Yasuhiro Uetani

Precipitation sequence of various kinds of metastable phases in Al-1.0mass% Mg2Si-0.4mass% Si alloy

The precipitation of three new types of metastable phases, i.e., TYPE-A, TYPE-B and TYPE-C, with different crystal structures from the β′ phase is proposed from our research on the change in crystal structures and formation sequence of metastable phases during the aging of the Al-1.0mass% Mg2Si-0.4mass% Si alloy by a combination of analytical high resolution electron microscopy and energy dispersive X-ray spectroscopy. The sequence of their formation is explained as follows. First, precipitation of the β′ phase and TYPE-B precipitate, then β′ dissolution into the matrix and degradation of the TYPE-B precipitate. Finally, predominant precipitation of the metastable TYPE-A precipitate. The TYPE-C precipitate appeared heterogeneously in the over-aged condition.

Cu-segregation at the Q'/α-Al interface in Al-Mg-Si-Cu alloy

Abstract Cu segregation was detected at the Q ′ /α-Al interface in an Al–Mg–Si–Cu alloy by energy-filtered transmission electron microscopy. By contrast, in a Cu-free Al–Mg–Si alloy no segregation was observed at the interface between the matrix and Type-C precipitate.

Precipitation sequence in a SiC/Al-Mg2Si alloy composite material

The precipitation sequence of an Al-1.0mass%Mg2Si composite material having 8 vol.% SiC particles was investigated by Vickers micro hardness and specific electrical resistivity measurements, and by TEM observation. The formation of GP zones was suppressed in the composite material and its age-hardenability was reduced. Distribution of precipitates in the composite material was coarser and their size was larger than that in the Al-1.0mass%Mg2Si alloy (base alloy). Some types of precipitates in the composite material were not similar to those found in the base alloy but were similar to those in an Al-1.0mass%Mg2Si alloys with excess silicon (the excess Si alloy). Especially, the metastable phases in the composite material aged at 473 K belonged to the type-A, type-B and type-C precipitates, which are typical metastable phases in the excess Si alloy, instead of the β′ phase that is a typical metastable phase in quasi-binary Al-Mg2Si alloys. The dislocations had little effect on the aging process of this composite material, because of the small number of dislocations introduced by the quenching after solution treatment.

High resolution energy-filtering transmission electron microscopy for equilibrium β-phase in an Al-Mg-Si alloy

High-resolution transmission electron microscopy (HRTEM) has become a popular technique to clarify the precipitation behavior of aluminum alloys. This technique can be used to obtain information on the periodicity of the crystal structure in nano-scaled regions. The chemical composition in such a nano-ordered region is best determined by another method, e.g., energy dispersive X-ray spectroscopy (EDX). However, energy-filtering transmission electron microscopy (EFTEM) succeeds in combining HRTEM and compositional information through electron energy loss spectroscopy (EELS). Recent EFTEM studies have mainly reported on semiconductor device materials. No studies have been reported concerning the crystal structures of precipitates in Al-Mg-Si alloys by EFTEM. This study reports the separation of the lattice images of magnesium and silicon of the equilibrium {beta}-Mg{sub 2}Si phase in an Al-Mg-Si alloy using a new type of 400 kV-EFTEM.

High-resolution elemental maps for three directions of Mg2Si phase in Al-Mg-Si alloy

Elemental maps of the Mg and Si sub-lattices of the Mg2Si phase in an Al-1.0mass% Mg2Si alloy were produced using an energy-filtering transmission electron microscope (EFTEM). Low magnification elemental maps were obtained using both low and high energy loss edges, and the intensities of the high energy loss edges were sufficiently high to allow the Mg2Si phase to be observed at high magnification. High-resolution core-loss images of Mg and Si-K edges were taken parallel to [001], [111] and [110] of the Mg2Si phase. In the [110] direction, Mg and Si atoms were successfully identified as sub-lattices. The Mg atoms formed a 0.39 nm diamond network, whereas the Si atoms formed a 0.32 nm by 0.22 nm rectangular network. This result is in good agreement with the projected potential of the Mg2Si phase in the [110] direction. This is the first report of magnesium and silicon atoms in the Mg2Si phase being successfully identified at the atomic level by EFTEM.

Hexagonal tabular β-phase in Al–Mg–Si–Cu alloy

Abstract A hexagonal plate-shaped β-phase was discovered in Al–0.70at.%Mg–0.36at.%Si–0.21at.%Cu alloy. This phase has the same crystal lattice as β-Mg 2 Si, commonly formed in Cu-free Al–Mg–Si alloys, but a different habit plane, and contains less than 2.0at.%Cu.

Age-Hardening Behaviour and HRTEM Observation of Precipitates in Excess Mg Type Al-Mg-Si-Ag Alloy

In this work, the age-hardening of Al- 1.0 mass% Mg2Si- 0.4 mass% Mg – 0.5 mass% Ag (ex.Mg-Ag alloy) alloy has been investigated. It showed increase of hardness and age-hardening response. Precipitates in this alloy aged at 523 K have been observed by high resolution transmission electron microscopy (HRTEM) and classified into five types based on characteristics in their HRTEM images.

Effect of Granule Size in Semi-Solid Slurry on Rheo-Extrusion of A7075 Aluminum Alloy

Rheo-extrusions of A7075 aluminum alloy were carried out utilizing semi-solid slurries with different solid granule sizes, which were made by a simple method combined a thin upright tube with a water-cooled tube. Every structure of slurries was granular and average solid granule sizes could be controlled by 0.05 to 0.11mm. These slurries were extruded to round bars at extrusion ratio of 36 and press ram speed of 10mm/s mainly, just after cooling to 833K ( fs > 0.9 ). All of the slurries could easily be extruded to bars with smooth surfaces at much low extrusion forces than those of hot-extrusions. Tensile strength of rheo-extruded bars after solution treatment increased with decreasing of the solid granule size. Peak hardness level at T6 condition equivalent to that of hot-extrusion could be obtained at the finest solid granule size.

Rheo-Extrusion of A7075 Aluminium Alloy Utilizing Semi-Solid Slurry Manufactured by Simple Method

In order to extrude A7075 aluminum alloy soundly from melt without using feed stock billet, rheo-extrusion was tried by utilizing semi-solid slurry with fine solid granules made by employing cooling tube. When the melt moving down inside thin tube was adequately cooled in different ways and introduced into an extrusion container kept at semi-solid temperature of 873K, structure of solidified slurries were granular and mean grain sizes of about 60 to 120μm could be obtained. Subsequently, these slurries were extruded to round bars at various extrusion ratios (28 to 64) and press ram speed of 10mm/s, just after cooling to 833K. The newly developed slurries could easily be extruded to bars with smooth surfaces at lower forces. Although every tensile strength of extruded bars were lower than that of hot-extruded one, there was a tendency that finer the solid granules in slurry, higher the tensile strength of extruded bar.

TEM Observation of Metastable Phases in Aged Al-Mg-Ge Alloys

The purpose of study is to investigate aging behavior, crystal structures of metastable phase and relative frequency of metastable phases in aged Al-Mg-Ge and Al-Mg-Ge-Si alloys using high resolution transmission electron microscope (HRTEM), energy dispersive X-ray spectroscopy (EDS) and electron energy-loss spectroscopy (EELS). Every alloy included rod-shaped precipitate which is the same as the typical metastable pahse, ’, in Al-Mg-Si alloy. Except to Mg-rich alloys, the Type-A precipitate, which is a typical metastable phase in the excess Si type Al-Mg-Si alloys and popular at over aged condition, was confirmed as a large rod-shaped precipitates in those alloys. This behavior is probably depends on the ratio of Mg/Ge. Also, Mg, Si and Ge were detected from the ’-phase in Al-Mg-Ge-Si alloy by EELS. This means that the ’-phase in Al-Mg-Ge-Si alloy consists of these 3 elements including Si, not just Ge to form metastable Mg2Ge.