Showing papers on "Aluminium alloy published in 2004"

Multi-Principal-Element Alloys with Improved Oxidation and Wear Resistance for Thermal Spray Coating

Abstract: Multi-principal-element alloy coatings of Al-Si alloys were prepared by a plasma spray method They not only exhibited a good oxidation resistance up to 1000 °C, but also possessed an excellent abrasive wear resistance approximately two times higher than those of SUJ2 and SKD61 Moreover, they displayed a high temperature precipitation hardening phenomenon up to 1100 °C which is novel and seldom found in conventional alloys

Correlation between strength and microstructure of ball-milled Al–Mg alloys determined by X-ray diffraction

Abstract: The microstructure of ball-milled Al base Al–Mg alloys is determined by the “Convolutional Multiple Whole Profile” fitting procedure proposed for the evaluation of X-ray diffraction peak profiles. The whole measured powder diffraction pattern is fitted by the sum of a polynomial background and physically well-established theoretical profile functions. The procedure provides the size distribution function of crystallites and the characteristic parameters of the dislocation structure. The mechanical strength of the specimens is correlated to the parameters of the microstructure by the Hall–Petch and the Taylor models. Both models show that the critical resolved shear stress saturates at a Mg-solute concentration of about 2 wt.% probably due to the clustering of the Mg-solute atoms.

Microstructural evolution in aluminium alloy 7050 during processing

Abstract: The microstructural evolution in AA7050 during post homogenization cooling, and its influence on behaviour during preheat, hot rolling, and solution treatment, has been investigated. It is shown that slow cooling, at a rate typical of industrial processing, leads to a complex sequence of large, heterogeneously nucleated precipitates. In particular, S-phase particles grow to over 7 μ m in diameter. These particles are retained during preheat to rolling, and are above the critical size required to act as particle stimulated nucleation sites for recrystallization. Furthermore, by removing solute they prevent the formation of fine particles during preheat. This leads to a final recrystallized fraction that is over four times larger in homogenized and slow cooled material than in material quenched rapidly from homogenization.

In situ fabrication of Al3Ti particle reinforced aluminium alloy metal–matrix composites

Abstract: Titanium tri-aluminide (Al 3 Ti) particles were dispersed homogeneously into a castable aluminium alloy matrix by the aluminothermic reduction of hexafluorotitanate (K 2 TiF 6 ) under different conditions. Al 3 Ti particles in different morphologies and sizes were produced by changing the fabrication conditions, such as composition of the flux, the temperature and holding time. The coarsening and growth of the Al 3 Ti particulates are principally affected by other elements present in the flux during fabrication. The effects of the temperature and holding time, alloying elements and the composition of flux on the dispersion of the reinforcement were examined by using SEM and X-ray diffraction techniques. The observed results are explained in terms of the different growth behaviour of the Al 3 Ti particles under different conditions. The dispersion of the Al 3 Ti particles and the Al/Al 3 Ti interfacial bonding are explained by the solidification of aluminium.

Effect of Mg addition on microstructure and mechanical properties of aluminum

Abstract: The effect of Mg addition on the microstructural evolution and mechanical properties of high-purity aluminum was studied over a wide range of strain, up to ∼8. The high strains were achieved by applying the equal-channel angular pressing technique. The stress–strain relationship was related to the evolution of the microstructure investigated by transmission electron microscopy and X-ray diffraction peak profile analysis. In the early stages of plastic deformation the interaction between the dislocations and the Mg solute atoms results in an increase of the flow stress with temperature. The stable microstructure is developed at higher strains owing to the Mg addition resulting in the saturation of the proof stress at higher strains in Al–Mg alloys.

Quasi-static and dynamic axial crushing of thin-walled circular stainless steel, mild steel and aluminium alloy tubes

Abstract: Quasi-static and dynamic axial crushing tests have been performed on circular thin-walled sections made of three materials: 304 stainless steel, aluminium alloy 6063-T6, and mild steel. The tests were arranged to investigate the mode transitions during the impact crushing of thin-walled tubes and the three materials were chosen for their distinctive individual characteristics, such as strain rate sensitive properties, pronounced strain hardening, etc. The stainless steel, aluminium alloy and mild steel shells have moderate diameter-to-thickness ratios, 2R/H, of 22, 33 and 26, respectively, and were examined over a range of different axial lengths that encompassed both classical progressive buckling and the global bending modes of failure. The tests were conducted at a standardised energy of 9 kJ, approximately, with a few tests repeated at a higher energy of 18 kJ. The shells were impacted at velocities up to 13.4 m/s with masses up to 502 kg. Standard collapse modes developed in the tubes and the associated energy absorbing characteristics have been examined and compared with previous studies on mild steel. Quasi-static and dynamic tensile test results on the materials are also reported and the critical slenderness ratios at the transition between the two principal modes of failure are identified. The effects of strain hardening, strain rate as well as inertia effects due to the individual characteristics of the three materials are explored.

LIBS limit of detection and plasma parameters of some elements in two different metallic matrices

Abstract: In the present work a detailed study has been performed on the effect of the matrix on the limit of detection (LOD) and the plasma parameters of the laser induced breakdown spectroscopy (LIBS) technique The LOD of magnesium, silicon, manganese and copper as minor elements was evaluated in aluminium standard sample alloys compared to the values of the LOD of the same elements in standard steel alloys The effect of changing the matrix on the laser induced plasma plume parameters, namely the plasma temperature Te and the electron density Ne, has been also studied Calibrations were achieved for the four elements with linear regression coefficients between 98–99% on average According to the obtained results Mn and Cu have the lowest LOD in the steel alloy matrix, while Mg has much lower LOD in the aluminium alloy matrix These results may be interpreted in view of the compatibility of the physical properties of the elements existing in the same matrix Approximately similar electronic structure and values of melting point, density, atomic weight, etc, may facilitate better conditions for energy transfer within the matrix From the application view point, it is possible for LIBS in the on-line industrial process control to follow up only a single element (that with the lowest LOD in such matrix) as a marker for the correct alloying in metals and mixing in pharmaceuticals

Aluminium Alloys - A Century of Age Hardening

Abstract: A century has elapsed since Alfred Wilm made the accidental discovery of age hardening in an aluminium alloy that became known as Duralumin. His work, and the gradual realization that hardening arose because of the presence of fine precipitates which provided barriers to the motion of dislocations, is a good example of the transition of metallurgy from an art to a science. A brief account is given of the development of age hardenable aluminium alloys and the way that modern experimental techniques allow precipitation processes to be understood on an atomic scale. Some contemporary issues in age hardening are then discussed.

Feasibility study of friction stir welding of 6061-T6 aluminium alloy with AISI 1018 steel:

Abstract: The present work demonstrates that friction stir welding (FSW) is a feasible route for joining 6061 aluminium (Al) alloy to AISI 1018 steel. The weld has a good weld quality and is free of cracks and porosity. The tensile failure happened at the boundary between the nugget and thermomechanically affected zone of the base Al alloy, indicating that the weld has a higher joining strength. Despite the fact that the hardness fluctuates strongly within the nugget, the average hardness of the nugget is substantially higher than that of the base Al alloy. During FSW, localized melting of the Al alloy in the nugget occurred, and the molten Al alloy reacted strongly with steel pieces spread through the nugget, which resulted in the formation of the Al-Fe intermetallic compounds, Al13Fe4 and Al5Fe2. The nugget consists of secondary phases including coarse steel pieces and Al-Fe intermetallic compounds, and an Al alloy matrix. These secondary phases contribute to the hardness of the weld.

The role of microstructure in localized corrosion of magnesium alloys

Abstract: The article presents new findings on the influence of microstructural changes on corrosion behavior of magnesium alloy AZ91 in chloride solution, with a particular attention to the role of the β phase (Mg17Al12) and the surrounding Al-rich-α area. The as-cast alloy was subjected to solutionizing and aging heat treatments, in order to incorporate variation in morphology and distribution of the intermetallic β phase and the surrounding Al-rich-α (also known as eutectic α). Although previous workers have ascribed the higher corrosion resistance of a fine-grained alloy to the formation of the finely distributed β phase, the present work suggests that it is the ratio of the β phase to the Al-rich-α that governs the localized corrosion of the aged alloy. Corrosion characteristics were investigated by immersion and electrochemical tests. Surface microtopography, optical microscopy, and scanning electron microscopy (SEM) were employed to characterize the localized corrosion.

Steel cathodic protection afforded by zinc, aluminium and zinc/aluminium alloy coatings in the atmosphere

Abstract: Zinc has traditionally been the metallic material most widely used to protect steel against atmospheric corrosion due to its ability to afford cathodic protection to steel in all types of natural atmospheres. In recent decades, aluminium and zinc/aluminium alloy coatings have been used instead of zinc in certain atmospheric applications. Although these coatings present some advantages over zinc, they are not able to cathodically protect steel substrates in all types of natural atmospheres. The present paper assesses the cathodic protection afforded by Al (flame spraying), Al/13 Si (hot dipping), 55Al/Zn (hot dipping), Zn/15Al (flame spraying), Zn/5Al (hot dipping), Zn (hot dipping), Zn (discontinuous hot dipping) and Zn (electroplating). Aluminium and aluminium-rich alloy coatings (55%Al/Zn) provide cathodic protection to the steel substrate only in atmospheres that are highly contaminated with chloride ions (>100 mg Cl − m −2 day −1 ) where these coatings become active.

Ferritic Fe–Al–Ni–Cr alloys with coherent precipitates for high-temperature applications

Abstract: Strengthening by a homogeneous distribution of a second phase is a concept that is widely employed in high-temperature materials. It is shown that suitable microstructures can be obtained in the Fe–Al–Ni–Cr system with ordered (Ni, Fe)Al precipitates in a ferritic matrix. These precipitates lead to higher levels of yield strength at elevated temperatures than conventional iron-base high-temperature alloys. The results show that the investigated materials exhibit the highest yield strength after solution heat treatment and lower values after aging, indicating precipitation of fine particles during air cooling. The decrease of yield strength in the latter case was more pronounced for alloys with a high precipitate content than for leaner alloys.

Microstructural investigation of nanocrystalline bulk Al–Mg alloy fabricated by cryomilling and extrusion

Abstract: The present study was undertaken to provide insight into the influence of extrusion temperature on microstructure in nanocrystalline Al–Mg alloy. The results show that the lower extrusion temperature yielded a microstructure that is more anisotropic relative to that present at the higher extrusion temperature. More specifically, the results show that at the lower temperature the nano single grains have a tendency to rotate towards the 〈1 1 1〉 direction, along the extrusion direction.

Some new characteristics of the strengthening phase in β-phase magnesium–lithium alloys containing aluminum and beryllium

Abstract: Hardness, optical-microscopy and X-ray diffraction studies on the strengthening phase in β-phase magnesium–lithium alloys containing different content of aluminum were carried out to give some new characteristics of the strengthening phase affecting lattice distortion and α-Mg precipitation in the β-matrix. In the presence of the strengthening-phase precipitates, the matrix lattice undergoes substantial strain characterized by peak broadening. The peak width in the β-matrix phase pattern can provide an indication of lattice strain caused by the strengthening-phase precipitates. The origin of α-Mg precipitation resulting from the decomposition of the strengthening phase into stable AlLi compound is also explained in the present work.

Laser shock peening on fatigue crack growth behaviour of aluminium alloy

Abstract: The effect of laser shock peening (LPS) in the fatigue crack growth behaviour of a 2024-T3 aluminium alloy with various notch geometries was investigated. LPS was performed under a 'confined ablation mode' using an Nd: glass laser at a laser power density of 5 GW cm -2 . A black paint coating layer and water layer was used as a sacrificial and plasma confinement layer, respectively. The shock wave propagates into the material, causing the surface layer to deform plastically, and thereby, develop a residual compressive stress at the surface. The residual compressive stress as a function of depth was measured by X-ray diffraction technique. The fatigue crack initiation life and fatigue crack growth rates of an Al alloy with different preexisting notch configurations were characterized and compared with those of the unpeened material. The results clearly show that LSP is an effective surface treatment technique for suppressing the fatigue crack growth of Al alloys with various preexisting notch configurations.

Using grain boundary engineering to evaluate the diffusion characteristics in ultrafine-grained Al–Mg and Al–Zn alloys

Abstract: Samples of dilute Al–Mg and Al–Zn alloys, containing a minor Sc addition, were processed by equal-channel angular pressing (ECAP) to achieve grain refinement and different distributions of the grain boundary misorientations. Diffusion experiments were conducted on fine-grained alloys with either low or high fractions of grain boundaries having high-angle misorientations and on unpressed coarse-grained samples. The diffusion couples were annealed at temperatures from 493 to 848 K and the interdiffusion coefficients were determined from the concentration profiles using the Boltzmann–Matano technique. The results show the interdiffusion coefficients tend to be higher in fine-grained alloys having high fractions of high-angle boundaries than in fine-grained alloys having high fractions of low-angle boundaries. The experimental data are used to estimate values for the grain boundary diffusion coefficients.