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About Journal
Journal: Chinese Journal of Rare Metals
Establishment year: 1977
Administrator: China Association for Science and Technology
Sponsor: The Nonferrous Metals Society of China;
China GRINM Group Co., Ltd.
Periodicity: Monthly
Tel:010-82241917/82240869
E-mail:rmchina@263.net
ISSN:0258-7076
CN:11-2111/TF
Chinese Journal of Rare Metals is a comprehensive journal, published monthly in Chinese, administrated by China Association for Science and Technology, and sponsored by The Nonferrous Metals Society of China and China GRINM Group Co., Ltd. Academician Haili Tu is the Editor-in-Chief. Chinese Journal of Rare Metalis included by American Engineering(EI compendex), the important database SCOPUS...(Details)
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Bake-Hardening Behavior and Mechanical Properties of Al-Mg-Si Alloys with Trace Cu
Cheng Dahang;Liu Zhenshan;Chen Kaixin;Zhao Jingwei;Shi Xiaocheng;Zhuang Linzhong;As the awareness of energy saving and emission reduction is gradually taking root in people's hearts, the trend towards automobile light weighting is inevitable. Aluminum alloys are extensively used as automotive lightweight materials due to their low density, high specific strength, good corrosion resistance, ease of processing and forming, and recyclability. Among these, 6 xxx series(Al-Mg-Si) aluminum alloys are particularly prevalent in the manufacture of automobile body panels due to their excellent properties such as medium-high strength and good formability. Al-Mg-Si alloys are heat-treatable and are reinforced alloys, and their main reinforcement mechanism is aging reinforcement, and β″ phase, which is the primary reinforcing phase within Al-Mg-Si alloys, is the sub-stabilized phase precipitated during the aging process. The precipitation behavior of Al-Mg-Si alloys can be modified by changing the composition or adjusting the heat treatment process, and Cu is frequently added to Al-Mg-Si alloys because the formation of a new precipitation phase, Q′, is observed during aging as well as the aging precipitation behavior of the alloys can be changed. Simulations indicate that the baking process for Al-Mg-Si alloy body panels should be conducted at 185 ℃ for 20 min, and this low-temperature, short-time treatment often fails to achieve the peak aging state of the alloy, and does not fully exploit the alloy's age-hardening potential of the alloy, leaving the alloy in an under-aged condition. There is a greater focus on the impact of Cu addition on the peak aging state of alloys, but fewer investigations have been conducted on the baking paint hardening behavior of Al-Mg-Si alloys in an under-aged condition with Cu addition. In summary, exploring the effect of Cu addition on the bake-hardening behavior of Al-Mg-Si alloy body sheets is of great significance. In this study, three alloy ingots with varying Cu contents—0, 0.1% and 0.2%—by introducing Cu into Al-0.6 Si-0.7 Si alloy and employing semi-continuous casting were produced. The ingots were then homogenized and processed through hot rolling, intermediate annealing, and cold rolling to achieve a 1 mm thick coldrolled sheet. The cold-rolled sheets were solution treated for 170 s at 555 ℃ in a salt bath furnace, followed by water quenching and a preageing treatment at 75 ℃ for 7 h to obtain T4P state alloy sheets. Subsequently, these T4P plates were subjected to an aging treatment at 185 ℃ for 20 min after pre-stretching by 2% to obtain T6B state plates. The microstructure and precipitation kinetic parameters of the alloy plates with different Cu contents were investigated using optical microscopy(OM), transmission electron microscopy(TEM) and differential scanning calorimetry(DSC). Mechanical property tests were conducted on an AG-XPlus 100 KN microcomputer-controlled electronic universal mechanical tester. Tensile specimens were cut from the cold-rolled plates perpendicular to the rolling direction to measure the yield strength of the alloy plates in both T4P and T6B states, determine the strength increment, and examine the impact of different Cu contents on the baking hardening behavior of the alloy. The microstructure analysis revealed that the grain structure of T4P state alloy was completely recrystallized, consisting of numerous equiaxed recrystallized grains. Despite some variations in the average grain size among the three alloys, the differences were minor and did not significantly affect strength. TEM results indicated that the precipitated phase in T6B state alloy remained β″ phase or Guinier-Preston(GP) region, but Cu-containing alloys exhibited higher precipitate density and finer particle size. The addition of Cu promoted the formation of β″ phase. Tensile test results showed that tensile strength increases with Cu content in the T4P alloy, while elongation remained unchanged. The yield strengths of T4P Base alloy, 0.1%Cu-added alloy and 0.2%Cu-added alloy were 93, 97 and 96 MPa, respectively. After a baking aging treatment at 185 ℃ for 20 min, the yield strengths increased to 180, 188 and 200 MPa, with strength increments (∆Rp0.2) of 87, 91 and 104 MPa, respectively, demonstrated that the baking hardening capacity of Al-Mg-Si alloys was enhanced with increasing Cu content. The activation energies(Q) for β″ phase precipitation during non-isothermal aging were calculated from DSC curves for Base alloy, 0.1%Cu-added alloy and 0.2%Cu-added alloy as 68.28, 63.48 and 55.42 kJ·mol-1, respectively. Kinetic equations predicting the precipitation rates for Base alloy, 0.1%Cu-added alloy and 0.2%Cu-added alloy were derived based on Q and kinetic parameters(k0, Tpeak, t) from the calculations: Y=1-exp[-4.45×1012t2 exp(-16426/T)], Y=1-exp[-5.76×1011t2 exp(-15270/T)], Y=1-exp[-1.51×1010t2 exp(-13332/T)]. Furthermore, the addition of 0.2%Cu significantly promoted the nucleation rate of β″ phase during aging, leading to increased hardness and a more rapid hardness increase within the first 20 min of aging at 185 ℃. The hardness of 0.2%Cu-added alloy increased from HV 70.9 to HV 100.3 (∆HV=HV 29.4) compared to Base alloy, which increased from HV 68.4 to HV 86.5 (∆HV=HV 18.1).
Heat Treatment, Microstructure and Properties of Al-Mg-Si Alloy with Sn/Sc Microalloying
Fu Yuanyang;Pan Shuai;Wu Jin;Zhu Yongjie;Zhang Deyu;Wang Bin;Wang Zheng;Sun Xiaofei;Wang Shuangbao;Al-Mg-Si(6×××) alloys have been widely used as light weight structural components in the automobiles, high-speed rail and aircraft etc. due to their high strength/weight ratio, good machinability, and relatively low cost. Optimizing their mechanical properties by rational design of microalloying and heat treatment regime is a subject of growing importance in the material science. The previous works have indicated that the negative effect of room-temperature storage on subsequent artificial aging of Al-Mg-Si alloys can be largely modified by Sn minor addition. This is because that Sn tends to combine with vacancies after quenching relative to Mg and Si atoms, eventually stabilizing vacancies and inhibiting the clustering process during room-temperature storage. In addition, the mechanical properties and corrosion resistance of Al-Mg-Si alloys can be improved by the addition of minor Sn due to the reduced size of precipitates and the width of precipitation free zones. Moreover, some research studies point out that the accelerated age-hardening response of Al-Mg-Si-Sn alloys is related to the rapid generation of the high-concentration vacancies and Sn-containing clusters with a large average size and Mg/Si ratio after quenching. Now it is accepted that Sc minor addition is in favor of improving the overall properties(including strength, plasticity, corrosion resistance and heat resistance) of Al-Mg-Si alloys. In general, Sc minor addition significantly influences the intrinsic precipitation behavior, Al gain size and precipitation free zone of Al-Mg-Si alloys. For example, Sc minor addition improves the strength of over-aged sample as a result of effective suppression of Sc on the transition of β″ to β′ precipitates, as well as the cross-sectional coarsening of β″ and one-dimensional precipitated phase. Sc minor addition refines alloy's grain size and forms a more protective corrosion product film, thus improving the alloy's corrosion resistance. Apart from the microalloying design, heat treatment is also considered a crucial strategy for improvement of the alloys' properties. The heat treatment of Al-Mg-Si alloys is observed to influence the age-hardening response and their final mechanical properties. However, the age hardening by heat treatment is negligible for some casting alloys with specific Mg/Si ratio. Some studies indicate that there is a potential for full T6(solution treatment+rapid quenching+artificial aging) and T5(high-temperature forming+cooling+artificial aging) heat treatments to improve the age-hardening response of the as-cast Al-Mg-Si alloys alloyed with Sc, Cr, and Zr. Nanoscale precipitates and coarse Al{L-End}7 Cr and Al{L-End}3 Zr intermetallic phases are responsible for the mechanical properties of the alloys after heat treatment. T5 heat treatment is effective to achieve the high tensile properties of Sc-containing alloys. The as-cast alloys with Sc addition exhibit the highest strength after T5 and the highest elongation after full T6 heat treatment. For Al-Mg-Si-Sn-Sc alloy, it behaves an apparently shortened peak hardening time, an increased thermal stability and a corrosion resistance compared with corresponding Al-Mg-Si-Sn alloy without Sc after heat treatment of long room-temperature storage time of 1 week+peak aging. The addition of Sc to Al-Mg-Si-Sn alloy results in a decreased diameter but an increased length of peak hardening β″-based precipitates under a designed double-stage aging regime(1-week room-temperature storage+artificial aging at 180 ℃). Also, a suppressed transition from Sc/Sn-containing β″ to β′ precipitates occurs in Al-Mg-Si-Sn-Sc alloy. Sn tends to occupy Si sites in the low-density cylinder of β″ precipitates. In addition, it is easy for Sn and Sc atoms to occupy the central sites of sub-B' in the precipitates. Nevertheless, the underlying mechanisms of Sn/Sc microalloying and heat treatment optimization that are critical in controlling both the microstructure and macroscopic properties are far from well understood, which largely impede the exploration of high-performance Al alloys. In this paper, microhardness, intergranular corrosion, electrochemical corrosion, conductivity testing, scanning electron microscopy(SEM), and transmission electron microscopy(TEM) were coupled to study the optimal solution parameters of Al-Mg-Si(-Sn/Sc) alloys before artificial aging at 180 ℃, as well as the influence of subsequent artificial peak aging and over aging on the alloys' properties and microstructure. The results indicated that the optimal solution parameter for the three alloys was 550 ℃/1 h. Under 550 ℃/1 h+180 ℃, addition of Sn to Al-Mg-Si alloy resulted in a decrease in corrosion resistance and the increases in both grain size and length of over aging β″ precipitates. Addition of Sc to Al-Mg-Si-Sn alloy improved corrosion resistance, reduced the grain size of Al matrix, and led to a length decrease of the over aging β″ precipitates. Over-aging treatment improved the intergranular corrosion resistance of the samples, but reduced their electrochemical corrosion properties. There were obvious Sn and Sc occupation for β″ precipitates in the peak-aging Al-Mg-Si-Sn-Sc alloy, and the structure of the precipitates containing Sn and Sc became more disordered in the overaged state. These results enriched fundamental understanding on the influence of microalloying elements on the non-equilibrium nanophase transformation in Al alloys, and had strong implications for the design of new alloys with excellent properties.
Microstructure and Properties of Al-Mg-Si-0.1La Aluminum Alloy with Different Rolling Temperature
Zhai Pengfei;Xing Shuqing;Li Yan;Gong Meina;Ma Yonglin;Hot rolling process is very important; it will affect the microstructure and mechanical properties of hot rolled products. In order to optimize the hot rolling process to produce high performance aluminum alloy, this paper adopted the characterization methods of optical microscope(OM), scanning electron microscope(SEM), electron backscattering diffraction(EBSD), transmission electron microscope(TEM) and room temperature tensile experiment. The effect of hot rolling temperature on the microstructure and mechanical properties of Al-Mg-Si-0.1 La aluminum alloy was studied. The results showed that the rolling temperature had great influence on the grain boundaries, recrystallization structure distribution, local orientation difference and dislocation density of Al-Mg-Si-0.1 La aluminum alloy. With the increase of rolling temperature, the number of small angle grain boundaries of Al-Mg-Si-0.1 La aluminum alloy gradually decreased, and the maximum value was 91.9% at 350 ℃, and the minimum value was 88.6% at 500 ℃. When the rolling temperature was 350 ℃, a large number of deformation structures appeared in the matrix, and a small amount of recovery structures appeared, and the recrystallization structures were very few and almost invisible in the matrix. At 500 ℃, the recrystallization structures and recovery structures increased, while the deformation structures decreased. This was because when the deformation occurred at a lower temperature, the driving force of recrystallization was insufficient but the recovery process was sufficient, so a high-volume fraction subcrystalline structure characterized by a small angle grain boundary was formed. When the rolling temperature was increased, the thermal activation process of atoms was increased, the driving force of grain movement was increased, and the recrystallization process was promoted. The recrystallization grains had large Angle grain boundaries, so the proportion of large angle grain boundaries was increased, and the proportion of recrystallization fraction was increased. When rolling at 350 ℃, the difference of orientation between grain boundary and part of grain was large, which meant that the degree of plastic strain inside grain was large. When the rolling temperature rose to 400 ℃, the orientation difference within the grain tended to a fixed value, and the strain distribution became uniform. When the rolling temperature continued to rise, the orientation difference inside and at the grain boundary of some grains was very small. With the increase of rolling temperature, Kernel Average Misorientation(KAM) value showed a decreasing trend, indicating that lower rolling temperature would increase the geometric dislocation density. Because Al-Mg-Si aluminum alloy was heat-treatable aluminum alloy, it was treated by solution aging after hot rolling deformation treatment. The results showed that the average grain size of T6 Al-Mg-Si-0.1 La aluminum alloy increased gradually with the increase of rolling temperature, and the recovery process of Al-Mg-Si-0.1 La aluminum alloy was weak when rolling at 350 ℃, and high-density dislocation could be accumulated to store a lot of energy, which promoted the full recrystallization during the aging process. The average grain size was significantly reduced, and fine equiaxed crystals with a size of 58 μm were obtained at 350 ℃. A large amount of stored energy was formed in Al-Mg-Si-0.1 La aluminum alloy matrix by low temperature rolling, and the grains were refined significantly after T6 heat treatment. At 350 ℃ hot rolling, due to the low rolling temperature, the deformation resistance of the sample increased, and the coarse second phase was fully broken during the deformation process, and the size was reduced. When rolling at low temperature, the recovery process was inhibited, and a large number of dislocation proliferated to obtain a high density of dislocation defects, which ultimately led to a significant reduction of the coarse number after heat treatment, improved the uniformity of the matrix, and was conducive to nanoscale enhanced phase precipitation. After rolling at 350 ℃ and T6 heat treatment, Al-Mg-Si-0.1 La aluminum alloy had the best mechanical properties, its tensile strength and elongation were 328 MPa and 9.3%, respectively. In this study, it was found that the tensile strength of Al-Mg-Si-0.1 La aluminum alloy gradually decreased with the increase of rolling temperature. In order to explore the reasons for the different mechanical properties of the alloy, the influence of grain boundary strengthening on the mechanical properties was first considered. The strength provided by grain boundary strengthening could be calculated by Hall-Petch formula. With the decrease of rolling temperature, the average grain size of the alloy decreased significantly, the total grain boundary area increased, and the hindrance to the dislocation increased, resulting in the alloy strength increasing. Dislocation density was also one of the main factors affecting mechanical properties. It could be seen from the formula of dislocation strengthening that the dislocation density was proportional to the alloy strength, so the lower the rolling temperature, the greater the dislocation density and the greater the alloy strength.
Microstructure and Texture Evolution of Aviation TA18 Tube during Annealing
Zhang Wei;Zhang Bing;Wang Xufeng;Zhou Jun;Liu Yue;Yang Feng;Zhang Haiqin;The titanium alloy tube (Ti-3Al-2.5V,equivalent to TA18 titanium alloy) is widely used in the manufacture of aerospace components that require certain strength and oxidation resistance requirements.These include high-pressure-resistant,lightweight hydraulic and fuel piping systems for aircraft and engines.TA18 titanium alloy is chosen for these applications because of its favorable mechanical and corrosion resistance properties,as well as its exceptional processing and welding characteristics.At present,internationally published studies on TA18 titanium alloy mainly focus on powder metallurgy,tube blank preparation,and tube performance testing and evaluation,among other topics.There are few such studies on the annealing process of TA18 titanium alloy tubes in foreign countries.Many studies have been carried out on the annealing process of TA18 titanium alloy tubes in China.But the focus is on the effect of annealing process on its mechanical properties,rather than on the texture evolution.To elucidate the microstructure and texture evolution of TA18 titanium alloy tube during annealing.In this paper，Φ12 mm×0.9 mm TA18 titanium alloy tubes annealed at 400,450,500,550,600,650,and 700℃were selected as the research objects.The microstructure,grain orientation,and texture evolution characteristics of cold-rolled and annealed tubes at different temperatures were investigated using electron backscatter diffraction (EBSD) techniques.The results showed that annealing had a certain effect on the microstructure and texture evolution of TA18 titanium alloy tube.Regarding microstructure evolution,the results demonstrated that the cold-rolled TA18 titanium alloy tube had an elongated deformation structure along the rolling direction (RD).After annealing at 400～600℃，TA18 titanium alloy tube microstructure still consisted of long deformed grains,and the grain boundary misorientation was mostly dominated by low-angle grain boundaries (LAGBs).After annealing at 650℃，numerous equiaxed grains could be observed in the deformed grains,and the grain boundary misorientation was dominated by high-angle grain boundaries(HAGBs).Nearly all of the original deformed microstructure transformed into equiaxed grains after annealing at 700℃.TA18 titanium alloy tubes exhibited recovery,recrystallization and grain growth at temperatures of 400～600,600～650 and 650 to 700℃，respectively.The new distortion-free grains were primarily nucleated and grew between the original deformed grains,and were predominantly distributed on the HAGBs of>10°.In terms of texture evolution,the results demonstrated that the original cold rolled TA18 titanium alloy tube showed a typical base plane bimodal texture of<0001>//ND (normal direction) on the{0001}plane,and ■ was mainly parallel to the RD direction of the tube.After annealing at 400～700℃，the base plane of TA18 titanium alloy tube was still dominated by<0001>//ND radial texture.The difference was that after annealing at 600～700℃，the ■ parallel to the RD of the tube gradually changes to■ parallel to the RD of the tube.From the{0001}basal plane,it could be seen that there was no obvious change in the radial texture factor of the basal plane during annealing,and there were three types of texture evolution during recrystallization annealing.The first type was that the{0001}■texture represented by the first kind of red grains gradually evolved into the{0001}■texture represented by the second kind of red grains.According to the spatial orientation relationship of closely spaced hexagonal metals,the grains rotated 30°around their c axis during the texture evolution,and the{0001}plane radial texture factor did not change.The second type was that the ■texture represented by the original green grain gradually evolves into the ■texture,represented by the red grains.The c axis of the grain gradually moved closer to ND,and the radial texture factor of the{0001}plane would increase.The third type was that the{0001}■texture represented by the original red grains gradually evolved into■,represented by the blue grains.The c axis of the grain gradually aligned with the transverse direction (TD),and the radial texture factor of{0001}plane will decrease.The above three types of texture evolution worked together in the annealing recrystallization stage,resulting in no significant change in the{0001}basal radial texture factor during the recrystallization process.Based on the fact that the annealing texture inherited the cold rolling texture characteristics of the tube to a certain extent,the texture control of aviation TA18 titanium alloy tube should focus on the selection of cold rolling deformation process parameters,to obtain high-performance TA18 titanium alloy tube that met the requirements of technical indicators.
Damage Failure Model of Titanium Aluminum Alloy for Cutting Simulation
Feng Shuo;Wang Jinhui;Li Na;Wang Limei;Niu Jintao;Qiao Yang;Fu Xiuli;Wang Xiangyu;Titanium aluminum alloy has the advantages of low density, high strength, high-temperature creep resistance and oxidation resistance, and can be used in complex service conditions, especially in high temperature and high pressure and other harsh service environments, but still maintain good mechanical and physical properties, is a kind of material that can be used in the aerospace industry instead of titanium alloys and nickel-based alloys, to achieve the weight reduction of aero-engines, and to increase the thrust-to-weight ratio. Due to the high strength and poor thermal conductivity of titanium aluminum alloys, there are obvious problems such as tool wear, high cutting temperature and poor surface integrity of the work piece during the cutting and machining of the material, which limits the application and promotion of this alloy material. At present, the traditional cutting processing research methods are costly and timeconsuming, compared with the use of finite element method to study the cutting force and temperature is a more economical and effective method. The accurate definition of material in cutting finite element simulation relies on the material's intrinsic model and damage failure model, the current researchers have more studies on the intrinsic model, but in cutting simulation, the intrinsic model alone cannot accurately simulate the process of chip separation, chip separation needs to be defined as the material's damage and damage evolution, but there is a lack of accurate titanium aluminum alloy damage failure model, which affects the accuracy of the cutting simulation. This paper took Ti-48 Al-2 Cr-2 Nb titanium aluminum alloy as the research object, and the failure strain, stress triaxiality and strain rate of this material were obtained through quasi-static tensile test of smooth specimen and notched specimen at different temperatures as well as dynamic tensile test, and the results of the tensile test of smooth specimen found that with the gradual increase of strain, the real stress of the material was also on the trend of increasing, and the material was not observed to have obvious yielding behavior. In addition, as the strain rate increases, the strength of the material also increased, which reflected the effect of strain rate on the strengthening of the material. The ultimate load became larger with the increase of loading speed, and the fracture diameter increased with the increase of loading speed, so the deformation of the material was smaller with the increase of loading speed. In the results of tensile tests of notched specimens, it was found that the failure strain decreases as the stress triaxiality increases. In the case of the same tensile speed and initial diameter, affected by the notched radius, the post-break diameter decreased with the increase of notched radius, indicating that the plastic deformation was gradually enhanced with the increase of notched radius. The dynamic tensile test results showed that with the temperature increased from 20 to 400 ℃, the plastic deformation of the material increased significantly, the stress also increased, indicating that at this time the strain strengthening was greater than the thermal softening, when the temperature continued to rise to 600 ℃, the plastic deformation of the material increased was still obvious, but the stress change was small, indicating that the strain strengthening and temperature softening to reach an equilibrium. The results of dynamic tensile specimen tests at a strain rate of 1000 s-1 showed that as the temperature continued to rise, the post-break cross-sectional area was decreasing, while the failure strain was increasing, indicating that the plastic deformation increased significantly with the rise in temperature. Since the stress triaxiality, strain rate and temperature were multiplicative and uncoupled, the five material parameters of the material could be obtained using the step-bystep fitting method, and the damage failure model was established by fitting the obtained material parameters. On this basis, the cutting process of the material under different cooling conditions of dry cutting, emulsion cooling cutting and liquid nitrogen cooling cutting was simulated, and it was found that serrated chips appeared under all three cooling conditions when the cutting speed of vc=150 m·min-1, and the degree of serrated chip morphology under the emulsion cooling conditions was smaller than that of dry cutting and liquid nitrogen cooling cutting, and different degrees of unitary chips appeared in both dry cutting and liquid nitrogen cooling cutting. The dry cutting and liquid nitrogen cooling cutting both showed different degrees of unit chips and even fracture, while the emulsion chips were still in continuous chip state and no unit chips appeared. Comparing with the chip morphology and cutting force during the actual right-angle cutting test, it was found that the chip morphology in the simulation and the actual test was basically consistent, indicating that the cutting simulation damage model of titanium-aluminum alloy established in this paper had high accuracy. The relative error between the simulation results of cutting force and the test results was within 10%, and the change trend of the simulation value was consistent with the change trend of the measured value, which also verified the accuracy of the damage failure model. The establishment of the damage failure model provided more accurate guidance for the cutting simulation of titanium aluminum alloy.
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