Inelasticity and precipitation of germanium from a solid solution in Al-Ge binary alloys (original) (raw)
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Physics of the Solid State, 2014
The structure, Young's modulus defect, and internal friction in aluminum-germanium alloys have been studied under conditions of longitudinal elastic vibrations with a strain amplitude in the range of 10-6-3 × 10 ⎯4 at frequencies about 100 kHz. The ribbon shaped samples of the alloys with the germanium content from 35 to 64 wt % have been produced by drawing from the melt by the Stepanov method at a rate of 0.1 mm/s. It has been shown that the dependences of the Young's modulus defect, logarithmic decrement, and vibration stress amplitude on the germanium content in the alloy at a constant strain amplitude have an extremum at 53 wt % Ge. This composition corresponds to the eutectic composition. The dependences of the Young's modulus defect, the decrement, and vibration stress amplitude at a constant microstrain amplitude have been explained by the vibrational displacements of dislocations, which depend on the alloy structure.
Effects of trace elements (Y and Ca) on the eutectic Ge in AleGe based alloys
Effects of trace elements (0.2Y and 0.2Ca (wt%) on the eutectic Ge in high purity Ale20Ge (wt%) alloys were investigated by multi-scale microstructure characterization techniques. Particularly, the distribution of trace elements (Y and Ca) within the eutectic Ge and/or at the interface between eutectic Ge and eutectic Al was investigated by atomic resolution high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) imaging and atom probe tomography (APT). The combined investigations indicate AleY and AleCa co-segregations. Such co-segregations change significant morphology and growth of the eutectic Ge. In addition, large Al 2 Ge 2 Y and Al 2 Ge 2 Ca phases were also measured. The modification of eutectic Ge is discussed in terms of previously postulated modification mechanisms: twin plane re-entrant edge growth mechanism, impurity-induced twinning, and growth restriction of eutectic Ge.
Metallurgical and Materials Transactions, 2015
It is shown that strength loss in a 6060 Al-Mg-Si alloy caused by reduction in solute can be compensated by adding back smaller quantities of Ag, Ge and Cu. Nine alloys were investigated. Ge was found to be the most effective addition, strongly refining the precipitation. The hardness is discussed in terms of statistics of the precipitates near a T6 condition, as acquired by transmission electron microscopy. Precipitates in some conditions were also investigated by high angle annular dark field scanning transmission electron microscopy. The added elements have strong influence on the main hardening precipitate, '', changing its structure and promoting disorder.
Germanium network connecting precipitates in an Mg-rich Al-Mg-Ge alloy
Journal of Electron Microscopy, 2010
Precipitates in an Al-0.87Mg-0.43Ge (at.%) alloy, heat-treated for 16 h at 200 degrees C, were investigated by transmission electron microscopy and annular dark-field scanning transmission electron microscopy (ADF-STEM). Earlier studies of Al-Mg-Si-(Cu) have shown that an Si network exists within all precipitates. Here, it was investigated whether the heavier, more easily detectable germanium atom would behave similarly. The precipitates were more similar to those found in Al-Mg-Si-Cu alloys with a high fraction of disordered phases than to ternary Al-Mg-Si. All precipitate cross-sections along [001]Al imaged by ADF-STEM showed that Ge atoms arrange in triangular columns separated by approximately 0.4 nm. Along these columns, the precipitate's 0.405-nm periodicity and coherency (along its needle axis) imply a Ge plane periodicity of 0.405 nm. A germanium network, therefore, exists in all precipitates in this alloy, with a hexagonal sub-cell (SC) a = b approximately 0.4 nm, c = 0.405 nm, which is very similar to the Si network in Al-Mg-Si-(Cu). The network always appears as ordered. Disorder in a precipitate must, therefore, be caused by the other atoms in the structure between Ge atoms. One difference between precipitates of the ternary systems Al-Mg-Ge and Al-Mg-Si is the orientation of the diamond element network (SC) base in {001}Al. In Al-Mg-Ge, a <100>SC edge falls along <100>Al. This coincides with the orientation in some precipitates in quaternary Al-Mg-Si-Cu. In ternary Al-Mg-Si, one SC base is parallel with a <510>Al direction.
Alloying of immiscible Ge with Al by ball milling
Materials Letters, 2003
Mechanical alloying (MA) is a versatile technique to produce nanocrystalline and amorphous alloys. Its special advantage is to form alloys of immiscible elements. High energy planetary ball milling has been used to produce Al -2 wt.% Ge alloy. Powders of Al (1 -125 Am) and Ge (0.5 -2 Am) were milled together with a powder to ball weight ratio of 1:20 up to 400 h. The size and shape of the elemental and alloy powder particles were examined in a scanning electron microscope (SEM) while their microanalysis was performed by energy dispersive system (EDS) attached with SEM. It has been observed that 300 h of milling produces homogeneous alloy. X-ray diffraction (XRD) patterns confirm complete alloying of Ge with Al. As the size of the atoms of Al and Ge are different, elastic strain energy because of misfit has been calculated to be about 2.6 kcal/mol. It has been concluded that among the factors contributing towards the enthalpy, stress exerted by dislocations on solute atoms is the major driving force for alloying. D
2014
Ultrafine-grained (UFG) binary Al-xMg (x=1, 5 and 7 wt %) alloys were processed by equal channel angular pressing (ECAP) at room temperature via route Bc combined with inter-pass annealing. The effects of Mg content, grain size and strain rate on mechanical properties and dynamic strain aging (DSA) behaviour of the Al-Mg alloys upon tensile testing at room temperature were studied. An increase in Mg content from 5 to 7 wt % leads to a pronounced increase in strength and uniform elongation in both the as-homogenized and as-ECAP Al-Mg alloys. Thereby, the Al-7Mg alloy, either prior to or after ECAP processing, possess significantly higher strength and comparable or even higher uniform elongation than the more dilute Al-Mg alloys. However, the as-ECAP Al-Mg alloys exhibit significantly higher strength but little work hardening and hence rather limited uniform elongation. In general, decreasing grain size leads to significant increase in strength while dramatic decrease in ductility.
Ordering and structural properties of liquid Al–Ge alloys
Journal of Non-crystalline Solids, 1999
A variational method based on thermodynamics of hard sphere system and pseudopotential perturbation scheme is used to determine the properties of mixing of liquid Al±Ge alloys as a function of composition. Entropy of mixing and concentration¯uctuations are then obtained for hard sphere systems which are compared with the results of the quasilattice theory. The nature of atomic order in the liquid is discussed from the results of the concentration¯uctuations in the long wavelength limit and from the chemical short range order. Ó 0022-3093/99/$ ± see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 -3 0 9 3 ( 9 9 ) 0 0 2 5 6 -2
Characterization of the structure and precipitation process in Al-Mg-Si and Al-Mg-Ge casting alloys
2015
The Al-Mg-Si alloys recently applied in foundry show an excellent combination of strength and plasticity, but information about composition structure phases and the effect of heat treatment on the precipitation process are rather scanty. Even less information is available for the Al-Mg-Ge system. Therefore, the aim of this thesis is to provide the knowledge about structure, composition and precipitates in nine Al-Mg-Si and Al-Mg-Ge casting alloys with and without Mn, Li and Sc+Zr additions. Three conditions, as cast, solution treated and aged, were investigated and the results were compared with those of three commercial alloys. The eutectic melting temperatures for both systems were recorded by differential scanning calorimetry and gave for Al-Mg-Si-587.0°C, for Al-Mg-Ge-629.0°C. It was shown that in as-cast state, the structure of an alloy having the nominal composition AlMg7Si3 consists of four phases: first-the Al based solid solution, second-the (Al)+(Mg 2 Si) eutectic, third-the primary Mg 2 Si crystals and fourth-the α-Al(Mn,Fe)Si phase. Similar phases were observed in the AlMg4.3Ge6.49 alloy: Al based solid solution, (Al)+(Mg 2 Ge) eutectic, primary Mg 2 Ge crystals and α-Al(Mn,Fe)Ge. After two days of storing in an as-cast condition, the solid solution in all tested alloys decomposes and forms zebra-crossing shaped precipitates. TEM examinations revealed that these precipitates nucleate heterogeneously on dislocations. The solution treatment at 575.0°C results in spheroidization of the eutectic, dissolution of the precipitates and formation of α-Al(Mn,Fe)Si dispersoids, nucleating on the surfaces of Mg 2 Si and Mg 2 Ge lamellas. In the Sc+Zr containing alloys, the formation of Al 3 (Sc 1-x Zr x) was detected after 120 min soaking. Further heating resulted in the growth of these precipitates. Aging of the Al-Mg-Si and the Al-Mg-Ge alloys leads to an increase of hardness in all studied alloys. This effect is mainly related to precipitation strengthening, via solid solution decomposition and formation of ''phase in the Al-Mg-Si alloys and U1 Ge phase in the Al-Mg-Ge alloys. Additionally, in Li-alloyed specimens, plates of β Mg 2 Si phase were observed together with small cubic-shaped ' Al 3 Li precipitates. The obtained results were compared with those of three commercial casting alloys, namely Magsimal 59 (Al-Mg-Si system), A201.0 (Al-Cu system) and A356.0 (Al-Si-Mg system). The macro and microhardness properties of the developed alloys are lower than those of the high strength A201.0 alloy, but higher than those of A356.0 casting alloy. This demonstrates the promising potential of the Al-Mg-Si and the Al-Mg-Ge system for the design of novel casting alloys and the development of the first Li-containing casting alloys with reduced density.