Advanced Aluminum Alloys Research Articles

Evaluation and Validation of Methods to Determine Limit Strain States with Focus on Modeling Ductile Fracture

In the manufacturing process of body in white components made from sheet metal it is state of the art to accompany the process by means of finite element analysis. A main criterion for determining a feasible tool design and production process parameters is the prediction of material failure, which can be categorized in instability and ductile fracture. The ductile fracture failure mode is more likely to occur, as more advanced high strength steels and aluminum alloys are used for body in white components. Therefore different approaches have been presented to model ductile fracture over the past years. This task is more challenging when the material is exposed to arbitrary loading paths that can occur in deep drawing processes. However there is no guideline for sheet metal forming applications to determine which models for predicting ductile fracture are suitable, which experiments are necessary and how calibration of model parameters and validation of model prediction can be performed. Additionally there is no standard established that prescribes the evaluation of limit strain states from experiments. Suitable limit strain states are a basic requirement for prediction of ductile fracture as they are used for calibration of fracture models. In this paper, two methods for evaluation of limit strains are discussed and applied to tensile specimens with circular hole and circular cut outs made from aluminum alloy AlSi0.6Mg0.5. One validation experiment is used to investigate failure prediction that is based on limit strain states from different evaluation methods.

Effect of Corrosion Damage on Fatigue Crack Initiation Mechanism and Growth Behavior of High Strength Aluminum Alloy

Corrosion damage are simulated through accelerated corrosion testing based on the complied environment spectrum, as result of high humidity atmosphere, salt fog, sulfur dioxide, acid rain and dry/wet alternation for aircraft structure during service.Prior corrosion and fatigue experiments are conducted for single edge notched specimen machined from 7B04-T74 advanced high strength aluminum alloy of aircraft critical structure. And the influence of different corrosion damage on fatigue crack initiation and propagation behavior is analyzed, as well as crack growth rate and fatigue life, to find the mechanism of corrosion damage on fatigue behavior. The results indicate that crack initiation site is mainly single pit in early corrosion stage, and the crack follows a relatively straight path. While the corrosion damage grows more severely, multiple small cracks initiate from several pits and there is obvious tunneling effect beneath pits, cracks follow zigzag path. The material microstructures compete with corrosion pits as crack origins.Corrosion damage seriously decreases fatigue life of aluminum alloy. Fatigue crack initiation life with corrosion damage equivalent to 12 years is only 2.2% of that without damage, which indicates crack initiation life is especially sensitive to corrosion damage.

ВОСПОМИНАНИЯ О ЛИЧНОСТИ С.И. КИШКИНОЙ И ЕЕ РОЛИ В РАЗВИТИИ СОВРЕМЕННЫХ АЛЮМИНИЕВЫХ СПЛАВОВ

ВОСПОМИНАНИЯ О ЛИЧНОСТИ С.И. КИШКИНОЙ И ЕЕ РОЛИ В РАЗВИТИИ СОВРЕМЕННЫХ АЛЮМИНИЕВЫХ СПЛАВОВ

On the Development and Computational Implementation of Complex Constitutive Models and Parameters’ Identification Procedures

Nowadays, the automotive industry has focused its attention to weight reduction of the vehicles to overcome environmental restrictions. For this purpose, new materials, namely, advanced high strength steels and aluminum alloys have emerged. These materials combine good formability and ductility, with a high tensile strength due to a multi-phase structure (for the steel alloys) and reduced weight (for the aluminum alloys). As a consequence of their advanced performances, complex constitutive models are required in order to describe the various mechanical features involved. In this work, the anisotropic plastic behavior of dual-phase steels and high strength aluminum alloys is described by the non-quadratic Yld2004-18p yield criterion, combined with a mixed isotropic-nonlinear kinematic hardening law. This phenomenological model allows for an accurate description of complex anisotropy and Bauschinger effects of the materials, which are essential for a reliable prediction of deep drawing and springback results using numerical simulations. To this end, an efficient computational implementation is needed, altogether with an inverse methodology to properly identify the constitutive parameters to be used as numerical simulation input. The constitutive model is implemented in the commercial finite element code ABAQUS as a user-defined material subroutine (UMAT). A multi-stage return mapping procedure, which utilizes the control of the potential residual, is implemented to integrate the constitutive equations at any instant of time (pseudo-time), during a deformation process. Additionally, an inverse methodology is developed to identify the constitutive model parameters of the studied alloys. The identification framework is based on an interface program that links an optimization software and the commercial finite element code. This methodology compares experimental data with the respective results numerically obtained. The implemented optimization process aims to minimize an objective function, which defines the difference between experimental and numerical results using the Levenberg-Marquardt gradient-based optimization method. The proposed integrated approach is validated in a number of benchmarks in sheet metal forming, including monotonic and cyclic loading, with the goal to infer about the modelling of anisotropic effects.

Foreign Object Damage Analysis of Aircraft Structural Materials

Present day aircraft industry is focusing on weight reduction and fuel usage optimization which would ultimately lead to greener aero structures. The major challenge is the material selection by considering the design, operation and accidental scenarios. Composites have been considered along with advanced aluminum alloys for aero structures. One of the extreme operational scenarios is foreign object damage onto aircraft outer surfaces. The papers focus on the impact capability analysis of composites and aluminum alloys. Overall methodology of meeting the certification requirement is discussed using numerical tools. Finite Element of an aircraft windshield & surround structure for the bird-strike requirement according to the Federal Aviation Administration (FAA) Certification Specifications is discussed. Various methods of bird modeling and impact analysis is presented. Analysis is made based on the obtained numerical results. The Analysis Software used for the impact analysis were LS-Dyna and Ansys along with Hyper-mesh was used for pre-processing (Mesh). The geometry is developed using Catia. The objective of the paper is to bring out the simulated impact strength of the aircraft panels get an insight into the impact strength while meeting other criteria. Analysis high lights the need for considering extreme operation scenario like bird strike (Impact) while aiming for better material options for aircraft structures. New Materials for aircraft structures have been developed to meet the growing demands of the weight reduction and better fuel usage optimization. While the research has been focusing on the strength and density aspect of material options like aluminum and composites extreme operational scenario like Foreign Objects Damage will induce high impact loads onto to structures. The criteria are addressed in FAA regulations. As the problems impact highly non linear in nature certification based on numerical results has been a challenge. Future materials development model should be directed to address the impact loads that areexpected during operation [1]. Focus of static strength and density criteria should also include the dynamic failure mechanisms like bird strike. In current work existing models of bird in numerical tools like LSDYNA is used. Meeting the Certification requirement can be better understood by using numerical tools. This is help us in final applicability og material while choosing design direction. Due to increased air traffic in recent decade’s bird strike is seen as major threat to air safety. In addition higher flight speed (high Mach) is leading to higher kinetic energy and huge impulsive force generation during the impact conditions. The probability of bird hit on outer surfaces of the aircraft is high based on earlier experience. The date available in the open literature shows the projected parts of fight need attention. The loss of life due to bird strike has been recorded to be significantly high number. Among the all components of aircraft front facing components of an aircraft which include the nacelles, windshield, wind leading edge, compressor blade, et care often most susceptible to such strikes. It is therefore critical to ensure that the different structural parts are able to withstand such high velocity impact for safe landing of the aircraft after the strike This essentially requires maintaining integrity while undergoing plastic deformation. Table1. Aircraft components and FAR Sections

Research on Initial Discontinuity State of an Advanced Aluminum Alloy Rolling Alclad Sheet

Initial Discontinuity State is the characteristic of aluminum alloy, it is a random parameter. According to an advanced aluminum alloy rolling alclad sheet, the coupons were carried out tension and fatigue test, stress ratio R=0.06, 0.2, 0.5 and the maximum stress level σmax=403, 370, 330, 310, 280, 260, 240, 220MPa through Material Test System 810. By use of scanning electron microscope, the tension and fatigue fracture surface was analyzed and the flaw size was obtained. The metallographic coupons were prepared, the constituent particles were surveyed using KH-7700 optical microscope and particulate size was gained. Based on measuring data, different distributions (Normal, Lognormal, Weibull, Logistic, Gumbel) were verified, the best-fit distributions of tension and fatigue facture flaw size is Lognormal distribution, as same as that of θ phase. However, that of S phase size is Weibull distribution.

Spray forming of hypereutectic Al–Si alloys

To develop advanced aluminum alloys with high silicon content, hypereutectic aluminum silicon alloys AlSi x ( x = 18, 25, and 35 wt.%) in the form of cylindrical billet have been spray formed under different thermal conditions. To help in spray forming parameter selection and interpretation of experimental results, phase diagram of the alloys and their thermochemical data such as liquid fractions and enthalpies in function of temperature have been calculated. The spray formed hypereutectic Al–Si alloys are typically composed of refined and uniformly distributed primary silicon and modified eutectic. Thermal conditions and silicon content of the deposited materials have significant influence on the metallurgical quality of the spray formed Al–Si alloys. Strong cooling condition is required for spray forming Al–Si alloys with high silicon content.

Assessment of the ability of conventional and advanced wrought aluminum alloys for mechanical performance in light-weight applications

A concept to assess the ability of advanced wrought aluminum alloys for mechanical performance in light-weight structures by involving quality indices is introduced. The involved quality index Q D has been originally suggested to evaluate the quality of aircraft aluminum alloys, by conjuncting tensile strength and ductility of the alloys in a single quantity and accounting also for the material’s scatter in mechanical properties. The methodology is extended such as to account also for the material’s density. The introduced specific quality index Q DS is exploited to evaluate and rank, according to their quality, a number of existing wrought aluminum alloys from the 2xxx, 6xxx, 7xxx and 8xxx series, which are widely used in aircraft structures. Advanced aluminum alloys from the 2xxx and 6xxx series, newly developed for aircraft structural applications are also characterized and their potential for mechanical performance is compared against the mechanical performance provided by the respective conventional alloys.

CHARACTERIZATION OF NANOSTRUCTURES IN BULK ALLOYS BY ELECTRICAL RESISTIVITY MEASUREMENTS

The control of nanostructural features such as clusters and precipitates offers tremendous potential for improvements in the properties of advanced alloys. However, due to their inherently small size characterization is a major problem. Techniques such as TEM, AFM, and FIM have sufficient resolution, however they are only able to sample a small volume of what is a bulk material. Other characterization techniques such as XRD and DSC are capable of producing more representative results but still have limitations. Electrical resistivity measurements are extremely simple and have been used to characterize conventional materials for many years. However, as the wavelength of the electrons in the metals is extremely small, the potential use of resistivity measurements for interrogating nanostructural features has not been fully explored. The paper presents how electrical resistivity measurements combined with more conventional techniques can be used to understand the evolution of the nanostructural state in advanced aluminum alloys.

Water atomised aluminium alloy powders

The new rapid solidification (RS) process based on high-pressure water atomisation (WA) of the melt for manufacturing of advanced aluminium alloys was realised in the form of a pilot plant. The problems of safe operation in the course of Al alloy powder production and powder quality were solved by the use of water solutions of inhibitors, by the control of suspension temperature and hydrogen ion exponent (pH), by the hydraulic classification of atomised products, and by the optimisation of dehydration procedure. The rate of powder–water interaction strongly depends on the value of pH. While the rate of room temperature reactions is very slow at pH 3.0–4.0, the increase of pH to 6.0 leads to an intensive powder oxidation. A set of powder metallurgy (PM) alloys for various applications was produced on the base of water atomised powders. The characteristics of tensile strength of such alloys essentially exceed those of cast materials of similar compositions.

Determining the role of surfaces and interfaces in the powder metallurgy processing of aluminum alloy powders

AbstractThe current options for solid‐state consolidation processing of powder‐based advanced aluminum alloys have been very limited and complicated, resulting in a segregation of the applications primarily to the aerospace segment. Throughout any consolidation sequence for aluminum powders, the oxide and/or hydroxide films on the typical powder surfaces can interfere with densification and interparticle bonding. In fact, the consolidation sequence for many low‐strength aluminum alloy powder metallurgy parts involves transient liquid‐phase sintering to massively disrupt the powder surfaces, producing improved bonding but introducing a coarsened resolidification microstructure. Although preventing aluminum oxide formation is nearly impossible during aluminum powder production, the gas atomization reaction synthesis (GARS) method—an advanced powder production technique—can modify the oxide coating and enable improved consolidation processing. This report compares the effects of the GARS process and other representative atomization processes on the surface structure and properties of aluminum powders and on their ability to sinter. The powders were characterized with transmission electron microscopy, scanning electron microscopy, Auger electron spectroscopy, quadrapole mass spectroscopy and with a new ultrasonic method for in situ sensing of the evolution of sintering. In general, a marked reduction in the surface film thickness and in the level of chemisorbed moisture and moisture‐borne impurities was observed in the GARS powders. This change in powder surface characteristics also was effective in promoting sintering processes in the GARS powders, as monitored by our new technique. An initial direct comparison of explosivity for the different types of aluminum powder revealed that the GARS powder also had a reduced hazard level. All of these findings indicate that the GARS approach to aluminum powder production may enable mass‐produced lightweight powder metallurgy parts from advanced aluminum alloys with simple consolidation processing techniques. Copyright © 2001 John Wiley & Sons, Ltd.

Transport aircraft — a challenge for aluminium alloys for the 21st century

AbstractThe anticipated size of the world airliner market over the period 1997-2016, and the resultant requirements for aluminium plate and extrusions to satisfy potential Airbus wing box production is reviewed.The ‘value’ of technology and the threat posed by polymer composites to the future of aluminium alloys for large transport aircraft wing box structures is discussed and the prospect is raised that there may be limited further development potential for conventional aluminium alloys within the civil transport wing context. This may then force a re-evaluation of the role of aluminium-lithium alloys and other non-conventional metallic materials as alternatives to polymer composites.Opportunities to maximise the cost-effectiveness of advanced aluminium alloys are discussed and the potential benefits of closer co-operation between the aircraft and aluminium industries highlighted within a joint technical and commercial framework.The ‘challenge’ to the aluminium industry is described as a continuing requirement to assist the aircraft manufacturer to offer ‘optimum value’ products to the airlines. Otherwise, alternative technologies such as polymer composites will emerge and the pre-eminent position of aluminium in civil transport aircraft will be eroded.

Localized deformation and elevated-temperature fracture of submicron-grain aluminum with dispersoids

Advanced aluminum alloys with thermally stable submicron grains, fine dispersoids, and metastable solute are limited uniquely by reduced ductility and toughness at elevated temperatures. The mechanism is controversial. Experimental results for cryogenically milled powder metallurgy Al extrusion (with 3 vol.% of 20 nm Al 2O 3, a 0.5 μm grain size, but no solute) establish that uniaxial tensile ductility, plane strain crack initiation fracture toughness K JICi, and tearing resistance T R decrease monotonically with increasing temperature from 25 to 325 °C. Fracture is by microvoid processes at all temperatures; reduced toughness correlates with changed void shape from spherical to irregular with some faceted walls. Strain-based micromechanical modeling predicts fracture toughness, and shows that temperature-dependent decreases in K JICi and T R are due to reduced yield strength, elastic modulus, and intrinsic fracture resistance. Since CM Al does not contain solute such as Fe, dynamic strain aging is not necessary for low-toughness fracture at elevated temperature. Rather, increased temperature reduces work and strain rate hardening between growing primary voids, leading to intravoid instability and coalescence at lowered strain. Decreased strain rate hardening is attributed to increased mobile dislocation density due to dislocation emission and detrapping from dispersoids in dynamically recovered dislocation-source-free grains.

Deformation Mechanisms of Positive Exponent Superplasticity in Advanced Aluminum Alloys with Nano or Near-Nano Scale Grained Structures

Deformation Mechanisms of Positive Exponent Superplasticity in Advanced Aluminum Alloys with Nano or Near-Nano Scale Grained Structures

Positive exponent superplasticity in advanced aluminum alloys with nano or near-nano scale grained structures

Abstract Very high strain rate superplasticity was observed in near-nano scale aluminum alloys. These alloy systems include the group of mechanically alloyed IN9021, IN90211, IN9052, IN905XL alloys and SiCp/IN9021 composite, an A-14wt.%Ni-14wt.%Mm (Mm is mischmetal) crystalline alloy consolidated from its amorphous powders and an Al-14wt.%Ni-7wt.%Mm-1wt.%Zr alloy consolidated from nanocrystalline powders, and an Al-7wt.%Cr-1wt.%Fe alloy produced by physical vapor deposition. In each of the above advanced alloy systems, large elongations of more than 500% were obtained at extremely high strain rates of more than 1 s−1 (called positive exponent superplasticity). In the mechanical alloyed IN9021 aluminum alloy with a fine grained structure 500 nm in size, a maximum elongation of 1250% was recorded at an extremely high strain rate of 50 s−1 at 823 K. In addition, a maximum elongation of 610% was obtained at a very high strain rate of 5 s−1 of 823 K in the mechanically alloyed 15vol.%SiCp/IN9021 aluminum composite. A maximum elongation of 650% was observed at a high strain rate of 1 s−1 in both AlNiMm and AlNiMmZr alloys consolidated from amorphous or nanocrystalline powders. Also a maximum elongation of 505% was obtained at a high strain rate of 1 s−1 in a VQ AlCrFe alloy.

Testing the Superplastic Flow Characteristics of Advanced Aluminum Alloys

Abstract Special test equipment is required in order to determine the superplastic flow characteristics of advanced aluminum alloys such as the low-density aluminum-lithium alloys and the high-temperature intermetallics (processed by rapid solidification, mechanically alloying, powder metallurgy techniques). The superplastic flow characteristics under optimum conditions of strain race and temperature are necessary as input data to the computer process model weed to predict optimum pressure-time cycles for the SPF process. Most published tensile flow stress data for superplastic deformation was developed under constant crosshead speeds and at atmospheric pressure. In order to establish accurate flow characteristics, testing must be conducted: (1) at a closely controlled temperature, (2) at a controlled constant true strain rate, and (3) under hydrostatic pressure (to prevent cavitation). This paper discusses the design and development of a test system with these capabilities and also highlights typical results for three aluminum-lithium alloys.

Rotary forging of advanced aluminium alloys : P.M. Standring, (University of Nottingham, Nottingham, England)

Rotary forging of advanced aluminium alloys : P.M. Standring, (University of Nottingham, Nottingham, England)

Applying the Ceracon process

The Ceracon consolidation process is recognized as an enabling technology by the advanced materials processing community. With its use in a broad range of conventional materials leading to cost reduction, significant commercial applications are emerging for this process. The process has been succesfully applied to RS alloy systems including advanced aluminium alloys, copper based alloys, iron and titanium aluminide systems. The major advantage is that consolidation is carried out below the solidus temperature of the material thus removing a problem in composites processing. Recently the process has been coupled with SHS to address formation of cermet materials. It has also been applied to CVD coated powders in the solid state.

Mechanical property data base from an air force/industry cooperative test program on advanced aluminium alloys: Phillips, M.A. and Thompson, S.R. Wright Research and Development Center Report No AD-A226 410/9/XAB June 1990 194 pp

Mechanical property data base from an air force/industry cooperative test program on advanced aluminium alloys: Phillips, M.A. and Thompson, S.R. Wright Research and Development Center Report No AD-A226 410/9/XAB June 1990 194 pp

Advanced aluminium alloys for aircraft and aerospace applications

Aluminium has been the dominant material in the aircraft industry for a half century due to its attractive combination of light weight, strength, ductility, corrosion resistance, ease of assembly and low cost. This dominance is being challenged by new materials offering potential weight savings and fuel economies. The aluminum industry has countered this challenge by developing a number of advanced materials of its own: rapidly solidified alloys, metal matrix composites and aluminum-lithium alloys. Performance and cost considerations favour the last in most situations, and a considerable effort is under way to commercialize AlLi alloy products. State-of-the-art aluminum lithium alloys show promising property levels, particularly strength and elastic modulus. Steady improvements in ductility and fracture toughness are resulting from industry-wide development work, particularly with the AlCuLi and AlLiCuMg alloy systems.