7xxx Series Aluminum Alloys Research Articles

Distinct fatigue limit of a 6XXX series aluminum alloy in relation to crack tip strain-aging

In this study, a conventional precipitation-hardened A6061-T6 alloy (base alloy) and a modified alloy containing excess solute magnesium (Mg) compared to the base alloy were compared in terms of high-cycle fatigue property. Particular attention was paid to the emergence of a distinct knee point on the fatigue life diagram together with a time-dependent strengthening (coaxing) effect in the modified alloy under various test conditions. An attempt using specimens with different defect size successfully revealed that a distinct knee, which was absent in the base alloy, was attributed to the threshold against small crack growth. The clear coaxing effect in the modified alloy was also explicitly confirmed in terms of the high ΔK value achieved by the arrested cracks regardless of the defect size. The comparative tests conducted under different environments and temperature conditions further confirmed that the crack tip strengthening, essentially caused by the strain-aging capability endowed to the modified alloy, operated most prominently in the ambient air at room temperature. Such results were rationally interpreted by incorporating a competitive interaction of solute Mg and hydrogen (H) with dislocations at the crack tip.

Experimental and Numerical Investigation on Strengthening Behavior of 7075 Aluminum Alloy Sheets in Hot Forming–Quenching Integrated Process

Abstract 7xxx-Series aluminum alloys have a wide application prospect in the automotive industry due to its higher strength than other series of aluminum alloy. However, little literature has been reported on the formability and strengthening behavior of 7xxx-series aluminum alloys for the structural components of body in white (BIW). In this paper, the formability and strengthening behavior of 7075-T6 were investigated systematically under hot forming–quenching (HFQ) integrated process. First, compound dies with rod-heated blank holder and water-cooled lower punch and upper die were set up for experiment. For low adhesion friction and high cooling rate, the optimum blanking temperature was determined as 400 °C. Second, forming state, thickness distribution, and temperature field were investigated through experiment and finite element simulations. A-pillar reinforcement panel was successfully manufactured based on the simulation results. The simulation data showed that the maximum thinning rate of the whole part is about 14.25%, and the maximum thickening rate is about 1.95%. Third, the formability and quench sensitivity of u7075-T6 were achieved through time–temperature–transformation (TTT) curves and continuous cooling precipitation (CCP) diagrams combined with the thermo-mechanical coupling simulation. Finally, the strengthening was measured by testing the tensile strength and Vickers hardness at different positions of formed parts after artificial aging process. The testing result showed that the strength of the formed parts after artificial aging at 120 °C for 24 h were 162.7–172.2 HV and 505–528 MPa, respectively.

On the suppression of Lüders elongation in high-strength Cu/Zn modified 5xxx series aluminum alloy

The deterioration in surface quality due to the formation of Lüders lines is a typical phenomenon in 5xxx series Al–Mg alloys. Traditional efforts show that an increase of the grain size results in the suppression of the Lüders elongation. This paper presents that the suppression of the Lüders elongation can be realized at a smaller grain size by the addition of Zn/Cu elements in the 5xxx series alloys and by pre-aging treatment. The alloys with (Zn + Cu)/Mg ratios below 1.0 result in an increase of the strength by the precipitation of T-Mg 32 (AlZnCu) 49 phase, and quite different from 7xxx series Al–Zn–Mg alloys strengthened by η-MgZn 2 precipitates. The decisive measurement for suppressing Lüders elongation is based on the depletion of Mg atom concentrations in the matrix due to the formation of GP zones after pre-aging treatment. • The 5xxx series Al alloy is modified with (Zn + Cu)/Mg ratios below 1.0. • The Lüders elongation can be suppressed in a smaller grain size at T4P temper. • The Hall-Petch coefficient for Lüders increases with the concentrations of Mg atoms. • The suppression of Lüders elongation is due to the formation of T precipitates.

Effect of Trace Elements on the Crystallization Temperature Interval and Properties of 5xxx Series Aluminum Alloys

The influence of alloying elements Er, Zr, Cu, Si and Zn on the crystallization temperature interval, microstructure, mechanical properties and corrosion behavior of Al-Mg-Mn alloy were studied by differential scanning calorimetry (DSC), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), tensile testing, electrochemical measurements and nitric acid mass loss test (NAMLT). The results show that the crystallization temperature range of Al-Mg-Mn alloy with addition of Zn decreased 4.7 °C. Cold rolled alloys mainly contain S texture, Copper texture, Brass texture, and Goss texture; the content of the S texture is the highest. With the addition of trace elements, the second phase Al3Er, Al3Zr, Al2CuMg, Mg2Si and MgZn2 can be formed, which can improve the tensile strength and yield strength of Al-Mg-Mn alloy. The addition of the alloying element Zn can also improve the intergranular corrosion resistance of the Al-Mg-Mn alloy.

The Use of Gas Extrusion for the Synthesis of a High-Strength Composite Based on a 5xxx Series Aluminum Alloy Strengthened with Carbon Nanostructures

Composite materials based on a 5xxx series aluminum alloy strengthened with 0.1 wt % of multiwalled carbon nanotubes (MWCNTs) or 0.1 wt % WC1 –x/MWCNTs were synthesized by high-energy ball milling and subsequent gas extrusion. The structural phase composition and physicomechanical properties of bulk composites are characterized. A comparison with published data on the properties of composites based on 5xxx series aluminum alloys reveals promises of using gas extrusion for consolidation, as well as the effectiveness of the use of strengthening microadditives of MWCNT hybrid nanostructures to increase strength.

Modelling Hydrogen Embrittlement using Density Functional Theory: A theoretical approach to understanding environmentally assisted cracking in 7xxx series aluminium alloys

The effects of H segregation to a Σ11 symmetric tilt Al grain boundary are investigated using atomistic simulations, as part of a wider study on cracking in 7xxx series alloys. Density functional theory based simulations of uniaxial straining of grain boundaries containing 11 different concentrations of H were performed under the cohesive zone fracture mechanics framework. The theoretical strength of grain boundaries is shown to be supressed by H segregation, and the cause of this is attributed to the prevention of the formation of Al ligaments across grain boundaries. Segregated concentrations of relevant alloying elements (Zn, Mg, and Cu) show minimal impact on the H embrittlement process investigated, namely H enhanced decohesion (HEDE). Further modelling, of H transport and grain boundary precipitates, is required to confirm the validity of the HEDE mechanism in the case of 7xxx alloys.

Mechanical and corrosion behaviour of aluminum alloy 5083 and its weldment for marine applications

Abstract 5xxx series aluminum alloys find increasing applications in the marine fabrication industries due to its unique mechanical and corrosion properties. The present attempt focuses the effect of metallurgical changes in mechanical behavior and corrosion resistance of Aluminium alloy 5083-H111 and its weldment. Gas tungsten arc welding (GTAW) process was used to fabricate the weld coupons using the filler metal ER 5183. Microstructure analysis was carried out in the fusion zone and compared to the heat affected zone and parent metal region. The mechanical behavior of the weld was compared with its parent metal by performing microhardness, impact toughness, tensile behavior and formability test. Electrochemical corrosion test revealed better corrosion resistance for parent metal sample than the weldment. The existence of Mg3Al2 precipitates in the weldment led to the reduction in corrosion resistance

Reduced ductility of 6XXX series aluminium alloys at high-temperatures and intermediate strain rates

Reduced ductility of 6XXX series aluminium alloys at high-temperatures and intermediate strain rates

Processing and precipitation strengthening of 6xxx series aluminium alloys: A review

Processing and precipitation strengthening of 6xxx series aluminium alloys: A review

Material characterization and damage assessment of an AA5352 aluminium alloy using digital image correlation

The emergence of reliable material characterization techniques in automotive and aeronautical industries, in particular sheet metal forming, promises to underpin a novel advance in materials research. In this regard, 5xxx series aluminium alloys deliver the largest formability range and can be deformed at room temperature. This study aims at determining the mechanical properties of the AA5352 aluminium alloy, using digital image correlation. Thus, tensile sheet specimens manufactured from the corresponding alloy are mechanically tested under a uniaxial condition and deformation fields are monitored. Considering the force/displacement response and stress/strain curves, the material Poisson’s ratio, Young’s modulus and anisotropy coefficient in the transverse direction are characterized by the experimental digital image correlation data. It intends to obtain accurate and reliable mechanical properties to be considered in the future processing analyses. Numerically, adopting the experimentally obtained material properties, the Gurson–Tvergaard–Needleman damage model is implemented using finite element method formulation to forecast the ductile fracture performance of the tested AA5352 sheet. The predicted results are then compared with the experimental digital image correlation solution verifying good agreement with the force/displacement response and the deformation fields. Overall, the acquired numerical results imply that the Gurson–Tvergaard–Needleman damage criterion is capable to render an accurate prediction upon a high stress triaxiality state.

Simultaneously enhanced strength and ductility of 6xxx Al alloys via manipulating meso-scale and nano-scale structures guided with phase equilibrium

Excellent comprehensive mechanical properties including good formability, high strength and high ductility are prior demands for Al-Mg-Si-Cu alloys. This study utilizes calculation of phase diagram (CALPHAD) to simplify the alloy design and meet these demands. Specifically, CALPHAD was used to finely tune the Mg/Si atomic ratio in solid solution and accurately control the type and content of second phases, especially to avoid the formation of the harmful constituent phase β-AlFeSi. Constituents and dispersoids of only α-AlFeMnSi phase were found in the alloy prepared. An optimized microstructure with fine grains, micro scale constituents, densely distributed submicron scale dispersoids and extremely dense nano precipitates provides effective impediment to dislocation gliding and induces transgranular fracture. Therefore, the designed alloy has better comprehensive mechanical properties than other 6xxx series aluminum alloys, including excellent formability, strength and ductility. The low T4P strength of 149 MPa as well as the high elongation of 26.1% implies the alloy's applicability to automobile body panel forming. The yield strength was rapidly improved from 149 MPa to 277 MPa during the paint bake ageing, because the number density of precipitates is twice as high as that of some other 6xxx alloys. Meanwhile, the elongation was kept at a high level of 20.0%.

Strain Rate and Temperature Dependent Plastic Response of AA7075 during Hot Forming

High strength 7xxx series aluminum alloys are being increasingly considered for automotive applications due to their superior specific strength compared to 6xxx series alloys. Complex structural components made from 7xxx series alloys need to be manufactured through warm forming or hot stamping due to their low ductility at room temperature. For hot stamping, the AA7075 blanks are heat treated to above 480°C, yielding a supersaturated solid solution, corresponding to a W temper state. The preheated blanks are then simultaneously formed and rapidly quenched using cooled dies. The entire forming process takes place in the W temper condition. The stamped parts are further subject to an artificial aging heat treatment to achieve the desired temper through precipitation hardening. Therefore, understanding the strain rate and temperature dependent plasticity behavior of AA7075-W is critical to establish optimum design parameters for the hot stamping process. The present work is concerned with the strain rate and temperature dependent plastic response of AA7075 in the W temper state. In particular, the results from a comprehensive experimental program on uniaxial tension specimens are presented. High temperature experiments are carried out at strain rates ranging from 0.001-2/s in a universal testing machine. An induction heating system with infrared high speed imaging is used to span the entire temperature range from 180°C to 480°C, over the full range of strain rates considered. Based on the experimental results, a candidate plasticity model with an empirical mixed Swift-Voce hardening law and a Johnson-Cook type strain rate and temperature dependence is calibrated.

Experimental study on the mechanical properties of 7xxx aluminium alloy sheet under different heat treatment conditions

Automotive bodies with high strength aluminium alloys have drawn increasing attentions due to their higher strength and lightweight capability. As one of high strength series of aluminum alloys, peak aged 7xxx series aluminum alloys exhibit superior strength of ∼ 600MPa to the conventional lower or moderate strength alloys. However, in spite of the high strength, the lower ductility has been a technical hurdle to be overcome for the material to be applied to press parts at room temperature, which leads to the development of forming technologies at elevated temperature, or namely hot forming. As an alternative to the hot forming, forming trial at room temperature has been made by performing prior solution heat treatment and quenching. This coupled heat treatment and cold forming increases the formability, while the strength needs to be recovered by additional post treatment. The treatment after forming (or deformation) includes natural aging and paint baking process inducing the artificial aging. The objective of the present study is to experimentally investigate the mechanical properties after different heat treatment conditions, which will be utilized for the future finite element simulations for the investigated forming technology.

Precipitation in an extruded AA7003 aluminium alloy: Observations of 6xxx-type hardening phases

Precipitation behavior in an industrially extruded AA7003 alloy has been studied using Transmission Electron Microscopy (TEM) together with Differential Scanning Calorimetry (DSC). Air Cooling (AC) after solution heat treatment results in quench induced heterogeneous precipitation of both β-Mg2Si and η-MgZn2 phases. Detailed TEM characterisation of resulting nanoscale precipitates after AC, or Water Quenching (WQ), and subsequent artificial ageing demonstrate that η′ and η2 hardening precipitates dominate in T6, whereas the overaged T7 state contains η2 and η1, where the latter accounts for approximately 50% of the relative phase fraction. The T7 state in addition forms 6xxx-type hardening precipitates only after WQ. Results presented here are expected to be relevant for any Si containing 7xxx alloy and open new possibilities for development of hybrid 6xxx- and 7xxx series aluminium alloys. This is discussed with respect to potential influence on mechanical- and corrosion properties.

Experimental and Numerical Investigation of the Effect of Different Temperature and Deformation Speeds on Mechanical Properties and Springback behaviour in Al-Zn-Mg-Cu Alloy

Thanks to their low density and high strength, the 7XXX series aluminum alloys are widely used as a support/beam parts in the aerospace industry. This alloy is target in the lightening studies of the automotive industry and surveys for sheet metal are still in progress. It is a series of alloys that can be applied to the aging process and has the most effect on mechanical properties. As formability is quite weak, methods are investigated. In this study, tensile test, bending test and Erichsen tests are performed at different deformation rates and temperatures. As a result of the experiments, it has been seen that the formability increases at high temperature and low deformation rates. If paint baking time is long, there will be no loss of strength. Also, the bending process is modeled with the help of the finite element analysis programs and the springback estimations are examined. It is seen that the results of the modeling process are quite successful. The effect of the strain rate sensitivity is determined.

Effect of Si content on the cracking behavior of selective laser melted Al7050

PurposeIt is a crucial issue to eliminate cracks for selective laser melting (SLM) 7xxx series aluminum alloy. This paper aims to study the effect of silicon content on the cracking behavior and the mechanism of eliminating crack of SLMed Al7050 alloy.Design/methodology/approachSix different silicon contents were added to the Al7050 powder. The crack density and crack count measuring from optical micrographs were utilized to judge the cracking susceptibility. The low melting phases analyzing from Jmatpro and the microstructure observing by EPMA and SEM were used to discuss the mechanism of eliminating the crack.FindingsThe cracking susceptibility of SLMed Al7050 alloy decreases with the increase of adding silicon content. When adding silicon, two new low-melting phases appeared: Mg2Si and Al5Cu2Mg8Si6. These low-melting phases offer much liquid feeding along the grain boundary and decrease the cracking susceptibility. Moreover, the grains are obviously refined after adding silicon. The fine grain can increase the total surface area of the grain boundary, which can reinforce the matrix and decrease the cracking susceptibility. High silicon content results in more low-melting phases and fine grains, which decreases the cracking susceptibility.Originality/valueThe investigation results can help to obtain crack-free SLMed Al7050 parts and deep knowledge on eliminating cracking mechanism of high-strength aluminum alloy fabricated by SLM.

Polyoptimisation of the refill friction stir spot welding parameters applied in joining 7075-T6 Alclad aluminium alloy sheets used in aircraft components

In the aerospace industry, the refill friction stir spot welding (RFSSW) method is increasingly used to join thin sheets, especially those made of 2xxx and 7xxx series aluminium alloys. This paper presents the results of spot welding lap joints of 7075-T6 aluminium alloy sheets. The load capacity of joints was determined by tensile/shear tests using a universal testing machine. The effect of tool plunge depth, tool rotational speed and duration of welding on joint load capacity and failure mode was investigated. The polyoptimisation of the values of welding process parameters was carried out to ensure the highest load capacity of the joint at a minimum variance of the results obtained. The selection of the optimal parameters of the RFSSW process was carried out using an adequate mathematical model obtained on the basis of Weierstrass’ theorem. It was found that tool rotational speed had the greatest impact on the load capacity of the joints. It was possible to increase the load capacity of the joint by increasing the duration of welding but only to a limited extent. The selection of optimal welding parameters requires a compromise solution, i.e. the selection of a tool rotational speed that ensured adequate plasticisation of the material with a welding duration that ensured that an appropriate joint microstructure was obtained and assured the required load capacity of the joint. The methodology of mathematical modelling of polyoptimisation presented can be useful in optimising similar joining processes.

Hot deformation behavior of 7A04 aluminum alloy at elevated temperature: constitutive modeling and verification

The hot deformation behaviour of one 7XXX series aluminium alloy, 7A04, has been studied by conducting isothermal hot compression tests with degree of compression up to 55% at the temperature ranging from 350 °C to 480 °C and strain rates ranging from 0.002 s−1 to 20s−1. Based on characteristic of the flow stress obtained from those tests, an extended Voce equation, which constant parameters were modified as Arrhenius-type type equation, was given and used to calculate the flow stresses under the conditions of the hot deformation. The parameters of extended Voce equation were determined by experimental results. The comparison between the experimental and predicted flow stress values at the hot compression parameters range indicated good agreement. The average absolute relative error, root mean square error and the correlation coefficient were found to be 4.9%, 4.8 MPa and 0.997, respectively, which confirmed the extended Voce model had good accuracy. Additional, a finite element simulation model of isothermal hot compression process was used to verify the new Voce equation and the results verified the accuracy of the new equation. The main softening mechanism of the hot deformation was dynamic recovery and was confirmed by optical microstructures.

Analysing the degree of sensitisation in 5xxx series aluminium alloys using artificial neural networks: A tool for alloy design

The 5xxx series aluminium alloys are susceptible to sensitisation during service at elevated temperatures. Sensitisation refers to deleterious grain boundary precipitation resulting in rapid intergranular corrosion in moist environments. A holistic understanding of the variables that can influence the degree of sensitisation in Al-Mg-Mn alloys is presented herein, including the exploration of some custom produced 5xxx series alloys that were prepared to create a significant dataset for which an artificial neural network (ANN) could be applied. An ANN model could reveal complex interactions between various factors that influence sensitisation, with the view to designing sensitisation resistant Al-Mg-Mn alloys.

Progress in Understanding Initiation of Intergranular Corrosion on AA6005 Aluminum Alloy with Low Copper Content

As part of an extensive research program to study recent, unexpected intergranular corrosion (IGC) on 6xxx series aluminum alloys (AlMgSi), this paper investigates the mechanism of initiation and early propagation of IGC on the extruded AA6005-T5 alloy with small Cu content (0.1 wt%) by use of advanced electron microscopy techniques applied for near surface characterization. Corrosion testing was restricted to the accelerated IGC test according to the standard BS ISO 11846, involving exposure to acidified chloride solution. The effect of modifying the as-received extruded surface by metallographic polishing, argon sputtering, and alkaline etching was investigated. Initiation of IGC was delayed on the as-received surface compared to the modified surface, caused by the presence of an approximately 8 nm thick crystalline oxide layer formed during extrusion. IGC initiated at the primary α-Al(Fe,Cu,Mn)Si particles for all types of surfaces. However, these particles corroded rapidly in the test solution forming a residue of Cu and Si on the exposed particle surface. This phenomenon, as well as enrichment of Cu on the Al matrix surface by dealloying, contributed increasingly to the formation of new effective cathodic sites and continuing propagation of IGC. The AlMgSiCu (Q) phase, present as primary and secondary particles, was relatively inert against both oxidation and reduction.