Heat-treatable Aluminum Alloys Research Articles

The beneficial effect of minor iron additions on the crack susceptibility of rapidly solidified aluminum alloy 6060 toward additive manufacturing applications

Solidification cracking presents a challenge for additive manufacturing of many materials, such as heat treatable aluminum alloys. The objectives of this article are to demonstrate the beneficial effect of minor Fe additions on crack elimination in rapidly solidified Al alloy 6060 and to elucidate the underlying mechanism. Blocks of 6060 + xFe (0 ≤ x ≤ 0.5) were cast and single-track laser melting trials were performed on the surface of the blocks to emulate solidification rates characteristic of additive manufacturing. Analysis of the melt pool cross sections revealed that cracks were present in all processing conditions for the baseline 6060 alloy, but a monotonic decrease in cracking was observed with increasing Fe content with no cracks observed in any conditions for the 6060 + 0.5Fe sample. Serial SEM imaging and FIB milling were used to reveal the 3D morphology of nanoscale particles in the melt pools, while TEM analysis was used to identify the phases. Discrete and nodular δ-AlFeSi particles were observed in samples containing 0.1–0.2 wt% Fe, while elongated and branched α-AlFeSi particles were observed in the 6060 + 0.5Fe sample. The crack mitigation mechanism is proposed to be due to bridging of the Al matrix by the AlFeSi particles, through the formation of a strong interface and mechanical interlocking, thereby resisting the thermally induced loads. It is concluded that minor Fe additions can effectively eliminate cracking in Al 6060, and that this cannot be explained by conventional mechanisms such as grain refinement or an increase in eutectic liquid.

Peripheral coarse grain formation in AA2024 and AA6063 aluminium alloys- A comparative study

Multifaceted mechanical and physical characteristics such as light weighting, high strength to weight ratio, electrical conductivity, and ease of fabrication have helped aluminium alloys to find its application in aerospace and automobile sectors. The most famous aluminium alloy used in extrusion is AA 6063 because of its 100% extrudability. AA2024 is from the family of hard alloys which finds its applications in the strength requirements and major alloying additions comprise of Cu, Mg which contributes to age/precipitation hardening phenomena. Because of its inherent nature of high strength, it is challenging to extrude. Extrusion is one of the major metals forming processes which involve several process parameters such as, temperature, strain rate, ram speed and post forming heat treatment operations. To attain the specific mechanical properties, microstructure of the extrudate is of utmost importance and evolution of the same needs to be understood. Heat treatable aluminium alloys series of 2xxx, 6xxx or 7xxx are prone to peripheral coarse grain structure, which is responsible for the loss of mechanical and corrosion performance. To eliminate PCG entirely or to minimize it is the fundamental interest of extrusion industries and to come up with a workable solution, it is necessary to twig the microstructure evolution of AA6063 and AA2024 alloy during extrusion and after heat treatment. The present work is aimed at comparative study of the PCG formation of press quenched samples in AA6063 and heat-treated (T6) samples of AA2024.

Kelvin-Voigt lumped parameter models for approximation of the Power-law Euler-Bernoulli beams

The purpose of this research is to initiate an investigation of the nonlinear material strain-rate damping effects on the amplitude and frequencies of some Euler-Bernoulli Beams. It is well known that the dynamic behaviors of most heat-treated metals can be modelled by using the power-law strain-rate dependent constitutive equations. Lumped parameter models for approximations of dynamic vibration of the power-law Euler-Bernoulli Beam subject to power-law strain-rate damping and concentrated loads are formulated. Analytic formulas of the lumped parameters, including effective the train-rate damping, are derived. The lumped-parameters are also evaluated numerically by a low-order Galerkin Method to validate and compare the lumped parameter model with another numerical model. Numerical examples made of some heat-treated aluminum and stainless-steel alloys are presented to illustrate the implications of the aforementioned lumped-parameter models on the dynamics of the beams. The results obtained in this work cover with the classical results in the literature for linear the materials as special cases. The novel lumped parameter models can provide useful insights for crashworthiness analysis of structures of heat treated metals and thermal plastics.

Enhancement of microstructure, micro-texture, and mechanical properties of Al6061 friction stir welds using the developed static shoulder welding tool

Dissolution of strengthening precipitates and grain coarsening are the key factors that dictate the mechanical properties of heat-treatable aluminium alloys. In this study, a feasible method of static shoulder friction stir welding (SSFSW) is used to reduce these adverse effects. A novel static shoulder friction welding tool is developed here in this study by incorporating rotating and non-rotating shoulders in a single tool. The effectiveness of the tool was evaluated by welding Al6061 plates under various conditions, such as conventional friction stir welding (CFSW), underwater friction stir welding (UWFSW), and SSFSW. The evolution of crystallographic texture and microstructural changes during the process is studied using electron back scattered diffraction and transmission electron microscopy. The results showed that SSFSW reduced grain size by 37% compared to UWFSW at the centre of the stir zone and increased the yield strength by 22.8% compared to CFSW. In addition, SSFSW showed a strong presence of γ-fibre, indicating improved formability and a 7.2% improvement in joint efficiency in terms of ultimate tensile strength due to a higher fraction of precipitates and higher dislocation density.

Cavitation behavior study of the aging heat treated aluminum alloy 7075

Aluminium-based alloy type 7075 is known for its good ductility, high mechanical strength, toughness and high fatigue strength, which is why it is mainly used in the construction of dynamically stressed parts in the structure of airplanes, vehicles and ships. Although it has these qualities, at present its behavior has not been studied at the hydrodynamic stresses that allow it to be used in parts that work in cavitation conditions, such as pump rotors and boat propeller blades. Therefore, the research in this paper highlights the behavior of laminated semi-finished structures and obtained by heat treatment of artificial aging at 180°C, with a maintenance time of one hour. Of the 7075 alloy at the demands generated by the vibrating cavity, created by the standard vibrating device with piezoceramic crystals (frequency of 20 kHz, amplitude of 50 µm and electrical power of 500 W). Analysis based on the curves MDE (t) and MDER (t), of the specific parameters of cavitation erosion MDEmax and MDERs as well as of the macro and microscopic images of the eroded structures of cavitation show that, compared to the delivered state (semi-finished), by the heat treatment applied the microstructure does not change cavitation

Study on the solid solution temperature of achieving ultra-high strength in wire-arc additive manufactured Al-Zn-Mg-Cu aluminum alloy

Al-Zn-Mg-Cu aluminum alloys are typically heat-treatable aluminum alloys. The heat treatment has a significant effect on the microstructure and mechanical properties of Al-Zn-Mg-Cu alloy. In this study, the solid solution temperature of achieving ultra-high strength in wire-arc additive manufactured 7B55 aluminum alloy was systematically investigated. The results showed that the microstructure of the as-deposited 7B55 aluminum alloy was composed of equiaxed grains with an average grain size of 4.2 ± 0.5 μm. A large number of the second phases were continuously distributed along grain boundaries. The precipitated phases within grains were mainly composed of the larger η phases and the smaller η′ phases, and the amount of precipitated phases was fewer. The second phases distributed along grain boundaries gradually dissolved into α-Al matrix with the increase of solid solution temperature, resulting in a higher supersaturation of the α-Al matrix and more homogeneous distribution of alloy elements. Combined with the results of DSC analysis, the optimal solid solution temperature of the 7B55 aluminum alloy was determined to be 480 °C. After solid solution of 480 °C，the microstructure was still composed of equiaxed grains with an average grain size of 4.8 ± 0.4 μm. The size of the grain did not grow significantly. A larger number of nanoscale fine GP zones, η′ phases and secondary Al3(Sc,Zr) particles were precipitated within the grains during subsequently artificial aging process, resulting in a significant increase in tensile properties. The ultimate tensile strength (UTS), yield strength (YS) and elongation (EL) reached 621 MPa, 555 MPa and 5.73%, respectively, which was significantly higher than the strength level of WAAM aluminum alloy reported among all the existing literature.

Investigation on evolution of microstructure and mechanical properties of heat-treatable 6010-S aluminium alloy during gas-based hot sheet metal forming process

Modern hot sheet metal forming processes offer the opportunity, especially in the automotive sector, to meet current demands for ultra-lightweight design. Due to the increased formability at the high process temperatures, high-strength aluminium alloys are increasingly coming into the focus of the industry. However, the complex thermo-mechanical interactions within these processes can lead to undesirable microstructural changes that could have a negative impact on the final mechanical properties. The purpose of this work is therefore to investigate the microstructural evolution of age-hardenable EN AW 6010-S alloy in the course of a modern gas-based sheet metal forming process and to quantify its influence on the resulting mechanical T6 properties. For this purpose, two different components were first formed at laboratory scale and the areas of microstructural interest were identified. Metallographic examinations and EBSD measurements were performed to visualize the influence of process temperature and deformation on the microstructure. EDX analysis helped to identify non-metallic phases. In the next step, artificial aging of the components was performed to increase the mechanical properties. Tensile tests and hardness measurements showed that the deformation and temperature have no negative influence on the final mechanical properties of the alloy.

Strength-ductility trade-off modulated by thermo-kinetic synergy of heat-treatable aluminum alloys

The strength-ductility trade-off behaviors for most metallic alloys are intrinsically depend on various microstructures formed during materials processing. Thermodynamics and kinetics of the involved phase transformation and concurrent/subsequent deformation play important roles in determining the overall microstructures and final performances. Since the mechanical responses of aluminum alloys can be mediated by introduction of nano-sized precipitates, taking the heat-treatable Al–Mg–Si alloys as representative, we herein investigate the strength-ductility trade-off behaviors from the thermo-kinetic synergy upon precipitation. It turns out that typical combination of high strength and large ductility for Al–Mg–Si alloys corresponds to certain synergistic effect between thermodynamics and kinetics, as reflected by large driving force and high energy barrier of precipitation, which is modulated by specific heat-treatment conditions. Such formulation of the strength-ductility and thermo-kinetic trade-off correlation has potential implications for guiding alloys design, as exemplified by the Al-0.46Mg-1.04Si alloy aged at 438 K with ideal strength and ductility match. The underlying mechanisms are illustrated via systematical analysis on the crystallography, thermodynamics and kinetics during precipitation of Al–Mg–Si alloys. Our investigation provides an innovative strategy to understand the strength-ductility trade-off phenomenon in light of the thermo-kinetic synergy, as dominated by composition and processing routes of metallic alloys.

Effect of metallic reinforcement and mechanically mixed layer on the tribological characteristics of Al-Zn-Mg alloy matrix composites under T6 treatment

Owing to their high strength, high specific modulus, low co-efficient of thermal expansion, and excellent wear resistance, aluminium metal matrix composites reinforced with hard ceramic particles are employed in different domains. The primary heat treatment method employed to enhance the desirable properties of heat-treatable aluminium alloys and their composites is T6 treatment. This study investigated the effects of metallic reinforcement and mechanically mixed layer on the tribological characteristics of Al-Zn-Mg alloy matrix composites. The microstructure, material transfer behavior, tribological characteristics, and wear mechanism of the worn surfaces were examined. A microstructural study revealed that the reinforcements would encourage grain refining, resulting in a 60.7% average size reduction. The wear rates have significantly reduced by 50.2% and 67.2%, respectively, with the introduction of 2.0 wt% of reinforcement and T6 treatment. There is a decreasing trend of wear rate as the weight percentage of reinforcement is increased, both in as-cast and peak-aged conditions. The refractory nature of precipitates formed during T6 treatment improves the hardness of the composite and thereby reduced the wear rate. Mechanically mixed layer (MML) is observed in the worn-out surface of peak-aged composites as revealed by the SEM analysis. Overall, the Al-Zn-Mg 6 wt. % grey cast iron composite showed excellent performance in tribological characteristics.

Geopolymer concrete-filled aluminium alloy tubular cross-sections

Composite steel–concrete members are adopted in structural applications as a cost-effective and high-speed construction practice. Exploiting the superior corrosion and strength-to-weight properties of structural aluminium, research on composite aluminium-concrete members has been reported. Aiming for an even more sustainable and durable structural member, this paper proposes combining structural aluminium alloys with low carbon geopolymer concrete (GC) to form a structural member with lower environmental footprint. To this end, an experimental programme on geopolymer concrete-filled aluminium alloy tubular (GCFAT) cross-sections is performed. A total of 24 tests on stub columns and 12 tests on beams were carried out. In particular, 4 square hollow sections infilled with one-part geopolymer concrete were tested under uniform compression and under uniaxial bending. The hollow sections were fabricated from 6082-T6 heat-treated aluminium alloy. The same cross-sections were also tested as bare and infilled with ordinary Portland cement (OPC) concrete for comparison purposes. It is shown that the strength of the composite sections is significantly increased compared to the bare ones. In particular, the average strength increase was in the range of 16.5%–93.3% and of 23%–93.1% for GC and OPC-aluminium stub columns, respectively. In beams, the strength increase was in the range of 14.1%–53.6% for GC-aluminium and of 10.2%–48.9% for OPC-aluminium specimens. In absence of codified design rules for geopolymer concrete-aluminium structures, design formulae based on the European standards for composite steel–concrete members, with the material properties of steel and concrete replaced by those of aluminium alloy and GC, respectively, are adopted. The obtained results demonstrated that the proposed design methodology is suitable for the design of GCFAT cross-sections and beams, providing reasonably accurate and consistent strength predictions. Overall, the potential of geopolymer concrete-filled aluminium tubular cross-sections as a novel cement-free, sustainable, and structurally efficient composite cross-section is demonstrated.

A Weldment Characteristics on Laser Welding of 2XXX Aluminum Alloys

In the aerospace industry, high-strength heat-treated aluminum alloys are increasingly being used for large wing structures, which are typically designed by welding thin skins to a pocketed frame structure to reduce weight. Owing to the limited welding area between the frame and the skin and the limited space in the chamber, laser welding is the most suitable manufacturing process. Therefore, the weld-ability and the strength of laser-welded aluminum frame-skin structure must be determined. In this study, AA2219 of the A2XXX alloy series was tested under various welding conditions. Analysis of the bead shape in the cross-section of the welded frame?skin revealed that the optimal welding conditions can be achieved when the ratio of the bead width to penetration (L/H) is minimal. The weld-ability of AA2219 was compared to that of AA2024 by examining the 1) spatter and porosity, 2) hardness in the heat-affected zone, and 3) tensile strength of the two alloys welded under the determined optimal welding conditions. The tensile strength of laser-welded AA2219 and AA2024 was 79% and 70% of that of the base material, respectively. Because the tensile strength value of the welded AA2219 was nearly equal to the yield strength value of the base material, the AA2219 laser-beam welding process can be applied to large wing structures.

Influence of heat treatment on corrosion behavior of Al–Mn–Mg–Sc–Zr alloy produced by laser powder bed fusion

Effect of heat treatments on the microstructure and corrosion behavior of Al–Mn–Mg–Sc–Zr alloy fabricated by laser powder bed fusion (LPBF) were systematically investigated. The results demonstrate that the 300 °C/5 h heat-treatment doesn't alter the typical bimodal grain distribution of LPBF-fabricated alloy. However, the grains at molten pool boundaries experience a significant growth after a 500 °C/5 h heat treatment, narrowing the gap of grain size between fine-grain (FG) region and coarse-grain (CG) region. It is also found that the heat treatments have an impact on Al3(Sc, Zr) and Al6(Mn, Fe) precipitates. Detailedly, the Al3(Sc, Zr) precipitates undergo a slight growth in size and obvious increase in quantity after heat treatment whilst the Al6(Mn, Fe) particles go through a rapid increase both in amount and size, especially for the alloy after being subject to a higher temperature heat treatment. As consequence, the heat-treated LPBF aluminum alloys exhibit worse corrosion resistance compared with their original state. The Al3(Sc, Zr) precipitates acting as micro-cathodes at molten pool boundaries accelerate the preferential corrosion of fine grain regions of 300 °C/5 h heat-treated alloy (HT-300). In contrast, the 500 °C/5 h heat-treated alloy (HT-500) tends to promote a more uniform corrosion due to the dissolution of the homogeneously distributed Al6(Mn, Fe) anodes on the alloy surface.

LPBF-Formed 2024Al Alloys: Process, Microstructure, Properties, and Thermal Cracking Behavior

2024Al is an Al-Cu-Mg series heat-treatable aluminum alloy with high strength and excellent damage resistance. To obtain a high-performance target component of LPBF-formed 2024Al, the effect of process parameters on density, microstructure, and performance is systematically investigated and the thermal cracking phenomenon is analyzed in detail. The results reveal that the optimization of process parameters can suppress the cracks generated during the LPBF forming of 2024Al to a certain extent. When the laser energy density is 741 J/mm3, the maximum density reaches 99.77%, whereas the tensile strength and elongation reach 330 ± 7 MPa and 9 ± 0.6%, respectively. Owing to the high Cu and Mg contents in 2024Al, the transverse strain rate of columnar grains during LPBF forming is easily higher than the sum of the transverse expansion rate of grains and the liquid phase filling rate at grain boundaries, resulting in strong thermal crack sensitivity. In addition, an extremely high cooling rate (−108 K/s) and heat input during LPBF forming reduce the liquid phase filling rate at grain boundaries to further aggravate the thermal cracking tendency. The current study provides experimental guidance for the preparation of high-quality, crack-less, or even crack-free 2024Al alloys.

Synchronous improvement of mechanical properties and corrosion resistance of novel heat-treatable 5xxx aluminum alloy by non-isothermal ageing

To overcome the trade-off between strength and corrosion resistance of traditional 5xxx aluminum alloys, in this paper, we investigate the evolution of microstructure, mechanical properties and intergranular corrosion (IGC) resistance of the novel heat-treatable Al-Mg-Zn-Ag alloy processed by isothermal or non-isothermal ageing (NIA). Results indicate that NIA can not only accelerate age hardening response greatly, but increase the number density of precipitates. Meanwhile, fast precipitation behavior in NIA process causes discontinuous distribution of grain boundary precipitates with finer-scale, which is instrumental in improving the IGC resistance. Hence, the strength and corrosion resistance of Al-Mg-Zn-Ag alloy are improved synchronously. Data availabilityThe raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.

An Experimental and Numerical Study on Aluminum Alloy Tailor Heat Treated Blanks

Information is presented on the conceptualization, experimental study, and numerical process simulation of tailor heat treated aluminum alloy blanks. This concept is intended to improve the forming behavior of aluminum parts in challenging conditions. The implementation requires precise control of laser heat treatment parameters within a suitable industrial framework. The study details material properties, heat treatment parameters, and experimental results for the strength and elongation properties of an AA6063-T6 aluminum alloy. Constitutive modeling is applied using the Hocket–Sherby equation, which allowed us to establish a correlation between laser heat treatment maximum temperature and the corresponding material softening degree. Based on the generated flow stress–strain curves, a numerical simulation of a representative case study was performed with Abaqus finite element software highlighting potential improvements of tailor heat treated blanks (THTB). The influence and effectiveness of heat-affected zone (HAZ) dimensions and material softening were analyzed.

Analysis of Tribological Performance of New Stamping Die Composite Inserts Using Strip Drawing Test

This article assesses the tribological performance of new composite tool sets for stamping dies. Four sets of composite countersamples were tested. These consisted of polyurethane resin with mineral filler (base variant) and modified with aluminium powder (10wt%) and roving fabric (5wt%). Strip samples for the strip drawing tests were cut from AMS5599 (Inconel 625) corrosion-resistant nickel alloy, AMS5510 (321) corrosion and heat-resistant steel and AMS6061-T4 heat treatable aluminium alloy sheet metals. The influence of the type of sample material on the coefficient of friction (COF) was observed. The smallest values of the COF over the entire range of clamping force values used on AMS5599 and AMS5510 sheets were observed during tests with countersamples made of the base variant of composite. When testing the AMS6061-T4 aluminium alloy sheet, the countersamples modified with roving fabric provided the lowest value of COF, which stabilised at a value of about 0.197 as pressure was increased.

Aluminium alloy channel columns: Testing, numerical modelling and design

Aluminium alloys can be employed in a wide range of structural applications offering high strength-to-weight ratio, whilst they can easily be extruded in various shapes. Channel (C-) sections have been increasingly employed as compression members, such as wall studs and chord members of roof trusses in framed residential and commercial buildings. However, relevant studies on their compressive behaviour are quite limited and thus a greater emphasis should be placed on providing a deeper understanding. Towards this direction, this paper examines the structural performance of C-sections under axial compression. An experimental and numerical investigation was performed on 6082-T6 heat-treated aluminium alloy C-section columns. In total, 6 fix-ended stub column tests were executed to examine the cross-sectional compressive behaviour, whilst 8 pin-ended column tests were conducted to study their minor-axis flexural buckling behaviour. The obtained experimental results were utilised to validate the developed finite element models. Subsequently, extensive parametric studies were carried out to generate additional performance data over a broad range of cross-sectional aspect ratios, and cross-sectional and member slendernesses. Both the experimentally and numerically obtained ultimate strengths are utilised to assess the accuracy of Eurocode 9 design provisions, including the flexural buckling curve. On the basis of the experimental and numerical results, a new flexural buckling curve is proposed improving the design accuracy. The applicability of the Direct Strength Method on the design of aluminium alloy C-sections subjected to axial compression is also evaluated resulting in the most accurate and consistent design strength predictions.

Optimization of the Mechanical Property of Friction Stir Welded Heat Treatable Aluminum Alloy by using Bio-Inspired Artificial Intelligence Algorithms

The concepts and inspiration of biological evolution in nature are used to create new and effective competing tactics in the burgeoning field of bio-inspired computing optimization algorithms. In the present work, nine specimens of similar alloys i.e., AA6262 were Friction Stir Welded. Spindle Speed (RPM), Traverse Speed (mm/min), and Plunge Depth (mm) were the input parameters while the Ultimate Tensile Strength (MPa) was an output parameter. The main objective of the work is to obtain the maximum optimized Ultimate Tensile Strength (MPa) by using Bio-Inspired Artificial Intelligence Algorithms i.e., Differential Evolution and Max Lipschitz optimization (Max LIPO) Algorithm. The results showed that the Differential Evolution algorithm resulted in a slightly higher value of the Ultimate Tensile Strength in comparison to the Max LIPO algorithm.

Nondestructive analysis of corrosion in ageing hardened AA6351 aluminium alloys

Aluminum alloys have been chosen over other lightweight structural materials because of their advantages regarding strength, long-term durability, and low cost. Aluminum comes under the category of highly reactive metals, where an inherently stable oxide layer can protect against aggressive corrosive conditions. Therefore, this research investigated the application of the ultrasonic nondestructive technique for inspection and monitoring of corrosion behavior of AA6351 heat-treated aluminum alloys. The samples were artificial age hardened at five different conditions. The complementary engineering experiments for materials evaluation included hardness, X-ray diffraction and salt spray tests. Overall findings showed correlations between ultrasonic and destructive data representing a fast, versatile and reliable inspection technique. Furthermore, findings show a significant correlation (>99%), thus supporting the benefits of the multiparametric ultrasonic test for heat treatment inspection and quality control of lightweight structural materials.

Investigating the multiscale effects of a novel post–weld composite processing treatment on minimizing weld softening in AA6061-T6 Al–alloy

The fusion welding of heat-treatable AA6061-T6 aluminum alloy results in significant joint softening which results in the ultimate tensile strength (UTS) and elongation (El) of the welded joint only reaching up to 60–70% and 40–50% of the base metal (BM), respectively. A post–weld composite processing treatment (PWCPT) that uses solution treatment (ST), artificial aging treatment (AT) and cold rolling (CR) has been proposed in this study to mitigate this issue. The effect of different composite process sequences and parameters on the microstructural characteristics and mechanical properties of the joints were investigated. The results show that the formation of the fine-grained microstructure in the fusion zone (FZ) and abnormal sandwich microstructure in the heat-affected zone (HAZ) was highly dependent on the dislocation density and fraction of the insoluble phases. By clarifying the strain characteristics of the joints, a strategy was developed to optimize the homogeneity of the microhardness distribution which improves joint ductility. The optimal PWCPT involved the ST and AT for the AA6061-T6 joint that was produced by tungsten inert gas (TIG) welding with filler wire, with subsequent cold rolling of the weld reinforcement to achieve a rolling reduction of 1.2 mm. The PWCPT could completely eliminate joint softening and improved the joint UTS and El to 100% and 88.6% of the BM, respectively. By systematically expounding the evolution law of microstructure and mechanical properties of the welded joint under the coupling of thermal and mechanical, the strengthening mechanism of the PWCPT is revealed.