纯镍与304不锈钢激光异种焊接的工艺及其接头的组织性能

采用高密度Nd:YAG固态连续激光器对N6纯镍和304奥氏体不锈钢进行了焊接工艺实验,探究了激光功率和离焦量对焊缝成形的影响。对接头进行了拉伸强度和硬度的测试,并结合光学显微镜(OM)、扫描电镜(SEM)、能谱分析仪(EDS)等手段分析了接头的微观组织。结果表明:N6纯镍一侧热影响区晶粒长大明显,焊缝区靠近两侧熔合线附近为向焊缝中心区域生长的柱状晶,焊缝中心区域存在细小的胞晶区域;N6热影响区的显微硬度最低,焊缝的显微硬度介于N6镍母材和304不锈钢母材之间;接头拉伸断裂位置在焊缝区,抗拉强度达到N6纯镍母材的90%以上,可以满足实际情况下的使用要求。拉伸断口表现为准解理断裂。

先进表征技术在铝铜异种金属激光焊接中的应用研究

本文对先进表征技术在铝铜异种金属激光焊接的概念、特点进行详细分析,以汽车、火车、飞机零部件焊接为例,从温度场表征技术、应力场表征技术、变形场表征技术三个方面入手,研究了先进表征技术在铝铜异种金属激光焊接中的应用。在此基础上,结合实际情况,对先进表征技术在铝铜异种金属激光焊接中的优化措施进行系统梳理,为充分发挥先进表征技术的各项功能作用、提高铝铜异种金属激光焊接质量奠定坚实基础。

高温高应变率下异种不锈钢激光焊接件的力学性能

利用改进的SHTB实验设备,对316L和304不锈钢焊接结构的动态力学性能进行了实验。提出了一种适用于焊接结构件的新型的SHTB夹持装置,并在应变率约103s-1、温度为25～500℃的环境下获得了焊接结构件动态应力-应变曲线。研究表明:随应变率的升高,结构件的屈服强度和抗拉强度随应变率的增大而增大,随温度的升高而降低,温度对结构件塑性流动应力的影响更明显。

YG20硬质合金/45~#钢激光焊缝的显微组织与腐蚀行为研究

利用5kW光纤激光作为热源,实现4mm厚的YG20硬质合金与45#钢的激光焊接。通过分析焊缝组织分布特征,观察焊缝在HNO_3、H_2O_2、村上试剂中浸蚀后的表面形貌,讨论了激光扫描速度对热胀系数差异较大的异种金属焊接后焊缝成形的影响规律。结果表明:当被焊材料厚度为4mm时,在激光功率为3.84kW、激光扫描速度为0.96m/min及离焦量为-8mm的条件下,可获得冶金结合良好的YG20硬质合金/45#钢焊接接头。

TiNi合金/不锈钢激光焊接头裂纹的形成和控制

采用低功率脉冲激光对0.2 mm厚的TiNi形状记忆合金/不锈钢异种材料进行焊接,对焊接接头的裂纹形态和元素分布进行了研究,分析裂纹的形成原因,提出裂纹控制的措施。结果表明,TiNi合金/不锈钢异种材料直接对接焊裂纹敏感性很大,仅通过调整激光焊接工艺参数无法避免裂纹的产生。裂纹产生的主要原因是不锈钢母材中的Fe元素大量进入焊缝,与Ti元素形成脆性金属间化合物导致焊缝变脆,在焊接应力作用下开裂。通过在TiNi合金与不锈钢之间预置纯Ni丝作为填充材料可以稀释焊缝中Fe和Ti元素的含量,对形成裂纹的脆性组织进行阻隔,避免裂纹的产生,焊接接头的平均抗拉强度达到580 MPa。

Welding of shape memory alloy to stainless steel for medical occluder

Dissimilar metal joining between NiTi shape memory alloy（SMA） and stainless steel was conducted.A cluster of NiTi SMA wires were first joined with tungsten inert gas（TIG） welding process,then the NiTi SMA TIG weld was welded to a stainless steel pipe with laser spot welding process.The microstructure of the welds was examined with an optical microscope and the elemental distribution in the welds was measured by electron probe microanalysis（EPMA）.The results show that TiC compounds dispersively distribute in the NiTi SMA TIG weld.However,the amount of TiC compounds greatly decreases around the fusion boundary of the laser spot weld between the NiTi SMA and stainless steel.Mutual diffusion between NiTi shape memory alloy and stainless steel happen within a short distance near the fusion boundary,and intermetallic compounds such as Ni3Ti＋（Fe,Ni）Ti appear around the fusion boundary.

Effect of process parameters on microstructure and properties of laser welded joints of aluminum/steel with Ni/Cu interlayer

The effects of laser parameters and interlayer material on the microstructure and properties of the welded joint between 6061 aluminum alloy and stainless steel were studied.The results show that the density and microstructure of the welded joint can be optimized by changing the laser power with 0.05 mm Cu foil and 0.1 mm Ni foil as interlayer.A large number of new Cu-Al binary phases were found near the aluminum alloy,which effectively inhibited the formation of the binary brittle phase of Fe-Al.The maximum shear force of 1350.96 N was obtained with laser power of 2200 W.The shear force of the welded joint increased to 1754.73 N when the thickness of the Cu foil thickness changed to 0.02 mm.

Transformation mechanism of secondary phase and its effect on intergranular corrosion in laser wire filling welding Ni-based alloy/304 stainless steel

To clarify the transformation mechanism of secondary phase and the mechanism of intergranular corrosion in laser welding Ni-based alloy (Hastelloy C-276)/304 stainless steel with filler wire,the secondary phase was analyzed by electron probe micro-analysis (EPMA) and transmission electron microscopy (TEM).The evaluation of intergranular corrosion resistance of the welded joints was conducted by double-loop electrochemical potentiokinetic reactivation(DL-EPR) method,and at the same time the chemical compositions of the corrosion surface were analyzed by energy-dispersive spectrometry (EDS).The results show that p phase has complete coherence relationship withμphase,and the coherent relationship is described as[001]p//■and[430]p//[0001]μ.Theμphase is rapidly transformed from p phase,which is the inhomogeneous phase transformation.The transformation of secondary phase will increase the susceptibility to intergranular corrosion.Therefore,the transformation of secondary phase should be avoided in the welding process.

Microstructure and high-temperature mechanical properties of laser beam welded TC4/TA15 dissimilar titanium alloy joints

The microstructure evolution and high-temperature mechanical properties of laser beam welded TC4/TA15 dissimilar titanium alloy joints under different welding parameters were studied.The results show that the weld fusion zone of TC4/TA15 dissimilar welded joints consists of coarsenedβcolumnar crystals that contain mainly acicularα’martensite.The heat affected zone is composed of the initialαphase and the transformedβstructure,and the width of heat affected zone on the TA15 side is narrower than that on the TC4 side.With increasing temperature,the yield strength and ultimate tensile strength of the TC4/TA15 dissimilar welded joints decrease and the highest plastic deformation is obtained at 800°C.The tensile strength of the dissimilar joints with different welding parameters and base material satisfies the following relation(from high to low):TA15 base material>dissimilar joints>TC4 base material.The microhardness of a cross-section of the TC4/TA15 dissimilar joints reaches a maximum at the centre of the weld and is reduced globally after heat treatment,but the microhardness distribution is not changed.An elevated temperature tensile fracture of the dissimilar joints is located on the side of the TC4 base material.Necking occurs during the tensile tests and the fracture characteristics are typical when ductility is present in the material.

Numerical simulation and experimental study of hybrid laser-electric arc welding between dissimilar Mg alloys

This work aims to establish a suitable numerical simulation model for hybrid laser-electric arc heat source welding of dissimilar Mg alloys between AZ31 and AZ80. Based on the energy conservation law and Fourier’s law of heat conduction, the differential equations of the three-dimensional temperature field for nonlinear transient heat conduction are built. According to the analysis of nonlinear transient heat transfer, the equations representing initial conditions and boundary conditions are obtained. The “double ellipsoidal heat source + 3D Gaussian heat source”combination was chosen to construct the laser-electric arc hybrid heat source. The weld bead morphologies and the distribution of temperature, stress, displacement and plastic strains are numerically simulated. The actual welding experiments were performed by a hybrid laser-electric arc welding machine. The interaction mechanism between laser and electric arc in the hybrid welding of Mg alloys is discussed in detail. The hybrid heat source can promote the absorption of laser energy and electric arc in the molten pool, resulting in more uniform energy distribution in the molten pool and the corresponding improvement of welding parameters. This work can provide theoretical guidance and data supports for the optimization of the hybrid laser-electric arc welding processes for Mg alloys.