足立 大樹

Mechanical properties of Hastelloy C-276 substrate with different pre-treatment were investigated. Discontinuous yielding was observed in the solution treated substrate after annealing at the maximum process temperature of IBAD and ISD. In the smooth rolled substrates, yield strength higher than 1 GPa can be attained and even after annealing continuous yielding can be maintained. Annealing enlarges elastic limit by pinning of the mobile dislocations. Microstructure observation using transmission electron microscopy shows that two kinds of candidates for the pinning site of the dislocations exist such as precipitates and short range ordering region in the discontinuous yielding substrate. Improvement of strain at quenching was confirmed by utilizing continuous yielding substrate with higher elastic limit.

The crystallographic orientation distribution, and its change as a function of creep deformation in Ni-based single crystal superalloys have been investigated by X-ray diffractometry. The distribution of the crystallographic orientation has significantly broadened by creep deformations. Directional broadening of the distribution agrees with creep dislocations having the burgers vector of 1/2 < 101 >. High temperature creep strain of superalloys can be estimated by a non-destractive test where the width of rocking curve of a diffraction peak is measured.

The crystallographic orientation distribution, and its change accompanied with tilting gamma / gamma' boundaries in Ni-based single crystal superalloys have been investigated by a theoretical elastic-plastic calculation, X-ray diffractometry and SEM-EBSD analysis. The distribution of the crystallographic orientation has significantly broadened by creep deformations. The broadening can be explained by an unbalance of the amount of creep dislocations of each slip system, which agrees with the result of elastic-plastic calculations. Creep strain of superalloys crept at a condition forming the raft structure can be estimated by the measurement of the width of rocking curve of a diffraction peak.

Metastable precipitates play important roles in a super high strength Al–Zn–Mg based alloy (Mesoalite<sup>®</sup>). The present study was undertaken to examine the composition of the metastable precipitates in Mesoalite<sup>®</sup> and the effect of Mn addition on the composition. The (Zn+Mg) concentration of η′ metastable precipitates detected by 3DAP (three dimensional atom probe) was ~25% in the alloy Al–4.1Zn–3.1Mg–0.57Cu–0.01Ag (at%). By comparing with the results of G.P. zones in an Al–Zn alloy, it was suggested that the intrusion of Al atoms from the matrix lowered the (Zn+Mg) concentration of metastable precipitates detected by 3DAP. A model to quantify the intrusion of Al atoms was developed and applied to the metastable precipitates. The (Zn+Mg) concentration was quantified to be ~65 at% at 383 K and ~75 at% at 413 K. When the alloy contained Mn, furthermore, it was suggested that Mn affected the Zn/Mg ratio of metastable precipitates by lowering the virtual Zn/Mg ratio of the specimen composition.

Metastable precipitates play important roles in a super high strength Al-Zn-Mg based alloy (Mesoalite®). The present study was undertaken to examine the composition of the metastable precipitates in Mesoalite® and the effect of Mn addition on the composition. The (Zn+Mg) concentration of η′ metastable precipitates detected by 3DAP (three dimensional atom probe) was ∼25% in the alloy Al-4.1Zn-3.1Mg-0.57Cu-0.01Ag (at%), By comparing with the results of G.P. zones in an Al-Zn alloy, it was suggested that the intrusion of Al atoms from the matrix lowered the (Zn+Mg) concentration of metastable precipitates detected by 3DAP. A model to quantify the intrusion of Al atoms was developed and applied to the metastable precipitates. The (Zn+Mg) concentration was quantified to be ∼65at% at 383 K and ∼75at% at 413 K. When the alloy contained Mn, furthermore, it was suggested that Mn affected the Zn/Mg ratio of metastable precipitates by lowering the virtual Zn/Mg ratio of the specimen composition.

Nanoparticles should be strong artificial pinning centers in high-temperature superconducting films. We successfully used pulse laser deposition to introduce gold nanoparticles in REBa2Cu3O7-δ (RE = Y, Gd) films. We used small angle X-ray scattering (SAXS) to obtain macroscopic information for the nanoparticles. SAXS showed that the average spacing and radius of the nanoparticles were 110-160 nm and 14-18 nm, respectively, which were consistent with the results from transmission electron microscopy. SAXS also suggested that the interface between the REBa2Cu3O7-δ matrix and the nanoparticles is sharp. This indicated that gold nanoparticles could work as strong artificial pinning centers. © 2006 Elsevier B.V. All rights reserved.

The influence of the stress intensity factor on the microstructure near fatigue crack tips in rail steels was investigated by the orientation analysis using high-resolution EBSP. Large changes in crystal orientation and formation of cell structure were observed around the crack, and a plastic deformation zone was confirmed to be formed by the stress concentration at the crack tip. The size of the maximum plastic zone perpendicular to the crack was quantitatively determined based on the Kernel Average Misorientation, which is the average misorientation between all neighboring pairs of measurement points in the grain, to be 6.9, 8.2 and &gt 50μm for K max = 9.55, 10.88 and 15.84 MPa·m 1/2, respectively. For ΔK eff = 10.39 MPa·m 1/2, a strongly plastic deformation zone of size in 1.3μm formed around the crack, and maximum plastic deformation zone was found outside the strongly plastic deformation zone. Although large misorientation (Δθ ∼ 37.5°) was observed between the strongly plastic deformation zone and the maximum plastic deformation zone, the fluctuation of the crystal orientation inside the strongly plastic deformation zone was comparatively small, and the dislocation density was considered to have been small as well. On the other hand, cell structure was observed in the maximum plastic zone. A large difference in the development of cell structure was observed between the grain having a crack and neighbor grain, indicating that the size of the plastic deformation zone depends strongly on the grain size.

The influence of the stress intensity factor on the microstructure near fatigue crack tips in rail steels was investigated by the orientation analysis using high-resolution EBSP. Large changes in crystal orientation and formation of cell structure were observed around the crack, and a plastic deformation zone was confirmed to be formed by the stress concentration at the crack tip. The size of the maximum plastic zone perpendicular to the crack was quantitatively determined based on the Kernel Average Misorientation, which is the average misorientation between all neighboring pairs of measurement points in the grain, to be 6.9, 8.2 and >50μm for K_<max>=9.55, 10.88 and 15.84 MPa・m^<1/2>, respectively. For ΔK_<eff>=10.39MPa・m^<1/2>, a strongly plastic deformation zone of size in 1.3μm formed around the crack, and maximum plastic deformation zone was found outside the strongly plastic deformation zone. Although large misorientation (Δθ〜37.5°) was observed between the strongly plastic deformation zone and the maximum plastic deformation zone, the fluctuation of the crystal orientation inside the strongly plastic deformation zone was comparatively small, and the dislocation density was considered to have been small as well. On the other hand, cell structure was observed in the maximum plastic zone. A large difference in the development of cell structure was observed between the grain having a crack and neighbor grain, indicating that the size of the plastic deformation zone depends strongly on the grain size.

In order to improve the high-temperature strength of an Al-Cu-Mg alloy, Mn was added at supersaturation to form a high-density dispersion of an intermetallic phase. In the P/M Al-3.6Mn6.4Cu-3.6Zn-1.7Mg alloy (mass%), rod-like Al-Mn-Cu-Zn quaternary intermetallic phases (Q phase) several hundred nanometers in length were dispersed in the matrix. The chemical composition of the Q phase was determined by TEM/EDX to be 78.8Al-12Mn-8Cu-1.2Zn (at%). The crystal system, space group, and lattice parameters of the unit cell were identified to be orthorhombic, Cmcm and a = 0.76, b = 2.11, c = 1.25 mn, respectively, by Rietveld analysis. Since the matrix of the alloy obtained was of the Al-Cu-Mg-(Zn) system, age-hardening occurred by formation of a GPB zone at room temperature and 448 K. At the peak level of age-hardening at room temperature, the tensile strength at room temperature was 704 MPa, and the elongations were 8.0%. The high temperature strengths at 523 and 573 K were 319 and 141 MPa, respectively, and the elongations were 17 and 34%, respectively.

The effect of extrusion rate and ratio on the Al3Zr induced dynamic recrystallization. (DRX) that occurs during hot extrusion of RS-P/M Al-Zn-Mg-Cu-Zr alloys was investigated. An increase in the logarithm of extrusion rate promoted DRX and lead to a monotonic increase in the number of fine grains. Although DRX was also promoted and the grain size reduced by an increase in extrusion ratio from 10 to 20, the DRX behavior hardly changed, even when the extrusion ratio exceeded 20. However, with increasing extrusion ratio, the width of fibrous grain, i.e., the unrecrystallized region, decreased and the tensile strength increased to 879 MPa. When the extrusion rate and ratio exceeded 54 mm/min and 20, respectively, a marked grain coarsening occurred upon solution treatment, and the tensile strength tended to decrease, because of the high dislocation density induced by hot extrusion. By annealing at 563 K before solution treatment, it was possible to prevent grain coarsening, and thus prevent the strength decrease.

The Mesoalite alloy is formed using rapidly solidified powder metallurgy (RS-P/M) by hot extruding the RS powder produced by the atomization method. Meso20 is a Mesoalite alloy with a chemical composition of Al-9.5Zn3Mg-1.5Cu-4Mn-0.04Ag (mass%). Meso20 contains fine grains and precipitated intermetallic Mn compounds, and has a tensile strength of 910 MPa. During hot extrusion, dynamic recrystallization occurs and the fine grains develop. During heat treatment of Meso20, rod-like and granular Mn intermetallic compounds precipitate. The rod-like compounds are about 1 Im in length and the granular compounds are about 1 Im in diameter. X-ray diffraction measurement transmission electron microscopy and energy dispersive X-ray (TEM/EDX) analysis and Rietveld analysis revealed the chemical composition of the granular and rod-like Mn intermetallic precipitates to be 86.5Al-10.9Mn-0.4Cu-0.9Zn-1.3Mg and 80.5Al-10.3Mn-4.2Cu-2.5Zn-2.5Mg (mass%), respectively. The granular and rod-like compounds were identified as the Al6Mn and Q phases, respectively, with both belonging to the space group Cmcm. The lattice constants of Al6Mn were a=0.754 nm, b=0.648 nm c=0.855 nm and those of the Q phase were a=0.765 nm b=2.34 nm c=1.25 nm. Meso10, with a chemical composition of Al-9.5Zn-3Mg-1.5Cu-0.04Ag (mass%), contains no Mn and does not have fine grains, but rather coarse fibrous grains elongated along the extrusion direction. Thus the Mn intermetallic precipitates in Meso20 clearly affect the formation of fine grains. Microstructure development was studied during hot extrusion by observation using high resolution Electron Back Scattering Pattern method. Fine grains were found to develop in areas, which were relatively abundant in granular Mn intermetallic precipitates.

The local geometry around hydrogen and activation energies for hydrogen transfer in undoped, Y-and Al-doped SrZO(4), have been studied using the density functional theory under the generalized gradient approximation. It is shown that strong, O-H bond is formed and orientated towards the outside of the ZrO6 octahedron in SrZrO3. The hydrogen tends to approach the dopant ion in the doped oxides. It is found that large local distortion is induced around hydrogen and dopant ion, and affects the activation energy of hydrogen transfer largely. The calculated activation energies are in agreement with the experimental values in the doped oxides.

Multiple cracking behavior and its relation to the grain boundary of the substrate steel were investigated. The crack spacing and its distribution of the specimens strained to prescribed strains were observed with a scanning electron microscope. The crystallographic orientation of the substrate grains was estimated from the electron back scattering pattern. The images of the cracks of the coating layer and grain bound-aries of the substrate steel were combined together with image processing software to know whether the cracking of coating layer initiates above the substrate grain boundaries or not. The main results are summarized as follows. (1) The cracking of the coating layer initiates in the regions just above the substrate grain boundaries. (2) The cracks that initiate above the substrate grain boundaries propagate transversely ; namely they propagate into the region, below which no substrate grain boundary exists. (3) It was suggested the cracking of the coating layer initiates above the small angle grain boundaries or above the grain boundaries intact to the grains with large Schmid factors. (4) In the multiple cracking process of the coating layer, the similarity of the crack spacing distribution to the grain boundary spacing distribution is kept.

The presence of Al3Zr precipitates promotes continuous dynamic recrystallization in Al-Zn-Mg alloys during hot extrusion, resulting in a fine-grained structure. The mechanism for this phenomenon was investigated by observing the change in microstructure under hot extrusion using high resolution EBSP. In the rear of the extrusion die mouth, grain boundary mobility is low since the flow stress is comparatively low and grain boundary migration is inhibited by Al3Zr particles. Thus, in order to reduce the deformation-induced high dislocation density, continuous dynamic recrystallization occurs, which does not involve long-range grain boundary migration, resulting in a finer-grained structure. The flow stress. and hence. the mobility of the grain boundary increase near the die month. This pomotes long-range grain boundary migration. which reduces the dislocation density. Continuous dynamic recrystallization is not observed under these conditions. Since Al3Zr precipitates inhibit long-range gain boundary migration. increase of the Al3Zr precipitate content expands the region where continuous dynamic recrystallization occurs towards the die mouth. resulting in a finer-grained structure.

The presence of Al3Zr precipitates promotes continuous dynamic recrystallization in Al-Zn-Mg alloys during hot extrusion, resulting in a fine-grained structure. The mechanism for this phenomenon was investigated by observing the change in microstructure under hot extrusion using high resolution EBSP. In the rear of the extrusion die mouth, grain boundary mobility is low since the flow stress is comparatively low and grain boundary migration is inhibited by Al3Zr particles. Thus, in order to reduce the deformation-induced high dislocation density, continuous dynamic recrystallization occurs, which does not involve long-range grain boundary migration, resulting in a finer-grained structure. The flow stress. and hence. the mobility of the grain boundary increase near the die month. This pomotes long-range grain boundary migration. which reduces the dislocation density. Continuous dynamic recrystallization is not observed under these conditions. Since Al3Zr precipitates inhibit long-range gain boundary migration. increase of the Al3Zr precipitate content expands the region where continuous dynamic recrystallization occurs towards the die mouth. resulting in a finer-grained structure.

In this study, the microstructure of hot-extruded and under-extruded Zr bearing aluminum alloys (Mesoalite 10^®-1.3mass%Zr) was investigated by high-resolution EBSP analysis and the effect of Zr addition on microstructure formation during hot extrusion was studied. In an extruded Zr free alloy, coarse fibrous grains elongated to the extrusion direction were predominantly evolved. And these grains were considered to be formed by elongation of the original equi-axial grains by extrusion. Whereas, in extruded Meso10-1.3Zr alloy, many fine grains were evolved near the grain boundaries of the fibrous grains. In under-extruded Meso10-1.3Zr alloy, inhomogeneous local strains were developed near random grain boundaries and new fine grains were formed by continuous dynamic recrystallization. It is considered that in aluminum alloys, the addition of Zr promotes continuous dynamic recrystallization during hot extrusion.

We have fabricated biaxially textured Ni and Ni-0.1 mass%Cr (Ni-Cr) tapes, and crystal orientation and microstructure of CeO<SUB>2</SUB> films deposited on the tapes by pulsed laser deposition were investigated. Recrystallized Ni-Cr tapes had a strong cube texture, {100}‹001› orientation, and the surface of the tapes was occupied by the (100) oriented grains. CeO<SUB>2</SUB> films grown on the Ni-Cr surface showed both the (100) preferred orientation and the strong in-plane alignment. Although recrystallized Ni tapes exhibited the {100}‹001› texture and the CeO<SUB>2</SUB> films subsequently deposited on the tapes also have (100) orientation, a large number of (111) oriented grains were included in the films. The difference between the films deposited on the Ni-Cr and the pure Ni tapes depended on the degree of the cube texture and the surface flatness of the tapes. The preferred orientation of CeO<SUB>2</SUB> films was also affected by the oxygen partial pressure during pulsed laser deposition, and the strong (100) orientation was attained under the pressure of 2.7×10<SUP>-3</SUP> Pa. Moreover, the degree of the (100) orientation of CeO<SUB>2</SUB> films was improved with increase of the film thickness. The microstructure of the films and its texture evolution mechanism were discussed.

We have fabricated biaxially textured Ni and Ni-0.1 mass%Cr (Ni-Cr) tapes, and crystal orientation and microstructure of CeO₂ films deposited on the tapes by pulsed laser deposition were investigated. Recrystallized Ni-Cr tapes had a strong cube texture, {100}‹001› orientation, and the surface of the tapes was occupied by the (100) oriented grains. CeO₂ films grown on the Ni-Cr surface showed both the (100) preferred orientation and the strong in-plane alignment. Although recrystallized Ni tapes exhibited the {100}‹001› texture and the CeO₂ films subsequently deposited on the tapes also have (100) orientation, a large number of (111) oriented grains were included in the films. The difference between the films deposited on the Ni-Cr and the pure Ni tapes depended on the degree of the cube texture and the surface flatness of the tapes. The preferred orientation of CeO₂ films was also affected by the oxygen partial pressure during pulsed laser deposition, and the strong (100) orientation was attained under the pressure of 2.7×10^-3 Pa. Moreover, the degree of the (100) orientation of CeO₂ films was improved with increase of the film thickness. The microstructure of the films and its texture evolution mechanism were discussed.

The stress corrosion cracking (SCC) resistance of hot-extruded P/M Al-Zn-Mg alloys, Mesoalite, was investigated as compared with that of I/M Al-Zn-Mg alloys and the correlation between stress corrosion resistance and microstracture was studied. SCC resistance about P/M alloys was high as compared with that of I/M alloys and when the solute concentration increased, reduction of SCC resistance about P/M alloys was not observed. The difference in width of PFZ, distribution of precipitates on grain boundary, the amount of metastable phase precipitated in the matrix, tilt angle of grain boundary, grain size and shape was investigated as a cause of the difference of SCC resistance. The large change in the size and shape of grain among these factors was observed. In the P/M alloys, the fiber-like grain elongated to the extruded direction was observed to the equi-axial grain having been observed in the I/M alloys. When stress was applied parallel to elongated grains, the stress perpendicular to the grain boundary was low. Since the SCC resistance is improved when the applied stress perpendicular to the grain boundary is small, it is concluded that the SCC resistance of the P/M alloys which has the fiber-like grain elongated to the ED became large.

The stress corrosion cracking (SCC) resistance of hot-extruded P/M Al–Zn–Mg alloys, Mesoalite, was investigated as compared with that of I/M Al–Zn–Mg alloys and the correlation between stress corrosion resistance and microstracture was studied. SCC resistance about P/M alloys was high as compared with that of I/M alloys and when the solute concentration increased, reduction of SCC resistance about P/M alloys was not observed. The difference in width of PFZ, distribution of precipitates on grain boundary, the amount of metastable phase precipitated in the matrix, tilt angle of grain boundary, grain size and shape was investigated as a cause of the difference of SCC resistance. The large change in the size and shape of grain among these factors was observed. In the P/M alloys, the fiber-like grain elongated to the extruded direction was observed to the equi-axial grain having been observed in the I/M alloys. When stress was applied parallel to elongated grains, the stress perpendicular to the grain boundary was low. Since the SCC resistance is improved when the applied stress perpendicular to the grain boundary is small, it is concluded that the SCC resistance of the P/M alloys which has the fiber-like grain elongated to the ED became large.

The super high strength Al–Zn–Mg based alloy (Mesoalite20^®) with a chemical composition of Al–9.5Zn–3Mg–1.5Cu–4Mn–0.5Zr–0.02Ag in mass% includes two type of precipitates of Q and Al₆Mn phases. The Q precipitates have a quaternary composition and fine rod-like shape, but Al₆Mn has round and irregular shape. After compaction of air-atomized powder by CIP, the Q and Al₆Mn phases precipitated in sequence during heating. By hot extrusion at 773 K, their precipitates flowed along extrusion direction and only Q precipitates aligned well, which have been known to be very effective to fiber-reinforcement. When increasing Mn content from 4 to 7 mass% with constant of 1.5 mass% Cu, the amount of Al₆Mn increased remarkably. Consequently the compressive strength and plastic elongation to fracture decreased with increasing Mn content. When increasing Cu content from 0.5 to 2.5 mass% with constant of 4 mass% Mn, on the other hand, the amount of Q phase increased and their mechanical property improved slightly with increasing Cu content. Therefore the present study has proposed a new alloy with higher Cu content, which gives higher strength than that of commercial Mesoalite 20.

Extremely high strength AlZnMgCu alloys are developed. The strength is suggested to be related to the multiple effect due to precipitation hardening and fiber reinforcement as well as fine grain strengthening. The contribution of nano-scale precipitates to the mechanical properties is analyzed.

Recently super-high strength alloys have been developed in Al-Zn-Mg based alloys. The major phase contributing the strength was suggested to be T' metastable phase by preliminary experiments. Here we report the details about precipitation behavior of T' metastable phase. The Vickers hardness test, SAXS measurement and DSC measurement were carried out for the specimens with different Zn/Mg ratio aged at 383 similar to 423K for various times. The highest Vickers hardness was 269 for the specimen with effective Zn/Mg=0.49, aged at 383K for 108ks. On the basis of the phase diagram and the results of DSC measurement, the region of three different kinds of metastable phase,T',eta' and beta' has been determined. From the SAXS measurement, the radius and the interparticle distance of metastable phase are found to increase monotonously by aging. The finer and denser T' precipitates grew comparing with other phases for the peak aging condition. The volume fraction tended to increase with increasing aging temperature. The electron density difference between the matrix and the T' precipitates became small.

The effects of thermo-mechanical treatment (TMT) on grain refining and high temperature deformation properties have been investigated for the alloy with chemical composition of AI-9.6Zn-3.OMg- 1.4Cu-0.04Ag-0.4Zr in mass% fabricated by hot-extrusion from rapidly solidified powders The present TMT consisted of aging at 498 K for precipitation of T phase (Mg32(Zn, Al)49) and subsequent warm rolling at the same temperature. Due to aging up to 7.2 ks at 498 K, extremely fine T phase precipitated homogeneously in the matrix. At the next warm rolling step, those fine precipitates contributed to form the uniform dislocation cell structure with high number density. The microstructure analysis by means of XRD and TEM made clear that their dislocation cell structure recrystallized continuously and transformed to very fine (sub-) grain structure with average size of 0.45 μm at the tensile testing temperature of 718 K. The fine grain structure was stabilized by the distribution of fine Al3Zr particles. Thus the high strain rate superplastic behavior realized for the warm rolled specimens after aging at 498 K for about 7.2 ks. On the other hand, the warm rolled specimens after aging at 498 K for the longer time than 18 ks formed a very coarse grain structure and resulted in a poor superplasticity. The reason has been discussed on the basis of discontinuous recrvstallization theorem.

The effects of thermo-mechanical treatment (TMT) on grain refining and high temperature deformation properties have been investigated for the alloy with chemical composition of Al–9.6Zn–3.0Mg–1.4Cu–0.04Ag–0.4Zr in mass% fabricated by hot-extrusion from rapidly solidified powders The present TMT consisted of aging at 498 K for precipitation of T phase (Mg<sub>32</sub>(Zn, Al)<sub>49</sub>) and subsequent warm rolling at the same temperature. Due to aging up to 7.2 ks at 498 K, extremely fine T phase precipitated homogeneously in the matrix. At the next warm rolling step, those fine precipitates contributed to form the uniform dislocation cell structure with high number density. The microstructure analysis by means of XRD and TEM made clear that their dislocation cell structure recrystallized continuously and transformed to very fine (sub-) grain structure with average size of 0.45 μm at the tensile testing temperature of 718 K. The fine grain structure was stabilized by the distribution of fine Al<sub>3</sub>Zr particles. Thus the high strain rate superplastic behavior realized for the warm rolled specimens after aging at 498 K for about 7.2 ks. On the other hand, the warm rolled specimens after aging at 498 K for the longer time than 18 ks formed a very coarse grain structure and resulted in a poor superplasticity. The reason has been discussed on the basis of discontinuous recrystallization theorem.

In order to investigate the nature of metastable phase appeared in super-high strength aluminium alloys (Mesoalite), several alloys were prepared by changing the Zn/Mg composition ratio, while Cu, Mn and Ag solute concentrations were kept constant. The effective Zn/Mg ratio dependence of the volume fraction (V_f) of metastable precipitates and the electron density difference (Δρ) between precipitate and matrix was determined from the small angle scattering intensity. The change of solute atom partition within the grains was previously reported to take place mainly for Zn and Mg during isothermal aging at 383 K. Based on the previous result, the phase diagrams of Al-Zn-Mg ternary systems were calculated by using a computer soft, ThermoCalc. In order to consider the coherent interface between matrix and metastable precipitates, the elastic strain energy was introduced into the chemical free energy. Two phases equilibria were calculated for α′+T′ and α′+η′ systems. The calculated results of V_f and Δρ could explain well the experimental data. Consequently, the metastable T′ phase is suggested to precipitate in the specimens with effective Zn/Mg ratio less than unity, while the η′ metastable phase appears in the specimen with the ratio of about 2.

High strength aluminum alloys were aged at 383 K. Their aluminum alloys were made clear to consist of two major substructures with different scale, metastable phase wilh a few nm size precipitated in the matrix and the quaternary rod-like intermediate phase with a few micrometer length containing Mn. Thc remarkable strengthening is dominantly attributed 10 the precipitation hardening due to fine metastable phase. In order to get further high strength, we have carried out systematic investigation using the various Al-Zn-Mg-Cu based alloys with different compositions of Zn and Mg. By a synchrotron radiation small angle scattering technique, the structure change of the alloys during isothermal aging was examined. The change of Vickers hardness during isothermal aging, could be well expressed as a function of the square root of particle size multiplied by volume fraction of metastable precipitates, suggesting the coherency strain model for the interaction of precipitate with dislocation. The coherency strain for each alloy was experimentally estimated.

High strength aluminum alloys were aged at 383 K. Their aluminum alloys were made clear to consist of two major substructures with different scale; metastable phase with a few nm size precipitated in the matrix and the quaternary rod-like intermediate phase with a few micrometer length containing Mn. The remarkable strengthening is dominantly attributed to the precipitation hardening due to fine metastable phase. In order to get further high strength, we have carried out systematic investigation using the various Al–Zn–Mg–Cu based alloys with different compositions of Zn and Mg. By a synchrotron radiation small angle scattering technique, the structure change of the alloys during isothermal aging was examined. The change of Vickers hardness during isothermal aging, could be well expressed as a function of the square root of particle size multiplied by volume fraction of metastable precipitates, suggesting the coherency strain model for the interaction of precipitate with dislocation. The coherency strain for each alloy was experimentally estimated.