6xxx Alloys Research Articles

Linking Spectrograph to Mechanical and Physical Properties of X7475 Experimental Alloys Produced from Recycling Beverage Cans for Bumper Beam Applications

The automobile industry intends to consume more aluminium alloys in an effort to reduce the greenhouse emissions through the cut in the weight of the passenger cars. Experimental X7475 aluminium alloy is a good candidate to achieve this mission. Past efforts targeted at exploring the aluminium for bumper beam applications and even the recovery of aluminium from recycled beverage can (RBC) were not with the aim of upgrading the 3xxx to a novel 7xxx alloy. The wt. % of Zn was 5.0, 4.5 and 4.0, while Mg was left at 1.50, 1.25 and 1.00 wt. % with Mn at a peak of 0.075, 0.050 average and a least wt. % of 0.025. Alloys were homogenized and taken through annealing (O), natural aging (T4) and artificial aging (T6). The effect of hardening phases such as MgZn2 (ICDD 034-0457) due to heat treatments on the physical and mechanical properties of the new X7475 alloys was investigated. Formation of precipitates affected the density and hardness of the alloys produced via stir casting route. A least hardness of 63.40 Hv was observed in alloy H with a density of 2.7264 g/cm3 while the maximum of 113.06 Hv was recorded against alloy C in as-cast (AC). The result has contributed to the database of experimental alloys with the possibilities of producing a new material from RBCs for bumper beam applications. Future investigation should employ design of experiment (DOE) in optimization of the heat treatment for better mechanical properties.

Hot deformation behavior and processing map development of cryorolled AA6063 alloy under compression and tension

The 6xxx series aluminium alloys are extensively used in the structural applications of automobile and aerospace. The strength of these alloys can be further improved by severe plastic deformation. The severely deformed aluminium alloys may experience severe thermal and mechanical process during development of structural components. Therefore, it is important to develop processing map for such severely deformed 6xxx alloys to understand its workability under various temperature and strain rate. In the current work, hot deformation of severely deformed (cryorolled-CR) AA6063 alloy was studied via hot tensile and hot compressive testing in temperature range of 300°C – 450°C and at strain rate of 0.001 s−1 – 10 s−1. The safe processing regions were established via processing map with the help of dynamic materials model (DMM). Also, the constitutive model was established and the activation energies were known to understand the deformation mechanism of CR AA6063 alloy in both tensile and compressive mode. Stable and unstable zones were identified from processing maps in both tensile and compressive mode of deformation. In tensile mode dynamic recovery and in compressive mode simultaneous action of dynamic recovery and dynamic recrystallization were primary mechanisms of deformation in stable region. However, instability region was identified by stress concentration cracking in both tension and compression modes of deformation. The average activation energy in compressive mode (196.57 kJ/mol) of deformation was found to be higher compared to tensile (151.55 kJ/mol) defamation. Microstructural evolution was used to establish a correlation between constitutive model and processing maps.

Effect of Annealing and Artificial Ageing Parameters on The Ultimate Tensile Strength and Elongation of New Al-(4-5) Zn- Mg-Mn-Cu Alloys Fabricated using Recycled Beverage Cans

The transport industry is one of the highest consumers of aluminium alloys. However, the quest for new and cheaper aluminium with properties comparable to the contenders has remain in the research domain for sometimes. Even at that, the literature is dearth of clear ideas on conversion of the huge RBCs to X7475 experimental alloys. In furtherance to the fabrication of a new 7xxx (Al-4-5Zn-1.5Mg-1.0Mn-0.35Cu) alloy from Recycled Beverage Cans (RBCs), the effect of annealing temperature (350 oC, 380 oC and 413 oC) and artificial ageing time (6, 10.5 and 15 hours) on the ultimate tensile strength (UTS) and elongation (e) were reported. Nine samples (S1-S9) of experimental alloys were fabricated and subjected to tensile tests, SEM/EDX and XRD analysis. Secondary phases like MgZn2, Cu2Mg precipitates as observed in the XRD supported an improved UTS. The elemental analysis revealed the presence of alloying compositions. An alloy fabricated using Al-5Zn-1.5Mg-1.0Mn-0.35Cu (S9), artificially aged at 6 h and annealed at 413 oC had the highest UTS of 362.2 MPa and an elongation of 3.09 mm (15.45 %). The result demonstrated that a new X7475 alloy was fabricated from RBCs with comparable mechanical properties with alloys fabricated using pure aluminium.

Microstructural Refinement and α‐Dispersoid Evolution in Direct‐Chill Cast Al–Mg–Si–Fe Alloy

High Fe levels, coarse grains, microstructural inhomogeneities, and coarse dispersoids for recrystallization suppression remain problems for industrial application of Al–Mg–Si (6xxx) alloys. Herein, Al–0.81%Mg–0.81%Si–0.7%Fe alloy billets are fabricated by direct chill (DC) casting at different casting speeds. The results indicate that high‐speed (300 mm min−1) DC casting can provide fine grains, refined Fe‐containing phases, relatively high solid–solute content, and improved distribution of Mn and Cr. After homogenization at 500 °C for 6 h, the α‐AlFeMnCrSi dispersoids in the high‐speed cast billet decrease in size and increase in number density, compared with the conventional cast billet (100 mm min−1). The low homogenization temperature (440 °C) also contributes to the size reduction and increases the number density of dispersoids. Air cooling after homogenization (holding temperature ≥500 °C) results in Q‐AlCuMgSi precipitation, which depends on the precipitated substrate of the α‐AlFeMnCrSi dispersoids. Moreover, the precipitation processes of α‐dispersoids and Q phases are discussed according to transmission electron microscopy (TEM) and high‐angle annular dark‐field scanning transmission election microscope (HAADF‐STEM) results. These results mean that high‐speed DC casting can effectively improve the as‐cast microstructure by increasing the cooling rate, and the as‐cast microstructural evolution promotes the precipitation of fine and dense α‐dispersoids from the α‐Al matrix.

Characterization of Intergranular Corrosion in AA 5xxx Al-Mg Alloys

Abstract Intergranular corrosion refers to a selective corrosion attack at the grain boundaries of polycrystalline materials. In engineering Al-Mg alloys of the AA 5xxx series it is caused by the formation of chemicallyless noble β-Al8Mg5 phases along the grain boundaries. The sensitivity of a material to intergranular corrosion can be assessed based on the mass losses in the so-called nitric acid mass loss test (NAMLT) according to ASTM G67. However, a detailed investigation of the underlying corrosion mechanisms requires that the β phases are made directly visible in the microstructure by metallographic methods. In the present work, the NAMLT mass losses of three AA 5xxx alloys with different Mg contents are compared with the results from two different etching methods. On the one hand, the alloys are etched in diluted phosphoric acid, a substance routinely used to examine the grain boundary occupancy in AA 5xxx materials. On the other hand, a newer etching method using a dilute ammonium persulfate solution is tested which etches the β-Al8Mg5 phases in the microstructure in a way that they can be examined at higher magnifications; even examinations in the scanning electron microscope are possible.

Modelling the Age-Hardening Precipitation by a Revised Langer and Schwartz Approach with Log-Normal Size Distribution

A new numerical modelling approach integrating the Langer and Schwartz approach and log-normal particle size distribution has been developed to depict the precipitation kinetics of age-hardening precipitates in Al alloys. The modelling framework has been implemented to predict the precipitation behavior of the key secondary phases in 6xxx and 7xxx Al alloys subjected to artificial aging. The simulation results are in good agreement with the available experimental data in terms of precipitate number density, radius, and volume fraction. The initial shape parameter of the log-normal size distribution entering the modeling framework turns to play an important role in affecting the later-stage evolution of precipitation. It is revealed that the evolution of size distribution is not significant when a small shape parameter is adopted in the modelling, while an initial large shape parameter will cause substantial broadening of the particle size distribution during aging. Regardless of the magnitude of shape parameter, a broadening of the particle size distribution as predicted by the present model is in agreement with experimental observations. It is also shown that large shape parameter will accelerate the coarsening rate at later aging stage, which induces fast decreasing of number density and increased growth rate of mean/critical radius. A comparison to the Euler-like multi-class approach demonstrates that the integration of more realistic log-normal distribution and Langer and Schwartz model make the present modelling faster and equivalently accurate in precipitation prediction.

Mechanical and microstructural behaviour of AA7075 aluminium alloy for sub-zero temperature sheet stamping process

Age-hardenable aluminium 7XXX alloy sheets represents a very attractive material for the aerospace field; however, their limited formability at room temperature restricts their adoption in the industrial context.In the present study, deformation of AA7075 sheets at temperatures lower than the room one is presented as a possible strategy to overcome this limitation.To this aim, a comprehensive experimental campaign was carried out on AA7075 sheets in peak aged condition at varying temperature and triaxiality states. Specifically, the temperature was changed from −100 °C to 300 °C whereas different stress triaxialities states were achieved by adopting different specimen configurations, namely smooth, notched and shear. A necking locus curve was presented and modelled. Results show that, regardless of the stress state, the uniform elongation monotonically increased as the testing temperature was reduced, favouring material formability. Microstructural and mechanical investigations carried out on the deformed samples revealed that deforming at temperatures higher than the room one drastically increased the number of coarse intermetallic particles. On the contrary, sub-zero deforming temperatures favoured the intermetallic particle fragmentation and the formation of high density of precipitates and dislocations.

Rationalizing Al-Mg, Al-Mg-Si, and multicomponent aluminum alloy design with segregation susceptibility predictions

Macro-segregation is a type of unacceptable defects, which normally occurs for aluminum alloys and other nonferrous alloys. In this work, the macro-segregation susceptibility (MAS) of commercial 5xxx and 6xxx alloys and Al-Mg and Al-Mg-Si alloys have been investigated via a criterion based on the solidification curves from thermodynamic calculations. Equilibrium solute distribution coefficients, k, with different initial alloying concentrations and their relationships with the MAS are discussed. Of all commercial 5xxx and 6xxx aluminum alloys, the AA5754, AA5182, AA6181A and AA6016 alloys have shown less susceptible to macro-segregation than others. Of all Al-Mg and Al-Mg-Si alloys in this study, Al-Mg alloys with higher Mg, and Al-Mg-Si alloys with both higher Mg and Si have shown less susceptible to macro-segregation than other compositions. Finally, the role of mass transfer behavior in improving macro-segregation is discussed from the perspective of thermodynamic and kinetic calculations.

Analytical solution for quenching of hot rolled aluminium plates without passing through C-curve

At the end of the hot rolling process, quenching is deployed for obtaining the desired microstructure and mechanical properties. During the quenching of aluminium plates, it is essential to optimize the process parameters such as the plate speed and cooling intensity for surpassing the C-curve. In this study, 1-D steady-state analytical model has been developed with the constant heat transfer boundary condition. The Eulerian computational domain contains the precooling and water cooling regions. Temperature drop starts in the precooling region itself due to back diffusion of heat, which originates from the water cooling region. Based on the analytical solution, the effect of plate speed and heat transfer coefficient on the cooling time has been investigated with the three non-dimensional parameters such as Peclect, Biot, and Fourier numbers. Typically, for the 2xxx (Al–Cu) alloys, every material point in the plate has to reach 350 °C within 0.2 s, which surpasses the nose of the C-curve where the phase transformation (CuAl2) severity can be reduced. This sets the limit for the maximum Fourier number and while keeping Peclect number as the independent variable, the minimum required water cooling in terms of Biot number is identified. The presented analytical solution provide the guidelines for selecting the appropriate combinations of plate speed and heat transfer coefficient for the quenching of continuously moving hot rolled plates. The results indicate that the nose of the C-curve can be surpassed easily by increasing the plate speed instead of reducing which contradicts the common notion.

Effect of Cu Content on Ageing Behavior for AA3104-H19 Can Body Sheet

AA3104 ingots with different Cu content (0.1wt.%, 0.2wt.% and 0.3wt.%) were prepared by DC casting, and then the ingots were processed to 0.26mm sheets with the method of making AA3104 can be body sheet. The AA3104-H19 sheets were aged at 180°C and the aging strengthen effect were found in the 0.2wt.%Cu and 0.3wt.%Cu alloys. Optical micrograph (OM), X-ray diffraction, high resolution transmission electron microscope were used on the sheets after different ageing time. Rod like coherency precipitates with the length about 5-10nm and the thickness about 2-3nm which were parallel to the [111] plane of the matrix was precipitated at peak aging (180°C-2h). According to the result of the thermodynamic phase diagram calculation, the precipitates should be S-Al2CuMg phase, but the structure of the precipitates were different from the precipitates reported in 2XXX alloy.

Hardness, quench sensitivity, and electrical conductivity of 7xxx Al alloys with high Zn concentrations

In this study, 7xxx (Al-Zn-Mg-Cu) alloys with high Zn concentrations were fabricated by increasing the Zn contents of 7085 Al alloys. The hardness, quench sensitivity, and electrical conductivity of the alloys and a 7085 Al alloy under peak-aged state were studied. The high Zn concentration alloys had higher η′ phase densities and lower quantities of Mg solid atoms than the 7085 Al alloy and thus exhibited higher hardness and electrical conductivity. The high Zn concentration alloys also exhibited slightly higher quench sensitivity than 7085 Al alloy, and the depth of the quenching layer of the alloy with 11.27 wt% Zn content reached 100 mm. This work confirmed that the novel 7xxx alloy with high Zn concentration showed balanced performance, exhibiting enhanced hardness and conductivity and reasonable quench sensitivity compared with the 7085 commercial Al alloy.

Revealing foundations of the intergranular corrosion of 5XXX and 6XXX Al alloys

Here, the nature of intergranular corrosion features and mechanisms for commercial 5083-H111, 6082-T6 and 6005A-T6 Al alloys are investigated comprehensively, supporting foundations for their management and maintenances under environmental conditions. It is found that the localized corrosions including the pitting, intergranular corrosion (IGC), exfoliation together with their coupling effects tend to the follow the direction and the morphology of precipitations and the elongated rolling/extrusion directions, suggesting grain refinement would be an effective approach to enhance the strength and IGC resistance. The microstructure characterizations and orientation statistics reveal the indicators improving durability and damage tolerance properties in the development of advanced Al alloys.

Characterisation of a High-Performance Al–Zn–Mg–Cu Alloy Designed for Wire Arc Additive Manufacturing

Ever-increasing demands of industrial manufacturing regarding mechanical properties require the development of novel alloys designed towards the respective manufacturing process. Here, we consider wire arc additive manufacturing. To this end, Al alloys with additions of Zn, Mg and Cu have been designed considering the requirements of good mechanical properties and limited hot cracking susceptibility. The samples were produced using the cold metal transfer pulse advanced (CMT-PADV) technique, known for its ability to produce lower porosity parts with smaller grain size. After material simulations to determine the optimal heat treatment, the samples were solution heat treated, quenched and aged to enhance their mechanical performance. Chemical analysis, mechanical properties and microstructure evolution were evaluated using optical light microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray fluorescence analysis and X-ray radiography, as well as tensile, fatigue and hardness tests. The objective of this research was to evaluate in detail the mechanical properties and microstructure of the newly designed high-performance Al–Zn-based alloy before and after ageing heat treatment. The only defects found in the parts built under optimised conditions were small dispersed porosities, without any visible cracks or lack of fusion. Furthermore, the mechanical properties are superior to those of commercial 7xxx alloys and remarkably independent of the testing direction (parallel or perpendicular to the deposit beads). The presented analyses are very promising regarding additive manufacturing of high-strength aluminium alloys.

First-principles calculation of interface binding strength and fracture performance of β’/Al interface in Al–Mg–Si–Cu alloy

High strength and high toughness are the key requirements of Al–Mg–Si (6xxx) alloys, and the performance of the precipitate phase directly affect the mechanical properties of the alloys. Among them, the β’ (Mg9Si5) precipitate has the strengthening effect for Al–Mg–Si alloy which has not been systematically studied. Therefore, we explore the essential mechanism of simultaneously enhancing the mechanical strength and fracture resistance of alloy from the perspective of two kinds of orientation relationships (ORs) precipitate/matrix by using density functional method. In this study, we obtain the thermodynamically stable interface structures by the calculation of adhesion work and interface energy. By analyzing the micro-structure and bond charge transfer at the interface, it is found that the Si–Al bond and the Mg–Al bond play a key role in interfacial bind strength and toughness, respectively. Based on the Griffith fracture theory, we point out that the initial fracture in the alloy is related to the element composition ratio, and β′ will not trigger fracture preferentially. An in-depth analysis of the electronic structure of atoms at β’/Al interface indicates that the difference between Si–Al bond and Mg–Al bond interactions mainly lies in the decomposition of bond strength and orbital hybridization. This research extends our knowledge of improving the strength and toughness of Al–Mg–Si alloy.

Formation of intermetallic phases during solidification in Al-Mg-Mn 5xxx alloys with various Mg levels

In the present study, four Al-Mg-Mn 5xxx alloys with different Mg levels (2-5 wt.%) were investigated for better understanding the evolution of intermetallic phases formed during solidification. Optical and scanning electron microscopes, electron backscattered diffraction and differential scanning calorimetry analyses in combination with thermodynamic calculation were used to identify various intermetallic phases. Results showed that the most dominant intermetallic phases are Al6(Mn,Fe), α-Al(Fe,Mn)Si, Al3Fe, Alm(Mn,Fe) and Mg2Si in experimental Al-Mg-Mn alloys, which is greatly dependant on the Mg levels. It is found that Chinese script α-Al(Fe,Mn)Si is the dominant iron-rich intermetallic phase for the alloys containing 2-3 wt.% Mg, while blocky Al6(Mn,Fe) and needle-like Al3(Mn,Fe) become the major phases for the alloy containing 4 wt.% Mg. Further increasing Mg content to 5 wt. %, the dominant phase transfers to blocky Al6(Mn,Fe) intermetallic. Meanwhile, the morphology of primary Mg2Si is changed from well-branched to plate-like with increasing Mg contents. In addition, β-Al3Mg2 and τ-Al6CuMg4 eutectic phases have been observed in the alloys with 3-5 wt. % Mg. A comparison on various intermetallic phases from the Scheil simulation and the actual as-cast microstructure is provided.

A New Approach to Implement High Strength 7075 Aluminum for Automotive Application

Aluminum alloys offer high specific strength than advanced high strength steels, making them preferred candidates for automotive light weighting. Among them, AA7075 aluminum alloy offers significantly higher strength than 5xxx and 6xxx alloys and is considered an attractive candidate by automotive OEMs for structural applications such as door intrusion beams, B pillars etc. There are several challenges in implementing AA7075, such as long artificial aging time to reach peak strength, joining method and corrosion resistance. In this study, an artificial aging practice that significantly reduces aging time was explored and its influence on mechanical properties of AA7075 was investigated in comparison with conventional peak age practice. In addition, this practice offers a potential solution for joining through self-piercing riveting. Moreover, the effect of artificial aging on corrosion, specifically intergranular corrosion (IGC) and stress corrosion cracking (SCC) was evaluated. The results are discussed with in depth analysis and correlation with microstructure.

Estimation of Extrusion Welding Conditions for 6xxx Aluminum Alloys

Extrusion of hollow shapes containing longitudinal welds from easy-to-weld aluminum alloys is realized in industrial practice by using porthole dies. In the work, an original method and a special modified device is presented that simulates conditions occurring in a welding chamber of the porthole dies. The weldability tests were performed for low and medium-component 6xxx alloys – in a wide range of welding temperatures and pressures. The seam welds strength were examined. The microhardness test was performed perpendicularly to the surface of welding. The microstructure of the material both in the welds region and outside them were examined by using light microscope and scanning microscope SEM. The chemical composition was examined used the EBSD method. Most favorable welding conditions for the tested alloys, allowing for obtaining high-strength welds were defined.

On the Numerical Prediction of Process-Dependent Properties of Current High-Performance Materials with Material Model *MAT_254 in LS-DYNA

Over the last years, the forecast quality in production and especially (cold) forming simulations has reached a high level at least for standard materials. It has become state-of-the-art to take the results of these process simulations into account e.g. for crashworthiness analyses. For most of the currently used high-performance materials, however, the manufacturing processes do not only result in plastic deformation and thinning of the parts. There usually is a thermal component to these processes, which significantly influences the microstructure of the material and results in a spatial distribution of material properties within the final part. In order to predict the later behavior of the part with the same quality as for standard materials and standard processes, the virtual process chain has to be closed and material models have to be used that are able to simulate the microstructure evolution during the process. The press-hardening of the manganese-boron steel grade 22MnB5 is, for example, a standard in automotive industry. For this material FEM software for process simulation tools like LS-DYNA were extended in the past to take the microstructure evolution into account. The implemented material models are tailored for this certain alloy and process. To ensure the usability of the simulation tool the material models were generalized. In LS-DYNA, material model *MAT_GENERALIZED_PHASECHANGE (*MAT_254) has been devised to serve this purpose. Core of the model is a phase evolution table that takes into account up to 24 individual phases and consequently defines up to 552 possible phase transformations, not all of which have to be defined. The appropriate transformation law for each of the phase changes can be chosen from a list of generic phase change mechanisms. Due to its relatively flexible input structure and generality of the implementation, the model has been successfully used for different processes such as press-hardening, welding, additive manufacturing, and heat treatment, and for different materials, such as ultra-high strength steels, aluminum 6xxx alloys and titanium. This contribution will introduce the material formulation in detail and show the recent extensions based on the microstructure evolution of titanium.

Processing and evaluation of Al/B4C particulate MMC’s: Tensile strength and wear properties under different elevated temperature test condition

In the present investigation, preheated K2TiF6 flux were blended with B4C particle (an average size of 33 µm) at 0.2 ratios and were incorporated into molten Al at 750 °C through conventional stir casting. Microstructural studies of as cast 6xxx alloy and composite were done using SEM/EDS/XRD. A fairly uniform distribution of B4C particles were observed throughout the matrix with few agglomeration at certain places. Ultimate tensile strength and wear behaviour of the prepared composite were tested using computer assisted UTM and Pin-On-Disk apparatus under elevated temperature (100 °C and 200 °C) respectively. The results shows that strength of composite decreases under the influence of temperature at all testing parameters. It is believed that material had undergone severe plastic deformation before the initiation of necking and mild brittle to severe ductile transition has occurred leading to catastrophic failure at high temperature and is evident from the fractography studies. The formation of tribo-coat or layer at the Pin sample and steel disc interface restricted the direct contact with each other. Further, the addition level of test temperature and developed frictional heat encourages Al atoms to diffuse faster at the slip plane resulting in severe wear from the material surface. Small narrow abrasive lines, particle de-bonding, softened tribolayer along with few wear debris adhered to worn surface (due to micro ploughing and oxidation) were observed on the surface of composite at all conditions under 200 °C test temperatures. Presence of “O” and “Fe” peak in the EDS pattern (on worn surface) confirms the existence of oxidation layer and micro ploughing on steel disc at higher test temperature.

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.