Al Alloy Components Research Articles

Studies on the microstructure and mechanical properties of AlCu4MgSi aluminum alloy repaired via electron beam directed energy deposition

Additive manufacturing (AM) technologies have been used to repair aluminum (Al) alloy components in many engineering structures. However, the use of AM technologies to repair Al-Cu alloys is still very limited, and the repair via electron beam directed energy deposition (EB-DED) has not been reported so far. In this work, the EB-DED repair was performed on AlCu4MgSi-O Al alloy substrate with the specially developed Al-Cu-Si wire (380D). The results show that wall structures with high metallurgical quality were successfully prepared. The deposit exhibits alternating fine grain zones and coarse grain zones. In the bottom layers of deposit, columnar grains growing along building direction dominate, while the middle and top layers mainly consist of equiaxed grains. In the AlCu4MgSi-O substrate, the heat-affected zone (HAZ) close to the fusion line undergoes recrystallization and completely transforms into fine equiaxed grains, while abnormal grain growth occurs and coarse grains are formed in the HAZ slightly away from the fusion line. From substrate to deposit, the intensity of texture gradually decreases. After EB-DED repair, the microhardnesses and strengths of the bottom layers and HAZ are significantly improved. The strengthening of HAZ is entirely attributed to precipitation strengthening, while the bottom layers are affected by both precipitation strengthening and dispersion strengthening. Tensile tests indicate that the repaired structure samples fracture from the interface between HAZ and base metal zone of the AlCu4MgSi-O substrate. EB-DED is demonstrated to be a promising technology to repair AlCu4MgSi alloy components, and this work can serve as a useful reference for the high-quality repair of Al-Cu alloy structural parts.

Tailoring properties of directed energy deposited Al-Mg alloy by balancing laser shock peening and heat treatment

Wire arc-directed energy deposition (WADED) has shown great advantages and potential in fabricating large-scale aluminum (Al) alloy components. However, WADED Al alloys typically exhibit low strength and reliability due to pore defects and lack of work hardening or precipitation strengthening. This study utilized a combination of laser shock peening (LSP) and annealing to regulate the microstructure of WADED Al-Mg4.5Mn alloy and enhance mechanical properties. The effects of LSP and annealing on phase composition, pore distribution, and microstructures at multiple scales were systematically investigated to reveal the mechanical property improving mechanism. The results demonstrated that LSP-induced plastic deformation formed a defect-free zone by closing near-surface pore defects. LSP created the hardened layer with gradient mechanical properties by inducing gradient changes in grain size, the number of low-angle grain boundaries (LAGBs), and dislocation density along the depth direction. The annealing process promoted grain coarsening and reduced excessive dislocations and LAGBs, weakening the work hardening effect caused by LSP. Furthermore, the high-density dislocations and high stored energy generated by LSP accelerated the recrystallization, facilitating growth of near-surface grains. The defect-free zone, dislocation strengthening, and LAGBs strengthening were responsible for the increase in strength, while the synergistic deformation between hardened layers and soft core facilitated maintaining excellent elongation. The strength and elongation of WADED Al alloy can be synergistically improved by balancing the effects of LSP and heat treatment.

An effective approach to improve microstructure and tribological properties of cold sprayed Al alloys

Abstract Cold spray is considered as an emerging technique for preparing wear-resistant metal matrix composite coatings on the surface of various kinds of metallic materials. In this work, a viable strategy of “cold spraying + hot rolling post-treatment” was successfully applied to prepare wear-resistant B4C/6061 Al composite coating on commercially available 6061 Al plates. The results revealed that hot rolling post-treatment results in uniform distribution of B4C particles in the alloy matrix, good inter-splat bonding, and sufficient plasticity in the splats through effective healing of the defects and splat boundaries in the as-sprayed deposit. As a result, the coating/substrate bonding strength in the hot rolled sample increased two-fold when compared with that of the as-sprayed sample. Moreover, hot rolling process resulted in much improved tribological properties of the coating with the wear rate ∼40% of that of the substrate. The obtained results indicated that the idea of combining cold spraying and hot rolling treatment is quite effective for improving the tribological properties of Al alloy plates. Further, this approach seems equally good for repairing/remanufacturing of unserviceable 6061 Al alloy components.

Two laser beam modulation of microstructure and residual stress field in cold sprayed Al alloy for recovering fatigue performance

The cold spray (CS) process has been demonstrated to be an attractive additive manufacturing technology for the development of freeforms and coatings from temperature-sensitive materials. However, owing to the lower bonding strength and inhomogeneous residual stress field distribution, the fatigue performance of CS deposition cannot satisfy the requirements of numerous engineering conditions. This study proposes a novel and promising approach to recover the fatigue performance of CS-repaired Al alloy components using two laser beam modulations. In the treatment, a millisecond laser is used during the CS process to heat the impact location in situ, by which the bonding mode is transformed from mechanical bonding to metallurgical bonding, and massive Al2O3 reinforcements of nano/micro size are formed in the coating. Thus, the bonding strength is significantly improved. Next, another nanosecond laser is used as a post-treatment to act on the area except the repaired region of the sample, which optimised the residual stress distribution around the repaired zone by the mechanical effects of the laser-induced ultra-high shock waves. Through the combination of these two lasers, the fatigue performance of CS-repaired Al alloy samples is successfully restored to its original condition. This study demonstrates that this compound process of CS technology and laser processing presents a wide range of possibilities for further development of advanced repair technology.

Microstructure Evaluation of the Potential of Additive Manufactured Dissimilar Titanium-Aluminum Alloys.

Pure titanium (Ti) ERTi-2 was accumulated on an aluminum (Al) alloy ER5356 component via wire and arc additive manufacturing. The effect of processing parameters, mainly the input heat per unit length, on Ti/Al components was investigated. The microstructure of the Ti deposited layer and the Ti/Al reaction layer was analyzed using optical microscopy, scanning electron microscope, energy-dispersive spectroscopy, and an X-ray diffractometer. The fabrication of the surface layer equivalent to pure Ti as the used wire or Ti-Al alloy on the Al alloy components was achieved under low and high input heat conditions, respectively, although the Ti/Al components had low joinability and cracks at the reaction layer. Finally, the potential of additive-manufactured Ti/Al components with reference to our results and previous reports was discussed.

Cracking mechanism and its susceptibility to scanning speed during laser power bed fusion processed high-strength 2024Al alloy

Laser powder bed fusion (L-PBF) is a promising technique for fabricating high-performance complex aluminum (Al) alloy components. However, conventional high-strength wrought Al alloys that are processed using L-PBF have limited application owing to their poor cracking resistance. To investigate the cracking mechanism, L-PBF was used to fabricate a 2024Al alloy. The resultant microstructure exhibited severe hot cracking, which occurred at grain boundaries with a high angle in both solidification and liquation cracks. Increasing the scanning speed increased the susceptibility to cracking. The effect of scanning speed on the eutectics content of Al2Cu and Al2CuMg and the residual stress in as-fabricated samples are discussed. Crack elimination at a low scanning speed could be ascribed to the lower thermal stresses and adequate liquid feeding during the late stage of solidification. In addition, based on the RDG (Rappaz-Drezet-Gremaud) model, a cracking susceptibility map was produced, in which the cracking susceptibility was determined to increase with an increase in the solidification rate, in agreement with experimental observation.

A357 aluminium alloy produced by LPBF: Tribological behaviour in dry sliding conditions

Laser Powder Bed Fusion (LPBF) is increasingly used in packaging, automotive and aerospace sectors for manufacturing Al alloy components where fatigue and wear damage can readily occur. Therefore, this work aims to assess the tribological behaviour of A357 alloy (AlSi7Mg0.6) produced by LPBF as a function of both printing parameters and heat treatment conditions, applying a novel T6 based on rapid solution followed by artificial aging, which improves the strength-ductility balance. Dry sliding tests (block-on-ring) were performed using A357 samples as stationary blocks against rotating quenched and tempered AISI 52100 (100Cr6) steel. LPBF samples were compared with A357 obtained by sand casting, subjected to Hot Isostatic Pressing (HIP) and conventional T6 heat treatment. Microstructural refinement induced by LPBF carried out in optimised conditions, even without post-processing treatments, reduced the wear rate in comparison to conventional sand-cast, HIP-ed and T6 heat-treated A357, while maintaining comparable coefficient of friction. The rapid solution T6 did not worsen the tribological behaviour of as-built LPBF A357 components, even though it induced a slight hardness decrease.

Friction stud riveting (FSR) of thick high-strength aluminum alloy structure

7-series aluminum (Al) alloy is a promising material that can meet the ever-increasing lightweight demand for transportation tools. However, the assembly between Al alloy and steel components brings challenges to the existing stud pre-embedded technology. This study proposes a friction stud riveting (FSR) process to achieve high-performance and high-efficiency embedding of steel studs in Al alloy parts by shank undercut, grooves interlock, and intermetallic compounds bonding. The stud geometry and FSR process were first optimized by evaluating the macro morphology of the joints. Then, the microscopic characterizations were performed to understand the material flow behavior, plastic deformation, and microstructure evolution of the joint induced by the feeding and rotation of the stud. The results indicate that the transient thermo-mechanical coupled FSR process leads to a continuous transition of sliding, mixed sliding-sticking, and sticking contact conditions between the stud and the Al alloy, resulting in a thermo-mechanical affected zone (TMAZ) outside the stud and a trapped Al alloy (TAA) inside the stud with diverse dynamic recrystallization (DRX) states and microstructures. The rotation state evolution and temperature gradients of the material within the TAA create two DRX bands that dominate the fracture behavior of TAA under tensile and shear loads. The strengths of the optimized steel stud-thick Al FSR joints reach 101.3% and 118.5% of the 7A52 Al alloy base material in tensile and shear tests, respectively, which solves the problem of low joining strength between steel stud and Al alloy plate due to the brittle and thick intermetallic compounds layers in conventional stud welding processes.

Effect of aging state on corrosion fatigue properties of 7075 aluminum alloy

The corrosion fatigue performance of Al alloy components is crucial for their engineering applications. This study focuses on the corrosion fatigue properties of 7075 Al alloys in three different aging states, i.e. over-aging (OA), peak-aging (PA) and under-aging (UA) states. The results show that the fatigue damage mechanism of the Al alloy is greatly affected by the stress level. In the high-stress region where the cyclic number is short, the fatigue damage is mainly caused by dislocations accumulation and stress concentration on the grain boundary. Compared with the UA state, the wave slip dislocations at the OA state are easy to accumulate and annihilate at the second phase boundaries, which reduces the fatigue damage degree at the grain boundaries. However, in the low-stress range where the cyclic number is large, the corrosion fatigue life of the Al alloy is mainly controlled by pitting-induced crack initiation. For the OA state, the spacing and size of the precipitated phase are large, so it is easy to trigger corrosive pitting, which reduces the corrosion fatigue performance of the alloy.

Upset Protrusion Joining (UPJ) characteristics of cast AM60 magnesium alloy to join with dissimilar material

Magnesium alloys have a significant benefit over the steel and aluminum alloys in manufacturing of components for many automotive and structural applications because of their extreme lightweight, low density, and high strength to weight ratio. However, one of the glaring impediments to the success of steels, aluminum, and magnesium-based multi-material integration for automotive industries is the ability to join these materials together without any cracking and corrosive damages during a performance. The present work aims to demonstrate a cost-effective, novel, and versatile joining technique, named Upset Protrusion Joining (UPJ), to mechanically and rapidly (1–2 s) join die-cast AM60 alloy to aluminum alloy sheet and evaluate its UPJ characteristics. Cast Mg plate has a cylindrical protrusion (11 mm diameter and 14 mm height) emanated perpendicular to its flat surface, and an aluminum sheet has a hole that accommodates the protrusion. Mg and Al alloy components are then clamped together, electrically heated, and compressed perpendicular to the protrusion axis. During compression, the protrusion expanded circumferentially to fill the hole as well as the region above the hole, and entrapped the Al sheet between the deformed (in a mushroom shape) head and the Mg plate. The effect of different UPJ process parameters such as applied current, current duration, compression loading rate, and compression distance is studied. The process demonstrated repeatability at given process conditions, and optimum process parameters were identified that produce visibly good joints (defect-free) and sufficient joint strengths when tested in the lap-shear mode under uniaxial tension. AM60 alloy showed a great promise as a candidate alloy to suit the UPJ method to adapt to automotive and other industrial manufacturing units to join with dissimilar wrought Al alloy sheets.

Strong in-plane anisotropy of creep ageing behavior in largely pre-deformed Al-Cu alloy: Experiments and constitutive modeling

Deformation anisotropy is one of the key factors affecting the dimensional accuracy and performance consistency of components manufactured from aluminum alloys. Understanding and modeling their anisotropic creep ageing behavior is thus essential for achieving precise creep age forming of Al alloy components. Creep ageing responses along varying loading directions have been investigated in an Al-Cu alloy heavily cold-rolled by 82.6% at room temperature. Although the large pre-deformation imparts markedly enhanced creep formability and strength-ductility balance, significant in-plane creep anisotropy (with an index of 49%) and slight anisotropy of the obtained yield strength (with an index of 5.6%) are observed for the creep ageing at 140 ℃ under 150 MPa. The creep deformation decreases evidently with the increasing angle between the loading direction and the rolling direction. The microstructure (grain morphology, texture, dislocation and precipitation, etc.) of the largely pre-deformed Al-Cu alloy before and after creep ageing are characterized in detail by X-ray diffraction, Electron backscattered diffraction and Scanning transmission electron microscopy. The multi-scale examinations unveil a hierarchical structure consisting of flattened grains, dislocation sub-structures considerably elongated along the rolling direction and plate-like precipitates in the investigated alloy. This comparative analysis suggests the strong creep anisotropy is mainly determined by the preferential alignment of dislocation cells with a width of ∼500 nm rather than the texture and precipitation. By introducing an orientation-dependent creep resistance caused by back-stress of the elongated dislocation nanostructure, a mechanism-based constitutive model is established to accurately describe the in-plane creep anisotropy. This work also provides guidance for tuning the creep anisotropy in largely pre-deformed Al-Cu alloy.

Enhancing creep formability and comprehensive property in Al–Mg–Si alloy by combinatorial pre-ageing and large pre-deformation

A thermal-mechanical route proceeding by pre-ageing and heavy cold-rolling has been developed to significantly improve both the creep formability and comprehensive properties in an Al–Mg–Si alloy. The uniform creep deformation increases by 2–5 times and the strength enhances by 60–140 MPa without sacrificing ductility compared to the conventional treatment. The pre-ageing at 180 °C could tune the density, mobility and distribution of the dislocations generated during cold-rolling.A physical metallurgical picture of the pre-ageing-dependent creep ageing in the cold-worked Al–Mg–Si alloy is established based on complementary transmission electron microscopy, differential scanning calorimetry and X-ray diffraction. Concurrent solutes precipitation and dislocation recovery contribute to the exceptional creep ageing response in the heavily cold-deformed Al–Mg–Si alloy. The high density dislocations could substantially promote the creep deformation and improve the strength-ductility balance. The fragmentation of grains and the inhibition of continuous precipitation along the grain boundary lead to a superior resistance to inter-granular corrosion. Our results demonstrate the application potential of solutes precipitation control before large pre-deformation in creep age forming of Al alloy components with unusual figures of merit.

3D X‐Ray Diffraction Characterization of Grain Growth and Recrystallization in Rolled Braze Clad Aluminum Sheet

Braze clad on aluminum (Al) sheets has enabled fast and convenient brazing assembly of complex heat exchangers. However, there are details in the brazing process that are not fully understood. Herein, 3D X‐ray diffraction (3DXRD) is used to investigate the grain position, size, and orientation before and after controlled atmosphere brazing (CAB). The outcomes are presented as maps of center‐of‐mass positions with relative grain size distribution and color‐coded grain orientations. The results show that, for braze clad Al sheets exposed to CAB simulation, it is possible to distinguish grains from the solidified AlSi alloy from those in the core Al alloy. It is also possible to distinguish new grains obtained through recrystallization during CAB. Hence, the study shows that stretching of the rolled Al sheet by 6% provides enough stored energy in the core material so that recrystallization occurs during CAB and, in addition, provides conditions for AlSi alloy grain growth into the core material. While the phenomenon is well known, it is poorly understood for processes in connection with brazing of mechanically formed Al alloy components in heat exchanger assemblies, and these results demonstrate the potential for gaining deeper insights through 3DXRD.

Manufacturing large 2A14 aluminium alloy cylinders by a warm rolling technology

This paper aims at the problem of high performance manufacturing of large 2A14 Al-alloy cylindrical components for aerospace applications. A warm rolling process was put forward to substantially refine the grains and secondary phases of 2A14 Al alloys. The results indicated that compared with hot rolling, warm rolling was easier to implement to form abundant subgrains and fully crushed the coarse particles. Coarse second phases dissolved and the precipitated T phases (AlCuMn) hindered the migration of grain boundaries and restrained grain growth during the heat treatment.The tensile strength, yield strength and elongation of the 2A14 aluminium alloy were significantly increased by 59 MPa (an increase of 14%), 71 MPa (an increase of 21%), 4% (an increase of 67%), respectively.

Effectiveness of the ultrasonic impact treatment in the retardation of the fatigue crack growth for 2024-T3 Al alloy components

Previous research has investigated the possibility of improving the retardation of the fatigue crack growth (FCG) by means of different treatments and techniques. Ultrasonic impact treatment (UIT) emerges as an alternative technique to improve the resistance of metallic components, mainly developed in materials after welding. Experiments on 2024-T3 aluminium alloys are described to determine the effect of the UIT in the fatigue crack growth. Two working conditions were studied varying three parameters of the UIT process, which were amplitude under load, impact frequency and feed rate, while the operating frequency of the ultrasonic generator was set to 36 kHz. The standard M(T) geometry specimen was chosen to be employed in fatigue testing to determine the crack length, crack growth rate and the crack front shape by means of an optical technique. Results suggested that the manipulated UIT parameters allow the crack growth retardation to the 2024-T3 Al alloys. Findings also suggested that the less severe treatment, the more crack growth retardation. Treatment duration and amount of impacts during treatment are two key parameters to optimize in order to find better improvements in this direction.

Optimization of Casting Yield in Multi-cavity Sand Moulds of Al-alloy Components

To produce casting with efficient use of material, energy, lead time and manpower is very essential to sustain in foundry industry. Mould with dense cast cavities or less number of cavities may lead to more solidification time, poor mechanical properties and defects like shrinkage, misrun and cold shut. It is proposed to design mould layout with selection of suitable combination of mould size and multiple number of cavities based on temperature distribution and solidification time which results in optimization of casting yield.Casting simulations are carried out for casting mould with single cavity based on mould size and variation of cavity –wall distance for Al-alloy component in green sand mould result in finding of minimum cavity wall gap. Double and multiple cavities moulds are simulated based on cavity-wall distance value and variation of cavity-cavity distance along with temperature distribution, solidification time and defects if any in cast part results in computing minimum cavity-cavity distance. Applying this in mould layout design, it leads into optimum mould layout and casting yield. AutoCAST-X1 simulation results are validated by experimentation for LM4 alloy cast in sand mould allocated with thermocouples and data acquisition system.

Laser opto-ultrasonic dual detection for simultaneous compositional, structural, and stress analyses for wire + arc additive manufacturing

The complex, nonequilibrium physical, chemical, and metallurgical nature of additive manufacturing (AM) tends to lead to uncontrollable and unpredictable material and structural properties. Therefore, real-time monitoring of AM is of great significance. However, current AM relies on separate postprocess analyses, which are usually destructive, costly, and time-consuming. In this study, we investigated a laser opto-ultrasonic dual (LOUD) detection approach for simultaneous and real-time detection of elemental compositions, structural defects, and residual stress in aluminium (Al) alloy components during wire + arc additive manufacturing (WAAM) processes. In this approach, a pulsed-laser beam was used to excite the surfaces of Al alloy samples to generate ultrasound and optical spectra. As a result, the compositional information can be obtained from the optical spectra, while the structural defects and residual stress distributions can be extracted from the ultrasonic signals. The silicon (Si) and copper (Cu) compositions obtained from optical spectral analyses are consistent with those obtained from the electron-probe microanalyses (EPMA). The 1 mm blowhole and the residual stress distribution of the sample were detected by the ultrasonic signals in the LOUD detection, which shows consistency with the conventional ultrasonic testing (UT). Both results indicate that the LOUD detection holds the promising of becoming an effective testing method for AM processes to ensure quality control and process feedback.

Microstructural evolution of Al2Cu phase and mechanical properties of the large-scale Al alloy components under different consecutive manufacturing processes

The large-scale Al alloy components are usually manufactured based on the ultra-large Al ingots through different manufacturing processes, i.e. direct-chill (DC) ultrasonic casting, multidirectional forging (MF), and solution-aging treatment (SAT). The Al2Cu particles with different microstructural features significantly affect the mechanical properties of such large-scale Al alloy components. In the present work, an ultra-large cylindrical 2219 Al alloy ingot (with a diameter of 1380 mm and a length of 3700 mm) was cast using ultrasonic casting technology. Then, the ingot experienced a MF process, followed by a slight SAT. The continuous microstructural variation across DC casting, MF process and SAT was examined regarding this ultra-large ingot, particularly for different types of (θ, θ′ and θ″) Al2Cu particles. Al2Cu particles mainly developed from solidification, precipitation and the MF-stimulated fragmentation. Most of the Al2Cu particles fragmented from θ-Al2Cu/α-Al eutectic networks still retained after SAT, but with partial dissolution. Other types of θ′- and/or θ″-Al2Cu particles were nearly dissolved into the α-Al matrix. SAT improved the ultimate tensile strength and the yield strength while MF evidently increased elongation. However, casting generated very low tensile strength. Further, the correlation between Al2Cu particles and mechanical properties was accordingly discussed.

The corrosion of aluminium alloy and release of intermetallic particles in nuclear reactor emergency core coolant: Implications for clogging of sump strainers

Abstract Clogging of sump strainers that filter the recirculation water in containment after a loss-of-coolant accident (LOCA) seriously impedes the continued cooling of nuclear reactor cores. In experiments examining the corrosion of aluminium alloy 6061, a common material in containment equipment, in borated solutions simulating the water chemistry of sump water after a LOCA, we found that Fe-bearing intermetallic particles, which were initially buried in the Al matrix, were progressively exposed as corrosion continued. Their cathodic nature vis-a-vis the Al matrix provoked continuous trenching around them until they were finally released into the test solution. Such particles released from Al alloy components in a reactor containment after a LOCA will be transported to the sump entrance with the recirculation flow and trapped by the debris bed that typically forms on the strainer surface, potentially aggravating strainer clogging. These Fe-bearing intermetallic particles, many of which had a rod or thin strip-like geometry, were identified to be mainly the cubic phase αc-Al(Fe,Mn)Si with an average size of about 2.15 μm; 11.5 g of particles with a volume of about 3.2 cm3 would be released with the dissolution of every 1 kg 6061 aluminium alloy.

Micro laser metal wire deposition of thin-walled Al alloy components: Process and material characterization

In this work, micro laser metal wire deposition (μLMWD) of 0.4 mm diameter 4047 Al-alloy (AlSi12) wire is demonstrated. A flash-pumped Nd:YAG laser producing ms-long pulses was used as the energy source. The processing conditions were studied for single and multi-layered tracks, seeking stable deposition conditions. Microhardness, microstructure and chemical composition were analysed. The results showed that thin walls with sub-mm thickness free of pores and cracks could be obtained using the μLMWD process. The material was characterized by a homogenous microhardness profile over the build direction with high values (approximately 120 HV). The improved mechanical properties were due to the redistribution of the Si in form of a micrometric network in the Al-matrix along the deposit. The process was found to be a promising option for producing freestanding components, as well as adding features to existing parts with tailored properties, especially for lightweight applications.