Role of alloying and heat treatment on microstructure and mechanical properties of cast Al-Li alloys:A review

Due to the prominent advantages of low density,high elastic modulus,high specific strength and specific stiffness,cast Al-Li alloys are suitable metallic materials for manufacturing complex large-sized components and are ideal structural materials for aerospace,defense and military industries.On the basis of the microstructural characteristics of cast Al-Li alloys,exploring the role of alloying and micro-alloying can stabilize their dominant position and further expand their application scope.In this review,the development progress of cast Al-Li alloys was summarized comprehensively.According to the latest research highlights,the influence of alloying and heat treatment on the microstructure and mechanical properties was systematically analyzed.The potential methods to improve the alloy performance were concluded.In response to the practical engineering requirements of cast Al-Li alloys,the scientific challenges and future research directions were discussed and prospected.

Microstructure and Hot Tearing Sensitivity Simulation and Parameters Optimization for the Centrifugal Casting of Al-Cu Alloy

Four typical theories on the formation of thermal tears:strength,liquid film,intergranular bridging,and solidifica-tion shrinkage compensation theories.From these theories,a number of criteria have been derived for predicting the formation of thermal cracks,such as the stress-based Niyama,Clyne,and RDG(Rapaz-Dreiser-Grimaud)criteria.In this paper,a mathematical model of horizontal centrifugal casting was established,and numerical simulation analysis was conducted for the centrifugal casting process of cylindrical Al-Cu alloy castings to investigate the effect of the centrifugal casting process conditions on the microstructure and hot tearing sensitivity of alloy castings by using the modified RDG hot tearing criterion.Results show that increasing the centrifugal rotation and pouring speeds can refine the microstructure of the alloy but increasing the pouring and mold preheating temperatures can lead to an increase in grain size.The grain size gradually transitions from fine grain on the outer layer to coarse grain on the inner layer.Meanwhile,combined with the modified RDG hot tearing criterion,the overall distribution of the castings’hot tearing sensitivity was analyzed.The analysis results indicate that the porosity in the middle region of the casting was large,and hot tearing defects were prone to occur.The hot tearing tendency on the inner side of the casting was greater than that on the outer side.The effects of centrifugal rotation speed,pouring temperature,and preheating temperature on the thermal sensitivity of Al-Cu alloy castings are summarized in this paper.This study revealed that the tendency of alloy hot cracking decreases with the increase of the centrifugal speed,and the maximum porosity of castings decreases first and then increases with the pouring temperature.As the preheating temperature increases,the overall maximum porosity of castings shows a decreasing trend.

Thin-walled and large-sized magnesium alloy die castings for passenger car cockpit:Application,materials,and manufacture

In order to effectively reduce energy consumption and increase range mile,new energy vehicles represented by Tesla have greatly aroused the application of integrated magnesium(Mg)alloy die casting technology in automobiles.Previously,the application of Mg alloys in automobiles,especially in automotive cockpit components,is quite extensive,while it has almost disappeared for a period of time due to its relatively high cost,causing a certain degree of information loss in the application technology of Mg alloy parts in automobiles.The rapid development of automotive technology has led to a higher requirement for the automotive components compared with those traditional one.Therefore,whatever the components themselves,or the Mg alloy materials and die casting process have to face an increasing challenge,needing to be upgraded.In addition,owing to its high integration characteristics,the application of Mg alloy die casting technology in large-sized and thin-walled automotive parts has inherent advantages and needs to be expanded urgently.Indeed,it necessitates exploring advance Mg alloys and new product structures and optimizing die casting processes.This article summarizes and analyzes the development status of thin-walled and large-sized die casting Mg alloy parts in passenger car cockpit and corresponding material selection methods,die casting processes as well as mold design techniques.Furthermore,this work will aid researchers in establishing a comprehensive understanding of the manufacture of thin-walled and large-sized die casting Mg alloy parts in automobile cockpit.It will also assist them in developing new Mg alloys with improved comprehensive performance and new processes to meet the high requirements for die casting automotive components.

Experimental observations on the nonproportional multiaxial ratchetting of cast AZ91 magnesium alloy at room temperature

The nonproportional multiaxial ratchetting of cast AZ91 magnesium (Mg) alloy was examined by performing a sequence of axial-torsional cyclic tests controlled by stress with various loading paths at room temperature (RT).The evolutionary characteristics and path dependence of multiaxial ratchetting were discussed.Results illustrate that the cast AZ91 Mg alloy exhibits considerable nonproportional additional softening during cyclic loading with multiple nonproportional multiaxial loading paths;multiaxial ratchetting presents strong path dependence,and axial ratchetting strains are larger under nonproportional loading paths than under uniaxial and proportional45°linear loading paths;multiaxial ratchetting becomes increasingly pronounced as the applied stress amplitude and axial mean stress increase.Moreover,stress-strain curves show a convex and symmetrical shape in axial/torsional directions.Multiaxial ratchetting exhibits quasi-shakedown after certain loading cycles.The abundant experimental data obtained in this work can be used to develop a cyclic plasticity model of cast Mg alloys.

Research progress on semi-continuous casting of magnesium alloys under external field

High-performance magnesium alloys are moving towards a trend of being produced on a large scale and in an integrated manner.The foundational key to their successful production is the high-quality cast ingots.Magnesium alloys produced through the conventional semi-continuous casting process inevitably contain casting defects,which makes it challenging to manufacture high-quality ingots.The integration of external field assisted controlled solidification technology,which combines physical fields such as electromagnetic and ultrasonic fields with traditional semi-continuous casting processes,enables the production of high-quality magnesium alloy ingots characterized by a homogeneous microstructure and absence of cracks.This article mainly summarizes the technical principles of those external field assisted casting process.The focus is on elaborating the refinement mechanism of different types of electromagnetic fields,ultrasonic fields,and combined physical fields during the solidification of magnesium alloys.Finally,the development prospects of producing highquality magnesium alloy ingots through semi-continuous casting under the external field were discussed.

I-DCGAN and TOPSIS-IFP:A simulation generation model for radiographic flaw detection images in light alloy castings and an algorithm for quality evaluation of generated images

The intelligent detection technology driven by X-ray images and deep learning represents the forefront of advanced techniques and development trends in flaw detection and automated evaluation of light alloy castings.However,the efficacy of deep learning models hinges upon a substantial abundance of flaw samples.The existing research on X-ray image augmentation for flaw detection suffers from shortcomings such as poor diversity of flaw samples and low reliability of quality evaluation.To this end,a novel approach was put forward,which involves the creation of the Interpolation-Deep Convolutional Generative Adversarial Network(I-DCGAN)for flaw detection image generation and a comprehensive evaluation algorithm named TOPSIS-IFP.I-DCGAN enables the generation of high-resolution,diverse simulated images with multiple appearances,achieving an improvement in sample diversity and quality while maintaining a relatively lower computational complexity.TOPSIS-IFP facilitates multi-dimensional quality evaluation,including aspects such as diversity,authenticity,image distribution difference,and image distortion degree.The results indicate that the X-ray radiographic images of magnesium and aluminum alloy castings achieve optimal performance when trained up to the 800th and 600th epochs,respectively.The TOPSIS-IFP value reaches 78.7%and 73.8%similarity to the ideal solution,respectively.Compared to single index evaluation,the TOPSIS-IFP algorithm achieves higher-quality simulated images at the optimal training epoch.This approach successfully mitigates the issue of unreliable quality associated with single index evaluation.The image generation and comprehensive quality evaluation method developed in this paper provides a novel approach for image augmentation in flaw recognition,holding significant importance for enhancing the robustness of subsequent flaw recognition networks.

Characteristics and distribution of microstructures in high pressure die cast alloys with X-ray microtomography:A review

Al and Mg alloy high pressure die castings(HPDC)are increasingly used in automotive industries.The microstructures in the castings have decisive effect on the casting mechanical properties,in which the microstructure characteristics are fundamental for the investigation of the microstructure-property relation.During the past decade,the microstructure characteristics of HPDC Al and Mg alloys,especially micro-pores andα-Fe,have been investigated from two-dimensional(2D)to threedimensional with X-ray micro-computed tomography(μ-CT).This paper provides an overview of the current understanding regarding the 3D characteristics and formation mechanisms of microstructures in HPDC alloys,their spatial distributions,and the impact on mechanical properties.Additionally,it outlines future research directions for the formation and control of heterogeneous microstructures in HPDC alloys.

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.

Effect of slow shot speed on externally solidified crystal,porosity and tensile property in a newly developed high-pressure die-cast Al-Si alloy

The effect of slow shot speed on externally solidified crystal(ESC),porosity and tensile property in a newly developed high-pressure die-cast Al-Si alloy was investigated by optical microscopy(OM),scanning electron microscopy(SEM)and laboratory computed tomography(CT).Results showed that the newly developed AlSi9MnMoV alloy exhibited improved mechanical properties when compared to the AlSi10MnMg alloy.The AlSi9MnMoV alloy,which was designed with trace multicomponent additions,displays a notable grain refining effect in comparison to the AlSi10MnMg alloy.Refining elements Ti,Zr,V,Nb,B promote heterogeneous nucleation and reduce the grain size of primaryα-Al.At a lower slow shot speed,the large ESCs are easier to form and gather,developing into the dendrite net and net-shrinkage.With an increase in slow shot speed,the size and number of ESCs and porosities significantly reduce.In addition,the distribution of ESCs is more dispersed and the net-shrinkage disappears.The tensile property is greatly improved by adopting a higher slow shot speed.The ultimate tensile strength is enhanced from 260.31 MPa to 290.31 MPa(increased by 11.52%),and the elongation is enhanced from 3.72%to 6.34%(increased by 70.52%).

Mechanical Evaluation of AZ80 Magnesium Alloy in Cast Wrought Form

Wrought magnesium alloy AZ80 with a thick section of 20 mm was prepared by squeeze casting (SC) and permanent steel mold casting (PSMC). The porosity measurements of the SC and PSMC depicted that SC AZ80 had a pore content of 0.52%, which was 77% lower than 2.21% of PSMC AZ80 counterpart. The YS, UTS, ef, E and strengthening rate of cast AZ80 were determined by mechanical pulling. The engineering stress versus strain bended lines showed that SC AZ80 had a YS of 84.7 MPa, a UTS of 168.2 MPa, 5.1% in ef, and 25.1 GPa in modulus. But, the YS, UTS and ef of the PSMC AZ80 specimen were only 71.6 MPa, 109.0 MPa, 1.9% and 21.9 GPa. The findings of the mechanical pulling evidently depicted that the YS, UTS, ef and E of SC AZ80 were 18%, 54%, 174% and 15% higher than PSMC counterpart. The computed resilience and toughness suggested that the SC AZ80 exhibited greater resistance to tensile loads during elastic deformation and possessed higher capacity to absorb energy during plastic deformation compared to the PSMC AZ80. At the beginning of permanent change, the strengthening rate of SC AZ80 was 10,341 MPa, which was 9% greater than 9489 MPa of PSMC AZ80. The high mechanical characteristics of SC AZ80 should be primarily attributed to its low porosity level. .

A comparative study on Sn macrosegregation behavior of ternary Al-Sn-Cu alloys prepared by gravity casting and squeeze casting

A comprehensive study on Sn macrosegregation behavior in ternary Al-Sn-Cu alloys was carried out by comparative analysis between gravity casting and squeeze casting samples.The microstructure and Sn distribution of the castings were characterized by metallography,scanning electron microscopy(SEM),energy-dispersive X-ray(EDX)spectroscopy,and a direct reading spectrometer.Results show that there are obvious differences in Sn morphology between gravity casting and squeeze casting alloys.Under squeeze casting condition,the grain size of the casting is smaller and the distribution ofβ(Sn)is uniform.This effectively reduces the segregation of triangular grain boundary as well as the segregation of Sn.The segregation types of Sn in gravity casting and squeeze casting samples are obviously different.The upper surfaces of gravity casting samples show severe negative segregation,while all the lower surfaces have positive segregation.Compared with gravity casting,squeeze casting solidifies under isostatic pressure.Due to the direct contact between the upper surface of the casting and the mold,the casting solidifies faster under higher undercooling degree and pressure.Consequently,the uniform distribution of Sn reduces the segregation phenomenon on the surface of the casting.

Recent advances on grain refinement of magnesium rare-earth alloys during the whole casting processes:A review

High-performance cast magnesium rare-earth(Mg-RE) alloys are one of the most important materials among all developed Mg alloy families, and have shown great potential in military and weapons, aerospace and aviation, orthopedic implants, etc. Controlling grain size and distribution of it is key to the promising mechanical performance of Mg-RE alloy casting components. During the casting of a real component, nearly every procedure in the fabrication process will influence the grain refinement effect. The procedure may include and may not be limited to the chemical inoculations, possibly applied physical fields, the interfere between grain refiner and purifications, and the casting techniques with different processing parameters. This paper reviews the recent advances and proposed future developments in these categories on grain refinement of cast Mg-RE alloys. The review will provide insights for the future design of grain refinement techniques,the choosing of processing parameters, and coping strategies for the failure of coarsening for cast Mg-RE components with high quality and good performance.

Effect of Ti and Ce Microalloy on Microstructure and Properties of Al-Si-Cu-Zr-Sr Cast Aluminum Alloy

The effect of Ti and Ce microalloying on the mechanical properties of Al-9Si-3.5Cu-0.2Zr-0.1Sr cast aluminum alloy was investigated,and it was hoped that the cast aluminum alloy with excellent comprehensive properties could be obtained.On the basis of Zr-Sr microalloyed cast aluminum alloy(Al-9Si-3.5Cu-0.2Zr-0.1Sr),the effects of 0.2Zr-0.1Sr-0.16Ti ternary microalloying and 0.2Zr-0.1Sr-0.16Ti-0.1Ce quaternary microalloying on the microstructure and properties of the alloy were investigated.The experimental results show that compared with Zr-Sr microalloying,Zr-Sr-Ti microalloying and Zr-Sr-Ti-Ce microalloying can effectively refine the microstructure,improve the modification effect of Si phase,and promote the improvement of Al_(2)Cu phase,thus improving the properties.The higher the degree of microalloying,the hardness is gradually increasing,but the electrical conductivity is gradually decreasing.Zr-Sr-Ti microalloying can increase the tensile strength of the alloy to 400.07 MPa and the elongation to 9.5%.Zr-Sr-Ti-Ce microalloying do not continue to improve the properties of the alloy,and the tensile strength and elongation after fracture decrease to a certain extent due to the addition of Ce.Therefore,the best comprehensive properties can be obtained by ZrSr-Ti microalloying(Al-9Si-3.5Cu-0.2Zr-0.1Sr-0.16Ti).

Experimental investigation on uniaxial cyclic plasticity of cast AZ91 magnesium alloy

The uniaxial cyclic plasticity of cast AZ91 magnesium(Mg) alloy was investigated by conducting a series of cyclic straining and stressing tests at room temperature, and a unique cyclic plasticity(especially for ratchetting) and its physical nature were revealed. The experimental results demonstrate that the cast AZ91 Mg alloy behaviors tension-compression symmetry, because the dislocation slipping and twinning occur during both the tensile and compressive deformations;although the cast AZ91 alloy presents a certain pseudo-elastic behavior during unloading due to the detwinning, there is no obvious S-shaped asymmetric hysteresis loop like that of wrought Mg alloy in the cyclic tensile-compressive tests, and an obvious cyclic hardening is observed;moreover, the ratchetting of the cast AZ91 alloy presented in the cyclic stressing tests depends remarkably on the prescribed mean stress and stress amplitude, but slightly changes with the stress rate, and the evolution of responding peak/valley strain greatly differs from that of wrought Mg alloys and stainless steels. This work provides rich experimental data for establishing the constitutive model of cast Mg alloys.

Effect of secondary aging on microstructure and properties of cast Al-Cu-Mg alloy

To obtain better comprehensive properties of cast Al-Cu-Mg alloys,the secondary aging(T6I6)process(including initial aging,interrupted aging and re-aging stages)was optimized by an orthogonal method.The microstructures of the optimized Al-Cu-Mg alloy were observed by means of scanning electron microscopy and transmission electron microscopy,and the properties were investigated by hardness measurements,tensile tests,exfoliation corrosion tests,and intergranular corrosion tests.Results show that the S phase andθ’phase simultaneously exist in the T6I6 treated alloy.Appropriately increasing the temperature of the interrupted aging in the T6I6 process can improve the mechanical properties and corrosion resistance of Al-Cu-Mg alloy.The optimal comprehensive properties(tensile strength of 443.6 MPa,hardness of 161.6 HV)of the alloy are obtained by initial aging at 180℃for 2 h,interrupted aging at 90℃for 30 min,and re-aging at 170℃for 4 h.

Effects of magnesium and copper additions on tensile properties of Al-Si-Cr die casting alloy under as-cast and T5 conditions

Aluminum high pressure die casting(HPDC)technology has evolved in the past decades,enabling stronger and larger one-piece casting with significant part consolidation.It also offers a higher design freedom for more mass-efficient thin-walled body structures.For body structures that require excellent ductility and fracture toughness to be joined with steel sheet via self-piercing riveting(for instance,shock towers and hinge pillars,etc.),a costly T7 heat treatment comprising a solution heat treatment at elevated temperatures(450℃-500℃)followed by an over-ageing heat treatment is needed to optimize microstructure for meeting product requirement.To enable cost-efficient mass production of HPDC body structures,it is important to eliminate the expensive T7 heat treatment without sacrificing mechanical properties.Optimizing die cast alloy chemistry is a potential solution to improve fracture toughness and ductility of the HPDC components.The present study intends to tailor the Mg and Cu additions for a new Al-Si-Cr type die casting alloy(registered as A379 with The Aluminum Association,USA)to achieve the desired tensile properties without using T7 heat treatment.It was found that Cu addition should be avoided,as it is not effective in enhancing strength while degrades tensile ductility.Mg addition is very effective in improving strength and has minor impact on tensile ductility.The investigated Al-Si-Cr alloy with a nominal composition of Al-8.5wt.%Si-0.3wt.%Cr-0.2wt.%Fe shows comparable tensile properties with the T7 treated AlSi10MnMg alloy which is currently used for manufacturing shock towers and hinge pillars.

基于ProCAST的一模多腔YL112铝合金压铸件数值模拟及工艺优化

针对YL112压铸铝合金一模多铸产品的组织性能均一性需求,采用ProCAST软件对典型一模多铸工艺进行模拟,比较了两种不同充型顺序的压铸方案。结果表明:基于顺序凝固一模多腔压铸件由于充型与凝固过程的温度场分布不均,导致近浇口端铸件出现明显缩松缩孔缺陷,造成铸件性能均一性差。后续采用等流程浇注系统,实现一模多腔铸件同时充型凝固过程,改善了铸件温度场分布,减少了工艺缺陷。经过实际生产验证,获得了组织性能均一性好的压铸件。

Solidification microstructure of Ti-43Al alloy by twin-roll strip casting

As a near-net-shape technology,the twin-roll strip casting(TRC)process can be considered to apply to the fabrication of TiAl alloy sheets.However,the control of the grain distribution is very important in strip casting because the mechanical properties of strips are directly determined by the solidification microstructure.A three-dimensional(3D)cellular automation finite-element(CAFE)model based on ProCAST software was established to simulate the solidification microstructure of Ti-43Al alloy.Then,the influence of casting temperature and the maximum nucleation density(nmax)on the solidification microstructure was investigated in detail.The simulation results provide a good explanation and prediction for the solidification microstructure in the molten pool before leaving the kissing point.Experimental and simulated microstructure show the common texture<001>orientation in the columnar grains zone.Finally,the microstructure evolution of the Ti-43Al alloy was analyzed and the solidification phase transformation path during the TSC process was determined,i.e.,L→L+β→β→β+α→α+γ+β/B2 phase under a faster cooling rate and L→L+β→β→β+α→γ+lamellar(α_(2)+γ)+β/B2 phase under a slower cooling rate.

Effect of Ti content on microstructures and mechanical properties of cast Al-2Li-2Cu-0.5Mg alloy

Ti is regarded as one of the promising grain refiners in cast Al-Li-Cu alloys,but few research works have been done on its independent role.In this study,the effect of Ti on the microstructure evolution and mechanical properties of cast Al-2Li-2Cu-0.5Mg base alloy was investigated.The results revealed that the grains can be prominently refined with the increase of Ti addition.After adding Ti,high density TiB_(2)-Al_(3)Ti composite particles with a low lattice misfit form as heterogeneous nucleation sites for the α-Al matrix.δ’(Al3Li) and T_(1)(Al_(2)CuLi) precipitates that provide enhanced strength are dominated in the alloys after T6 aging treatment.The average size of both δ’ and half-width of δ’-precipitation free zone(PFZ) decreases gradually with the increase of Ti content.This is because the higher binding energy between Ti atoms and vacancies limits the diffusion efficiency of Li atoms,and thus results in a higher ductility.Additionally,no nano-sized Al_(3)Ti or core-shell structure of Al_(3)(Li,Ti) particles are found.The tensile property test results indicate that the Al-2Li-2Cu-0.5Mg alloy achieves optimal properties after aging at 175 °C for 32 h when 0.15wt.% Ti is added.It exhibits a yield strength of 352±5 MPa,an ultimate tensile strength of 423±6 MPa,and an elongation of(3±0.4)%.These findings are expected to offer a reliable theoretical guidance for the industrial composition design of the Al-Li-Cu series cast alloys.

Microstructure and mechanical properties of Co-28Cr-6Mo-0.22C investment castings by current solution treatment

This study examined the impact of current solution treatment on the microstructure and mechanical properties of the Co-28Cr-6Mo-0.22C alloy investment castings.The findings reveal that the current solution treatment significantly promotes the dissolution of carbides at a lower temperature.The optimal conditions for solution treatment are determined as a solution temperature of 1,125°C and a holding time of 5.0 min.Under these parameters,the size and volume fraction of precipitated phases in the investment castings are measured as6.2μm and 1.1vol.%.The yield strength,ultimate tensile strength,and total elongation of the Co-28Cr-6Mo-0.22C investment castings are 535 MPa,760 MPa,and 12.6%,respectively.These values exceed those obtained with the conventional solution treatment at 1,200°C for 4.0 h.The findings suggest a phase transformation of M_(23)C_(6)→σ+C following the current solution treatment at 1,125°C for 5.0 min.In comparison,the traditional solution treatment at 1,200°C for 4.0 h leads to the formation of M_(23)C_(6)and M_(6)C carbides.It is noteworthy that the non-thermal effect of the current during the solution treatment modifies the free energy of both the matrix and precipitation phase.This modification lowers the phase transition temperature of the M_(23)C_(6)→σ+C reaction,thereby facilitating the dissolution of carbides.As a result,the current solution treatment approach achieves carbide dissolution at a lower temperature and within a significantly shorter time when compared to the traditional solution treatment methods.