Relationship between elements migration ofα-AlFeMnSi phase and micro-galvanic corrosion sensitivity of Al-Zn-Mg alloy

First principles calculations and scanning Kelvin probe force microscopy(SKPFM)were used to investigate the effect of elements migration ofα-AlFeMnSi phase on micro-galvanic corrosion behavior of Al-Zn-Mg alloy.The simulation results showed that the average work function difference between theα-AlFeMnSi phase and Al matrix decreased from 0.232 to 0.065 eV due to the synchronous migration of elements Fe-Mn-Si.Specifically,as the elements Fe-Si migration during the extrusion process,the average Volta potential difference detected by SKPFM between theα-AlFeMnSi phase and Al matrix dropped down to 432.383 mV from 648.370 mV.Thus,the elements migration reduced the micro-galvanic corrosion sensitivity of Al-Zn-Mg alloy.To reach the calculated low micro-galvanic tendency betweenα-AlFeMnSi phase and Al matrix,the diffusion of Mn should be promoted during extruding process.

Ageing Effect on Hardness and Microstructure of Al-Zn-Mg Alloys

Experimental results of the investigation on the hardness of two Al-Zn-Mg alloys [Al-10.0 Zn-4.0 Mg and Al-8.5 Zn-3.0 Mg (wt pct)] aged in the temperature range 60～310℃ for different intervals of time from 1/4 h to 168 h are presented. Both the alloys were found to show identical behaviour of hardness with ageing time. Alloy with higher Zn and Mg content had higher hardness than the alloy with lower solute content. There were three ranges of temperature in which different types of precipitates formed and affected the hardness. Some of the grain boundaries were found to migrate and precipitate free zone has been observed.

Fracture Toughness of Cast Al-Zn-Mg Alloys

Compact tension specimens of as-cast Al-3Zn-2Mg and Al-7Zn-2Mg (in wt pct) alloys were subjected to fracture toughness tests at room temperature according to specification5 laid down in ASTM E-399-81. It was found that increasing the Zn content, grain refinement and increasing the solidification rate lead to an increase in the fracture toughness of the material.

STRUCTURE OF Al-Mn-Zn-Mg ALLOY POWDER

The structure of Al-Mn-Zn-Mg alloy powder annealed at 800℃ has been studied by transmisston electron microscopy(TEM).An approximant phase(named as C-phase) to the decagonal phase was found and its crystal structure was determined It belongs to c-center orthorhombic lattice with a=2.35 nm,b=3.27 nm and c=1.22 nm.We stillfound a hexagonal phase with a=0.7) nm and c=0.79 nm,(named as phase) in the annealed alloy powder.The annealed alloy powder is composed of the C-phase,the phase,the decagonal phase and Al solid solution.

Effect of cooling rate and composition on microstructures and properties of Zn-Mg alloys

The Zn-Mg alloys with Mg additions of 35%,40% and 45%(mass fraction) were prepared by conventional casting method,with the aim to develop new biodegradable materials. The effects of cooling rate and composition on the microstructures,hardness and corrosion resistance were studied by XRD,SEM,microhardness and corrosion testing techniques. The corrosion behaviors of experimental alloys in simulated body fluids were analyzed. The results show that the amount of the petal-like MgZn2 phase decreases,as well as the hardness of the alloys,but that of the polygonal MgZn2 phase increases with the increase of Mg content when the cooling rate is constant. When the alloy composition is constant,the MgZn2 phase changes easily from petal-like to polygon,and the hardness decreases with the decrease of the cooling rate.

Microstructure evolution and Al_3(Sc_(1-x)Zr_x) precipitates' kinetics in Al-Zn-Mg alloy during homogenization

The microstructure evolutions of two Al-Zn-Mg alloys,one of which was alloyed with Sc and Zr,and the kinetics of Al3(Sc1-xZrx) precipitates in the Al-Zn-Mg alloy during homogenization were investigated.Both alloys under as-cast condition with supersaturated,non-equilibrium T(Mg 32(Al,Zn) 49) phase and impurities phase were displayed.When the homogenization temperatures are below 350 C,Zn and Mg atoms precipitate from matrix;however,when the temperatures are above 400 C,T phase dissolves into matrix,enhancing solid-solution strengthening.Kinetics of Al3(Sc1-x Zr x) precipitates was studied based on Jmat Pro software calculation and the difference values between the hardness of the two alloys in each homogenization condition.The calculations predict that the Sc and Zr solubilities in α-Al decline with the presence of Mg and Zn.Investigation of the difference values reveals that when the temperature is between 300 C and 350 C,the nucleation rate of Al3(Sc1-xZrx) precipitates is the highest and the strengthening effect from Al3(Sc1-xZrx) precipitates is the best.After homogenization at 470 C for 12 h,non-equilibrium T phase disappears,while impurity phase remains.The mean diameter of Al3(Sc1-xZrx) precipitates is around 18 nm.Ideas about better fulfilling the potentials of Sc and Zr were proposed at last.

Effect of high-temperature pre-precipitation on mechanical properties and stress corrosion cracking of Al-Zn-Mg alloys

In order to improve the stress corrosion cracking resistance of the weldable Al Zn Mg alloys with medium strength, the near solvus pre precipitation following high temperature solution treatment was performed on LC52 and 7039 aluminum alloys. The effect of the pre precipitation on the microstructure, age hardening and stress corrosion cracking of LC52 and 7039 alloy was investigated. The results show that the near solvus pre precipitation can be limited on grain boundary and can enhance the discontinuity of grain boundary precipitates. The stress corrosion cracking resistance of aged Al Zn Mg alloys can be improved with non deteriorated strength and plasticity via pre precipitation.

Solidification path calculations of Al-Zn-Mg alloys in Al-rich corner

The solidification paths of Al-Zn-Mg alloys in the Al-rich corner were investigated. The thermodynamic data for the calculation are obtained by direct coupling with the CALPHAD software Thermo-Calc via its TQ6-interface and the COST2 database. The influences of the initial compositions and the extent of solid back diffusion on the solidification path were numerically investigated by sample calculation of the ternary Al-Zn-Mg alloys. The calculation results of solidification paths of the selected alloys: Al-Zn-3 Mg(in wt.%), Al-5 Zn-10 Mg, Al-2.5Zn-15Mg, Al-10Zn-20.5 Mg, Al-8Zn-25 Mg, were: L→(L+α-Al), L→(L+α-Al)→(L+α-Al+TAU), L→(L+α-Al)→(L+α-Al+Al Mg_β), L→(L+α-Al)→(L+α-Al+TAU)→(L+α-Al+TAU+Al Mg_β), L→(L+α-Al)→(L+α-Al+Al Mg_β)→(L+α-Al+TAU+Al Mg_β), respectively. The results show that the initial compositions and the extent of solid back diffusion have a great influence on solidification path, and the amounts of eutectic phase increase with the decrease of the solid back diffusion coefficient. The equilibrium solute partition coefficients for Zn and Mg in alloys are also calculated and their influence on micro-segregation in the primary solidification of Al-5Zn-10 Mg alloy is analyzed.

Effect of trace rare earth element Er on Al-Zn-Mg alloy

Al-6Zn-2Mg and Al-6Zn-2Mg-0.4Er alloys were prepared by cast metallurgy. The effects of trace Er on the mechanical properties, recrystallization behavior and age-hardening characteristic of Al-Zn-Mg alloy were studied. The effect of Er on microstructures was also studied by OM, XRD, SEM, EDS and TEM. The results show that the addition of Er on Al-6Zn-2Mg alloy is capable of refining grains obviously. The addition of Er can improve the strength considerably by strengthening mechanisms of precipitation and grain refinement. With the addition of Er into Al-6Zn-2Mg alloy, the aging process is quickened and the age-hardening effect is heightened. Er additive can retard the recrystallizing behavior of Al-6Zn-2Mg alloy and cause the increase of recrystallization temperature due to the pinning effect of fine dispersed Al3Er precipitates on dislocations and subgrain boundaries.

Synergistic effect of gradient Zn content and multiscale particles on the mechanical properties of Al-Zn-Mg-Cu alloys with coupling distribution of coarse-fine grains

This study investigated the influence of graded Zn content on the evolution of precipitated and iron-rich phases and grain struc-ture of the alloys,designed and developed the Al–8.0Zn–1.5Mg–1.5Cu–0.2Fe(wt%)alloy with high strength and formability.With the increase of Zn content,forming the coupling distribution of multiscale precipitates and iron-rich phases with a reasonable matching ratio and dispersion distribution characteristics is easy.This phenomenon induces the formation of cell-like structures with alternate distribu-tion of coarse and fine grains,and the average plasticity–strain ratio(characterizing the formability)of the pre-aged alloy with a high strength is up to 0.708.Results reveal the evolution and influence mechanisms of multiscale second-phase particles and the corresponding high formability mechanism of the alloys.The developed coupling control process exhibits considerable potential,revealing remarkable improvements in the room temperature formability of high-strength Al–Zn–Mg–Cu alloys.

高强Al-Zn-Mg-Cu合金静态再结晶模型及组织演变

采用Gleeble 3800热模拟试验机对航空用Al-Zn-Mg-Cu合金的热变形行为进行了测试,对变形后的微观组织进行了表征,系统分析了静态软化行为,建立了静态再结晶动力学模型。结果表明:实验用航空Al-Zn-Mg-Cu合金的静态再结晶激活能为129162 J·mol^(-1),静态再结晶体积分数受变形温度、变形程度、变形速率的影响,且变形温度对静态再结晶影响最明显;变形速率一定时,变形温度越高,道次停留时间的影响越不明显;350℃低温变形后,α-Al基体晶粒内部仍存在大量的位错缠结;400℃中温变形后,位错运动能够充分进行,部分晶粒发生了再结晶;450℃高温变形后,基体晶粒基本全部完成了再结晶,基体晶粒内部发现5~25 nm尺寸范围的Al-Zn-Mg-Cu四元相粒子;对于不同热变形条件,模型预测值的误差在0.008~0.0625范围内,动力学模型的计算结果精确度较高。

Relationship between the unique microstructures and behaviors of high-entropy alloys

High-entropy alloys(HEAs),which were introduced as a pioneering concept in 2004,have captured the keen interest of nu-merous researchers.Entropy,in this context,can be perceived as representing disorder and randomness.By contrast,elemental composi-tions within alloy systems occupy specific structural sites in space,a concept referred to as structure.In accordance with Shannon entropy,structure is analogous to information.Generally,the arrangement of atoms within a material,termed its structure,plays a pivotal role in dictating its properties.In addition to expanding the array of options for alloy composites,HEAs afford ample opportunities for diverse structural designs.The profound influence of distinct structural features on the exceptional behaviors of alloys is underscored by numer-ous examples.These features include remarkably high fracture strength with excellent ductility,antiballistic capability,exceptional radi-ation resistance,and corrosion resistance.In this paper,we delve into various unique material structures and properties while elucidating the intricate relationship between structure and performance.

Microstructure and damping properties of LPSO phase dominant Mg-Ni-Y and Mg-Zn-Ni-Y alloys

This work studied the microstructure,mechanical properties and damping properties of Mg_(95.34)Ni_(2)Y_(2.66) and Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloys systematically.The difference in the evolution of the long-period stacked ordered(LPSO)phase in the two alloys during heat treatment was the focus.The morphology of the as-cast Mg_(95.34)Ni_(2)Y_(2.66)presented a disordered network.After heat treatment at 773 K for 2 hours,the eutectic phase was integrated into the matrix,and the LPSO phase maintained the 18R structure.As Zn partially replaced Ni,the crystal grains became rounded in the cast alloy,and lamellar LPSO phases and more solid solution atoms were contained in the matrix after heat treatment of the Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloy.Both Zn and the heat treatment had a significant effect on damping.Obvious dislocation internal friction peaks and grain boundary internal friction peaks were found after temperature-dependent damping of the Mg_(95.34)Ni_(2)Y_(2.66)and Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloys.After heat treatment,the dislocation peak was significantly increased,especially in the alloy Mg_(95.34)Ni_(2)Y_(2).66.The annealed Mg_(95.34)Ni_(2)Y_(2.66)alloy with a rod-shaped LPSO phase exhibited a good damping performance of 0.14 atε=10^(−3),which was due to the difference between the second phase and solid solution atom content.These factors also affected the dynamic modulus of the alloy.The results of this study will help in further development of high-damping magnesium alloys.

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.

Prediction of the thermal conductivity of Mg–Al–La alloys by CALPHAD method

Mg-Al alloys have excellent strength and ductility but relatively low thermal conductivity due to Al addition.The accurate prediction of thermal conductivity is a prerequisite for designing Mg-Al alloys with high thermal conductivity.Thus,databases for predicting temperature-and composition-dependent thermal conductivities must be established.In this study,Mg-Al-La alloys with different contents of Al2La,Al3La,and Al11La3phases and solid solubility of Al in the α-Mg phase were designed.The influence of the second phase(s) and Al solid solubility on thermal conductivity was investigated.Experimental results revealed a second phase transformation from Al_(2)La to Al_(3)La and further to Al_(11)La_(3)with the increasing Al content at a constant La amount.The degree of the negative effect of the second phase(s) on thermal diffusivity followed the sequence of Al2La>Al3La>Al_(11)La_(3).Compared with the second phase,an increase in the solid solubility of Al in α-Mg remarkably reduced the thermal conductivity.On the basis of the experimental data,a database of the reciprocal thermal diffusivity of the Mg-Al-La system was established by calculation of the phase diagram (CALPHAD)method.With a standard error of±1.2 W/(m·K),the predicted results were in good agreement with the experimental data.The established database can be used to design Mg-Al alloys with high thermal conductivity and provide valuable guidance for expanding their application prospects.

Machine learning-assisted efficient design of Cu-based shape memory alloy with specific phase transition temperature

The martensitic transformation temperature is the basis for the application of shape memory alloys(SMAs),and the ability to quickly and accurately predict the transformation temperature of SMAs has very important practical significance.In this work,machine learning(ML)methods were utilized to accelerate the search for shape memory alloys with targeted properties(phase transition temperature).A group of component data was selected to design shape memory alloys using reverse design method from numerous unexplored data.Component modeling and feature modeling were used to predict the phase transition temperature of the shape memory alloys.The experimental results of the shape memory alloys were obtained to verify the effectiveness of the support vector regression(SVR)model.The results show that the machine learning model can obtain target materials more efficiently and pertinently,and realize the accurate and rapid design of shape memory alloys with specific target phase transition temperature.On this basis,the relationship between phase transition temperature and material descriptors is analyzed,and it is proved that the key factors affecting the phase transition temperature of shape memory alloys are based on the strength of the bond energy between atoms.This work provides new ideas for the controllable design and performance optimization of Cu-based shape memory alloys.

Influence of layer thickness on formation quality,microstructure,mechanical properties,and corrosion resistance of WE43 magnesium alloy fabricated by laser powder bed fusion

Laser powder bed fusion(L-PBF)of Mg alloys has provided tremendous opportunities for customized production of aeronautical and medical parts.Layer thickness(LT)is of great significance to the L-PBF process but has not been studied for Mg alloys.In this study,WE43 Mg alloy bulk cubes,porous scaffolds,and thin walls with layer thicknesses of 10,20,30,and 40μm were fabricated.The required laser energy input increased with increasing layer thickness and was different for the bulk cubes and porous scaffolds.Porosity tended to occur at the connection joints in porous scaffolds for LT40 and could be eliminated by reducing the laser energy input.For thin wall parts,a large overhang angle or a small wall thickness resulted in porosity when a large layer thicknesses was used,and the porosity disappeared by reducing the layer thickness or laser energy input.A deeper keyhole penetration was found in all occasions with porosity,explaining the influence of layer thickness,geometrical structure,and laser energy input on the porosity.All the samples achieved a high fusion quality with a relative density of over 99.5%using the optimized laser energy input.The increased layer thickness resulted to more precipitation phases,finer grain sizes and decreased grain texture.With the similar high fusion quality,the tensile strength and elongation of bulk samples were significantly improved from 257 MPa and 1.41%with the 10μm layer to 287 MPa and 15.12%with the 40μm layer,in accordance with the microstructural change.The effect of layer thickness on the compressive properties of porous scaffolds was limited.However,the corrosion rate of bulk samples accelerated with increasing the layer thickness,mainly attributed to the increased number of precipitation phases.

Greatly enhanced corrosion/wear resistances of epoxy coating for Mg alloy through a synergistic effect between functionalized graphene and insulated blocking layer

The poor corrosion and wear resistances of Mg alloys seriously limit their potential applications in various industries.The conventional epoxy coating easily forms many intrinsic defects during the solidification process,which cannot provide sufficient protection.In the current study,we design a double-layer epoxy composite coating on Mg alloy with enhanced anti-corrosion/wear properties,via the spin-assisted assembly technique.The outer layer is functionalized graphene(FG)in waterborne epoxy resin(WEP)and the inner layer is Ce-based conversion(Ce)film.The FG sheets can be homogeneously dispersed within the epoxy matrix to fill the intrinsic defects and improve the barrier capability.The Ce film connects the outer layer with the substrate,showing the transition effect.The corrosion rate of Ce/WEP/FG composite coating is 2131 times lower than that of bare Mg alloy,and the wear rate is decreased by~90%.The improved corrosion resistance is attributed to the labyrinth effect(hindering the penetration of corrosive medium)and the obstruction of galvanic coupling behavior.The synergistic effect derived from the FG sheet and blocking layer exhibits great potential in realizing the improvement of multi-functional integration,which will open up a new avenue for the development of novel composite protection coatings of Mg alloys.

Microstructure and thermal properties of dissimilar M300–CuCr1Zr alloys by multi-material laser-based powder bed fusion

Multi-material laser-based powder bed fusion (PBF-LB) allows manufacturing of parts with 3-dimensional gradient and additional functionality in a single step. This research focuses on the combination of thermally-conductive CuCr1Zr with hard M300 tool steel.Two interface configurations of M300 on CuCr1Zr and CuCr1Zr on M300 were investigated. Ultra-fine grains form at the interface due to the low mutual solubility of Cu and steel. The material mixing zone size is dependent on the configurations and tunable in the range of0.1–0.3 mm by introducing a separate set of parameters for the interface layers. Microcracks and pores mainly occur in the transition zone.Regardless of these defects, the thermal diffusivity of bimetallic parts with 50vol% of CuCr1Zr significantly increases by 70%–150%compared to pure M300. The thermal diffusivity of CuCr1Zr and the hardness of M300 steel can be enhanced simultaneously by applying the aging heat treatment.

基于机器学习的Al-Zn-Mg-Cu合金快速设计

提出一种基于机器学习的合金快速设计系统(ARDS),以定制所需性能的合金制备策略或预测制备策略所对应的合金性能。为此,分别对3种回归算法:线性回归(LR)、支持向量回归(SVR)和人工神经网络(BPNN)进行建模和比较以训练多性能预测模型。其中,应用SVR构建的机器学习模型被证明是最佳的。然后,基于生成对抗网络(GAN)模型原理,构建Al-Zn-Mg-Cu系铝合金快速设计系统(ARDS)。对ARDS的预测可靠性进行验证。结果表明,为了能够获得准确的制备策略,系统中极限抗拉强度(UTS)、屈服强度(YS)和伸长率(EL)的输入上限分别约为790 MPa、730 MPa和28%。此外,基于ARDS预测结果,制备了一种性能优异的新型铝合金材料,其UTS为764 MPa、YS为732 MPa、EL为10.1%,进一步验证了ARDS的可靠性。