Effects of under-aging treatment on microstructure and mechanical properties of squeeze-cast Al-Zn-Mg-Cu alloy

The effects of under-aging treatment on the microstructure and mechanical properties of Al-Zn-Mg-Cu alloy produced by squeeze casting were investigated using optical microscopy (OM), X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and hardness and tensile testing. The results showed that most of secondary phases were dissolved into α(Al) matrix while no significant grain growth happened under the condition of solution treatment at 470 °C for 4 h. Due to the strengthening effect of GP zones, for alloys treated by under-aging process, the increase of aging time and aging temperature improved the ultimate tensile strength (UTS) and yield strength (YS), but decreased the elongation (δ) to some extent. By utilizing appropriate aging time and temperature, the best combination of strength and ductility could be obtained to fulfill the design requirements of automobile components.     

Ultrasonic characterization of residual stresses in steel rods using a laser line source and piezoelectric transducers

The surface residual stresses in steel rods made of the same material but with different heat treatments have been studied from Rayleigh wave velocity measurements using the laser ultrasonics technique and piezoelectric transducers. The Rayleigh wave velocities, both along the circumference and in the axis direction on the cylindrical surface of every rod, are measured and compared with one another in order to evaluate qualitatively the surface stress state for each rod. The experimental results clearly show that the Rayleigh wave velocities on the cylindrical surfaces of these rods are different, and the results obtained by laser ultrasound are in good agreement with those measured with piezoelectric transducers. From the measured velocities, different stress states have been identified for these rods according to the heat treatments they have undergone.     

盲孔法测量高残余应力的可靠性与精确度

钻孔法测量残余应力的范围是应力不超过材料屈服极限的一半。但是在许多情况下,钻孔法是用于测量焊接残余应力,而该应力峰值往往接近材料的屈服极限。本文探讨了盲孔法测量高残余应力的可靠性与精确度。为了模拟工程应用中测量残余应力的实际过程,本文采用标定的方法,即在试验机保持一定载荷不变的条件下进行贴片与钻孔操作,测得释放应变值。试验结果表明,用测得释放应变值计算出的应力值与标定应力值吻合较好,最大绝对误差仅为21 MPa。     

耐热钢厚壁管环焊残余应力的有限元分析

以热-弹塑性理论为基础，建立了厚壁管环焊残余应力的二维轴对称有限元模型，利用ANSYS有限元分析软件，模拟了耐热钢厚壁管环焊对接的应力分布。结果表明，焊缝内表面及其附近处的轴向应力和环向应力均是拉应力，而外表面是压应力，接头处内表面应力水平高于外表面；径向应力数值远低于环向应力和轴向应力；各方向残余应力的最大值均位于距管道外表层一定距离处，其数值大小接近于材料的屈服点应力。     

The influence of some rolling parameters on the residual stresses after rolling

A 2D analysis of the deformation process in the rolling gap is presented. Flat strip rolling is considered for a low carbon steel at a temperature of 1000°C.

2D — Finite Element models with a rotating workroll have been installed using the Abaqus/Explicit-Code. The workroll is modelled as a rigid body. The main subject of the analysis is to show the influence of the phenomena taking place at the entrance to the rolling gap on the development of the stress and the strain fields in the rolled material. It can be shown that due to the shearing process the backward slip exists of the three zones A, B, C. The importance of these zones depends strongly on the shape coefficient Δ. The elastic — plastic modelling of the material behaviour allows the calculation of the residual stresses.     

预拉伸对新淬火态2A12硬铝合金残余应力和力学性能的影响

对新淬火态2A12硬铝合金不同预拉伸量下的残余应力和力学性能进行了研究,得到了取得最小残余应力值的预拉伸量,分析了新淬火态铝合金薄板表面残余应力的方向问题,并对屈服强度和抗拉强度在不同拉伸量下的分布规律作了探讨。     

BT20钛合金电子束焊接残余应力三维有限元数值模拟

研究钛合金电子束焊接构件残余应力的大小和分布，了解残余应力的形成机理，具有十分重要的理论和实际意义。作者利用ANSYS程序模拟了BT20钛合金电子束焊态和焊后电子束局部热处理的实际焊接温度场以及焊接接头应力场的变化和残余应力的分布。计算结果表明，钛合金薄板焊缝中心残余拉应力的峰值达到焊缝金属屈服强度σn的60％-70％；焊后电子束局部热处理可以降低焊缝中心处的拉伸残余应力值，降低约50％左右；用所建模型计算得到的数值结果规律与实测的残余应力值基本一致。     

铝合金搅拌摩擦焊接头残余应力测试分析

采用小孔法研究厚2 mm的6061-T5铝合金搅拌摩擦焊对接接头残余应力的分布规律,分别测量接头处垂直、平行于焊缝的残余应力,并进行了计算分析。结果显示,搅拌摩擦焊接头残余应力在焊缝及其附近区域无论是垂直还是在平行焊缝方向的均承受压应力,且随小孔深度的增加而增加。垂直和平行于焊缝方向的残余应力呈现出周期性分布,且它们在前进侧的周期相比于后退侧较小;残余应力在焊缝两侧呈不对称分布,后退侧应力值较高,其残余应力峰值出现在后退侧轴肩作用区域边缘处,其值分别为93 MPa和100 MPa。     

Microstructures and mechanical properties ofAZ91D magnesium alloy processed by low pressure die casting

AZ91D alloy components were cast by low pressure die casting （LPDC） process. The mechanical properties of cast components with different microstructural features （shrinkage and distribution of MgtTAlt2 second phase） were investigated under as-east states. Compared with gravity casting, AZ91D with LPDC has much coarser grain size and second phases（Mg17Al12 and Al8Mn5）. The different size and distribution of Mg17All2 phase and shrinkage correspond to different mechanical properties. The ultimate tensile strengths and elongations are mainly decided by the content and distribution of shrinkage porosity, while the yield strengths are determined by the percentage and distribution of Mg17Al12 phase. The more and finer Mg17Al12 phase in the alloy, the relatively higher the yield strengths are. In the alloy without shrinkage, the mechanical properties are mainly determined by the size and distribution of Mg17Al1l2 phase. The finer Mg17Al12 phase, the better the mechanical properties are. Under optimal process, the density and mechanical properties of LPDC AZ91D are improved with fine microstructures.     

环肋圆柱壳结构焊接残余应力和变形的数值模拟

运用有限元软件ANSYS的APDL语言,对耐压圆柱壳结构的焊接残余应力和变形编制计算程序,运用生死单元技术,对结构进行焊接热应力分析,得到环肋圆柱壳结构的焊接残余应力分布和焊接残余变形.计算结果表明,轴向焊接残余应力在结构肋骨附近呈双峰形态,以及残余变形在焊缝处(肋骨所在位置)最为剧烈,焊接轴向残余应力总体上来说比较小...     

时效对ADC12压铸铝合金组织和性能的影响

通过微观组织观察、拉伸性能测试和尺寸稳定性测试等研究了时效工艺对ADC12压铸铝合金微观组织、力学性能和尺寸稳定性的影响。结果表明,随时效时间或温度增加,合金内部逐渐弥散析出强化粒子相,合金强度呈上升趋势;进一步增加时效时间或温度,强化粒子相开始聚集长大,合金强度下降。在时效后的保温处理过程中,影响试样尺寸的因素主要有两个,一是残余应力,二是固态相变。时效温度较低或时间较短时,残余应力消除造成的试样尺寸变长占据主导地位,试样尺寸伸长。随时效时间或温度增加,固态相变造成的试样变短占据主导地位,试样尺寸变化由正值转为负值,即试样缩短。综合考虑合金的拉伸性能、经济效益及尺寸变化尽量小的原则,ADC12合金合适的时效工艺为200~220 ℃×4 h或220~240 ℃×2 h。     

Effects of zonal heat treatment on residual stresses and mechanical properties of electron beam welded TC4 alloy plates

Zonal heat treatment(ZHT) was conducted in situ to 14.5 mm-thick TC4 alloy plates by means of defocused electron beam after welding. The effects of ZHT on residual stresses, microstructures and mechanical properties of electron beam welded joints were investigated. Experimental results show residual stresses after welding are mostly relieved through ZHT, and the maximum values of longitudinal tensile stress and transverse compressive stress reduce by 76% and 65%, respectively. The tensile strength and ductility of welded joint after ZHT at slow scanning velocity are improved because of the reduction of residual stress and the microstructural changes of the base and weld metal. ZHT at fast scanning velocity is detrimental to the ductility of welded joint, which is resulted from insufficiently coarsened alpha phase in the fusion zone and the appearance of martensite in the base metal.     

机械振动对铸造铝合金组织和性能的影响

分析振动方式对ZL101铝合金消失模铸件组织和力学性能的影响。结果表明,机械振动后合金组织明显细化;垂直振动时,合金晶粒尺寸最小,孔隙率最低,抗拉强度最大;ZL101合金垂直振动后,不同厚度处的组织存在较大差别,厚度越大,振动细化效果越显著。     

板翅结构钎焊残余应力与热变形的有限元分析

对微小尺寸的镍基钎焊不锈钢板翅结构在真空钎焊过程中产生的残余应力分布与热变形状况进行研究分析.采用有限元方法对三层结构的钎焊过程进行了热-力分析,分析考虑真空钎焊的加热特点同时考虑板翅材料和镍基钎料与温度相关的材料特性,得到了钎焊过程中结构的温度变化规律以及钎焊后的残余应力分布和热变形特征.结果表明,隔板与翅片具有不同的热变形特征,板翅钎焊接头钎角处应力状况复杂,易萌生裂纹导致板翅结构的失效,需要选择合适的钎焊时间以得到较好的钎焊接头.     

Applied mechanics in grinding. Part 7: residual stresses induced by the full coupling of mechanical deformation, thermal deformation and phase transformation

In this final part of the series research on residual stresses in ground components, the full coupling of mechanical deformation, thermal deformation and phase transformation during grinding was investigated using the finite element method. It was found that all the components of surface residual stresses become tensile when phase transformation takes place. This phenomenon is independent of the cooling conditions and type of grinding operations and is affected only slightly by the variation of surface mechanical traction. The distribution of the residual stress in grinding direction is nearly linear in both the martensite and non-martensite zones. However, the location of the maximum residual stress is related to the surface mechanical traction and depth of martensite transformation.     

Influence of dopant on the behavior under thermal cycling of two plasma- sprayed zirconia coatings Part 2: residual stresses

The evolution of coating morphology and surface residual stresses was followed for three different pow-ders: zirconia stabilized with 8 wt% yttria (YSZ), 9.9 wt% dysprosia (DSZ), and 9.8 wt% ytterbia (YbSZ). The YSZ reference powder was fused and crushed (-45 +22 μm), and the other two were agglom-erated and sintered (-90 +10 μm). According to the size distributions and manufacturing process, the plasma-sprayed YSZ particles were fully molten, resulting in dense coatings with good contact between the splats; the DSZ and, especially, the YbSZ particles were partially molten. In general, the surface residual stresses were slightly compressive before thermal cycling. The YSZ and DSZ coatings were insensitive to aging (600 h in air at room temperature), as shown by the surface stress evolution, which was not the case for YbSZ coatings. Six hundred furnace thermal cycles from 1100 °C to room temperature indicated excellent behavior of YSZ and DSZ coatings, with almost no variation of sur-face residual stresses, compared to a high dispersion for YbSZ coatings with the development of macrocracks parallel and perpendicular to the substrate within the coating. Part 1 of this article was printed in the Journal of Thermal Spray Tech-nology, Vol 5 (No. 4), 1996, p 431-438.     

Thermal residual stresses and stress distributions under tensile and compressive loadings of short fiber reinforced metal matrix composites

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Effects of processing on texture,internal stresses and mechanical properties during the pulsed electrodeposition of nanocrystalline and ultrafine-grained nickel

The mechanical properties of nanocrystalline and ultrafine-grained metals strongly depend on grain size, grain boundary segregation, texture and internal stresses. In this paper a thorough systematic analysis is given on the influence of different pulsed electrodeposition processing parameters and grain refiners on the grain size, texture and segregation of Ni and thus on internal stresses. The grain refiner content of the electrolyte, mainly the saccharin content, and the pulse parameters on- and off-time as well as the pulse current density were varied systematically. The combination of different methods of stress and texture analysis allows, among other things, a careful discussion of the influence of saccharin on stress and texture development. Massive tensile specimens were produced with different grain sizes and deformed in incremental load tests. These tests clearly demonstrate the strong effect of the production process on the deformation behavior under constant load.     

Effect of welding methods on the magnitude of residual stresses in welding up cracks in grey cast iron casing components*

It is shown that the magnitude of residual stresses in welding up cracks in casing components is not sufficient to distort them and depends on the welding method. The behaviour of the residual stresses is the same for all methods investigated in these investigations. The deformation work of a welded joint in tensile or shear loading depends on the welding method and determines the probability of formation of weld zone cracks.