10,235 research outputs found
The assessment of GPB2/S" structures in Al-Cu-Mg alloys
No full textBased on experimental data presented in the literature, we propose a new structure for GPB2/S?? with the composition of Al10Cu3Mg3, which is aluminium-rich compared to S phase (Al2CuMg). The proposed structure is coherent with the fcc. Al matrix, is formed by the replacement of some Al atoms with Cu/Mg, and has orthorhombic structure (space group Imm2) with lattice parameters a = 0.405 nm, b = 1.62 nm and c = 0.405 nm. Simulated high resolution electron microscopy images and simulated diffraction patterns are compared with experimental data on a range of Al–Cu–Mg alloys. A good correspondence is found
The thermodynamics of and strengthening due to co-clusters: general theory and application to the case of Al-Cu-Mg alloys
Get PDFCo-clusters in ternary or higher order metallic alloys are metastable structures involving two or more distinct alloying atoms that retain the structure of the host lattice. A thermodynamic model based on a single interaction energy of dissimilar nearest neighbour alloying elements is presented, and a model for the strengthening due to these co-cluster dimers is derived. The model includes a new treatment of (short-) order strengthening relevant to these co-clusters and further encompasses modulus hardening and chemical hardening. The models are tested against data on a wide range of Al-Cu-Mg alloys treated at temperatures between 20 and 220ºC. Both quantitative calorimetry data on the enthalpy change due to co-cluster formation and strengthening due to co-clusters is predicted well. It is shown that in general (short-range) order strengthening will be the main strengthening mechanism
A new structure of Nd1+?Fe4B4 phase in NdFeB magnet
No full textA new structure for Nd1+eFe4B4 phase has been observed, which has the same structure as Gd1+eFe4B4. The compound has Pccn structure with a = 0.71 nm and c = 2.74 nm, and its composition was found to be Nd2Fe7B7
Estimation of dislocation densities in cold rolled Al-Mg-Cu-Mn alloys by combination of yield strength data, EBSD and strength models
No full textAl-Mg-Cu-Mn alloys have been developed for the packaging industry, in which large cold-working deformations are normally applied that can produce high dislocation densities. In this study, we present a simplified model for the yield strength contributions and apply that to obtain the dislocation densities by determining the orientation factors, which can be obtained via the crystal information of electron backscatter diffraction (EBSD). One alloy subjected to three cold-rolling reductions (10%, 40% and 90%) has been analysed by EBSD, and the density of dislocations are estimated using the strengthening model. This assessment suggests that dislocation densities by the Taylor model are roughly consistent but slightly lower than those determined by transmission electron microscopy
A model for the yield strength of Al-Zn-Mg-Cu alloys
No full textA model for the yield strength of multi-component alloys is presented and applied to overaged Al–Zn–Mg–Cu alloys (7xxx series). The model is based on an approximation of the strengthening due to precipitate bypassing during precipitate coarsening and takes account of ternary and higher order systems. It takes account of the influence of supersaturation on precipitation rates and of volume fraction on coarsening rates, as well crystallographic texture and recrystallisation. The model has been successfully used to fit and predict the yield strength data of 21 Al–Zn–Mg–Cu alloys, with compositions spread over the whole range of commercial alloying compositions, and which were aged for a range of times and temperatures to produce yield strengths ranging from 400 to 600 MPa. All but one of the microstructural and reaction rate parameters in the model are determined on the basis of microstructural data, with one parameter fitted to yield strength data. The resulting accuracy in predicting unseen proof strength data is 14 MPa. In support of the model, microstructures and phase transformations of 7xxx alloys were studied by a range of techniques, including differential scanning calorimetry (DSC), electron backscatter diffraction (EBSD) in an SEM with a field emission gun (FEG-SEM)
A simple approach of determination of the crystallographic orientation: Applications and accuracy
No full textA simple analytical solution for the crystallographic orientation is described. This method is based on one indexed Kikuchi pair in a known zone rather than the corresponding diffraction spots. The accuracy of this method is shown to be better than 0.1° even for cases in which a zone axis deviates by a large angle (e.g. 10°) from the centre of the beam direction. This approach simplifies experiments beacuse only one pair of Kikuchi lines and a zone axis are needed, and is especially suited when it is difficult or cumbersome to resolve a second pair of Kikuchi lines with sufficient accuracy
Two types of S phase precipitates in Al-Cu-Mg alloys
No full textTransmission electron microscopy (TEM) and differential scanning calorimetry (DSC) have been used to study S phase precipitation in an Al-4.2Cu-1.5Mg-0.6Mn-0.5Si (AA2024) and an Al-4.2Cu-1.5Mg-0.6Mn-0.08Si (AA2324) (wt-%) alloy. In DSC experiments on as solution treated samples two distinct exothermic peaks are observed in the range 250 to 350°C, whereas only one peak is observed in solution treated and subsequently stretched or cold worked samples. Samples heated to 270°C and 400°C at a rate of 10°C/min in the DSC have been studied by TEM. The selected area diffraction patterns show that S phase precipitates with the classic orientation relationship form during the lower temperature peak, and for the solution treated samples, the higher temperature peak is caused by the formation of a second type of S phase precipitates which have an orientation relationship that is rotated by ~4 degrees to the classic one. The effects of Si and cold work on the formation of second type of S precipitates have been discussed
Precipitation hardening in Al-Cu-Mg alloys revisited
Get PDFTransmission electron microscopy, differential scanning calorimetry and hardness tests have been used to study the precipitation sequence on artificial ageing of a stretched Al–Cu–Mg alloy. The samples were aged for different times at 150 and 190 °C, respectively. Some orthorhombic GPB2/S? is present in samples aged at 150 °C for 48 h, which is at the very start of the second stage of hardening. The combined experiments clearly show that the second stage hardening is dominated by S phase, which forms a dense precipitate structure at the peak hardness stage, whilst no significant amounts of other phases or zones are detected
New insights on molecular systematics of opsariichthid fishes based on cytochrome b sequencing
No full text- …
