6xxx Alloys Research Articles

Investigating the interdependence of microstructure and properties in low-Cu content Al-Zn-Mg alloys via thermodynamic calculation

This paper redesigned the Al-Zn-Mg alloy composition by thermodynamic calculations and experiments, and also explained the precipitation strengthening of the 7xxx alloy. At a Zn/Mg ratio of 3.3–5.3, only the η phase is present. The η phase was experimentally verified as the main contributor to precipitation strengthening. The Al-7.6Zn-2.2Mg-0.2Cu-0.2Cr-0.4Mn-0.15Zr alloy exhibited excellent mechanical properties, with yield and tensile strengths of 510 MPa and 542 MPa under T6 treatment. The low copper content 7xxx alloy designed in this study achieves a yield strength exceeding 500 MPa solely through the compositional design of the Zn/Mg ratio.

Influence of material position and tool axis offset on the stir zone material flow and joint integrity of friction stir welded dissimilar AA5083 and AA7050 alloys

The present investigation aims to establish the influence of tool axis offset and the relative position of materials on the stir zone (SZ) material flow and joint characteristics of friction stir (FS) butt welded dissimilar AA5083-H111 and AA7050-T7651 aluminium alloys. The FS welding trials were conducted by systematically varying the tool axis offset from zero to 1 mm, with an increment of 0.25 mm, to both the advancing side (AS) and retreating side (RS) of the joint by keeping AA7050 and AA5083 alloys at the AS and RS of the joint, respectively. The welding speed, tool rotational speed, axial force and tool tilt angle were held constant. The results showed that for the given relative position of the alloys, the tool axis offset has significant influence on the SZ material flow pattern and the evolution of microstructure in the joint zone. The microhardness has a heterogeneous distribution across the joint and it is found to be sensitive to the tool axis offset. The highest hardness values are observed for the joints FS welded at 1 mm tool axis offset to the AS and the lowest for the joints welded at 1 mm tool axis offset to the RS of the joint. The joint fabricated at 0.5 mm tool axis offset to the AS has exhibited the highest joint strength of 303 MPa (joint efficiency of 98.4 %). Also, within the limits of tool axis offset experimented, the joint integrity is less sensitive to the variation of tool axis offset to both the AS and RS of the joint. The softening of the HAZ on the weaker AA5083 alloy side (for high heat generation cases) and the weakening of the SZ towards the bottom (for low heat generation cases) are the main factors limiting the joint strength. The studies showed that in FSW of dissimilar 5xxx and 7xxx alloys, appropriate selection of tool axis offset and relative position of the alloys are critical for producing joints with excellent joint efficiency.

Revisiting Ag addition in 7xxx aluminum alloys: Insights into its impact on the microstructure and properties of an Al-Zn-Mg-Cu-Zr alloy with a Zn/Mg ratio of 4

In this study, the influence of minor Ag addition on the microstructure, mechanical and corrosion properties of an Al-Zn-Mg-Cu-Zr (7449) alloy with Zn/Mg ratio of 4 was systematically investigated using various materials characterization techniques, Slow Strain Rate Test (SSRT), Potentiodynamic Polarization (PDP) and Intergranular Corrosion (IGC) measurements. Microstructure characterization by Scanning Electron Microscopy (SEM) and Differential Scanning Calorimetry (DSC) showed that Ag partitioning in the eutectic Mg(Zn,Cu,Al)2 phase occurs resulting in an increase in its solvus line. After processing to the T4 condition, Ag was partially in solid solution with the excess forming an Ag-rich AlAgZnMgCu phase. Scanning-Transmission Electron Microscopy (STEM) showed evidence of quench-induced η-Mg(Zn,Cu,Al)2 precipitates at the grain boundaries (GBs) in the T4 condition with ∼3 at.% Ag in the Ag-modified alloy. STEM and Atom Probe Tomography (APT) confirmed that ∼1 at. % Ag was present in both the matrix and GB precipitates in the Ag-modified alloy after T76 aging. Furthermore, the frequently reported decrease in the PFZ width with Ag addition was not observed after T76 aging, with both alloys having a similar PFZ width. Despite higher hardness/strength in the T4 condition with Ag addition, no enhanced age hardening response and alteration of the precipitation kinetics was observed during artificial aging at 121 °C. In fact, Ag addition in a 7xxx alloy with Zn/Mg ratio of 4 was found to be detrimental to mechanical properties, stress corrosion cracking, pitting and IGC resistance after T76 aging, which is attributed to the presence of the Ag-rich AlAgZnMgCu phase.

Effect of Mg/Si ratio on synergistic improvement of formability and yield strength in Al-Mg-Si-Zn alloys

The design of Al-Mg-Si-Zn series alloys combines the advantages of 6xxx and 7xxx series alloys and breaks through the limitations of strength and formability matching of traditional alloys. In this study, we achieved an exceptional strength-formability combination in the Al-0.84Mg-0.79Si-3.38Zn (wt.%) alloy. Following a solution treatment at 550 °C for 3 min, the alloy exhibited an elongation of ∼36.8%, with a yield strength of ∼356 MPa after artificial aging at 175 °C for 8 h. The effects of different Mg/Si ratios (∼0.6, ∼1.2, and ∼2.5, at.%) on the strength-formability interplay in Al-Mg-Si-Zn alloys were investigated. The alloy with a low Mg/Si ratio (∼0.6) facilitated the precipitation of fine β'' phases characterized by a high number density (∼8.4 nm−3 × 10−5). A Mg/Si ratio of ∼1.2 proved advantageous for precipitating larger β'' phases with a higher volume fraction (∼0.69%), resulting in an elevated precipitation strengthening effect (∼290 MPa). However, with an increase in the Mg/Si ratio to ∼2.5, the reduced availability of Si atoms for forming Mg-Si clusters led to a decrease in the number density of precipitates. Additionally, the interaction among Fe, Mn, and Si elements resulted in the presence of blocky α-Al(FeMn)Si phases, as opposed to the needle-like β-AlFeSi phases, in the alloy with a Mg/Si ratio of ∼1.2. This effectively prevented the degradation of elongation. Our findings present a comprehensive strategy for the compositional design of high-performance aluminum alloys.

Strength of bulk aluminum-boron alloys containing helium produced by 10B(n,α)7Li reaction in nuclear reactor

The study of metals and alloys containing helium has garnered significant attention within the nuclear energy community. However, there is limited research on the mechanical behavior of bulk alloys implanted with helium. This study investigates the mechanical properties of several Al-Boron alloys implanted with helium using controlled manipulation of helium doses via boron content under a consistent neutron dose. Results show that HemVn may contribute to strength by approximately 8.4–15 MPa and 16.8–23 MPa for helium doses 3.08 × 1019/cm3 and 6.84 × 1019/cm3, respectively, while lattice damages due to neutron-aluminum reaction contribute to strength by 24∼27 MPa. Subsequent annealing leads to the formation of helium bubbles, resulting in a slightly higher strengthening effect compared to HemVn. Additionally, the work hardening behavior of the alloys can be explained by the Voce model, drawing inspiration from the resemblance between helium bubbles and nanoprecipitates in 7xxx alloys. These findings provide insights to the nuclear energy community.

Influence of a Preageing Treatment on the Cluster Formation and the Further Ageing Route in Al–Mg–Si Extrusion Alloys

Herein, the influence of one‐ and two‐step preageing treatments prior to the artificial ageing step to peak age condition for three different 6xxx alloys, from low to high alloy content, is investigated. Analysis of the preaged conditions using atom probe tomography (APT) reveals a broad distribution of Mg and Si clusters, with some instances of Guinier‐Preston I zones present. Additionally, the high alloyed system exhibits a growth of precipitates toward a needle‐like shaped. These clusters formed during the preageing treatment serve as nucleation sites in the subsequent artificial ageing treatment, leading to an increase in hardness. Microstructural analysis conducted using transmission electron microscopy and APT demonstrates a reduction in the average precipitate length and a more narrow size distribution for T6 condition. This indicates that the preageing treatment results in a decreased portion of already overaged precipitates compared to the direct aged condition. Consequently, the more narrow size distribution of the precipitates leads to more effective hardening of the material, as a higher portion of precipitates is at or close to their optimum size. The investigations highlight the significant influence and positive effect of a preageing treatment at lower temperatures on the subsequent artificial ageing treatment.

Processing Techniques and Metallurgical Perspectives and Their Potential Correlation in Aluminum Bottle Manufacturing for Sustainable Packaging Solutions

This study explores the potential of aluminum wine bottles as a sustainable alternative to traditional glass bottles, emphasizing their recyclability and environmental advantages. It reviews the potential use of Al-Mn-Mg 3xxx alloys in beverage can bodies and examines various applications of aluminum containers in packaging, including recyclable beverage containers. The manufacturing processes for aluminum bottles, including casting, rolling, punching, and deformation techniques, are discussed in detail, with a particular focus on their impact on mechanical properties and microstructure. The preference for 1xxx aluminum alloys in impact extrusion is explained, highlighting their lower flow stress and higher formability compared to 3xxx alloys, and the microstructural changes induced by various processing steps are analyzed. Challenges related to using recycled aluminum and their effects on mechanical properties and microstructure during aluminum bottle production are also addressed. One objective is to increase the proportion of recycled alloyed material used in aluminum bottle manufacturing. Depending on the technique employed, the fraction of alloyed recycled material can vary. The percentage of recycled alloyed material (3xxx series Al alloys) in cold backward impact extrusion could be raised by 60%. High-speed blow forming could facilitate the production of aluminum bottles with a recycled alloyed material ranging from 50 to 100% of the 3xxx series aluminum can body alloys. The high-speed drawing and ironing (DWI) process can produce large-format aluminum bottles (up to 750 mL), utilizing at least 90% of the recycled 3xxx series can body stock. Furthermore, the paper discusses the importance of optimized heat treatment designs in enhancing mechanical properties and controlling microstructural evolution in alloyed aluminum materials, such as 3xxx series alloys. The study concludes with a need for further research to deepen our understanding of the metallurgical aspects of aluminum bottle manufacturing and to optimize the use of recycled aluminum in packaging solutions, with a specific focus on improving mechanical properties and microstructural integrity. This comprehensive review aims to contribute to the development of more sustainable packaging practices in the beverage industry by providing insights into the interplay between manufacturing processes, mechanical properties, and microstructure of aluminum bottles.

Differential scanning calorimetry of age-hardenable aluminium alloys: effects of sample preparation, experimental conditions, and baseline correction

Precipitation processes in age hardenable aluminium alloys are often investigated by differential scanning calorimetry (DSC). The endothermic and exothermic peaks of the DSC signal correspond to the dissolution and formation of phases, respectively. However, parasitic effects can lead to an unintended curvature of the DSC signal. Although a baseline correction can be used, some imperfections typically remain. Additionally, sample preparation and experimental conditions can influence the precipitation sequence itself and, therefore, the DSC curve. In this study, we investigate the influence of sample preparation by milling and punching on DSC curves for three different aluminium alloys: EN AW-2024, EN AW-6082, and EN AW-7075. Additionally, the influence of quenching and natural ageing was investigated for EN AW-6082. We found that deformation introduced by punching the DSC samples with a piercing die after heat treatment leads to a change in the precipitation kinetics in 2xxx, 6xxx, and 7xxx series alloys. The influence was strongest for punching the samples after solution heat treatment and less significant for punching after artificial ageing. The influence of sample preparation can be avoided by punching the samples before solution heat treatment. If this is not practicable, milling of the samples is a good alternative. The choice of quenching medium and short storage at room temperature before measurement (5 min) had only small effects on the DSC curves. Moreover, the start temperature of the measurement was found to be crucial. For observing phases forming below 100 °C and for low-bias baseline correction, the measurement should start at low-temperatures (i.e. ∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim$$\\end{document} − 50 °C).

Microstructure, tensile and bending properties of extruded Al–Mg–Si 6xxx alloys with individual and combined additions of Zr and Mn

This study investigates the effects of individual and combined additions of Mn and Zr on the microstructure, extrudability, tensile and bending properties of extruded Al–Mg–Si 6xxx alloys processed under different homogenization and extrusion conditions. The overall mechanical performances of three alloys are compared and ranked based on the yield strength, bend angle, and bending anisotropy. The results show that compared with an individual addition of Mn or Zr, a combined addition of Mn and Zr (alloy MnZr) results in a higher number density and volume fraction of two types of Mn- and Zr-bearing dispersoids. In the as-extruded condition, the best overall mechanical performance is demonstrated after homogenization at 400 °C and extrusion at 500 °C, particularly for alloy MnZr. After a T5 treatment, alloy MnZr homogenized at 550 °C exhibits a higher yield strength and better bendability than single Mn or Zr additions or other processing conditions. In contrast, the alloy with an individual addition of Zr exhibits an inferior mechanical performance under most processing conditions. The best overall mechanical performance is achieved by alloy MnZr in both as-extruded and T5 conditions.

Microstructure evolution and strengthening mechanisms of a high-performance TiN-reinforced Al–Mn–Mg–Sc–Zr alloy processed by laser powder bed fusion

In this work, a high-strength crack-free TiN/Al–Mn–Mg–Sc–Zr composite was fabricated by laser powder bed fusion (L-PBF). A large amount of uniformly distributed L12-Al3(Ti, Sc, Zr) nanoparticles were formed during the L-PBF process due to the partial melting and decomposition of TiN nanoparticles under a high temperature. These L12–Al3(Ti, Sc, Zr) nanoparticles exhibited a highly coherent lattice relationship with the Al matrix. All the prepared TiN/Al–Mn–Mg–Sc–Zr composite samples exhibit ultrafine grain microstructure. In addition, the as-built composite containing 1.5 wt% TiN shows an excellent tensile property with a yield strength of over 580 MPa and an elongation of over 8 %, which were much higher than those of wrought 7xxx alloys. The effects of various strengthening mechanisms were quantitatively estimated and the high strength of the alloy was mainly attributed to the refined microstructure, solid solution strengthening, and precipitation strengthening contributed by L12–Al3(Ti, Sc, Zr) nanoparticles.

Influence of the combined additions Mn, Cr or Ni on the formation of dispersoids and mechanical properties of Al–Mg–Si–Cu alloys

The effect of individual and combined additions of different transition metals (TMs), Mn, Cr, and Ni, on the precipitation of dispersoids and the final mechanical properties of Al–Mg–Si–Cu alloys was systematically studied by scanning electron microscopy, transmission electron microscopy and tensile testing. The various TM additions examined are found to induce notably different dispersoid precipitation behaviors. The combined addition of Mn, Cr produces the highest number density of dispersoids among the three TM-added alloys examined, due to the incorporation of Cr promoting the precipitation of the α-Al(Mn, Cr, Fe)Si dispersoid. By contrast, the combined addition of Mn, Ni slightly suppresses the precipitation of the α-Al(Mn, Ni, Fe)Si dispersoid compared with individual Mn addition. The presence of a fine dispersoid microstructure can moderately increase the strength, and strongly increase the elongation, especially for the case of the combined Mn, Cr added alloy, where the elongation is increased almost threefold compared with the base alloy. An excellent strength-elongation combination, with an ultimate tensile strength of 421.9 ± 2.2 MPa and an elongation of 18.2 ± 3.6, is achieved for this alloy. This property is superior to most reported 6xxx alloys. The main reasons for this result are the presence of a high number density of dispersoids promoting grain refinement, providing high Orowan hardening, and reducing stress concentration on the grain boundary. The findings of this work are expected to provide guidance for developing new Al–Mg–Si–Cu alloys with excellent comprehensive mechanical properties.

Enhancing the strength and sensitization resistance of 5xxx alloys via nanoscale clustering induced by room-temperature cyclic plasticity

Non-heat-treatable 5xxx Al alloys exhibit good corrosion resistance but can be susceptible to intergranular corrosion in service. This study applies a cyclic strengthening method to the AA5083 alloy, resulting in a significant increase in yield strength (∼300 MPa) and tensile strength (∼385 MPa) due to the formation of Mg-Al solute clusters confirmed by scanning transmission electron microscopy and atom probe tomography. After a two-month sensitization treatment at 70 °C, the clusters delay the formation of Mg-rich precipitates at grain boundaries, enhancing the resistance to sensitization. This new approach strengthens Al-Mg alloys and offers potential for manipulating the corrosion resistance and sensitization susceptibility.

Friction stir welding of dissimilar AA7050 and AA5083 aluminium alloys: Microstructural and mechanical characterization

In this study, dissimilar aluminium alloys, AA7050-T7651 and AA5083-H111, with 5 mm thickness were friction stir butt welded and the microstructural and mechanical properties of the joints are investigated. The experiments were carried out at tool rotational speeds of 800, 1000 and 1200 rpm while keeping the tool traverse speed, axial force and tool tilt angle, respectively, at constant values of 30 mm/min, 3.5 kN and 1.5°. A tool axis offset of 0.25 mm towards the 7xxx alloy side that fixed by a detailed preliminary study was used in all the trials. All the fabricated joints were externally defect-free and the fractured tensile specimens showed that the joints have fractured in the thermo-mechanically affected zone (TMAZ) at the AA5083-H111 alloy side. The highest ultimate tensile strength of 294 MPa (96% joint efficiency) was observed for the joint fabricated at tool rotation speed of 1000 rpm. The location of fracture together with the microstructure observation at the joint zone showed that the coarsening of grains and loss of cold work are the causes of fracture of the tensile specimen at the TMAZ of the 5083-alloy side. In addition, significant grain coarsening and dissolution of precipitates are observed at the heat-affected zone and TMAZ at the 7050-alloy side at tool rotational speeds of 1000 rpm and 1200 rpm. The study testified that the tool rotational speed has a significant influence on the microstructure and tensile properties of the dissimilar joints.

Investigation of the Formability of AA6010 in an Integrated Forming and Hardening Process Aiming to Reduce the Energy Consumption in High Volume Production of Automotive Components

Hot deformation and in-die quenching of aluminum components for the automotive industry is a cost and energy efficient technique that has been developed and thoroughly evaluated in recent years. The performance of this process is considered higher when compared to traditional cold metal forming due to shorter process times, low-cost machinery, and a high level of structural integrity in fabricated parts. The work presented in this paper provides several approaches for the formability of age hardenable 6xxx alloy sheets when forming at different temperatures. Warm tensile testing and formability cup testing were carried out to investigate the alloy formability at different temperatures. The results indicate that the formability of candidate alloys is not significantly affected by deformation temperatures or conditions, which provides great freedom when designing an automated production process with high productivity and minimal environmental impact. The candidate alloy can be deep drawn without severe thinning at the whole temperature range, from room temperature (RT) to solutionizing temperature.

Effect of cooling rate on the composition and chemical heterogeneity of quench-induced grain boundary η-phase precipitates in 7xxx aluminium alloys

The mechanical properties and stress corrosion cracking (SCC) resistance of 7xxx series aluminium alloys are significantly affected by the composition and distribution of precipitates formed during heat treatment. In particular, their quench sensitivity is related to the formation of η-phase precipitates that nucleate heterogeneously on grain boundaries at lower cooling rates after solution treatment, which has been a key factor restricting the gauge of hot rolled plates in the aerospace industry. To better understand the effects of slower cooling rates on the composition of quench-induced grain boundary precipitates (Q-GBPs) found in thick plate 7xxx alloys, plasma focused ion beam and high-resolution scanning transmission electron microscopy were used to obtain accurate composition data. The η-phase Q-GBPs have a complex- branched morphology, which develops higher aspect ratios and secondary arms as the cooling rate is reduced. Only a small change in average composition of Q-GBPs was found with cooling rate; but a large scatter was observed. This is caused by significant Zn/Cu/Al composition gradients developing along their principal growth directions in both AA7050 and AA7085 alloys. This concentration gradient did not reduce significantly after a T76 treatment. Simulations of Q-GBP growth with different cooling rates using a CALPHAD-informed phase-field model, with the η-phase represented by a two-sublattice model, gave results consistent with experimental observations. Chemical gradients were predicted to develop in the Q-GBPs due to the changing local equilibrium at the growth front during the cooling. The influence of this non-homogeneous microchemistry on the SCC behaviour of 7xxx alloys is briefly discussed.

Effect of Mn on Hot Workability and Processing Maps of Al-Mg-Mn 5xxx Alloys

Effect of Mn on Hot Workability and Processing Maps of Al-Mg-Mn 5xxx Alloys

Effect of filling materials on microstructure and properties of CMT-laser beam oscillation hybrid welding behavior of dissimilar Al–Mg–Si alloys

Laser oscillation-assisted cold metal transfer hybrid welding was conducted on 2.0 mm-thick 6082 and a new 6xxx aluminum alloys. The influence of wire composition on microstructure and mechanical properties of the 6082 and new 6xxx alloy joints is studied. Our results show that, due to the difference in surface tension, the cross section of a joint filled with ER4047 wire typically presents a wider U-shape profile, while the ER5183 filled joint shows a relatively narrower V-shape profile. The average grain size of the ER5183 joint is smaller than that of the ER4047 joint. The ER4047 joint exhibits better fluidity, resulting in a higher proportion of high-angle boundaries compared to the ER5183 joint, which we attribute to the higher Si content. Equiaxed grains are also observed near the fusion boundary on the new 6xxx side, while no equiaxed grain formation is observed on the 6082 side. EDS data demonstrates severe elemental segregation in the center of weld and the partially melted zone, suggesting that multiple secondary phases form unevenly within inter-dendritic regions and grain boundaries of α-Al during the welding process. The microhardness of the weld zone and the heat-affected zone on both sides in the ER5183 joint is higher than that of the ER4047 joint. The corrosion test evidences that the ER5183 joint has a slightly better corrosion resistance than the ER4047 joint. Our findings provide a new understanding on joining of dissimilar Al–Mg–Si alloys and guide the selection of appropriate filling materials and welding processes.

Structure Evolution and Mechanical Properties of Sheet Al–2Cu–1.5Mn–1Mg–1Zn (wt.%) Alloy Designed for Al20Cu2Mn3 Disperoids

This work was focused on studying the possibility of increasing the strength of non-heat-treatable sheet alloy Al2Cu1.5Mn (wt.%) by the joint addition of 1% Mg and 1% Zn. The effect of these elements on the structure and mechanical properties of the new sheet Al2Cu1.5Mn alloy designed for Al20Cu2Mn3 dispersoids has been studied by calculations and experimental methods. The obtained data on the phase composition, microstructure, and physical and mechanical properties of the new alloy for different processing routes (including hot rolling, cold rolling, and annealing) have been compared with those for the ternary Mg- and Zn-free alloy. It has been shown that the formation of nanosized Al20Cu2Mn3 dispersoids (~7 vol.%) provides for the preservation of the non-recrystallized grain structure after annealing at up to 400 °C (3 h), while Mg and Zn have a positive effect on the strength due to the formation of alloyed aluminum solid solution. As a result, cold-rolled sheets of the Al2Cu1.5Mn1Mg1Zn model alloy showed a substantially higher strength performance after annealing at 400 °C in comparison with the ternary reference alloy. In particular, the UTS is ~360 vs. ~300 MPa, and the YS is 280 vs. 230 MPa. For the example of the Al2Cu1.5Mn1Mg1Zn model alloy, it has been shown that the system is promising for designing new heat-resistant alloys as a sustainable alternative to the 2xxx alloys. The new alloy has an advantage over the commercial alloys (particularly, 2219, 2024, 2014), not only in manufacturability but also in thermal stability. The sheet production cycle for the model alloy is much shorter because the stages of homogenization, solution treatment, and water quenching are excluded.

Environment-Induced Crack Initiation and Early Stages of Crack Growth in Aluminum Alloys, Part 2

A second group of ‘state-of-the-art’ contributions [1-4] by invited researchers on the ‘Environment-Induced Crack Initiation and Early Stages of Crack Growth in Aluminum Alloys’ appear in this issue, complementing the papers published in the January 2023 issue of Corrosion [5-8]. The second section, presented herein, includes an overview of the experimental study of the initiation of environment-induced cracking (EIC) in aluminum alloys conducted since the 1950’s [1], showing crack initiation typically dominates the total life experienced during both service-life for structural applications and for smooth tensile test specimens subjected to conventional standard EIC testing. The review also reveals, although research conducted over the last 30 years almost exclusively focus on EIC propagation, there are notable exceptions worthy of re-evaluation and further study using modern in-situ advanced experimental techniques, paying particular attention to the roles of creep, crack-arrest and surface conditions during EIC initiation, paying particular attention the immediate sub-surface layers. The three additional papers in this collection are experimental studies. One investigates the significant differences in EIC initiation observed from fatigue pre-cracks and corrosion-induced fissures under controlled electrochemical conditions in a sensitized AA5456-H116 fracture mechanics test specimen exposed to a marine environment [2]. The final two papers involve testing conducted on high Zn-content Al-Zn-Mg-Cu 7xxx series alloys [3, 4]: one involves two commercial thick pate commercial high Zn content new-generation alloys [3], AA7449 and AA7085 in the T7651 temper and provides a detailed description of EIC initiation and its transition to long-crack growth during exposure to water vapor at 70 °C. Information gleaned from in-situ time-lapse, optical imaging over large areas has enabled the exact initiation sites to be identified and investigated with high-resolution fractographic studies. In the final paper [4] based on the deformation and fracture behavior of a high Zn-content Al-Zn-Mg-Cu 7xxx alloy observed in situ using synchrotron radiation X-ray tomography, it is proposed the dispersion of Mn-based second-phase particles may offer a novel approach for preventing hydrogen embrittlement in 7xxx series aluminum alloys.

Processing and microstructure–property relations of Al-Mg-Si-Fe crossover alloys

This study introduces new alloys, which combine the age-hardening capability of Al-Mg-Si alloys with the microstructure-controlling effect on processing of primary Fe-rich intermetallic phases used in foil stock. In detail, the processing and microstructure–property relations in new crossover aluminum alloys derived from 6xxx and 8xxx foil stock alloys, is shown. A highly Fe-rich intermetallic phase content was deployed to conceptually mimic high scrap content. Fast and slow solidification rates were applied to represent thin strip and direct chill casting, respectively. The effects of adding Fe and Mn to alloy 6016 were examined, while the Si consumed in primary phases was partly adjusted to maintain age-hardening potential. It was shown that upon thermomechanical processing, primary intermetallic phases in the new alloys are finely fragmented and well dispersed, resulting in strong grain refinement and a uniform texture. Attractive combinations of strength and ductility were revealed, also in material processed under direct chill casting conditions. The new alloys’ high elongation values of up to 30%, and their age-hardening response, were similar to those seen in commercial alloy 6016, while their strain hardening capacity was significantly greater. This can be attributed mainly to the formation of geometrically necessary dislocations near primary Fe-rich intermetallic phases. The study discusses microstructure refinement on the basis of particle stimulated nucleation. It uses a simple model to describe the individual contributions to yield strength, including the effect of primary phases. It also models the effect of these particles on increased strain hardening and ductility.