Susumu Ikeno

Effect of Crystal Grain Orientation on Grain Boundary Fracture in Polycrystalline Al‐Zn‐Mg‐Cu Alloy

An Al-Zn-Mg alloy has been known as one of the aluminum alloys with the good age-hardening ability and high strength among commercial aluminum alloys [1]. However, the Al-Zn-Mg alloy usually causes intergranular fracture because of stress concentration at grain boundary to show low ductibility and low toughness. The route of crack propagation for intergranular fracture was considered by Schmid factor (S.F.) and stress transmission factor (Nij) by crystal orientation to the tensile axis [2]. In this study, S.F. and Nij was calculated to tensile axis in Al-Zn-Mg-Cu alloy, and we studied relation between S.F., Nij and the route of crack propagation for intergranular fracture. As a result, the grain boundaries in Al-Zn-Mg-Cu alloy mostly fractured in the group D with the angle of 40°-60°, 80°-90°.

HRTEM Observation of Precipitation in Mg-Gd-Y Alloys during Aging at 473K

Mg-Gd-Y alloys are expected that improves mechanical properties at the room temperature. In this study, Mg-Gd-Y alloys have been investigated to clarify the effect of the Gd/Y ratio and total amount of solute atoms on age-hardening and precipitation using HRTEM and calculations of images and electron density by first principal. In the specimen at as-quenched condition, the row contrasts consisted of bright and dark dots lying on the \({\{ 1\bar 100\} _{Mg}}\) planes, which were considered to monolayer were observed.

Age-Hardening Behavior of Al-Mg 2 Si Alloys with Different Mn and Fe Contents

Microstructure and aging hardness variation of Al-Mg-Si alloys with different Mn or Fe content were investigated to reveal the effect of Mn or Fe on the age hardening behavior of Al-Mg-Si alloy using transmission electron microscopy. The peak hardness of the alloys with small content of Mn or Fe is higher than that of the base alloy; the peak hardness of the alloy with 0.2at.%Fe is similar to that of the base alloy but the peak hardness of the alloy with 0.25at.%Mn is lower than that of the base alloy. Si is expensed to form the dispersoid of AlMnSi or AlFeSi in the alloy with 0.25at.%Mn or 0.2at.%Fe.

TEM Observation of Precipitates in Ag‐Added Al‐Mg‐Si Alloys

The influence of addition of the small amount of transition metals to Al-Mg-Si alloy had reported by many researchers. In the previous our work, β′ phase in alloys Al — 1.0 mass% Mg2Si -0.5 mass% Ag (Ag-addition) and Al -1.0 mass% Mg2Si (base) were investigated by high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED), in order to understand the effect of Ag. In addition, the distribution of Ag was investigated by energy filtered mapping and high annular angular dark field scanning transmission electron microscopy (HAADF-STEM). One Ag-containing atomic column was observed per β’ unit cell, and the unit cell symmetry is slightly changed as compared with the Ag-free β’. In this work, the microstructure of G.P. zone and β’’ phase was investigated by TEM observation, which were formed before β’ phase. The deformed sample by high pressure torsion (HPT) technique before aging was also investigated to understand its effect for aging in this alloy.

Effect of Cold‐Rolling on Age Hardening in Excess Mg‐Type Al‐Mg‐Si Alloys Including Some Minor Elements

It has been known that transition metals improve the mechanical property of Al-Mg-Si alloy. The thermo-mechanical treatment is also effective to improve the strength of Al-Mg-Si alloy. In this work, the aging behavior of deformed excess Mg-type Al-Mg-Si alloy including Ag,Cu,Pt was investigated by hardness test and TEM observation. The value of the maximum hardness increased and the aging time to the maximum hardness became shorter by increasing the amount of the deformation. The age-hardening ability (ΔHV) was decreased with increasing amount of the deformation. The effect of additional element on AHV was also similar to the result of the deformation described above. Comparing the value of the maximum hardness for the alloys aged at 423–523 K, the ex. Mg-Cu alloy was the highest, the ex. Mg-Ag alloy was middle, and the ex. Mg and ex. Mg-Pt alloys were the lowest because of total amounts of added elements.

TEM Observation of Precipitates in Al‐Mg‐Ge Alloys with Different Mg2Ge Contents

It has been known that Al-Mg-Ge alloy shows the similar precipitation sequence to Al-Mg-Si alloy, and its equilibrium phase is β-Mg2Ge according to its phase diagram. In this study, the precipitation sequence of Al-Mg-Ge alloys containing different contents of Mg2Ge has been investigated by hardness test, TEM and HRTEM observation to understand the effect of Mg2Ge contents on age-hardening behavior of these alloys. The hardness of as-quenched and peak-aged samples was improved by increasing Mg2Ge contents. There was no big difference between peak hardness of the alloys with higher Mg2Ge contents aged at 423, 473 and 523 K, which was different from the result of the alloys with lower Mg2Ge contents. The precipitates in the peak-aged samples were classified as some metastable phases, i.e. the β’-phase and parallelogram-type precipitates by HRTEM observation. The relative frequency of these precipitates in the matrix changed with Mg2Ge contents.

Age-hardening Behavior of MgB2 Particle Dispersed Al Alloy Composite Materials

In this work, aging behavior of MgB2 particle dispersed Al-1 mass%Mg2Si alloy composite material which including 4, 8 and 50 vol. % MgB2, was investigated by hardness test and TEM observation to know their age-hardenability. The age-hardenability was observed for the composite materials with 4 and 8 vol. % MgB2 but not for that with 50 vol. % MgB2. The precipitates in these composite materials were also investigated using TEM.

Effect of Cu or Ag Addition on Tensile Deformation in Al‐Zn‐Mg Alloys

In this work, Al-Zn-Mg alloys, which were added with Cu or Ag, were prepared to compare the effect of the additional elements on tensile deformation. Hardness measurement, tensile test, SEM observation have been performed in order to understand the relationship between tensile deformation and crystallographic orientation of Al-Zn-Mg alloys. The addition of Cu or Ag increases the tensile strength of the alloy though decreases the elongation slightly comparing with the base alloy.

Rheo-Extrusion of Hypoeutectic Al-Si-Mg-Fe Alloy

Improvement of poor ductility in normally processed Al-6.7%Si-0.33%Mg-1.2%Fe alloy with coarse intermetallic compound β phases was tried by the rheo-extrusion process utilizing semi-solid slurry, which had been made by a newly developed octagonal rotor process. The obtained slurry had relatively fine solid granules and considerably smaller β phases than those of the usual castings. When rheo-extrusion tests at the constant extrusion ratio of 36 and at the ram speed of 5mm/s were carried out at various semi-solid temperatures, the round bars of 6mm diameter with smooth sound surfaces were obtained except for the tip portions in the every extrusion conditions. Microstructures of the bars consisted of relatively fine equiaxed α-Al grains, indeterminate shaped eutectic silicon and β phases. If a forced-air cooling treatment was given at the adequate position under the die out-let during rheo-extrsion, the extruded bar had an excellent tensile strength and ductility even in T6 aging condition, comparable with those of the iron-free alloy.

Effect of Ag and Cu Contents on the Age Hardning Behavior of Al-Zn-Mg Alloys

Al-Zn-Mg alloy has been known as one of the aluminum alloys with the good age-hardening ability and the high strength among commercial aluminum alloys. The mechanical property of the limited ductility, however, is required to further improvement. In this work, three alloys, which were added Cu or Ag into the Al-Zn-Mg-Si alloy, were prepared to compare the effect of the additional elements on the aging behavior. The content of Ag and Cu were 0.2 at.% and 0.2at.%, respectively. The age-hardening behavior and microstructures of those alloys were investigated by hardness measurement, high resolution transmission electron microscope (HRTEM) and selected area electron diffraction (SAED) technique. Ag or Cu added alloy showed higher peak hardness than Ag or Cu free alloy. According to addition of Ag or Cu, the number density of the precipitates increased than Ag or Cu free alloy.