%(Sc+Zr) (mass fraction, %), and without Sc, Zr addition were prepared by ingot metallurgy. By using optical microscopy, transmission electronic microscopy and scanning electron microscopy, the effects of microalloying elements of Sc, Zr on the microstructure of super-high-strength Al-Zn-Mg-Cu alloys related to mechanical properties were investigated. The tensile properties and microstructures of the studied alloys under different heat treatment conditions were studied. The addition of minor Sc, Zr results in the formation of Al3(Sc, Zr) particles. These particles are highly effective in refining the microstructures, retarding recrystallization, pinning dislocations and subboundaries. The strength of Al-Zn-Mg-Cu alloys was greatly improved by simultaneously adding minor Sc, Zr, meanwhile the ductility of the studied alloys remains at a higher level. The 0.36%(Sc+Zr) alloys gain the optimal properties after 465 °C/h solution and 120 °C/24 h aging. The increment of strength is mainly due to strengthening of fine grain and substructure and precipitation of Al3(Sc, Zr) particles.

Effects of vacuum, pouring temperature and pattern thickness on the heat transfer of magnesium alloy lost foam casting(LFC) process were explored. The results indicate that without vacuum a positive thermal gradient from the gate to the end of the casting was formed immediately after the mold filling. The average temperature of the casting, the temperature gradient and solidification times increase significantly with pouring temperature and pattern thickness. Vacuum plays a quite different role in the heat transfer during mould filling and solidification periods: it significantly increases the cooling rate of the filling melt, but decreases the cooling rate of the casting during solidification period. The temperature of the liquid metal drops sharply and varies greatly with no apparent mode in the casting after the mold filling. The amplitude of temperature fluctuations in the casting increases with vacuum, pouring temperature and pattern thickness. The average temperature increases with pouring temperature and pattern thickness, but less rapidly than that without vacuum. The effect of vacuum on the solidification times of castings is found to depend on pouring temperature, vacuum makes solidification times increase greatly at high pouring temperature, while decreases slightly at low pouring temperature.

The microstructures of different treated Al-5Mg-0.2Sc-0.1Zr alloys have been studied with optical microscopy and transmission electron microscope (TEM). Coherent particles with the matrix were found in as-cast sample, composite Al3Sc/Al3Zr particles were found after 13 h homogenized treatment under 470 °C. Coherent precipitates pinned dislocations and low-angle grain boundaries, and then restrained recrystallization. All kinds of particles of different treatments were not larger than 40 nm. After high-temperature stabilization treatments, most particles remain coherent with the matrix. The reasons of microstructure change at different treated conditions have been analyzed.

We melted five types of Al-Zn-Cu-Mg-Zr alloys and added 0.0, 0.1, 0.2, 0.3, and 0.5 (wt.%) of scandium. Its influence on the microstructure of alloys and their mechanical properties is studied with the help of optical transmission and scanning electron microscopes. An insignificant amount of scandium promoted the formation of Al3 (Sc, Zr) particles. These particles efficiently clean the microstructure, decelerate and preserve recrystallization, and fix dislocations and substructures. The strength of the alloys increases for high levels of plasticity. It is shown that the optimal properties of the alloys with 0.21% Sc are attained after holding in a solution for 40 min at 475°C and aging for 24 h at 120°C. The strength of the alloys increases mainly as a result of dispersion solidification and microstructural hardening with Al3 (Sc, Zr) particles.