Wrought Aluminum Alloys Research Articles

Characterization of pulsed-tungsten inert gas (PTIG) welding on AA5754-H111 alloy: mechanical properties and microstructural analysis

Abstract Aluminium and its alloys were widely used in engineering because they are lightweight, strong, and resistant to corrosion. However, using standard arc welding techniques can be difficult when dealing with such materials. Pulsed-Tungsten Inert Gas (PTIG) welding is being researched as a potential solution to this problem. This study is the first to investigate the use of the straightforward and intuitive PTIG technique on the ubiquitous AA5754 wrought aluminium alloy. Welded samples were supplied for examination of mechanical parameters such as surface hardness and strength under impact and tensile loading. The results of a statistical analysis of the mechanical characterization of a PTIG-welded permanent joint fabricated from AA5754 aluminium alloy were presented and discussed. The heat-affected zone (HAZ) on the AA5754 retracting side of the weld had a hardness of 50–70 Hv0.5, while the HAZ on the AA5756 side had a hardness of 90–100 Hv0.5, as measured by testing on the perfect weld specimen. Samples taken from different parts of the weldment all showed that the HAZ is the softest and weakest. The shattered surface of the welded sample consisted of flat facets and quasi-cleavage patterns, as revealed by scanning electron microscopy. Analysis of the HAZ microstructure revealed widespread dissolution of Mg2Si precipitates in the AA5754-H111.

Texture-Induced Corrosion Resistance of Dissimilar AA7204/AA6082 Friction Stir Welded Joints.

The quasi in situ EBSD test was applied to study the effect of grain orientation on corrosion behaviors of the thermomechanically affected zone I (TMAZ I) of dissimilar AA6082/AA7204 friction stir welding (FSW) joints in this work. The results show that the structure with grain orientation close to the brass texture ({110}<112>) has excellent corrosion resistance, which contributes to the better corrosion performance of the TMAZ I of the 7204-AS joint than the 7204-RS joint. Furthermore, the brass texture around by S texture ({213}<364>) in the TMAZ I of the 7204-AS joint is slightly corroded, and the orientation of the remaining structure is closer to the ({110}<112>) than before, which indicates that the corrosion, like deformation, is carried out alongside the {110} plane for the structure with grain orientation near {110}<112>. Those findings could provide new insight into the designed FSW joints and improve the corrosion resistance of the wrought aluminum alloy.

Microstructure features induced by fatigue crack initiation up to very-high-cycle regime for an additively manufactured aluminium alloy

Fatigue failure can still occur beyond 107 cycles, i.e. very-high-cycle fatigue (VHCF), in many metallic materials, such as aluminium alloys and high-strength steels. For VHCF of high-strength steels, a fine granular area (FGA) surrounding an inclusion is commonly identified as the characteristic region of crack initiation on the fracture surface. However, no such FGA feature and related crack initiation behaviour were observed in VHCF of conventionally cast or wrought aluminium alloys. Here, we first reported the distinct mechanisms of crack initiation and early growth, namely the microstructure feature and the role of FGA in VHCF performance for an additively manufactured (AM) AlSi10Mg alloy. The AM pores play a key role in fatigue crack initiation similar to that of the inclusions in high-strength steels, resulting in almost identical FGA behaviour for different materials under a range of mean stress with a stress ratio at R < 0 or R > 0. The profile microstructure of FGA is identified as a nanograin layer with Si rearrangement and grain boundary transition. This process consumes a large amount of cyclic plastic energy making FGA undertake a vast majority of VHCF life. These results will deepen the understanding of VHCF nature and shed light on crack initiation mechanism of other aluminium and AM alloys.

Additive manufacturing of crack-free Al-alloy with coarsening-resistant τ1-CeAlSi strengthening phase

Wrought aluminium alloys popular for automotive and aerospace applications are susceptible to solidification cracking when fabricated via laser powder bed fusion (LPBF). Another long-standing and common issue for these alloys is microstructure coarsening and corresponding strength loss caused by elevated temperature exposure. To tackle these challenges, this study designs and develops a class of 1–4 wt% Ce modified Al6061 alloys. The best alloy, with 3 wt% Ce, achieves crack-free fabrication via LPBF due to a reduction in the solidification temperature range and a new solidification pathway that achieved 0.9 solid mass fraction at just 14 °C below the solidification onset. Furthermore, a fine microstructure consisting of coarsening-resistant τ1-CeAlSi eutectic forms, and after hot isostatic pressing, the tensile strength and elongation of the 3 wt% Ce alloy can reach 153 ± 6 MPa and 18.3% at room temperature and 89 ± 6 MPa and 32.5% at 200 °C, respectively. The observed ductility is attributed to nanoscale dispersion of discrete, coarsening resistant τ1-CeAlSi particles within grains and to the presence of large columnar α-Al grains. Meanwhile, solidification cracking was inhibited by continuous grain boundary τ1-CeAlSi eutectic accumulation, which converted to discrete nanoscale τ1-CeAlSi after hot isostatic pressing. This research uncovers a simple and effective approach of designing Al-alloys for LPBF with great potential for both room temperature and high temperature applications in automotive and aerospace industries.

Effect of thermophysical properties on porosity and microstructure of laser welded cast and wrought aluminum alloy dissimilar lap joints

The influence of thermophysical properties of materials on the porosity and microstructure of dissimilar lap joints between laser-welded Al–Si–Mg cast and Al–Mg–Si–Cu wrought aluminum alloys was investigated. The low thermal conductivity and viscosity of the weld would promote bubble escape, while the high electrical conductivity of the base material would increase the melt depth and reduce the convection intensity in the melt pool, thus increasing the difficulty of bubble escape. The variation in thermophysical properties did not significantly impact the distribution of elements, the type of precipitated phases, and the dislocation density, however, it did affect grain morphology. Differences in thermal diffusion coefficients between base materials created conditions for constitutional supercooling, increasing the likelihood of a columnar-to-equiaxed transition. Moreover, the temperature difference between the liquid phase lines of the weld and base materials facilitated the liquid base material flushed into the weld to solidify before mixing, resulting in an “island” formation. This “island” acted as a heterogeneous nucleation site, leading to equiaxed grain layer formation in the lowest zone of the weld. The variations in thermophysical properties exerted an influence on the tensile strength by impacting both the melt depth and the grain morphology of the weld but did not yield a significant impact on the average microhardness.

Very High Cycle Fatigue Data Acquisition Using High-Accuracy Ultrasonic Fatigue Testing Equipment

Abstract Fatigue testing at ultrasonic frequency is a powerful method for rapid generation of high and very high cycle fatigue data. High accuracy of cyclic loading is the basis for reproducible test results, which can be obtained with closed-loop control of vibration amplitude and resonance frequency. Self-heating of test specimens can be suppressed by intermittent (pulse-pause) loading. In the present work, the high-accuracy ultrasonic fatigue testing equipment developed at the University of Natural Resources and Life Science, Vienna (BOKU) is described, and systematic investigations are presented that demonstrate the effects of cycling frequency, specimen size, and intermittent loading. Data obtained with additively manufactured (AMed) austenitic stainless steel 316L at 19 kHz are compared with electromagnetic resonation test results measured at 90 Hz. No influence of cycling frequency on fatigue lifetimes and fatigue limit was found when specimens of comparable size were used for tests at 19 kHz and 90 Hz. In contrast, the use of as-built specimens with smaller testing volume resulted in an increase in cyclic strength, demonstrating a size effect on fatigue properties. Polishing the surfaces of AMed specimens increased the fatigue limit by a factor of two. Furthermore, ultrasonic fatigue tests with intermittent loading and four different pulse lengths as well as continuous cycling were performed. The tests were conducted with wrought aluminum alloy 7075-T651 and with specimens containing small artificial surface defects. Similar lifetimes were measured in all testing series. Moreover, the same fatigue limit is found for all pulse lengths and for continuous cycling. This demonstrates that pulsed loading is a most suitable method to avoid specimen heating at ultrasonic frequency and that there is no influence on measured fatigue properties if ultrasonic loading is appropriately controlled. Measurement artifacts could be identified and avoided by measuring and recording all load amplitudes during ultrasonic fatigue tests.

Spatial and directional characterization of wire and arc additive manufactured aluminum alloy using phased array ultrasonic backscattering method

Pores, grains, or textures can collectively cause microstructural inhomogeneity and anisotropy in metallic materials fabricated by additive manufacturing. In this study, a phased array ultrasonic method is developed to characterize the inhomogeneity and anisotropy of wire and arc additively manufactured components by performing both beams focusing and steering. Two backscattering features, i.e., the integrated backscattering intensity and the root mean square of the backscattering signals, are employed to quantify the microstructural inhomogeneity and anisotropy, respectively. An experimental investigation is performed using an aluminum sample fabricated by wire and arc additive manufacturing. The ultrasonic measurements, performed on wire and arc additive manufactured 2319 aluminum alloy, show that the sample is inhomogeneous and weakly anisotropic. Metallography, electron backscatter diffraction, and X-ray computed tomography are used to verify the ultrasonic results. An ultrasonic scattering model is used to identify the influence of grains on the backscattering coefficient. Compared with a wrought aluminum alloy, the complex microstructure in additively manufactured material significantly influence the backscattering coefficient, and the presence of pores cannot be neglected in ultrasonic-based nondestructive evaluation for wire and arc additive manufactured metals.

Effect of Aging on Impact Toughness and Fracture Behavior of Three Wrought Aluminum Alloys

Herein, the effect of the aging state on the impact toughness of three typical wrought Al alloys (7075, 2024, and 6A01) is investigated. At room temperature, the fracture mode of the three aluminum alloys at different aging states is a ductile transgranular fracture. At low temperatures, high‐strength aluminum alloys exhibit a mixture fracture of transgranular and intergranular, while medium‐strength aluminum alloys are still dominated by transgranular fractures. The effect of the aging state on the impact toughness of aluminum alloys was analyzed based on the deformation mechanism and morphology near grain boundaries. The underaged state with planar slip dislocations exhibits good plasticity and work‐hardening ability, which reduces the strain localization caused by dislocation plugging and thus improves the impact toughness of the alloy. Furthermore, the fine grain boundary precipitates and the narrow precipitation‐free zone of the underaged increase the uniform deformation capacity near the grain boundaries and inhibit the initiation and propagation of cracks. Compared with high‐strength aluminum alloys, medium‐strength aluminum alloys exhibit higher impact toughness due to the formation of a larger plastic zone and shear lip area during impact.

On the Utility of the Thermal-Pseudo Mechanical Model’s Residual Stress Prediction Capability for the Development of Friction Stir Processing

This paper investigates the thermal-pseudo mechanical (TPM) model’s residual stress prediction capability for its utility in developing friction stir processing (FSP). Specifically, two FSP tests under different processing conditions were conducted, and the corresponding simulations were carried out to verify if the TPM model can predict residual stresses for various tool radii and workpiece materials. The model successfully predicted residual stresses with an error less than 4% for one of the tests but failed to work for the other test. Further simulations under different FSP conditions proved that the TPM model works for cast aluminum alloys and wrought aluminum alloys. In addition, the large FSP tool used was found to be the reason for the model’s failure on one of the tests. This indicates that there is a range of tool radii for which the TPM model is applicable. As a solution, this paper suggests modifications to the TPM model based on calibration to the FSP test temperatures. The resulting residual stress prediction is accurate and differs from the experimentally characterized stress values by only 6.5 MPa. The calibrated TPM model requires FSP to be carried out when using a tool with a different radius. Following that, the effect on residual stresses due to changes in the other process parameters, such as the tool traverse & rotation speeds and the clamping conditions, can be predicted.

Microstructure and corrosion resistance of chromate conversion coating on cold sprayed aluminum alloy 2024

This paper examines the microstructure and corrosion resistance of chromate conversion coating (CCC) on cold sprayed (CS) aluminum alloy 2024. CCC is an effective surface treatment for aluminum aircraft alloy to improve paint adhesion as well as corrosion resistance. Although the studies of CCC on wrought aluminum alloy have been extensively conducted, understanding the interaction of CCC applied to CS deposits has not yet been addressed in the literature. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and focused ion beam (FIB) were employed for investigating the microstructure of CCC on CS2024 deposits. Potentiodynamic testing, electrochemical impedance spectroscopy (EIS), and immersion testing were performed to probe into corrosion performance of CCC on CS deposit. The results demonstrated that unique intermetallic networks inside the CS deposit formed CCC with more heterogeneous microstructure compared to CCC on wrought counterparts. Although wrought and CS 2024 presented similar corrosion resistance within a short exposure time (<48 h), CCC on CS deposits was more susceptible to corrosion damage, revealed by EIS with an extended exposure time (>48 h). Additionally, distinctive corrosion propagation of CCC on CS deposits along intermetallic networks and prior particle boundaries was seen from the immersion test.

Advances in galvanic corrosion of aluminum alloys

Two lightweight materials were evaluated: a wrought aluminum alloy (AA1) and a cast aluminum alloy (AA2), always coupled to a low-carbon steel (CS). Both the electric potential and pH distributions, of two bare systems (CS-AA1 and CS-AA2) subjected to full immersion conditions in 0.06 M NaCl, are discussed in detail from the experimental and numerical point of views. In conjunction with a miniaturized electrochemical cell and a LAQUAtwin® sensor that allows pH measurements of viscous liquids, solids, and even powder samples, agar hydrogels were used to gather new transient information used to validate a tertiary current distribution model, which was solved by using the finite element method (FEM). The numerical predictions perfectly match with the experimental distributions. The two experimental methodologies exhibit excellent performance for studying galvanic corrosion phenomena, providing reliable and precise results.

Gigacycle Fatigue Properties of Wrought Aluminum Alloys

Fatigue data sheets of the National Institute for Materials Science disclose the results of gigacycle fatigue tests conducted on wrought aluminum alloys. The materials tested were hot-rolled plates and extruded round bars of A5083P-O (two heats), A7075-T6 (three heats), and A6061-T6 (three heats). The fatigue testing methods were rotating-bending at 100 Hz, ultrasonic at 20 kHz, and uniaxial at 100 Hz. The rotating-bending fatigue tests were conducted for 3 years to reach 1010 cycles. The ultrasonic and uniaxial fatigue tests were also conducted at high stress ratios. This study analyzed the fatigue life data, clarifying frequency effects, presence or absence of fatigue limits, and stress ratio effects. The three types of fatigue tests revealed equivalent results, meaning that frequency effects and stress gradient effects were negligible in the wrought aluminum alloys. Frequency effects were visible in several cast aluminum alloys owing to the influence of humidity, but the wrought aluminum alloys were observed to be insensitive to humidity. Many specimens were fractured at >107 cycles, whereas the degradation of fatigue strength after 107 cycles was very small in A5083P-O but large in A7075-T6 and A6061-T6. A5083P-O revealed fatigue limits at around 107 cycles. The heat treatment effects determined the presence or absence of fatigue limits because the equivalent tensile strengths between A6061-T6 and A5083P-O excluded the possibility of tensile strength effects. The stress ratio effects on gigacycle fatigue strengths of the wrought aluminum alloys are reasonable and can be estimated in conventional ways.

Study on nano-treating of Al-Mg-Si-Cu alloys with TiC nanoparticles

The 6xxx series wrought aluminum alloys (Al-Mg-Si-Cu) provide good formability and high strength potential, especially with high Cu additions. However, the large freezing ranges of these alloys often cause hot cracking susceptibility in solidification-based processes, such as casting, welding, and 3D printing. In this work, nano-treating, which is to tune the manufacturability and microstructure of metals by a small addition of nanoparticles, was applied to Al-Mg-Si-Cu alloys during casting. This study shows that nano-treating can effectively refine microstructure, eliminate hot cracking, and promote the dissolution of alloying elements. Tensile tests showed that nanoparticles enable strengthening. An extensive study on the TiC nanoparticle effect on Al-Mg-Si-Cu with various Mg and Si contents was conducted. This work provides valuable insights for rational design of nano-treated Al-Mg-Si-Cu alloys to achieve optimal combination of strength and ductility.

A Review of Progress in the Study of Al-Mg-Zn(-Cu) Wrought Alloys

Modern industrial development has put forward higher demands on the performance of metallic structural materials, especially in terms of light weight, high strength and corrosion resistance. All of these characteristics are of particular importance in transportation fields. As one of the most representative structural materials, aluminum and alloys have exhibited significant advantages in light weight. Most of the alloys are prominently featured in one specific aspect. The overall performance still needs to be improved. In recent years, researchers have developed Al-Mg-Zn(-Cu) alloy, a new wrought aluminum alloy, whose design strategy is known as “crossover alloying”. This novel alloy is an age-hardened Al-Mg alloy with a T-Mg32(Al, X)49 (X is Zn, Cu) phase as the main strengthening phase. This system of alloys exhibits excellent properties in terms of strength and corrosion resistance, which makes it promising for applications in automotive, marine, aerospace and other fields. This paper summarizes the research progress of Al-Mg-Zn(-Cu) alloy, and analyzes the basic methods of microstructural control in terms of composition design and property research. Finally, the future directions of this alloy are proposed.

Laser powder bed fusion of Zr-modified Al-Cu-Mg alloy: Processability and elevated-temperature mechanical properties

• Hot-cracking was affected by the volume fraction and size of the equiaxed grains. • The nucleation potency of L1 2 -Al 3 Zr phase was evaluated based on the E2EM model. • Both as-fabricated and T6-treated samples exhibited excellent YS from 150 °C to 350 °C. Zr modification is an effective method for improving hot-cracking resistance and elevated-temperature mechanical properties during laser powder bed fusion (L-PBF) of traditional medium and high strength wrought aluminum alloys. This study investigated the L-PBF processability and elevated-temperature mechanical properties of a Zr-modified 2024Al alloy. It was found that the hot-cracking susceptibility increased with the increased scanning speed, which was in reasonable agreement with the modified Rappaz–Drezet–Gremaud criterion. Furthermore, the primary L1 2 -Al 3 Zr precipitates, which acted as efficient nucleation sites, precipitated at the fusion boundary of the melt pool, leading to the formation of a heterogeneous grain structure. The yield strength (YS) of the as-fabricated samples at 150, 250, and 350 °C was 363, 210, and 48 MPa, respectively. Despite the slight decrease to 360 MPa of the YS when tested at 150 °C, owing to the additional precipitate strengthening from the L1 2 -Al 3 Zr precipitates, the YS achieved yield strengths of 253 and 69 MPa, an increase of 20.5% and 30.4%, when tested at 250 and 350 °C, respectively. The yield strengths in both the as-fabricated and T6-treated conditions tested at 150 and 250 °C were comparable to those of casting Al-Cu-Mg-Ag alloys and superior to those of traditionally heat-resistant 2219-T6 and 2618-T6 of Al-Cu alloys.

Wrought and cast aluminum flows in China in the context of electric vehicle diffusion and automotive lightweighting

Electrification and vehicle weight reduction (lightweighting) trends are driving demand for wrought aluminum alloys. Given that aluminum scrap is currently downgraded as it is recycled into cast aluminum alloys, an imbalance in aluminum cycles is predicted to occur. We identified secondary aluminum flows by distinguishing alloy type in China with material flow analysis. Considering the adoption of advanced recovery techniques and the trends towards greater use of electric vehicles and vehicle lightweighting, we also estimated changes in the automotive demand for wrought and cast alloys along with aluminum scrap generation, as well as the reduced amount of primary aluminum used in automobiles. The results revealed the potential to recycle about 87−183 kt of wrought alloys in 2019 and about 1,054−7,152 kt in 2050 within a well-managed vehicle recycling system, thereby reducing the amount of primary aluminum ingot required for automobile production by 10−37% between 2019 to 2050.

Secondary ageing and formability of an Al-Cu-Mg alloy (2024) in W and under-aged tempers

AA2024, a high-strength aluminum wrought alloy, is widely used in the production of aircraft components, for example, frames and stringers. While the alloy is relatively soft and formable in the solution heat treated and quenched state (W temper), rapid onset of natural ageing increases hardness and decreases ductility within few hours, creating a logistical challenge for the fabrication of frames by roll forming and bending, or other sheet metal forming operations. Here we investigate pre-ageing heat treatments of AA2024 with the aim of creating more stable and formable material conditions. The progression of materials properties after heat treatment is compared to natural ageing by extensive tensile test time series. An inhibition of secondary natural ageing by pre-ageing is demonstrated and a possible microstructural explanation is presented based on transmission electron microscopy and differential scanning calorimetry: S-phase is present in the pre-aged temper, and we suggest that the formation of Mg/Cu-clusters is suppressed. Formability is assessed by forming limit curves and finite element simulation of three-roll-push bending of frame profiles. We found improved processability of the pre-aged temper compared to a one week naturally aged condition: The forming limits are increased, and wrinkling in the bending simulations is reduced.

Effect of V on the microstructure and mechanical property of Al-Mg-Si alloy by adding Al3V phase

The effect of V microalloying on the microstructure and mechanical properties of Al-Mg-Si wrought aluminum alloy by adding the Al-4V (wt.%) master alloy containing the single type of Al3V phases was studied by optical microscope, scanning electron microscope and energy spectrum analysis. The results showed that adding V into the Al-1.6Mg-1.2Si (wt.%) alloy by means of Al3V phases significantly refined the as-cast alloy structure and reduced the grain size by 3.30%. During homogenization heat treatment, dispersed spherical V-containing phase precipitated from the matrix and strongly inhibited the recrystallization grain growth during the T6 heat treatment. The mechanical properties of T6 alloy was improved significantly when the minor V was added by means of Al3V phases, with the tensile strength (UTS) and yield strength (YS) increased by 1.21% and 2.42% respectively while elongation (EL) increased significantly by 130%.

Solid state recycling of used aluminum alloy beverage cans by thermomechanical consolidation

ABSTRACT Solid-state recycling of used aluminum alloy beverage cans was accomplished by thermomechanical consolidation of the sheet fragments produced by shredding the cans. Different samples were obtained using two thermomechanical consolidation routes, one involving direct hot extrusion of a sheet fragment compact and the other involving upset hot-forging of a sheet fragment compact followed by hot extrusion of the forged ingot. The microstructures and mechanical properties of the samples were investigated. It was found that the samples contained less pores and exhibited better mechanical properties with a higher extrusion temperature and involving upset forging than with only hot extrusion, the highest tensile strength is 209.5 MPa and the largest elongation to fracture is 29.1%. The surface layers of the samples exhibited a clearly higher strength and tensile ductility than the interior. They also showed significantly different fracture behaviors, with the former being like fully ductile fracture and the latter involving delamination of the sheet fragments, suggesting that the bonding between the fragments is significantly stronger in the surface layer, possibly due to a higher amount of plastic deformation in it. Overall, the best quality solid state recycled material has tensile properties comparable with those of wrought aluminum alloy with the same composition.

Manufacturing of high strength thin-walled aluminum 6063 tubes through severe plastic deformation combined with peak-aging treatment

Thin-walled aluminum tubes are widely used for different structural purposes, and therefore, the development of new methods for strengthening these elements is critical. This matter is especially true for aluminum alloys 6xxx since their maximum strengths projected through peak-aging are considerably lower than the similar strength of other wrought aluminum alloys like 2xxx and 7xxx. Although different works have proposed the imposition of severe plastic deformation for strengthening of 6xxx alloys, the application of this method for thin-walled tubes has been less studied due to the complexities of the severe plastic deformation processing of thin-walled tubes. In this study, the manufacturing of high-strength thin-walled aluminum 6063 tubes through the imposition of a new severe plastic deformation process and a subsequent post-aging treatment at two different temperatures is studied. For this purpose, the tension test is applied to measure the strength variation. Also, the electron backscattering diffraction equipped with scanning electron microscopy and the X-ray diffraction experiments are applied to investigate the microstructural evolution. Results show that the proposed approach can be successfully applied to the manufacturing of high-strength thin-walled aluminum 6063 tubes. Also, the strengthening effect of this procedure is attributed to an increase in the dislocation density and refinement of grains during the imposition of severe plastic deformation and an appearance of finer precipitates during the peak-aging treatment.