等径道角挤压预变形AZ61镁合金在半固态等温处理中的微观组织演变(英文)

利用金相显微镜和图像分析设备对等径道角挤压预变形AZ61镁合金在半固态等温处理中的微观组织演变进行研究。先利用等径道角挤压对AZ61镁合金铸坯在310℃进行应变诱导,然后将其在半固态进行不同时间的等温处理。研究结果表明:挤压道次、等温处理温度和变形路径影响预变形AZ61镁合金在半固态等温处理中的微观组织演变过程。在将等温处理温度从530℃升高至560℃的过程中,合金的平均晶粒尺寸从22μm增大到35μm。当等温处理温度为575℃时,平均晶粒尺寸减小。当等径道角挤压的变形路径为BC时,预变形AZ61镁合金在半固态等温处理中获得的微观组织晶粒尺寸最小。     

循环淬火对22MnCrNiMo系泊链钢组织和性能的影响

22MnCrNiMo钢是用于制造R4级海洋工程系泊链的新型钢种,为了使其达到R4S级系泊链的综合力学性能,比较系统地研究了22MnCrNiMo钢两次快速加热循环淬火调质热处理工艺及组织和力学性能的变化规律.结果表明,该钢经循环淬火处理后获得了细小均匀的奥氏体晶粒,晶粒平均尺寸由原始轧制态的38μm细化到约10μm,综合性能得到明显提高.尤其是韧性与一次加热淬火调质处理的相比,-20℃冲击功值提高近40%,完全达到R4S级系泊链的综合力学性能要求.     

Microstructural evolution and mechanical properties of severely deformed Al-12Si casting alloy by equal-channel angular extrusion

Microstructural evolution and mechanical properties of Al-12Si alloy subjected to equal-channel angular extrusion (ECAE) were investigated. The high stresses imposed in ECAE led to the fragmentation of the needle-shaped eutectic silicon plates into smaller particles. The length and width of the Si particles decreased from 35.5±31.8 μm and 13.7±8.9 μm without ECAE to 2.7±1.1 μm and 1.3±0.4 μm after six ECAE passes, respectively. The average aspect ratio of 3.2±1.8 for the Si particles in the as-cast condition decreased to 1.18±0.8 after six ECAE passes with a corresponding increase in the average roundness of 0.26±0.19 to 0.61±0.19. ECAE increased the strength, ductility, and impact toughness of the alloy. The increase in the tensile and yield strengths after six passes was about 68 % and 100 %, respectively. The alloy after six ECAE passes exhibited 12 % elongation to failure, which was almost eight times higher than that of the as-cast alloy. The absorbed energy increased with an increase in the number of passes, finally reaching 11. 5 J/cm² after six passes, which is about four times higher than that of the as-cast alloy.     

Microstructure characterization and quasi-static failure behavior of resistance spot welds of AA6111-T4 aluminum alloy

The microstructure, microhardness and quasi-static failure behavior of resistance spot welds of AA6111-T4 aluminum alloy were experimentally investigated. Optical metallography and high-resolution hardness traverses were utilized to characterize the weld nugget, heat affected zone and base metal. The AA6111 spot welds displayed a softer nugget and hardened heat affected zone, compared with the base metal. The through-thickness hardness of the base metal sheet was not constant and had to be carefully considered to determine the effect of welding on material properties. Quasi-static lap-shear tensile tests were used to determine the failure load and failure mode. All tensile specimens failed through the interfacial fracture. This failure mode is consistent with the observed reduced hardness in the weld nugget.     

固溶前预退火处理对6111铝合金组织与性能的影响

系统研究了固溶前预退火温度对6111铝合金冷轧板和T4P态组织和力学性能的影响。测试了力学性能,计算了LDR值;表征了显微组织、SEM组织和XRD织构构成。结果表明:预退火温度对6111铝合金的屈服强度影响较小;经300 ℃×2 h预退火处理后,抗拉强度发生明显降低,由245 MPa降低到230 MPa;当预退火温度高于100 ℃后,伸长率呈直线下降。n值和r值均随预退火温度先升高后降低,n值在200 ℃时达到最大值0.289,r值在100 ℃时达到最大值0.958。200 ℃×2 h预退火处理后,LDR值达到最大值2.005。经300 ℃×2 h预退火处理后,T4P态基体晶粒尺寸明显长大,在60~150 μm范围。200 ℃×2 h预退火处理试样,T4P态Cube织构体积分数最高,达到了13.5%。     

Warm forging of aluminium alloys: a new approach for time compression of the forging sequence

A new forging sequence, including a warm forging process, is proposed in order to obtain time compression in the production of forgings in heat treatable aluminium alloys. It offers the advantage of eliminating time consuming and expensive heat treatments. The proposed sequence consists of a solution treatment, followed by water quenching and then by warm forging that produces a fine precipitate structure characterised by high mechanical properties. The optimal warm forging condition was investigated by evaluating the strength and ductility values of the forgings by means of compression testing. The warm forging operation of the AA 6082 aluminium alloy, in the as-solutioned condition, at a temperature of about 240°C, after the natural ageing, provides mechanical properties that are almost coincident with those obtained after conventional forging sequences including an artificial ageing treatment. It was also observed that at such temperature the mechanical properties of the warm-forged parts are not significantly affected by the die speed.     

Preparation of semi-solid billet of magnesium alloy and its thixoforming

Preparation of semi-solid billet of magnesium alloy and thixoforming was investigated by applying equal channel angularextrusion to magnesium alloy.The results show that mechanical properties of AZ91D alloy at room temperature,such as yieldstrength(YS),ultimate tensile strength(UTS)and elongation,are enhanced greatly by four-pass equal channel angularextrusion(ECAE)at 573 K and microstructure of AZ91D alloy is refined to the average grain size of 20μm.Through using ECAE asstrain induced step in SIMA and completing melt activated step by semi-solid isothermal treatment,semi-solid billet with finespheroidal grains of 25μm can be prepared successfully.Compared with common SIMA,thixoformed satellite angle framecomponents using semi-solid billet prepared by new SIMA have higher mechanical properties at room temperature and hightemperature of 373 K.     

Parametric study on crashworthiness of automotive sheet alloy

Crashworthiness (or collision performance) is a critical design factor in optimizing automotive part products. In this study, a numerical sensitivity analysis was performed to investigate the effects of material properties on crashworthiness for automotive sheet materials. As standard material parameters, the measured mechanical properties of AA 6111-T4 sheet were considered, based on the anisotropic non-quadratic yield function, YId2004-18p, and a combination type non-linear isotropic-kinematic hardening law. The constitutive law was implemented into codes of the commercial finite element program ABAQUS, using user material subroutines. As for process simulations, spring-back after forming as well as sheet forming and collision were included in this evaluation.     

Effect of aluminium sheet surface conditions on feasibility and quality of resistance spot welding

A study investigating the effect of sheet surface condition on resistance spot welding (RSW) of aluminium has been carried out. This concentrates on two automotive aluminium alloys; AA5754 and AA6111, used for structural and closure applications respectively. The results show the marked effect that surface condition can have on the RSW process. For AA5754 sheet incomplete removal of a ‘disrupted surface layer’ prior to surface pretreatment is shown to have a detrimental effect on the RSW process. The solid wax lubricant used to assist metal forming leads to unpredictable changes in contact resistance, and consequently affects the process stability. For AA6111 closures the final surface topography can influence the RSW process. Standard ‘mill’ and electro-discharge textured (EDT) finish sheet surfaces were examined and preliminary results suggest that both are suitable for welding. The successful application of RSW of aluminium sheet requires careful consideration of the sheet surface condition. This requires close collaboration between material suppliers and automotive manufacturers.     

提高Al-Zn-Mg-Cu铝合金薄板T76状态电导率的热处理工艺研究

试验研究不同固溶温度、二级时效温度和保温时间对Al-Zn-Mg-Cu铝合金薄板力学性能及电导率的影响。结果表明,随着固溶温度提高,板材的强度提高,伸长率降低,电导率变化不大;随着二级时效温度升高,板材的强度降低,伸长率稍有降低,电导率平稳升高;随着二级时效保温时间延长,板材的强度下降,伸长率变化不大,电导率逐渐升高。该合金板材T76状态的适宜固溶温度为(467±2)℃,双级时效制度为(120±3)℃5 h+(166+3)℃36 h。     

ECAP with back pressure for optimum strength and ductility in aluminium alloy 6016. Part 2: Mechanical properties and texture

The simultaneous increase in strength and ductility of aluminium alloy 6016 processed by equal channel angular pressing (ECAP) was investigated. A complete study of microstructure, texture and mechanical properties after ECAP processing with and without back pressure was carried out for the O temper. The simultaneous increase in strength and ductility of AA6016-O with number of ECAP passes was explained by the use of back pressure during ECAP. A maximum ductility of ～100% was obtained at the temperature of 200 °C and strain rate of 10^?4 s^?1, which is a significant improvement on the ductility exhibited by AA6016 (～89%) after a conventional thermomechanical treatment at a much higher temperature of 500 °C. The mechanical behaviour was interpreted in the context of the textures developed in the material. A significant amount of texture rotation due to applied back pressure was found.     

Numerical Investigations on the Influence of Superimposed Double-Sided Pressure on the Formability of Biaxially Stretched AA6111-T4 Sheet Metal

Lightweight materials have been widely used in aerospace, automobile industries to meet the requirement of structural weight reduction. Due to their limited plasticity at room temperature, however, lightweight materials always exhibit distinctly poor forming capability in comparison with conventional deep drawing steels. Based on the phenomenon that the superimposed hydrostatic pressure can improve the plasticity of metal, many kinds of double-sided pressure forming processes have been proposed. In the present study, the Gurson-Tvergaard-Needleman (GTN) damage model combined with finite element method is used to investigate the influence of double-sided pressure on the deformation behavior of biaxially stretched AA6111-T4 sheet metal, including nucleation and growth of microvoids, evaluation of stress triaxiality, and so forth. The Marciniak-Kuczynski (M-K) localized necking model is used to predict the right-hand side of the forming limit diagram (FLD) of sheet metal under superimposed double-sided pressure. It is found that the superimposed double-sided pressure has no obvious effect on the nucleation of microvoids. However, the superimposed double-sided pressure can suppress the growth and coalescence of microvoids. The forming limit curve (FLC) of the biaxially stretched AA6111-T4 sheet metal under the superimposed double-sided pressure is improved and the fracture locus shifts to the left. Furthermore, the formability increase value is sensitive to the strain path.     

基于双辊铸轧的Al-Zn-Mg-Cu系合金冷轧后的再结晶行为

将双辊铸轧运用于制造Al-Zn-Mg-Cu合金带材。研究带材减薄率及热处理温度对合金再结晶行为的影响。结果表明：在冷轧率为60％、热处理制度为500℃的条件下处理1h时,合金带材具有细晶组织（平均晶粒尺寸约为13μm,晶粒纵横比约为1．7）和高的力学性能（UTS≥360MPa,δ≥20％）。研究了微观组织对Al-Zn-Mg-Cu合金带材力学性能的影响。合适的双棍铸轧热处理及加工工艺能制造低价、高强的Al-Zn-Mg-Cu合金带材。     

Hot stamping of AA5083 aluminium alloy sheets

The paper is aimed at proving the feasibility of producing sheet components by stamping AA5083 sheets at elevated temperature and strain rate. Laboratory tensile and Nakajima-type tests were carried out to evaluate the material flow stress, ductility and fracture limits sensitivity to temperature and strain rate, and therefore to determine the optimal combination of process parameters assuring both maximum formability and effective post-deformation mechanical properties. Industrial trials were conducted on an automotive component to validate the laboratory results.     

Production,structure, texture,and mechanical properties of severely deformed magnesium

Methods of the severe plastic deformation (SPD) of pure magnesium at room temperature, namely, transverse extrusion and hydroextrusion in a self-destroyed shell, have been developed. The maximum true strain of the samples after the hydroextrusion was e ~ 3.2; in the course of transverse extrusion and subsequent cold rolling, a true strain of e ~ 6.0 was achieved. The structure and mechanical properties of the magnesium samples have been studied in different structural states. It has been shown that the SPD led to a decrease in the grain size d to ~2 μm; the relative elongation at fracture δ increased to ~20%. No active twinning has been revealed. The reasons for the high plasticity of magnesium after SPD according to the deformation modes suggested are discussed from the viewpoint of the hierarchy of the observed structural states.     

Tailored heat treated accumulative roll bonded aluminum blanks: failure under bending stresses

Ultrafine-grained accumulative roll bonded (ARB) sheet metals of aluminum alloys have a high potential for lightweight construction. The mechanical properties can be enhanced regarding strength and ductility by the combination of ARB and a local heat treatment according to the Tailor Heat Treated Blanks technology. The present investigation focuses on the failure behavior of ultrafine-grained ARB blanks. Due to the low formability of these high-strength ARB metals, a detailed understanding of the failure mechanisms is essential. For this purpose, an established approach to determine the different stages of damage of the material for conventional materials is now applied to multilayered aluminum in the as-received and heat-treated condition. In this context, air bending tests are used to qualify and quantify the bending and forming behavior of ARB sheets of AA1050A and AA6016 aluminum alloys.     

时效处理对7A20铝合金时效硬化响应和晶间腐蚀的影响

研究了自然时效(NA)效应对7A20铝合金人工时效硬化行为的影响,测试了其维氏硬度和力学性能,运用金相显微镜、扫描电镜和透射电镜表征了其微观组织演变情况。结果表明:固溶处理后的试样在室温放置过程中表现出明显的自然时效效应。经3天(NA3)和8天(NA8)自然时效处理后的试样,人工时效初期均出现了时效软化效应,经2 h人工时效后,显微硬度分别降低25.3%和22.7%。不同热处理后试样的基体晶粒无明显差异,但晶内结构却有明显差别。热处理后的试样,在晶界处均存在20 nm左右的PFZ区。NA3+160 ℃×40 h和NA8+160 ℃×40 h的试样,晶内短棒状析出相数量增多。固溶处理后直接进行人工时效,抗晶间腐蚀性能最好,腐蚀深度为80~120 μm。NA3和NA8试样经160 ℃×40 h人工时效后,其晶间腐蚀深度分别达到了100~140 μm和120~160 μm,且有明显的脱落现象。     

Effect of Heat Treatment on Microstructure and Mechanical Properties of A380 Aluminum Alloy Deposited by Cold Spray

The microstructure and mechanical properties of cold-sprayed bulk A380 alloy were investigated after heat treatment at various conditions, using optical and electron microscopy and tensile and hardness tests, respectively. The results revealed that heat treatment increased the strength and ductility of the cold-sprayed A380 alloy deposits compared with as-sprayed state. Heat treatment showed two different effects on the mechanical properties of the deposits. On the one hand, it resulted in effective diffusion at interparticle boundaries that altered the particle bonding mechanism from pure mechanical interlocking to metallurgical bonding. Thus, the strength and ductility of the material were greatly enhanced. On the other hand, interparticle diffusion during high-temperature heat treatment resulted in growth of the Si phase and pores, which ultimately reduced the strength and elongation of the alloy. This observation was consistent with the hardness results, which showed a decreasing trend with increase of the heat treatment temperature.     

Effects of heat treatment on mechanical properties of ODS nickel-based superalloy sheets prepared by EB-PVD

A Y2O3 dispersion strengthened nickel-based superalloy sheet(0.15 mm thick) was prepared by electron beam physical vapor deposition(EB-PVD) technology.Different heat treatments were used to improve the mechanical properties of the alloy sheet.Differential thermal analysis(DTA) was used to examine the thermal stability of the as-deposited sheet.Element contents,phase composition and microstructure investigations on as-deposited and heat treated specimens were performed by X-ray fluorescence spectrometer(XRF),X-ray diffraction(XRD) and scanning electron microscopy(SEM).Tensile tests were conducted at room temperature on specimens as-deposited and heat treated.The results show that the as-deposited sheet is composed of equiaxed grains on the substrate side and columnar grains on the evaporation side.The as-deposited sheet shows poor ductility due to micropores between columnar grains.The strength and ductility can be improved effectively by annealing at 800°C for 3 h.For samples treated at 1100°C,the strength drops down due to the precipitates of Y3Al5O12(YAG).     

Mechanical properties and microstructure evolution in incremental forming of AA5754 and AA6061 aluminum alloys

This study performs single point incremental forming (SPIF) on two aluminum alloys (i.e. AA5754 and AA6061), and analyzes their post forming mechanical properties and microstructure evolution. The forming parameters namely wall angle (35°–55°), feed rate (1–4 m/min), spindle rotational speed (50–1000 r/min), and lubricant (grease and hydraulic oil) are varied to probe detailed processing effects. The pre- and post-SPIF mechanical properties and microstructures are characterized by conducting tensile tests and optical microscopy, respectively. It is shown that an increase in the wall angle, feed rate and rotational speed causes microscopic variations in the alloys such that the grains of AA5754 and the second phase particles of AA6061 elongate. As a result, the ultimate tensile strength of the formed parts is increased by 10% for AA5754 and by 8% for AA6061. And, the ductility of AA5754 is decreased from 22.9% to 12% and that of AA6061 is decreased from 16% to 10.7%. Regarding the lubricant effect, it is shown that the mechanical properties remain insensitive to the type of lubricant employed. These results indicate that SPIF processing modifies the microstructure of Al alloys in a way to enhance the strength at the cost of ductility.