Thermal stability, determining the material ability of retaining its properties at required temperatures over extended service time, is becoming the next frontier for aluminum alloys. Its improvement would substantially expand their range of structural applications, especially in automotive and aerospace industries. This report explains the fundamentals of thermal stability; definitions, the properties involved; and the deterioration indicators during thermal/thermomechanical exposures, including an impact of accidental fire, and testing techniques. For individual classes of alloys, efforts aimed at identifying factors stabilizing their microstructure at service temperatures are described. Particular attention is paid to attempts of increasing the current upper service limit of high-temperature grades. In addition to alloying aluminum with a variety of elements to create the thermally stable microstructure, in particular, transition and rare-earth metals, parallel efforts are explored through applying novel routes of alloy processing, such as rapid solidification, powder metallurgy and additive manufacturing, engineering alloys in a liquid state prior to casting, and post-casting treatments. The goal is to overcome the present barriers and to develop novel aluminum alloys with superior properties that are stable across the temperature and time space, required by modern designs.

Thermal Stability of Aluminum Alloys.

The structure determination of Al20Cu2Mn3 by near atomic resolution chemical mapping

Referee: Dr. D. Julian McClements, Department of Food Science, Chenoweth Laboratory, University of Massachusetts, Amherst, MA 01003 In most conventional rheometers, notably the coaxial cylinders and capillary viscometers, the food specimen is pressed into a narrow gap and its structure is altered by uncontrolled shear. Also, most semiliquid foods exhibit slip, and consequently the measurements do not always reflect their true rheological properties. A feasible solution to these two problems is squeezing flow viscometry where the specimen, practically intact and with or without suspended particles, is squeezed between parallel plates. The outward flow pattern mainly depends on the friction between the fluid and plates or its absence (“lubricated squeezing flow”). Among the possible test geometries, the one of constant area and changing volume is the most practical for foods. The test can be performed at a constant displacement rate using common Universal Testing Machines or under constant loads (creep array). The tests output is in the form of a force-height, force-time, or height-time relationship, from which several rheological parameters can be derived. With the current state of the art, the method can only be applied at small displacement rates. Despite the method's crudeness, its results are remarkably reproducible and sensitive to textural differences among semiliquid food products. The flow patterns observed in foods do not always follow the predictions of rheological models originally developed for polymer melts because of the foods' unique microstructures. The implications of these discrepancies and the role that artifacts may play are evaluated in light of theoretical and practical considerations. The use of squeezing flow viscometry to quantify rheological changes that occur during a product's handling and to determine whether they are perceived sensorily is suggested.

Squeezing flow viscometry for non-elastic semi liquid foods - Theory and Applications

http://www.imr.cas.cn/yjtd/mxlTeam/yjcg_mxltd/fblw_mxltd/201505/W020150513415219909876.pdf

Multiple twins of a decagonal approximant embedded in S-Al2CuMg phase resulting in pitting initiation of a 2024Al alloy

Al-Cu-Mn matrix alloy in the form of chips with zirconium in amounts of 5, 10 and 20 wt% was subjected to mechanical alloying. After milling in a ball mill for 20 h the prepared powders were annealed and hot-pressed. X-ray diffraction analysis was used to study the effect of zirconium content on the phase composition and microstructural parameters of the materials. The study showed that mechanical alloying leads to the formation of an Al-based nanocrystalline supersaturated solid solution with a zirconium content of up to 20%. With an increase in the zirconium concentration the microhardness of the powder alloys increases to 440 HV. The subsequent precipitation hardening as a result from the precipitation of metastable Al3Zr (L12) phase with a maximum content of 28 vol% causes an increase in the microhardness to 520 HV. The hot-pressed specimens exhibit very good room temperature and high temperature strength which increases with zirconium content.

Strengthening of mechanically alloyed Al-based alloy with high Zr contents

The Thermo-Calc software is used for quantitative analysis of the Al – Cu – Mn – Zr diagram as a base for creating new refractory aluminum alloys. Comparison of the characteristics of the phase composition of a commercial aluminum alloy of type 1201 and a novel ALTEK aluminum alloy is performed. The ranges of concentrations and temperatures are determined for obtaining a maximum content of Al20Cu2Mn3 dispersoids providing high refractoriness of the ALTEK alloy.

Quantitative analysis of the Al – Cu – Mn – Zr phase diagram as a base for deformable refractory aluminum alloys

The phase composition of the Al–Ni–Mn–Fe–Si–Zr system is analysed as applied to heat resistant nikalines (aluminum alloys of a new generation based on Ni containing eutectic), which are strengthened by the Al3Zr (L12) nanoparticles. It is shown that the presence of iron and silicon considerably complicates the phase analysis when compared with the AN4Mts2 base alloy. Silicon strongly widens the crystallization range, which increases the tendency of the alloy to form hot cracks during casting. It is shown that economically doped nikaline AN2ZhMts substantially exceeds the most heat resistant cast aluminum alloys of the AM5 grade in the totality of its main characteristics (heat resistance and mechanical and production properties).

Perspective high strength aluminium alloys of new generation based on Al–Ni–Mn–Fe–Si–Zr system

The phase composition of the AlNiMnFeSiZr system was analyzed with respect to new-generation heat resistant casting aluminum alloys based on a Ni-containing eutectic, which are strengthened by the Al3Zr (L12) nanoparticles. It is shown that the presence of iron and silicon considerably complicates the phase analysis compared with the AlNiMnFe base alloy. Alloys with low silicon content have a sufficiently good casting property, which enables fabrication of thin-walled castings, not inferior to AA356 alloy types widely used to cast complex shapes. Addition of silicon to the AlNiMnFe base alloy sharply deteriorates hot cracks. Silicon greatly decreases the solubility of Zr at (Al), which is reflected on hot brittleness of Al2%Ni1%Mn0,5%Fe-0,2%Zr system alloys.

Optimization of the Compositions of the High Strength Casting Aluminium Alloys Based on Nickel Eutectic

The phase composition of the AlNiMnFeSiZr system is analyzed as applied to heat resistant nikalines (aluminum alloys of a new generation based on Ni containing eutectic), which are strengthened by the Al3Zr (L12) nanoparticles. It is shown that the presence of iron and silicon considerably complicates the phase analysis when compared with the AN4Mts2 base alloy. Silicon strongly widens the crystallization range, which increases the tendency of the alloy to form hot cracks during casting. It is shown that economically doped nikaline AN2ZhMts substantially exceeds the most heat resistant cast aluminum alloys of the AM5 grade in the totality of its main characteristics (heat resistance and mechanical and production properties).

Scientifically Based Choice of Heat-Resistant Cast Aluminum Alloys of New Generation

High-pressure fluorination of multi-walled carbon nanotubes (MWNTs) sheet was performed at room temperature. This fluorine treatment increases the electrical conductivity of MWNTs sheet. In addition, low-temperature conductivity measurement data gives a good fit to variable-range hopping (VRH) model. Thus, VRH model was adopted to study and understand the increase in electrical conductivity. Estimation of the degree of disorder from the experimental data and VRH model indicate that degree of disorder of fluorinated multi-walled carbon nanotubes (FMWNTs) is higher than that of MWNTs. Higher degree of disorder of FMWNTs sheet substantiate the increase in electrical conductivity when compared to MWNTs. Scanning Electron Microscopy (SEM) and Raman analysis shows that change in structural disorder of FMWNTs network. Effect of fluorination on activation energy was also studied. The activation energy reduces with lower temperatures. The estimated values of temperature coefficient of resistance also show the increase in degree of disorder of FMWNTs. The change in electrical properties of FMWNTs is a much-needed requirement in the application of nano-electronics.

Dauletkhan Smagulov

Papers

Quantitative analysis of the Al – Cu – Mn – Zr phase diagram as a base for deformable refractory aluminum alloys

Perspective high strength aluminium alloys of new generation based on Al–Ni–Mn–Fe–Si–Zr system

Optimization of the Compositions of the High Strength Casting Aluminium Alloys Based on Nickel Eutectic

Scientifically Based Choice of Heat-Resistant Cast Aluminum Alloys of New Generation

Effect of high-pressure fluorination on electrical properties of multi-walled carbon nanotubes sheet