Structure Of Aluminum Alloys Research Articles

Molecular dynamic simulation of edge dislocation-void interaction in pure Al and Al-Mg alloy

In this study, the interaction of edge dislocations with nano-scale voids was investigated for the face centered cubic (FCC) structure of pure aluminum and Al-Mg alloy. The effect of Mg solute atoms on the Peierls stress (required for dislocation motion) at different temperatures, and the critical resolved shear stress (CRSS) for dislocation-void interaction was investigated in this study. In addition, the influences of void diameter (1, 2 and 3nm), inter-void distance (7.5 and 15nm) in a void array, and of temperature (300K) on resolved shear stress were determined. It was found that substitutional Mg atoms was highly effective on improving the mechanical behavior of the Al lattice and on the type of dislocation-void interaction (simultaneous or separate passing of partial dislocations). In addition, it was obtained that no void-induced climbing occurred during the interactions for these systems. Higher void diameter and in particular lower inter-void spacing led to a considerable increase in the CRSS, while the latter changed the type of dislocation-void interaction. Finally, it was shown that Peierls stress was decreased for pure aluminum from 0K to 10K, while different results were obtained for Al-Mg alloy that were discussed in detail.

Methodology for aluminium part machining quality improvement considering mechanical properties and process conditions

The manufacturing of structural aluminium alloy parts requires several steps of both forming processes and heat treatments. Before machining, which is usually the last step of the manufacturing, the workpiece has thus undergone multiple manufacturing steps involving unequal plastic deformations which are source of residual stresses. During machining, where up to 90% of the initial workpiece volume can be removed, the mechanical equilibrium of the part evolves constantly with the redistribution of the initial residual stresses. For thick, large and complex parts in highly alloyed aluminium, this redistribution of the residual stresses can leads to an unexpected behaviour of the workpiece and is the main reason for both workpiece deflections (during machining) and post-machining distortions (after unclamping). These two phenomena can lead to the nonconformity of the part with the geometrical and dimensional tolerance specifications and therefore to the rejection of the part or to additional conforming steps. As a consequence, the mechanical behaviour of the workpiece has to be considered during the definition of the machining process plan to improve the machining accuracy and the robustness of the process and thus to ensure the conformity of the machined part with the dimensional and geometrical specifications, i.e. to ensure the desired machining quality. In this paper, the numerical tool developed in [1] is used to conduct an analysis on the influence of the initial workpiece residual stress state, of the fixture layout as well as of the machining sequence on the machining quality. This analysis is performed on a part which has been specially designed and which can be considered as being representative of real aerospace parts. Several comparisons with experimental results are performed, one of them using digital image correlation (DIC) measurements. Results obtained show a good agreement, validating both the prediction of the behaviour of the workpiece during machining and the prediction of the machined part geometry. Based on the results of this analysis, a classification of the parameters has been performed depending on their influence on the machining quality. A first methodology allowing to define machining process plans adapted to the initial workpiece stress state has then been created based on the previous classification. This methodology is composed of a procedure and basic guidelines which are both presented in detail. An example of an application of this methodology is then introduced, demonstrating the benefits of the approach developed in this work.

The Effects of Corrosive Media on Fatigue Performance of Structural Aluminum Alloys

The effects of corrosive media on rotating bending fatigue lives (the cyclic numbers from 104 to 108) of different aluminum alloys were investigated, which involved the corrosion fatigue lives of five kinds of aluminum alloys in air, at 3.5 wt. % and 5.0 wt. % NaCl aqueous solutions. Experimental results indicate that corrosive media have different harmful influences on fatigue lives of different aluminum alloys, in which the differences of corrosion fatigue lives depend strongly on the plastic property (such as the elongation parameter) of aluminum alloys and whether to exist with and without fracture mode II. The other various influence factors (such as the dropping corrosive liquid rate, the loading style, and the nondimensionalization of strength) of corrosion fatigue lives in three media were also discussed in detail by using the typical cases. Furthermore, fracture morphologies and characteristics of samples, which showed the different fatigue cracking behaviors of aluminum alloys in three media, were investigated by scanning electron microscopy (SEM) in this paper.

Manufacture of composites based on aluminum and shungite under high pressure conditions

In this work, the structure of aluminum alloy modified with shungite carbon additives after high-pressure thermal treatment is studied. Introducing shungite carbon into an aluminum matrix is shown to inhibit aluminum grain growth and to increase the microhardness of the composite.

The continuous strength method for the design of aluminium alloy structural elements

Aluminium alloys are nonlinear metallic materials with rounded stress–strain curves that are not well represented by the simplified elastic-perfectly plastic material model used in most existing design specifications. Departing from current practice, the continuous strength method (CSM) is a recently developed design approach for aluminium alloy structures, which gives consideration to strain hardening for non-slender sections. The CSM is a deformation-based method and employs a base curve to define the continuous relationship between cross-section slenderness and deformation capacity. This paper explains the background and the two key components of the CSM: (1) the base curve, which is extended herein such that the method covers both non-slender and slender sections and (2) the strain hardening material model. Three international design specifications from America, Australia/New Zealand and Europe, as well as the CSM are compared with approximately 900 aluminium alloy experimental and numerical results. Reliability analyses have been carried out to assess the reliability level of different design methods according to both the American Institute of Steel Construction (AISC) and European Standard (EN 1990) approaches. Finally, worked examples of the CSM for aluminium alloy stub columns and continuous beams are illustrated in this paper.

Flexural response of aluminium alloy SHS and RHS with internal stiffeners

Tubular profiles, such as square and rectangular hollow sections (SHS and RHS) are widely used in a range of structural engineering applications. Their thin-walled nature means that local buckling is a key design concern, which is usually addressed by adhering to specified slenderness limits. An alternative approach is to employ local plate stiffeners, which can be practically achieved in extruded aluminium alloy sections through the introduction of internal cross stiffeners. The flexural behaviour and design of aluminium alloy SHS and RHS with internal stiffeners is the subject of investigation of the present paper. The primary aims of the study are to generate experimental and numerical data for these new types of cross-section in bending, as well as to assess the applicability of different approaches to their design at cross-sectional and system levels. First, an experimental investigation was performed on aluminium alloy SHS and RHS beams with internal stiffeners subjected to three-point bending, four-point bending and five-point bending (i.e. continuous beams over three supports) of three different configurations. Finite element (FE) models were also developed and validated against the presented test data. Once validated, the models were employed to generate additional structural performance data through numerical parametric studies. Comparisons are then made between the experimental/numerical capacities and the design capacities predicted using a series of international design specifications for aluminium alloy structures, as well as the continuous strength method (CSM). The design strengths predicted by the American and Australian/New Zealand specifications were found to be conservative, while improved predictions are achieved by Eurocode 9. The most accurate and consistent predictions are obtained using the CSM, which was able to capture the significant observed strain hardening at the cross-sectional level and moment redistribution at the global system level.

Experimental investigation on the post-fire mechanical properties of structural aluminum alloys 6061-T6 and 7075-T73

Aluminum alloys are increasingly used in engineering structures. During fire hazards, aluminum alloy structures are inevitably exposed to elevated temperatures. Provided structural collapse does not occur after a fire, a reliable evaluation of the residual performances of the structures is needed to decide whether the structures should be dismantled, repaired, or directly reused. Therefore, an experimental investigation was conducted to reveal the post-fire mechanical properties of two widely used structural aluminum alloys, namely, 6061-T6 and 7075-T73. Specimens were initially heated to nine various pre-selected temperatures up to 550°C and subsequently cooled down to ambient temperature by two different methods: air cooling and water cooling. Tensile coupon tests were performed on the specimens until fracture, and the post-fire stress–strain curves, elastic modulus, yield strength, ultimate strength, and ductility were obtained. The mechanical properties of 6061-T6 were dramatically reduced after exposure to temperatures exceeding 300°C. For 7075-T73, the corresponding temperature was 200°C. The post-fire mechanical properties were obviously influenced by cooling methods, particularly after cooling from a relatively high fire temperature. New predictive equations, where the influences of different cooling methods were incorporated, were proposed to evaluate the post-fire mechanical properties of the aluminum alloys 6061-T6 and 7075-T73. The results presented in this study are expected to lead to an accurate assessment of the post-fire performances of aluminum alloy structures.

Structure and properties of ultra fine grained aluminium alloys after laser surface treatment

The presented investigation results concern the influence of laser heat treatment on the structure and properties of aluminium alloys that underwent severe plastic deformation using the equal channel angular pressing method. The initial stage of this study aimed at determining the possibility of improving the mechanical properties of core material using the severe plastic deformation process method and the subsequent partial recrystallization process that allows obtaining equivalent ductility and grain refinement. The next stage involving investigating the surface modification of the fine grained alloy by remelting and feeding silicon carbide powder into the molten material and to end solidification. To modify the surface layer of aluminium alloy, the Ytterbium Laser System YLS‐4000 has been used, with the applied power of the laser beam in the range of 1.2 kW and 2.0 kW. The linear laser scan rate was 0.4 m/min. Results of the conducted treatments a core material with better mechanical properties, in comparison to initial state, was obtained whereas laser surface treatment allows to obtain composite surface with increased hardness and enhanced wear resistance when compared to substrate material.

Study on the Surface Integrity of a Thin-Walled Aluminum Alloy Structure after a Bilateral Slid Rolling Process

For studying the influence of a bilateral slid rolling process (BSRP) on the surface integrity of a thin-walled aluminum alloy structure, and revealing the generation mechanism of residual stresses, a self-designed BSRP appliance was used to conduct rolling experiments. With the aid of a surface optical profiler, an X-ray stress analyzer, and a scanning electron microscope (SEM), the differences in surface integrity before and after BSRP were explored. The internal changing mechanism of physical as well as mechanical properties was probed. The results show that surface roughness (Ra) is reduced by 23.7%, microhardness is increased by 21.6%, and the depth of the hardening layer is about 100 μm. Serious plastic deformation was observed within the subsurface of the rolled region. The residual stress distributions along the depth of the rolling surface and milling surface were tested respectively. Residual stresses with deep and high amplitudes were generated via the BSRP. Based on the analysis of the microstructure, the generation mechanism of the residual stresses was probed. The residual stress of the rolling area consisted of two sections: microscopic stresses caused by local plastic deformation and macroscopic stresses caused by overall non-uniform deformation.

Equivalent crack size model for pre-corrosion fatigue life prediction of aluminum alloy 7075-T6

Corrosion damage can significantly reduce the service life of aluminum alloy structures and endanger the structural integrity of aircraft. Here, aiming at center-hole sheet specimens of aluminum alloy 7075-T6, uniaxial fatigue tests and post-fracture analysis are performed to investigate the effect of corrosion pits on the pre-corrosion fatigue behavior. Then the best correlated parameters between corrosion pits and equivalent cracks are identified through Pearson correlation analysis. It is found that for single-crack initiations arECS (equivalent crack depth∗aspect ratio) vs. arcri (critical pit depth∗aspect ratio) are best correlated with correlation coefficient of 0.9, while the best correlated parameters for multi-crack initiations are arECS (equivalent crack depth∗aspect ratio) vs. rcri (aspect ratio) with correlation coefficient of 0.69. Equivalent crack size (ECS) models are correspondingly developed with these best correlated parameters for single- and multi-crack initiations, respectively. The pre-corrosion fatigue lives predicted with our models agree well with the experimental results and the maximum error factor is about 1.6.

Anti-icing and anticontamination properties of coatings induced by surface structure

The development of the first model coatings with innovative surface structures, anti-icing, and anticontamination properties could be implemented in the EU-project CleanSky. A porous aluminum alloy structure created by anodization was filled with fluid silicon oil polydimethylsiloxane. At the surface, the silicon oil was modified with vacuum ultraviolet-light to form a thin and solid hydrophobic layer. For further investigations, laser-structured metal surfaces were copied and reproduced with a coating and afterward filled with fluoro-modified oils. Additionally, aluminum alloy AA2024 samples were pickled and treated with hot water to create micro- and nanostructures at the surface. These samples were also filled with different fluoro-modified and nonmodified oils. After application, the surface properties were analyzed with special tests for functionality regarding anti-ice and anticontamination properties.

Properties of the Aluminium Alloy EN AC-51100 after Laser Surface Treatment

In this paper, the influence of a laser surface treatment on the structure and properties of aluminium alloy has been determined. The aim of this work was to improve the tribological properties of the surface layer of the EN AC-51100 aluminium alloy by simultaneously melting and feeding silicon carbide particles into the molten pool. The silicon carbide powder was introduced into the liquid metal using a gravity feeder within a constant feed rate of 1 g/min. A high power diode laser (HPDL) was used for remelting. Laser beam energies used in experiments were 1.8 kW, 2.0 kW and 2.2 kW, combined with the constant velocity of 50 mm/min. As a result of the laser treatment on the aluminium alloy, a composite layer with greater hardness and wear resistance compared to the based material was obtained.

Survey of Detection, Mitigation, and Repair Technologies to Address Problems Caused by Sensitization of Al-Mg Alloys on Navy Ships

Structural aluminum alloys are used in marine applications where light weight and increased speed are paramount. The 5xxx series alloys are the ideal choice, providing an optimum combination of as-welded strength and general corrosion resistance. A particular concern is sensitization in service. Aluminum is considered sensitized when a nearly continuous network of β phase forms along the grain boundaries. The β phase is anodic to the Al matrix, and, when exposed to sea water and sufficient loading, provides a clear pathway to stress corrosion cracking (SCC). The degree of β-phase precipitation is driven by a combination of time and elevated temperature. For over a decade, SCC of Al superstructures has plagued Navy ships. To address this issue, relevant technologies have been adopted, adapted, and developed to combat this issue. More specifically, the technology areas involve the detection of sensitization, the mitigation of SCC, and the replacement of corrupt materials. The technologies discussed herein a...

Влияние структуры на сопротивление пластической деформации алюминиевого сплава 1560 после обработки методом прессования рифлением

In present work the effect of structural changes in the samples, made of 1560 aluminum alloy rolled sheet products of 1.5 mm in thickness, as a result of groove pressing treatment was investigated. The mechanical properties of the material in the as-received condition and after severe plastic deformation are investigated experimentally in a quasi-static uniaxial tensile tests at a strain rate of 1 s^-1. Microhardness of aluminum alloy 1560 as-received condition samples and groove pressed samples was measured by Vickers method. The changes of microhardness rolled sheet 1.5 mm in thickness after groove pressing were determined. It was found that after four treatment cycles rolled alloy sheet, yield strength and fracture resistance was increased in 1.4 and 1.5 times, respectively, and microhardness value increased in ~ 2.7 times. It was found that the hardening of the investigated alloy is accompanied by decrease ultimate strain to failure of 20%. Analysis of results of changes in 1560 aluminum alloy grain structure after groove pressing treatment, conducted by electron backscatter diffraction was presented. The results obtained in present work confirmed with data obtained in previous studies on the impact of severe plastic deformation on the grain structure and mechanical properties of aluminum alloy 1560.

Local buckling of slender aluminium sections exposed to fire

The mechanical properties of aluminium alloys reduce at mode-rately elevated temperatures. This means that aluminium alloy structures are sensitive to fire exposure. They are also sensitive to instability phenomena, such as local buckling. This thesis presents an experimental and numerical research into the behaviour of alu-minium alloy compression members exposed to fire conditions. Uniaxial tests are carried out in order to determine the mechanica! properties of aluminium alloys exposed to elevated temperatures. A model for the mechanical properties when exposed to fire con-ditions is developed based on these tests. In order to study the local buckling phenomenon, compression tests at elevated temperatures are conducted on square hollow sections and angular sections. Finite element models are develo-ped and validated using these tests. A parameter study has been carried out with the validated finite element models. Based on the results, a design model is develo-ped, which gives the ultimate resistance for local buckling as a function of the cross-sectional dimensions and the mechanical properties. The design model provides a first and essential step in the fire design of slender aluminium alloy members.

Acoustic emission location on aluminum alloy structure by using FBG sensors and PSO method

Acoustic emission location is important for finding the structural crack and ensuring the structural safety. In this paper, an acoustic emission location method by using fiber Bragg grating (FBG) sensors and particle swarm optimization (PSO) algorithm were investigated. Four FBG sensors were used to form a sensing network to detect the acoustic emission signals. According to the signals, the quadrilateral array location equations were established. By analyzing the acoustic emission signal propagation characteristics, the solution of location equations was converted to an optimization problem. Thus, acoustic emission location can be achieved by using an improved PSO algorithm, which was realized by using the information fusion of multiple standards PSO, to solve the optimization problem. Finally, acoustic emission location system was established and verified on an aluminum alloy plate. The experimental results showed that the average location error was 0.010 m. This paper provided a reliable method for aluminum alloy structural acoustic emission location.

Influence of Weld Defects and Postweld Heat Treatment of Gas Tungsten Arc-Welded AA-6061-T651 Aluminum Alloy

Welding defects and the reduction of mechanical performances are the foremost problems for fusion welded aluminum alloys joints. The influences of weld defects and postweld heat treatment (PWHT) on tensile properties of gas tungsten arc (GTA) welded aluminum alloy AA-6061-T651 joints are investigated in this current study. All welded specimens are nondestructively inspected with phased array ultrasonic testing (PAUT) to classify weld defect and measure the projected defects area-ratio (AR). Ultimate tensile strength (UTS) decreased linearly with the increase of the size of weld defect but tensile toughness behaved nonlinearly with defect size. Depending on defect size, defective samples' joint efficiency (JE) varied from 35% to 48% of base metal's (BM) UTS. Defect-free as-welded (AW) specimens observed to have 53% and 34% JE based on UTS and yield strength (YS) of BM, respectively. PWHT was applied on defect-free welded specimens to improve tensile properties by precipitation hardening, microstructures refining, and removal of postweld residual stresses. Solution treatment (ST) (at 540 °C) followed by varying levels of artificial age-hardening (AH) time was investigated to obtain optimum tensile properties. For GTA-welded AA-6061-T651, peak aging time was 5 hr at 180 °C. PWHT specimens showed 85% JE based on UTS and up to a 71% JE based on YS of BM. However, toughness values decreased about 29% due to the presence of precipitate-free fusion zones. The experimental investigations can be used to establish weld acceptance/rejection criteria and for the design of welded aluminum alloy structures.

Impact of External Actions upon Structure of Aluminium Alloys and Composites

Presented are research results of impact of low-frequency vibration, ultrasonic, magneto-hydrodynamic (MHD) and plasma treatment of alloys, in liquid state and two-phase condition, upon structure and properties of silumins and silumin-based nanocomposites.

Impact of External Actions upon Structure of Aluminium Alloys and Composites

Presented are research results of impact of low-frequency vibration, ultrasonic, magneto-hydrodynamic (MHD) and plasma treatment of alloys, in liquid state and two-phase condition, upon structure and properties of silumins and silumin-based nanocomposites.

Numerical simulation of fatigue crack propagation in friction stir welded joint made of Al 2024-T351 alloy

In this work, fatigue crack propagation in thin-walled aluminium alloy structure with two friction stir welded T joints has been simulated numerically. Crack propagation in stiffened part of the structure between two friction stir welded T joints is analysed by using the eXtended Finite Element Method (XFEM), including software ABAQUS, as well as MORFEO, for modelling and results display. Tensile fatigue loading is applied, with stress ratio R=0, and maximum stress σmax=10MPa. Material properties (Al 2024-T351, as used in aeronautical industry) in different welded joints zones are adopted from available literature data. Following results are obtained by numerical analysis: stress–strain and displacement state in the structure, position of the crack tip and value of stress intensity factor for every crack propagation step, as well as the structural life estimation, i.e. number of load cycles, N, also for each crack propagation step. Using these results the number of cycles at which the crack starts to propagate in an unstable manner is predicted.