aluminum alloy

摘要： To obtain the aluminum alloy with high thermal and mechanical properties,the effects of alloying elements and the second phases on the thermal conductivity of Al alloys were investigated by CALPHAD and first-principles calculation,respectively.The properties of the second phases,including Young's modulus,Poisson's ratio and minimum thermal conductivity,were systematically studied.Results show that the ranking order of the effects of the alloying elements on the thermal conductivity is Mg>Cu>Fe>Si,and for Al-12Si alloys,the mathematical model of the relationship between the alloying elements and the thermal conductivity can be expressed as λ=ax^(2)-bx+c when the second phase precipitates in the matrix.All kinds of ternary phases of Al-Fe-Si have higher deformation resistance,rigidity,theoretical hardness,Debye temperature and thermal conductivity than the other phases which possibly exist in the Al-12Si alloys.Based on the guidance of CALPHAD and first-principles calculation,the optimized chemical composition of Al alloy with high conductivity is Al-11.5Si-0.4Fe-0.2Mg(wt.%)with a thermal conductivity of 137.50 W·m^(-1)·K^(-1)and a hardness of 81.3 HBW.

摘要： Central region coarse grains and centerline segregation are common defects in aluminum ingots fabricated by direct chill(DC)casting.A double cooling field was introduced into the DC casting process to reduce these defects,whereby the external cooling was supplied by the mold and water jets,and intercooling was achieved by inserting a rod of the same alloy into the molten pool along the central axis of the ingot.Rather than forming a good metallurgical interface during solid-liquid compound casting,in the present work,the purpose of inserting the rod is to enforce internal cooling and consequently decrease the sump depth.Moreover,the insertion provides more nucleation sites with the unmoltenα-Al particles.The structure and the macrosegregation of 2024 Al alloy ingots prepared by DC casting with and without the inserts were investigated.Results show that when the inserting position is 50 mm above the upper edge of the graphite ring,significant grain refinement in the central region of the ingot and a reduced centerline segregation are achieved.

摘要： Single-pass deposits of 6061 aluminum alloy with a single-layer thickness of 4 mm were fabricated by force-controlled friction-and extrusion-based additive manufacturing.The formation characteristics of the interface,which were achieved by using a featureless shoulder,were investigated and elucidated.The microstructure and bonding strength of the final build both with and without heat treatment were explored.A pronounced microstructural heterogeneity was observed throughout the thickness of the final build.Grains at the interface with Cu,{213},and Goss orientations prevailed,which were refined to approximately 4.0μm.Nearly all of the hardening precipitates were dissolved,resulting in the bonding interface displaying the lowest hardness.The fresh layer,subjected to thermal processes and plastic deformation only once,was dominated by a strong recrystallization texture with a Cube orientation.The previous layer,subjected twice to thermal processes and plastic deformation,was governed by P-and Goss-related components.The ultimate tensile strength along the build direction in asdeposited and heat-treated states could reach 57.0%and 82.9%of the extruded 6061-T651 aluminum alloy.

摘要： The application of ultrasonic vibration to the casting process can be realized through mould(die)vibration.However,the resonant vibration of the mould is always accompanied by a non-uniform vibration distribution at different parts,which may induce a complex liquid flow and affect the casting fluidity during the mould filling process.The influence of non-uniform ultrasonic vibration on the fluidity of liquid AlSi9Cu3 alloy was studied by mould vibration with different vibration gradients.It is found that ultrasonic mould vibration can generate two opposite effects on the casting fluidity:the first,ultrasonic cavitation in melt induced by mould vibration promotes the casting fluidity;the second,the non-uniform mould vibration can induce a melt flow toward the weak vibration areas and turbulence there,consequently decreasing the casting fluidity.When the melt flow and turbulence are violent enough to offset the promoting effect of cavitation on fluidity,the ultrasonic vibration will finally induce a resultant decrease of casting fluidity.The decreasing effect is proportional to the vibration gradient.

摘要： At present,conventional flame correction has shortcomings such as random heating route and low efficiency.The welding seam of the aluminum alloy ship frame skin structure is concentrated and the frame restraint is large.It is difficult to control and eliminate the local convex deformation after welding.In order to improve the conventional orthopedic technology and improve the orthopedic efficiency,the pre-elastic deformation technology is proposed.Using the method of combining numerical simulation and experiment,the orthopedic effect of conventional and pre-elastic orthopedic technology is studied,and the influence of pre-deformation variables and heating path on deformation control of the frame skin structure after welding is simulated.The simulation results show that the technical key to the control of convex deformation lies in the control of the pre-elastic deformation and the setting of the heating route.The experimental verification results show that the pre-elastic deformation technology has a better control effect than conventional orthopedics,can significantly improve the orthopedic efficiency,and provides a new method for deformation control in the shipbuilding industry.

摘要： Integral thin shells made of high strength aluminum alloys are urgently needed in new generation transportation equipment. There are challenges to overcoming the co-existing problems of wrinkling and splitting by the cold forming and hot forming processes. An innovative technology of ultra-low temperature forming has been invented for aluminum alloy thin shells by the new phenomenon of ‘dual enhancement effect’. That means plasticity and hardening are enhanced simultaneously at ultra-low temperatures. In this perspective, the dual enhancement effect is described, and the development, current state and prospects of this new forming method are introduced. This innovative method can provide a new approach for integral aluminum alloy components with large size, ultra-thin thickness, and high strength. An integral tank dome of rocket with 2 m in diameter was formed by using a blank sheet with the same thickness as the final component, breaking through the limit value of thickness-diameter ratio.

摘要： The electrolyte temperature has a great influence on the performance of the coating prepared by micro-arc oxidation (MAO). The behavior of MAO discharge in the changing electrolyte temperature has been investigated. Compared to constant electrolyte temperature in conventional MAO process, the process has different discharge characteristics under the changing electrolyte temperature. The amplitude of pulse voltage was detected to study the change of discharge characteristic under the constant-current control of MAO power supply. Three successive discharge stages were differentiated by the variable the pulse voltage versus process time. Since there were significant changes in the sound, the sound signals were acquired and the audio analysis was used to describe the changing of the MAO discharge at different stages. Optical emission spectroscopy (OES) was employed in situ to unveil how the micro-discharge changed with the temperature increasing. Scanning electron microscopy (SEM) was used to characterize the morphology of the coatings on 6N01 aluminum alloy prepared by normal process with the constant-temperature control of the MAO electrolyte and by the process under the changing electrolyte temperature. A mode of film growth and micro-discharge was given to describe the effects of the changing electrolyte temperature in the whole MAO process.

摘要： The asymmetric thermo-physical mechanism of the resistance spot welding technique with intermediate frequency(2 kHz)and direct current(RSWIFDC)on the high strength aluminum(Al)alloy TL091 was studied here in view of the Peltier effect.On the basis of the analysis of the electrode cap surface erosion state and the shape-position of the nugget,it was concluded that asymmetric thermo-physical phenomenon occurred on both ends of the nugget,and even had an influence upon the shape-forming coefficient and the vertical position deviation of the nugget,and the erosion degree of the electrode caps.In this work,the relative thermo-physical model of the welding was established combined with the Peltier effect and the spot welding characteristics.Accordingly the relative welding phenomena,such as nugget center deviation and different erosion degree of the electrode cap surface,was explained clearly using the model related with the Peltier effect for the first time.This model provides important theoretical basis for future study and application of Al alloy spot welding,based on which,effective works may be done to promote the quality of the Al alloy welded joints and to obtain favorable control upon parameters of Al alloy welding for electrode caps.

摘要： Polymeric nanofibers are a promising technology to protect the metal surfaces from corrosion.Through the literature search,the use of polyacrylonitrile nanofibres(PANNFs)as a corrosion inhibitor coating for aluminum alloys has not been evaluated.This work includes the development of a new,lightweight,high surface area and efficient coating of PANNFs that produced using electrospinning process to resist the corrosion of aluminum alloys(AA5083)which immersed in 0.6 M NaCl at alkaline medium(pH=12)and acidic medium(pH=1)at a range of temperatures(293–323)K.The PANNFs coating was successfully deposited on AA 5083 specimens,where these samples were considered as a collector electrode in the electrospinning process.The corrosion experiments of the aluminum alloys coated with PANNFs before and after immersion in both corrosive mediums were investigated using cyclic potential polarization(CPP).The results confirmed that the PANNFs coating was able to protect the surface of the aluminum specimens from corrosion,by reducing the corrosion current and increasing the surface polarization resistance,thus reducing the corrosion rate.The protection efficiency was found in the alkaline medium 98.8%while in the acidic medium 83.3%.So,it was in both mediums decreased with the increase in temperature.The shape,distribution and size of the polymeric nanofibers that formed the coating were also examined using field emission scanning electron microscopy(FE-SEM)and the percentages of the structural components of these fibers were detected using the X-ray dispersion spectroscopy(EDS).The surface of aluminum specimens was completely covered by PANNFs.These electrospun nanofibers have worn out and lined up spacing after immersion in the corrosive mediums.The diameters average of PANNFs was found to be about 200 and 150 nm before and after immersion,respectively.

摘要： During heat treatment or mechanical processing,most polycrystalline materials experience grain growth,which significantly affects their mechanical properties.Microstructure simulation on a mesoscopic scale is an important way of studying grain growth.A key research focus of this type of method has long been how to efficiently and accurately simulate the grain growth caused by a non-uniform temperature field with temperature gradients.In this work,we propose an improved 3D Monte Carlo Potts(MCP)method to quantitatively study the relationship between non-uniform temperature fields and final grain morphologies.Properties of the aluminum alloy AA6061-T6 are used to establish a trial calculation model and to verify the algorithms with existing experimental results in literature.The detailed grain growth process of the 6061-T6 aluminum alloy under different temperature fields is then obtained,and grain morphologies at various positions are analyzed.Results indicate that while absolute temperature and duration time are the primary factors determining the final grain size,the temperature gradient also has strong influence on the grain morphologies.The relationships between temperatures,temperature gradients and grain growth process have been established.The proposed MCP algorithm can be applied to different types of materials when the proper parameters are used.

摘要： The vibrations in milling process include two parts，I.e. Self-excited vibration（chatter) and forced vibration. Stability due to the chatter and surface location error（SLE) induced by the forced vibration are derived by using the temporal finite element analysis（TFEA). Corresponding to the 3D stability charts（SC) and SLE diagrams are constructed. The results show the transition between the autonomous model for turning and the discrete map model of highly interrupted cutting. And it is also shown that the SLE is especially large at those spindle speed，where high depths of cut are achievable without chatter. Thus，the influences of chatter stability and resonance due to the forced vibration should be considered in dynamic optimization of milling system，simultaneously. The results are confirmed experimentally on a high-speed milling center.

摘要： The vibrations in milling process include two parts，I.e. Self-excited vibration（chatter) and forced vibration. Stability due to the chatter and surface location error（SLE) induced by the forced vibration are derived by using the temporal finite element analysis（TFEA). Corresponding to the 3D stability charts（SC) and SLE diagrams are constructed. The results show the transition between the autonomous model for turning and the discrete map model of highly interrupted cutting. And it is also shown that the SLE is especially large at those spindle speed，where high depths of cut are achievable without chatter. Thus，the influences of chatter stability and resonance due to the forced vibration should be considered in dynamic optimization of milling system，simultaneously. The results are confirmed experimentally on a high-speed milling center.

摘要： The vibrations in milling process include two parts，I.e. Self-excited vibration（chatter) and forced vibration. Stability due to the chatter and surface location error（SLE) induced by the forced vibration are derived by using the temporal finite element analysis（TFEA). Corresponding to the 3D stability charts（SC) and SLE diagrams are constructed. The results show the transition between the autonomous model for turning and the discrete map model of highly interrupted cutting. And it is also shown that the SLE is especially large at those spindle speed，where high depths of cut are achievable without chatter. Thus，the influences of chatter stability and resonance due to the forced vibration should be considered in dynamic optimization of milling system，simultaneously. The results are confirmed experimentally on a high-speed milling center.

摘要： The vibrations in milling process include two parts，I.e. Self-excited vibration（chatter) and forced vibration. Stability due to the chatter and surface location error（SLE) induced by the forced vibration are derived by using the temporal finite element analysis（TFEA). Corresponding to the 3D stability charts（SC) and SLE diagrams are constructed. The results show the transition between the autonomous model for turning and the discrete map model of highly interrupted cutting. And it is also shown that the SLE is especially large at those spindle speed，where high depths of cut are achievable without chatter. Thus，the influences of chatter stability and resonance due to the forced vibration should be considered in dynamic optimization of milling system，simultaneously. The results are confirmed experimentally on a high-speed milling center.

摘要： The vibrations in milling process include two parts，I.e. Self-excited vibration（chatter) and forced vibration. Stability due to the chatter and surface location error（SLE) induced by the forced vibration are derived by using the temporal finite element analysis（TFEA). Corresponding to the 3D stability charts（SC) and SLE diagrams are constructed. The results show the transition between the autonomous model for turning and the discrete map model of highly interrupted cutting. And it is also shown that the SLE is especially large at those spindle speed，where high depths of cut are achievable without chatter. Thus，the influences of chatter stability and resonance due to the forced vibration should be considered in dynamic optimization of milling system，simultaneously. The results are confirmed experimentally on a high-speed milling center.