Review on laser directed energy deposited aluminum alloys

Lightweight aluminum(Al)alloys have been widely used in frontier fields like aerospace and automotive industries,which attracts great interest in additive manufacturing(AM)to process high-value Al parts.As a mainstream AM technique,laser-directed energy deposition(LDED)shows good scalability to meet the requirements for large-format component manufacturing and repair.However,LDED Al alloys are highly challenging due to their inherent poor printability(e.g.low laser absorption,high oxidation sensitivity and cracking tendency).To further promote the development of LDED high-performance Al alloys,this review offers a deep understanding of the challenges and strategies to improve printability in LDED Al alloys.The porosity,cracking,distortion,inclusions,element evaporation and resultant inferior mechanical properties(worse than laser powder bed fusion)are the key challenges in LDED Al alloys.Processing parameter optimizations,in-situ alloy design,reinforcing particle addition and field assistance are the efficient approaches to improving the printability and performance of LDED Al alloys.The underlying correlations between processes,alloy innovation,characteristic microstructures,and achievable performances in LDED Al alloys are discussed.The benchmark mechanical properties and primary strengthening mechanism of LDED Al alloys are summarized.This review aims to provide a critical and in-depth evaluation of current progress in LDED Al alloys.Future opportunities and perspectives in LDED high-performance Al alloys are also outlined.

High corrosion and wear resistant electroless Ni–P gradient coatings on aviation aluminum alloy parts

A Ni–P alloy gradient coating consisting of multiple electroless Ni–P layers with various phosphorus contents was prepared on the aviation aluminum alloy. Several characterization and electrochemical techniques were used to characterize the different Ni–P coatings’ morphologies, phase structures, elemental compositions, and corrosion protection. The gradient coating showed good adhesion and high corrosion and wear resistance, enabling the application of aluminum alloy in harsh environments. The results showed that the double zinc immersion was vital in obtaining excellent adhesion (81.2 N). The optimal coating was not peeled and shredded even after bending tests with angles higher than 90°and was not corroded visually after 500 h of neutral salt spray test at 35℃. The high corrosion resistance was attributed to the misaligning of these micro defects in the three different nickel alloy layers and the amorphous structure of the high P content in the outer layer. These findings guide the exploration of functional gradient coatings that meet the high application requirement of aluminum alloy parts in complicated and harsh aviation environments.

Ultra-large aluminum shape casting:Opportunities and challenges

Ultra-large aluminum shape castings have been increasingly used in automotive vehicles,particularly in electric vehicles for light-weighting and vehicle manufacturing cost reduction.As most of them are structural components subject to both quasi-static,dynamic and cyclic loading,the quality and quantifiable performance of the ultra-large aluminum shape castings is critical to their success in both design and manufacturing.This paper briefly reviews some application examples of ultra-large aluminum castings in automotive industry and outlines their advantages and benefits.Factors affecting quality,microstructure and mechanical properties of ultra-large aluminum castings are evaluated and discussed as aluminum shape casting processing is very complex and often involves many competing mechanisms,multi-physics phenomena,and potentially large uncertainties that significantly influence the casting quality and performance.Metallurgical analysis and mechanical property assessment of an ultra-large aluminum shape casting are presented.Challenges are highlighted and suggestions are made for robust design and manufacturing of ultra-large aluminum castings.

Synthesis of Organic-Inorganic Hybrid Aluminum Hypophosphite Microspheres Flame Retardant and Its Flame Retardant Research on Thermoplastic Polyurethane

Aluminum hypophosphite microspheres(AHP) were synthesized by hydrothermal method using NaH2PO2·H2O and AlCl3·6H2O as raw materials, and then the AHP microspheres were polymerized by surface polymerization of micro-nanospheres with cyclic cross-linked poly(cyclotriphosphazene-co-4,4'-sulfonyldiphenol)(PZS). A new organic-inorganic poly(phosphonitrile)-modified aluminum hypophosphite microspheres(PZS-AHP) were synthesized by encapsulation and applied to flame retardant thermoplastic polyurethane(TPU). The microstructure and chemical composition of the PZS-AHP microsphere were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray spectroscopy. The thermal stability of PZS-AHP microsphere was explored with thermogravimetric analysis. Thermogravimetric data indicate that the PZS-AHP microspheres have excellent thermal stability. The thermal and flame-retarding properties of the TPU composites were evaluated by thermogravimetric(TG), limited oxygen index tests(LOI), and cone calorimeter test(CCT). The TPU composite achieved vertical burning(UL-94) V-0 grade and LOI value reached 29.2% when 10 wt% PZS-AHP was incorporated. Compared with those of pure TPU, the peak heat release rate(pHRR) and total heat release(THR) of TPU/10%PZS-AHP decreased by 82.2% and 42.5%, respectively. The results of CCT indicated that PZS-AHP microsphere could improve the flame retardancy of TPU composites.

Improvement of Microstructure and Mechanical Properties of Rapid Cooling Friction Stir-welded A1050 Pure Aluminum

Two-mm thick A1050 pure aluminum plates were successfully joined by conventional and rapid cooling friction stir welding(FSW), respectively. The microstructure and mechanical properties of the welded joints were investigated by electron backscatter diffraction characterization, Vickers hardness measurements, and tensile testing. The results showed that liquid CO_(2) coolant significantly reduced the peak temperature and increased the cooling rate, so the rapidly cooled FSW joint exhibited fine grains with a large number of dislocations. The grain refinement mechanism of the FSW A1050 pure aluminum joint was primarily attributed to the combined effects of continuous dynamic recrystallization, grain subdivision, and geometric dynamic recrystallization. Compared with conventional FSW, the yield strength, ultimate tensile strength, and fracture elongation of rapidly cooled FSW joint were significantly enhanced, and the welding efficiency was increased from 80% to 93%. The enhanced mechanical properties and improved synergy of strength and ductility were obtained due to the increased dislocation density and remarkable grain refinement. The wear of the tool can produce several WC particles retained in the joint, and the contribution of second phase strengthening to the enhanced strength should not be ignored.

Revisiting aluminum current collector in lithium-ion batteries:Corrosion and countermeasures

With the large-scale service of lithium-ion batteries(LIBs),their failures have attracted significant attentions.While the decay of active materials is the primary cause for LIB failures,the degradation of auxiliary materials,such as current collector corrosion,should not be disregarded.Therefore,it is necessary to conduct a comprehensive review in this field.In this review,from the perspectives of electrochemistry and materials,we systematically summarize the corrosion behavior of aluminum cathode current collector and propose corresponding countermeasures.Firstly,the corrosion type is clarified based on the properties of passivation layers in different organic electrolyte components.Furthermore,a thoroughgoing analysis is presented to examine the impact of various factors on aluminum corrosion,including lithium salts,organic solvents,water impurities,and operating conditions.Subsequently,strategies for electrolyte and protection layer employed to suppress corrosion are discussed in detail.Lastly and most importantly,we provide insights and recommendations to prevent corrosion of current collectors,facilitate the development of advanced current collectors and the implementation of next-generation high-voltage stable LIBs.

AP assembled on ultrafine aluminum particle and its application to NEPE propellant

Coating modification is an important way to enhance the reactivity of aluminum powder.In this paper,ammonium perchlorate and aluminum powder were assembled into energetic microunits by liquid deposition method.Spherical particles with AP as shell and ultrafine aluminum powder as the core(Al@AP)were gained.The micromorphology results show that the coated particles are about 5μm,and the coating layer is evenly distributed on the outer surface of aluminum powder,indicating a complete coating.The energetic microunits were implanted into the nitrate ester plasticizing adhesive system(NEPE)as solid phase fillers.The effect of filler on the rheological properties,safety,mechanical properties,thermal reaction and energy properties of the system was analyzed by comparing with the raw aluminum filler.The test results show that the rheological properties,mechanical properties and pressure index of NEPE containing system Al@AP meets the requirements of solid propellant charging.Compared with Al based propellant,the mechanical sensitivity and thermal sensitivity are decreased,the safety is better,and the explosion heat of the propellant is increased by 7.8%.The engine test shows that the specific impulse is increased by 1.2 s.Al@AP can improve the energy output and safety of NEPE propellant,and has potential application prospects in high-energy propellants.

Structure and dynamical properties during solidification of liquid aluminum induced by cooling and compression

The structural transformation from a liquid into a crystalline solid is an important subject in condensed matter physics and materials science. In the present study, first-principles molecular dynamics calculations are performed to investigate the structure and properties of aluminum during the solidification which is induced by cooling and compression. In the cooling process and compression process, it is found that the icosahedral short-range order is initially enhanced and then begin to decay, the face-centered cubic short-range order eventually becomes dominant before it transforms into a crystalline solid.

Impact of cooling rate on exfoliation corrosion resistance of a Li-containing 7xxx aluminum alloy

The impact of cooling rate after solution heat treatment on exfoliation corrosion resistance of a Li-containing 7xxx aluminum alloy was investigated by accelerated immersion and electrochemical impedance spectroscopy test,optical microscope,electron backscatter diffraction and scanning transmission electron microscope.With the decrease of cooling rate from 1700℃/s to 4℃/s,exfoliation corrosion resistance of the aged specimens decreases with rating changing from EA to EC and the maximum corrosion depth increasing from about 169.4μm to 632.1μm.Exfoliation corrosion tends to develop along grain boundaries in the specimens with cooling rates higher than about 31℃/s and along both grain boundaries and sub-grain boundaries in the specimens with lower cooling rates.The reason has been discussed based on the changes of the microstructure and microchemistry at grain boundaries and sub-grain boundaries due to slow cooling.

Effect of combination of ultraviolet radiation and biocide on fungal-induced corrosion of high-strength 7075 aluminum alloy

The effect of ultraviolet(UV)radiation and biocide benzalkonium chloride(BKC)on fungal-induced corrosion of AA7075 induced by Aspergillus terreus(A.terreus)was deeply studied using analysis of biological activity,surface analysis,and electrochemical measurements.Results demonstrated that the planktonic and sessile spore concentrations decline by more than two orders of magnitude when UV radiation and BKC are combinedly used compared with the control.UV radiation can inhibit the biological activity of A.terreus and influence the stability of passive film of AA7075.Except for direct disinfection,the physical adsorption of BKC on the specimen can effectively inhibit the attachment of A.terreus.The combination of UV radiation and BKC can much more effectively inhibit the corrosion of AA,especially pitting corrosion,due to their synergistic effect.The combined application of UV radiation and BKC can be a good method to effectively inhibit fungal-induced corrosion.

Reversible aqueous aluminum metal batteries enabled by a water-in-salt electrolyte

Aluminum(Al),the most abundant metallic element on the earth crust,has been reckoned as a promising battery material for its the highest theoretical volume capacity(8046 mAh cm^(-3)).Being rechargeable in ionic liquid electrolytes,however,the Al anode and battery case suffer from corrosion.On the other hand,Al is irreversible in aqueous electrolyte with severe hydrogen evolution reaction.Here,we demonstrate a water-in-salt aluminum ion electrolyte(WISE)based on Al and lithium salts to tackle the above challenges.In the WISE system,water molecules can be confined within the Li^(+)solvation structures.This diminished Al^(3+)-H_(2)O interaction essentially eliminates the hydrolysis effect,effectively protecting Al anode from corrosion.Therefore,long-term Al plating/stripping can be realized.Furthermore,two types of high-performance full batteries have been demonstrated using copper hexacyanoferrate(CuHCF,a Prussian Blue Analogues)and LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM)as cathodes.The reversibility of Al anode laid the foundation for low cost rechargeable batteries suffering for large-scale energy storage.Broader context:Al batteries are expected to become a safe and sustainable alternative to lithium batteries.For decades,chase for a feasible Al secondary battery has not been successful.The key challenge is to find suitable cathode and electrolyte materials,together with which Al anode battery can function reversibly.Currently,fatal drawbacks have impeded the practical application of Al metal batteries(AMBs),such as sustained corrosion of Al anode and battery case in ionic liquid electrolytes,irreversibility issues as well as severe hydrogen evolution reaction during cycling in aqueous electrolyte.Therefore,electrolyte and their electrochemical kinetics play a vital role in the performance and environmental operating limitations of high-energy Al metal batteries.In this work,we demonstrate a nearly neutral Al ion water-in-salt electrolyte(WISE)to tackle the above challenges.The WISE shows excellent stability in the open atmosphere.The distinct solvation-sheath structure of Al^(3+)in the WISE system would protect Al metal anodes from corrosion and eliminate hydrogen evolution reaction effectively,further promoting the reversibility of Al metal anodes with dendrite-free morphology.Moreover,such a WISE exhibits superior compatibility with LiNi_(0.3)Co_(0.3)Mn_(0.3)O_(2)(NCM)and copper hexacyanoferrate(CuHCF)cathodes and long-term stabilities with high coulombic efficiency(CE)can be attained for full batteries with the WISE.The approach in this study can furnish an opportunity to develop reversible AMBs and lay the foundation for other potential multivalent-metalbased secondary batteries suffering from interface passivation and poor reversibility,which suggest the promise of multivalent metal batteries and their applications in large-scale energy storage.

Effect of quenching cooling rate on residual stress and microstructure evolution of 6061 aluminum alloy

In this study,the cooling rate was manipulated by quenching with water of different temperatures(30,60 and 100℃).Surface and internal residual stresses in the quenched 6061 aluminum alloy samples were measured using hole-drilling and crack compliance methods,respectively.Then,the processability of the quenched samples was evaluated at cryogenic temperatures.The mechanical properties of the as-aged samples were assessed,and microstructure evolution was analyzed.The surface residual stresses of samples W30℃,W60℃and W100℃is−178.7,−161.7 and−117.2 MPa,respectively along x-direction,respectively;and−191.2,−172.1 and−126.2 MPa,respectively along y-direction.The sample quenched in boiling water displaying the lowest residual stress(~34%and~60%reduction in the surface and core).The generation and distribution of quenching residual stress could be attributed to the lattice distortion gradient.Desirable plasticity was also exhibited in the samples with relatively low quenching cooling rates at cryogenic temperatures.The strengthes of the as-aged samples are 291.2 to 270.1 MPa as the quenching water temperature increase from 30℃to 100℃.Fine and homogeneous β"phases were observed in the as-aged sample quenched with boiling water due to the clusters and Guinier-Preston zones(GP zones)premature precipitated during quenching process.

Simulation of Dynamic Recrystallization in 7075 Aluminum Alloy Using Cellular Automaton

The evolution of microstructure during hot deformation is key to achieving good mechanical properties in aluminum alloys.We have developed a cellular automaton(CA) based model to simulate the microstructural evolution in 7075 aluminum alloy during hot deformation.Isothermal compression tests were conducted to obtain material parameters for 7075 aluminum alloy,leading to the establishment of models for dislocation density,nucleation of recrystallized grains,and grain growth.Integrating these aspects with grain topological deformation,our CA model effectively predicts flow stress,dynamic recrystallization(DRX) volume fraction,and average grain size under diverse deformation conditions.A systematic comparison was made between electron back scattered diffraction(EBSD) maps and CA model simulated under different deformation temperatures(573 to 723 K),strain rates(0.001 to 1 s^(-1)),and strain amounts(30% to 70%).These analyses indicate that large strain,high temperature,and low strain rate facilitate dynamic recrystallization and grain refinement.The results from the CA model show good accuracy and predictive capability,with experimental error within 10%.

Cryogenic springback of 2219-W aluminum alloy sheet through V-shaped bending

A V-shaped bending device was established to evaluate the effects of temperature and bending fillet radius on springback behavior of 2219-W aluminum alloy at cryogenic temperatures.The cryogenic springback mechanism was elucidated through mechanical analyses and numerical simulations.The results indicated that the springback angle at cryogenic temperatures was greater than that at room temperature.The springback angle increased further as the temperature returned to ambient conditions,attributed to the combined effects of the “dual enhancement effect” and thermal expansion.Notably,a critical fillet radius made the springback angle zero for 90° V-shaped bending.The critical fillet radius at cryogenic temperatures was smaller than that at room temperature,owing to the influence of temperature variations on the bending moment ratio between the forward bending section at the fillet and the reverse bending section of the straight arm.

Preparation and properties of high-energy-density aluminum/boroncontaining gelled fuels

Energetic nanofluid fuel has caught the attention of the field of aerospace liquid propellant for its high energy density(HED), but it suffers from the inevitable solid-liquid phase separation problem. To resolve this problem, herein we synthesized the high-Al-/B-containing(up to 30%(mass)) HED gelled fuels, with low-molecular-mass organic gellant Z, which show high net heat of combustion(NHOC), density, storage stability, and thixotropic properties. The characterizations indicate that the application of energetic particles to the gelled fuels obviously destroys their fibrous network structures but can provide the new particle-gellant gelation microstructures, resulting in the comparable stability between 1.0%(mass) Z/JP-10 + 30%(mass) Al or B and pure JP-10 gelled fuel. Moreover, the gelled fuels with high-content Al or B exhibit high shear-thinning property, recovery capability, and mechanical strength, which are favorable for their storage and utilization. Importantly, the prepared 1.0%(mass) Z/JP-10 + 30%(mass) B(or 1.0%(mass) Z/JP-10 + 30%(mass) Al) shows the density and NHOC 1.27 times(1.30) and 1.43 times(1.21)higher than pure JP-10, respectively. This work provides a facile and valid approach to the manufacturing of HED gelled fuels with high content of energetic particles for gel propellants.

Cross-section distortion and springback characteristics of double-cavity aluminum profile in force controlled stretch-bending

3D elastic-plastic FE model for simulating the force controlled stretch-bending process of double-cavity aluminum profile was established using hybrid explicit−implicit solvent method.Considering the computational accuracy and efficiency,the optimal choices of numerical parameters and algorithms in FE modelling were determined.The formation mechanisms of cross-section distortion and springback were revealed.The effects of pre-stretching,post-stretching,friction,and the addition of internal fillers on forming quality were investigated.The results show that the stress state of profile in stretch-bending is uniaxial with only a circumferential stress.The stress distribution along the length direction of profile is non-uniform and the maximum tensile stress is located at a certain distance away from the center of profile.As aluminum profile is gradually attached to bending die,the distribution characteristic of cross-section distortion along the length direction of profile changes from V-shape to W-shape.After unloading the forming tools,cross-section distortion decreases obviously due to the stress relaxation,with a maximum distortion difference of 13%before and after unloading.As pre-stretching and post-stretching forces increase,cross-section distortion increases gradually,while springback first decreases and then remains unchanged.With increasing friction between bending die and profile,cross-section distortion slightly decreases,while springback increases.Cross-section distortion decreases by 83%with adding PVC fillers into the cavities of profile,while springback increases by 192.2%.

Modeling of recrystallization behaviour of AA6xxx aluminum alloy during extrusion process

An innovative approach was introduced for the development of a AA6063 recrystallization model.This method incorporated a regression-based technique for the determination of material constants and introduced novel equations for assessing the grain size evolution.Calibration and validation of this methodology involved a combination of experimentally acquired microstructural data from the extrusion of three different AA6063 profiles and results from the simulation using the Qform Extrusion UK finite element code.The outcomes proved the agreement between experimental findings and numerical prediction of the microstructural evolution.The trend of the grain size variation based on different process parameters was accurately simulated,both after dynamic and static recrystallization,with an error of less than 25% in almost the whole sampling computations.

Effect of Heat Treatment on Microstructure and Mechanical Properties of Multiscale SiC_p Hybrid Reinforced 6061 Aluminum Matrix Composites

The performance of solid solution aging treatment on aluminum matrix composites prepared by powder metallurgy and reinforced with 6061 aluminum alloy powder as matrix;meanwhile, nano silicon carbide particles(nm Si Cp), submicron silicon carbide particles(1 μm Si Cp) and Ti particles were studied. The Al/Si Cp composite powder was prepared by high-energy ball milling, and then cold-pressed, sintered, hotextruded, and then heat-treated with different solution temperatures and aging times for the extruded composites. Optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy(EDS), X-ray diffractometer(XRD) and extrusion testing were used to analyze and test the microstructure and mechanical properties of aluminum matrix composites. The results show that after the multi-stage solid solution at 530 ℃×2 h+535 ℃×2 h+540 ℃×2 h, the particles are mainly equiaxed grains and uniformly distributed. There is no reinforcement agglomeration, and the surface is dense and the insoluble phase is basically dissolved. In the matrix, the strengthening effect is good, and the hardness and compressive strength are 179.43 HV and 680.42 MPa, respectively. Under this solution process, when the aluminum matrix composites are aged at 170 ℃ for 10 h, the hardness and compressive strength can reach their peaks and increase to 195.82 HV and 721.48 MPa, respectively.

Selection of shaped charges parameters for producing aluminum particles with velocities in the range of 2.5-16 km/s

Testing rocket and space technology objects in ground conditions for resistance to the impact of meteoroids and fragments of space debris can be carried out using shaped charges. To substantiate the design parameters of shaped charges that ensure the formation of aluminum particles in a wide velocity range(from 2.5 to 16 km/s), numerical modeling of the formation process was carried out within the framework of a two-dimensional axisymmetric problem of continuum mechanics using three different computing codes to increase the reliability of the results. The calculations consider shaped charges with a diameter of 20-100 mm with aluminum liners of various shapes. It is shown that the formation of particles with velocities close to the lower limit of the considered range is ensured by gently sloping segmental liners of degressive thickness. To form higher-velocity particles with velocities over 5 km/s, it is proposed to use combined liners, the jet-forming part of which has the shape of a hemisphere of constant thickness or the shape of a semi-ellipsoid or semi-superellipsoid of rotation of degressive thickness.

Microstructure and properties of 35 kg large aluminum alloy flywheel housing components formed by squeeze casting with local pressure compensation

The squeeze casting method with local pressure compensation was proposed to form a flywheel housing component with a weight of 35 kg.The numerical simulation,microstructure observation and phase characterization were performed,and the influence of local pressure compensation on feeding of thick-wall position,microstructure and mechanical properties of the formed components were discussed.Results show that the molten metal keeps a good fluidity and the filling is complete during the filling process.Although the solidification at thick-wall positions of the mounting ports is slow,the local pressure compensation effectively realizes the local forced feeding,significantly eliminating the shrinkage cavity defects.In the microstructure of AlSi9Mg alloy,α-Al primarily consists of fragmented dendrites and rosette grains,while eutectic Si predominantly comprises needles and short rods.The impact of local pressure compensation on strength is relatively minimal,yet its influence on elongation is considerable.Following local pressure compensation,the average elongation at the compensated areas is 9.18%,which represents a 44.90%higher than that before compensation.The average tensile strength is 209.1 MPa,and the average yield strength is 100.6 MPa.The local pressure compensation can significantly reduce or even eliminate the internal defects in the 35 kg large-weight components formed by squeeze casting.