MIG焊叠加对铝合金FSW焊残余应力的影响研究

文中针对4 mm厚6A01-T5铝合金FSW焊缝叠加MIG焊,研究了MIG焊叠加对FSW焊残余应力分布的影响。研究结果表明:FSW焊残余应力在焊缝两侧分布不对称,前进侧残余应力较大,峰值残余应力位于前进侧热机影响区附近; MIG焊叠加FSW焊后残余应力同样分布不对称,峰值残余应力位于叠加MIG焊缝中心附近;与FSW焊相比,叠加MIG焊后正面残余应力均有一定程度降低且FSW后退侧叠加时横向残余应力下降最明显,叠加MIG焊后背面纵向残余应力下降不明显,横向残余应力均呈增大趋势,且FSW后退侧热机影响区叠加时的横向残余应力增加最显著。     

地铁用SUS301L奥氏体不锈钢激光焊接头残余应力研究

对地铁用SUS301L奥氏体不锈钢激光焊和熔化极活性气体保护焊(MAG)焊接接头的残余应力进行了X射线衍射测试分析.测试结果表明:激光焊和MAG焊接头均存在较大值的残余拉应力,残余应力分布趋势相同.激光焊接头残余应力峰值低于MAG焊接头残余应力峰值,这是由于激光焊热输入量较小,对母材热影响较小,母材塑性压缩效应低造成的.     

约束条件对奥氏体不锈钢对接接头残余应力的影响

为了准确评价奥氏体不锈钢的焊接残余应力,采用X射线衍射法进行应力测试,并通过对等强度梁应力的X射线测试,得出316L奥氏体不锈钢测试的最优参数。使用该测试参数对两种约束条件下的奥氏体不锈钢焊接接头残余应力进行测试。结果表明:使用X射线衍射法测量奥氏体不锈钢残余应力,应以(311)晶面为衍射晶面,且Mn靶的测试效果优于Cr靶。两种不同约束条件下纵向残余应力沿横向和纵向的分布情况相同,但预置反变形的纵向拉、压应力值均大于背板约束的纵向拉、压应力。横向残余应力沿横向随距焊缝距离的增加变化趋势有所不同。随距焊缝的距离增加,反变形条件下横向残余应力逐渐恢复至初始状态,而背板约束时仍保留一定的残余拉应力。横向残余应力沿纵向的分布趋势相同。     

阵列射流冲击热沉搅拌摩擦焊接新方法

基于动态低应力无变形技术的原理,设计开发了阵列射流冲击热沉搅拌摩擦焊接新方法.结果表明,采用该方法可以有效减小搅拌摩擦焊接头残余应力,焊后试件基本无变形.采用射流冲击热沉的动态低应力无变形搅拌摩擦焊接头残余应力分布规律与常规搅拌摩擦焊类似,但应力峰值明显降低,约为常规FSW接头应力峰值的45%,可以实现FSW薄壁结构的低应力无变形焊接.该项技术可以提高一些铝合金材料FSW接头性能,具有较好的技术经济价值.     

薄壁铝合金搅拌摩擦焊焊接应力变形与控制

搅拌摩擦焊(FSW)焊接残余应力变形表现出与传统熔焊不同的规律,文中研究了薄壁铝合金搅拌摩擦焊残余应力分布规律和焊接变形控制方法,结果表明,纵向残余应力峰值并非出现于焊缝中心,热影响区和热机影响区是残余应力相对较大的区域.基于动态低应力无变形焊接方法,设计开发了一套热沉系统,进行了动态低应力无变形FSW试验.研究表明,动态低应力无变形焊接技术可以有效减小搅拌摩擦焊接头残余应力和变形,接头残余应力分布规律与常规搅拌摩擦焊接头残余应力分布类似,但应力峰值降低50%以上.     

2099铝锂合金搅拌摩擦焊接头的微观组织

通过显微硬度测试、金相观察、EBSD和透射电镜观察等手段研究T83态2099铝锂合金挤压型材搅拌摩擦焊(FSW)焊缝的微观组织和硬度分布。结果表明:基材呈部分再结晶组织,主要析出相为T1相和δ′相,存在{112}111铜型、S织构和立方织构。焊接区域的晶粒尺寸均小于基材,且该区域在焊接过程中基材的原有析出相发生溶解后重新析出细小的δ′相。焊缝区的硬度由于晶粒尺寸和析出相的变化整体下降,呈W型分布,热机械影响区的硬度最低。热机械影响区和热影响区分别以{112}110织构和{112}111铜型织构为主,且都存在较弱的{001}120再结晶织构。焊核区发生动态再结晶,存在大量旋转立方织构。     

2195-F态铝锂合金TIG焊和FSW焊后残余应力分析

采用盲孔法和压痕法,分别对2195-F态铝锂合金手工TIG焊和FSW焊后残余应力进行测量. 结果表明,盲孔法的测量值普遍高于压痕法. 两种焊接方法,近焊缝区的纵向应力均高于横向应力;横向应力整体表现为压应力或小于50 MPa的拉应力;纵向应力在热影响区附近表现为大于焊缝的拉应力. 焊缝区附近,手工TIG焊纵向残余应力大于FSW,且纵向残余应力表现为较大的拉应力,最大值接近于接头的屈服强度;焊缝区外,手工TIG焊和FSW残余应力值相差不大,其横向残余应力基本表现为很小的拉应力或者压应力.     

工艺参数对铝合金搅拌摩擦焊变形和残余应力的影响及优化

FSW作为先进固相连接技术,广泛应用于轨道交通车辆生产制造中。文中结合理论与试验研究了FSW工艺参数对6005A-T6铝合金枕梁搅拌摩擦焊接头残余应力与焊接变形的影响,首先建立了枕梁有限元模型,采用顺序热力耦合的方法,计算了不同工况下焊接接头的残余应力与变形,进而开展枕梁结构搅拌摩擦焊试验,采用钻孔法对焊接试件进行了残余应力测试,并对仿真分析和试验检测结果进行了对比分析,然后对仿真结果开展了正交试验、极差分析、回归分析得出残余应力与焊接变形和焊接工艺参数的关系式,最后对所得数学模型进行粒子群优化分析。结果表明,焊接速度一定时,提升一定的主轴转速,低焊速下横向残余应力峰值变化量更大,而高焊速下纵向残余应力、焊接变形峰值变化量更大;主轴转速一定时,提升一定的焊接速度,低主轴转速下横向残余应力、焊接变形峰值变化量更大,而高主轴转速下纵向残余应力峰值变化量更大;采用粒子优化算法所得的最优残余应力与焊接变形组合为残余应力峰值199.9 MPa,焊接变形峰值0.352 mm,对应焊接参数为焊接速度461.6 mm/min,主轴转速300 r/min,其优化效果为6.13%。文中所得结论为枕梁及其类...     

缆式焊丝埋弧焊残余应力有限元分析

采用直径为2.4 mm的7根分焊丝,其中一根分焊丝（称为中心丝）位于中间,其余6根分焊丝（称为外围丝）围绕中心丝绞合组成直径为7.2 mm的缆式焊丝.试验用22 mm厚DH36船用钢板进行平对接缆式焊丝埋弧焊,采用小孔法对焊接接头进行残余应力测试;基于热弹塑性理论,建立缆式焊丝埋弧焊残余应力有限元数值分析模型,利用ANSYS软件对缆式焊丝埋弧焊残余应力进行模拟计算.结果表明,缆式焊丝埋弧焊的应力分布特征和幅值与单丝埋弧焊相近,纵向应力在焊缝及近缝区表现为拉应力,应力峰值为363 MPa;横向应力较小,焊缝上下部位呈现拉应力,中间呈现压应力.     

2024/7075异种铝合金搅拌摩擦焊的晶体取向演化

使用光学显微镜、电子背散射衍射（EBSD）对比研究了2024/7075异种铝合金搅拌摩擦焊（FSW）接头及母材的组织特征、晶界特征和织构的演化.结果表明,后退侧热力影响区晶粒的小角度晶界含量较母材明显增大而前进侧热力影响区晶粒的小角度晶界含量与母材相比没有明显变化,焊核区发生了动态再结晶,大角度晶界含量明显增加.后退侧2024铝合金为弱取向组织,前进侧7075铝合金母材、热影响区以及热机影响区具有较强的S织构{123}<634>、黄铜织构{011}<211>和R织构{124}<211>,焊核区为等轴再结晶晶粒,没有明显的择优取向.     

Effective γ-surfaces in {111} plane in FCC Ni and L12 Ni3Al intermetallic compound

The well-known concept of γ surfaces originally suggested by Prof. Vitek is extended to the case of a shift of one part of a crystal with respect to the other part in two adjacent {111} planes of a stacking fault. The proposed approach is used to construct the effective γ surfaces in the {111} plane in fcc Ni and L1₂ Ni₃Al of intermetallic compound. It is shown that Ni₃Al can have five metastable stacking faults in this plane, namely, an intrinsic superlattice stacking fault, an extrinsic superlattice stacking fault, a complex stacking fault, an antiphase boundary, and a complex extrinsic stacking fault. The existence of the latter in the {111} plane in the L1₂ Ni₃Al intermetallic compound has not been reported previously. The shift of the crystal in two close-packed planes in fcc Ni makes it possible to avoid the formation of a high-energy stacking fault which arises when constructing an ordinary γ-surface, as well as to self-consistently include the extrinsic stacking fault into consideration.     

形变Ni_3Al多晶体中的对称型堆垛层错及其形成机理SCIEI

本文报告了对称型堆垛层错是Ni_3Al多晶体形变缺陷的重要组成部分。这种对称型堆垛层错的产生,是由分布在相邻{111}晶面上的位错偶在切应力的作用下进行移动、分解和合并销毁的结果。     

Microstructural design of high-strength aluminum alloys

A summary is presented of recent attempts to model the effects of precipitate shape, orientation, and distribution on yield strength and age-hardening response, using appropriate versions of the Orowan equation and models of precipitation strengthening developed for Al alloys containing a single uniform distribution of rationally oriented plate-or rod-shaped precipitates, which are either shearable or shear resistant. It is demonstrated that these models of particle strengthening are capable of predictions that are in excellent quantitative agreement with experimental observations that high tensile yield strength is associated with microstructures containing a high density of intrinsically strong, plate-shaped precipitates with {111}_α or {100}_α habit planes and large aspect ratio. The authors predict that further improvement in the strength of existing Al alloys might be achieved by increasing the number density and/or aspect ratio of rationally oriented precipitate plates.     

Residual stress measurement of Al/steel dissimilar friction stir weld

ABSTRACT

The dissimilar welds between aluminium (Al) alloy, A6061-T6, and stainless steel, type 304, were fabricated by a friction stir welding (FSW) technique. The FSW tool was offset to Al side and the probe was inserted only into Al plate. The softening occurred in Al side due to the heat input during FSW, while the hardness increased by the post-ageing treatment. Tensile strength of dissimilar weld also increased about 8.5% by the post-ageing. The residual stresses were measured based on the cos α method. The residual stresses parallel to the weld line, σ_xr, were predominantly tensile, while those perpendicular to the weld line, σ_yr, were compressive. Post-ageing treatment had little effect on the residual stresses.     

Nanoscale structural evolution of Al3Sc precipitates in Al(Sc) alloys

Precipitation of the Al₃Sc (L1₂) phase in aluminum alloys, containing 0.1, 0.2 or 0.3 wt% Sc, is studied with conventional transmission and high-resolution (HREM) electron microscopies. The exact morphologies of the Al₃Sc precipitates were determined for the first time by HREM, in Al–0.1 wt% Sc and Al–0.3 wt% Sc alloys. The experimentally determined equilibrium shape of the Al₃Sc precipitates, at 300°C and 0.3 wt% Sc, has 26 facets, which are the 6 {100} (cube), 12 {110} (rhombic dodecahedron), and 8 {111} (octahedron) planes, a Great Rhombicuboctahedron. This equilibrium morphology had been predicted by first principles calculations of the pertinent interfacial energies. The coarsening kinetics obey the (time)^1/3 kinetic law of Lifshitz–Slyozov–Wagner theory and they yield an activation energy for diffusion, 164±9 kJ/mol, that is in agreement with the values obtained from tracer diffusion measurements of Sc in Al and first principles calculations, which implies diffusion-controlled coarsening.     

Crystallographic analysis of the martensitic transformation in medium-carbon steel with packet martensite

Based on X-ray diffraction studies of the martensite texture in a single martensite packet, exact orientation relationships between the orientations of martensite crystallites and the original austenite single crystal in medium-carbon steel 37KhN3A have been determined to be as follows: (011)_α||(1; 0.990; 1.009)_γ to an accuracy of \( \pm 0.15^\circ ,{\left[ {01\overline 1 } \right]_\alpha }||{\left[ {1;1.163; - 2.133} \right]_\gamma }\) to an accuracy of ±0.15°. It has been shown that the orientation relationships proved to be almost the same as in the Fe–31% Ni alloy with a twinned martensite with close lattice parameters. Therefore, the conclusion has been drawn that the mechanism of the lattice deformation upon the martensitic transformation is the same in both alloys. It is described as follows. The lattice deformation occurs by shear on the (111) plane in the \({\left[ {11\overline 2 } \right]_{_\gamma }}\) direction and is accompanied by an additional change in the dimensions in the mutually perpendicular directions \({\left[ {11\overline 2 } \right]_{_\gamma }},\left[ {111} \right],\;and{\left[ {1\overline 1 0} \right]_{_\gamma }}\). The invariantlattice deformation is implemented by slip in martensite on the planes of the (112)_α type in the direction \({\left[ {\overline 1 \overline 1 1} \right]_\alpha }\). One of the 24 crystallographically equivalent variants of the transformation mechanism has been considered. Apart from this type of deformation, an additional deformation of martensite is possible that does not change its orientation. It has been shown that the orientation of the martensite crystallite calculated via the phenomenological theory of the martensitic transformations (PTMT) differs by approximately 1° from the experimentally determined orientation. This refers to both the lath and twinned martensite. In the twinned martensite, the invariant plane obtained in the PTMT calculations and the habit plane coincide. In lath martensite of 37KhN3A steel, the invariant plane of the martensite crystal obtained in PTMT calculations deviates by ~25° from the orientation of the surface of the martensite plate (habit plane), which is close to the (111)_γ plane. An explanation of this phenomenon is given.     

Crystal structure of ultrathin lamellar precipitates

The crystal structure of lamellar precipitates formed in alloys 1213 (Al-Cu-Ag), V-1461 (Al-Cu-Li) and V-1469 (Al-Cu-Li-Ag) has been studied during age hardening. The experimental studies have been performed using transmission electron microscopy. The precipitates have {111} habits and thicknesses of several atomic planes. In diffraction patterns, these plates give a system of diffuse streaks. These ultrathin plates scatter electrons similar to two-dimensional crystal lattices. It is shown that thin plates of precipitates in alloys 1213, V-1461, and V-1469 give identical systems of diffuse streaks. The two-dimensional crystal lattices that give the system of these streaks have a hexagonal symmetry with the following orientation relationship: {ie481-1} and the lattice parameter a _f = 0.495 nm (there is no lattice parameter c _f for two-dimensional lattices). A sequence of the steps of reconstruction of the spatial structure of plane precipitates is proposed in terms of their thickness, structures of two-dimensional lattices, and type of precipitates (extrinsic or intrinsic). The influence of Ag on the structure of lamellar precipitates in the V-1469 alloy is discussed.     

The crystallography of stress corrosion cracking in face centered cubic single crystals

The crystallography of transgranular stress corrosion cracking was studied for single crystals of α-brass (tested in 14 N NH₃), copper (tested in 1 M NaNO₂), and 304L austenitic stainless steel (tested in boiling 45 wt% MgCl₂). All fracture surfaces had characteristic flat parallel facets separated by crystallographic and/or fan-shaped steps. In α-brass and copper the facets consisted of {110} planes with the crystallographic steps following {111} planes. In 304L austenitic stainless steel cracking occurred primarily on the {100}, but secondary cracking on {110} was also found. Very smooth crystallographic-like steps were observed, generally following {100} planes. It is concluded that stress corrosion cracking in all systems tested occurred by cleavage. It is suggested that the stress corrosion cracks propagate on the lowest surface energy planes.     

化学气相沉积钨单晶管材表面电解蚀刻形成的{110}晶面形貌

报导了具有<111>晶向(轴向)的管状钼单晶基体化学气相沉积(CVD)钨单晶涂层的电解蚀刻工艺及形成的{110}晶面形貌。实验发现,通过电解蚀刻,表面的{110}晶面可以完全被蚀刻出来。蚀刻出来的{110}晶面呈台阶结构,并同<111>晶轴相平行。蚀刻出来的{110}晶面在圆管的表面分成均等六个区。每个区内{110}晶面的台阶面的宽度呈现周期性的变化,开始台阶面较宽,逐渐变窄,然后通过一过渡区后,进入下一周期,{110}晶面的台阶面的宽度又逐渐变宽。     

Off-axis texture in nanostructured Ti1 − xAlxN thin films

Standard θ-2θ and pole figure X-ray diffraction techniques were used to study structural properties and preferred orientation of nanostructured TiAlN thin films prepared using cathodic arc deposition. Systematic collection of reflections from lattice planes {111}, {200}, {220}, and {311} showed that the in-plane orientation of crystallites exhibits cylindrical symmetry with random distribution of crystallites, while the out-of-plane growth presents strong texture which is inclined with respect to the surface normal. This brings the crystallographic orientation of fibre texture towards high indices lattice planes (113) and (115) contrary to traditionally grown films that develop a preferred orientation following to low indices close-packed planes (111) and (200). The origin of inclined growth is discussed taking into account the role of crystallographic defects in particular twin faults that develop in the lattice of growing crystal and change the stacking sequences of atom layers.