环境温湿度对铝合金焊缝气孔和力学性能的影响

对于高速轨道客车铝车身的生产制造,气孔是焊接中最常见的缺陷。采用X射线法研究了不同温度和湿度下铝合金6082和5083熔化极氩弧焊(MIG)焊缝的气孔情况。结果表明,在焊接过程中环境的绝对湿度(是温度和湿度的综合体现)对焊缝的气孔率有重要影响,铝合金6082焊缝的气孔敏感性要比铝合金5083高。在拉伸试验中铝合金6082接头的断裂位置一般在焊接热影响区(HAZ),随着绝对湿度的增加,接头的抗拉强度和断后伸长率几乎保持不变,但接头的正弯和背弯角度分别减小了74.4%和64.4%。铝合金5083接头的断裂位置一般出现在熔合区,随着绝对湿度的增加,接头的抗拉强度和断后伸长率分别减小了4.0%和15.7%,但是弯曲性能变化不大。     

The effect of controlled shot peening on fusion welded joints

This work examines the effect of controlled shot peening (CSP) treatment on the fatigue strength of an ASTM A516 grade 70 carbon steel welded joint. Metallurgical modifications, hardness, elemental compositions, and internal discontinuities, such as porosity, inclusions, lack of penetration, and undercut found in treated and untreated fusion welded joints, were characterized. The fatigue results of as-welded and peened skimmed joints were compared. It was observed that the effect of the CSP and skimming processes improved the fatigue life of the fusion weld by 50% on MMA-welded, 63% on MIG-welded, and 60% on TIG-welded samples.     

环境温湿度对铝合金焊缝气孔和力学性能的影响

对于高速轨道客车铝车身的生产制造,气孔是焊接中最常见的缺陷.采用X射线法研究了不同温度和湿度下铝合金6082和5083熔化极氩弧焊(MIG)焊缝的气孔情况.结果表明,在焊接过程中环境的绝对湿度(是温度和湿度的综合体现)对焊缝的气孔率有重要影响,铝合金6082焊缝的气孔敏感性要比铝合金5083高.在拉伸试验中铝合金6082接头的断裂位置一般在焊接热影响区(HAZ),随着绝对湿度的增加,接头的抗拉强度和断后伸长率几乎保持不变,但接头的正弯和背弯角度分别减小了74.4％和64.4％.铝合金5083接头的断裂位置一般出现在熔合区,随着绝对湿度的增加,接头的抗拉强度和断后伸长率分别减小了4.0％和15.7％,但是弯曲性能变化不大.     

Comparison of fatigue properties between friction stir welds and TIG welds

对比分析了搅拌摩擦和氩弧焊两种工艺方法对铝合金焊接接头疲劳性能的影响,建立了焊接接头的S-N曲线,结果表明：在相同的载荷条件下,搅拌磨擦焊接接头的疲劳性能优于氩弧焊接头。搅拌摩擦焊接头疲劳寿命N=106次的疲劳强度值约为59~65MPa之间。对焊接接头显微组织的分析表明：搅拌摩擦焊接接头具有比氩弧焊接头更为细小的晶粒和狭窄的焊接热影响区,阻碍了滑移带的形成和裂纹的扩展,从而提高了接头的疲劳性能。TIG焊接接头疲劳端口分析显示,焊接缺陷是主要的疲劳裂纹源。     

热处理温度对TC17(α+β)/TC17(β)钛合金线性摩擦焊接头组织及力学性能的影响

对TC17(α+β)/TC17(β)钛合金线性摩擦焊接头进行热处理实验,采用光学显微镜(OM),扫描电子显微镜(SEM)和显微硬度仪等检测手段,研究不同热处理温度对焊接接头微观组织及力学性能的影响。结果表明:焊态下,接头焊缝区发生再结晶,界面处为亚稳定β相组织,显微硬度低于母材,接头高周疲劳强度为345 MPa。TC17(α+β)侧热力影响区因焊接速率过快,残留了大量的初生α相。经过焊后热处理,亚稳定β相分解,焊缝析出弥散的(α+β)相。随着热处理温度的升高,细小的次生α相长大,部分发生球化。热处理后,因亚稳定β相分解,焊缝及热力影响区的显微硬度大幅度升高,接头疲劳强度平均提高65 MPa;随着热处理温度的升高,接头热力影响区的断裂韧度增加。     

Improvement of weld temperature distribution and mechanical properties of 7050 aluminum alloy butt joints by submerged friction stir welding

Submerged friction stir welding (FSW) in cold and hot water, as well as in air, was carried out for 7050 aluminum alloys. The weld thermal cycles and transverse distributions of the microhardness of the weld joints were measured, and their tensile properties were tested. The fracture surfaces of the tensile specimens were observed, and the microstructures at the fracture region were investigated. The results show that the peak temperature during welding in air was up to 380 °C, while the peak temperatures during welding in cold and hot water were about 220 and 300 °C, respectively. The temperature at the retreated side of the joint was higher than that at the advanced side for all weld joints. The distributions of microhardness exhibited a typical “W” shape. The width of the low hardness zone varied with the weld ambient conditions. The minimum hardness zone was located at the heat affected zone (HAZ) of the weld joints. Better tensile properties were achieved for joint welded in hot water, and the strength ratio of the weld joint to the base metal was up to 92%. The tensile fracture position was located at the low hardness zone of the weld joints. The fracture surfaces exhibited a mixture of dimples and quasi-cleavage planes for the joints welded in cold and hot water, and only dimples for the joint welded in air.     

高强度钢框架梁柱节点焊接构造的断裂性能试验研究

为研究高强度钢材焊缝连接在实际节点构造中的断裂性能,选取代表实际梁柱节点局部焊接构造的十字型焊接接头试件,采用对接熔透焊和角焊缝两种焊缝类型,完成了20个高强度钢材典型焊接构造在单调拉伸和往复加载下的断裂性能试验,研究了高强钢焊接构造断裂机理,探讨了焊缝类型、荷载类型及钢材强度对典型构造细节断裂性能的影响。研究结果表明,焊缝类型对高强钢焊接构造断裂性能有较大影响,拉-卸载作用导致高强钢焊接节点热影响区材料损伤开裂,往复加载幅值越大,高强钢焊接节点的缺陷敏感性越大,越容易发生断裂失效。试验得到对接熔透焊和角焊缝试件在单调拉伸和往复加载下的断裂临界伸长量和临界荷载,为发展高强度钢材节点焊缝区域的断裂分析模型提供依据。     

Fatigue strength of mash seam welded joints

Reversed bending fatigue tests have been conducted using four series of mash seam welded joints obtained from the coupling of two different steels and plate thicknesses. Fatigue strength was evaluated and the effects of material property changes resulting from welding were studied. Fatigue strength of all series of the welded joints decreased slightly compared with that of the base steel. Type of steel and plate thickness in the welded samples exerted very little influence on fatigue strength. In the welded joints between steels with the same plate thickness, fatigue failure took place at a location away from the weld zone in the plate with the lower strength, while in the welded joints between plates of different thickness, failure occurred at the shoulder between the thin and thick plate, i.e. at the weld zone. Regardless of the type of steel and the plate thicknesses joined, fatigue strengths of the mash seam welded joints were slightly higher than those of the laser welded butt joints.     

Rib loading effects on weld root fatigue failure modes at rib‐to‐deck welded joint

The service life of orthotropic steel decks is dependent on the fatigue resistance of rib‐to‐deck welded joints, which is often tested using two kinds of experimental models in terms of the rib loading condition. Different weld root fatigue failure modes have been observed in the different models, but the role of rib loading remains unclear. This paper aims to clarify the effect of rib loadings on the weld root fatigue failure modes at rib‐to‐deck welded joints. The loadings are decomposed into the deck loadings and rib loadings according to the principle of superposition. Formulae of the weld root notch stress intensity factors and T‐stress under rib loadings are developed by multiparameter regression analysis and subsequently used for the local stress analysis. The fatigue failure modes determined from the local stress field agree well with the experimental results. The results reveal that the weld root failure modes depend on the rib loadings but are independent of the weld geometries. The averaged strain energy density (SED) that can capture both weld geometry and loading condition effects is used to correlate the fatigue test data of different weld root failure modes. The SED is capable of evaluating the fatigue strength of the rib‐to‐deck welded joint failed by different weld root failure modes with a narrow scatter band.     

Low cycle fatigue strength of butt-welded steel joint by means of new testing system with image technique

In this study, we investigated the low cycle fatigue strength of welded joints using a new fatigue testing system in which the image analysis technique was used to measure the strains in specimens. After checking the validity of the testing system, we used this new system to conduct fatigue tests on welded joint specimens. The test results indicate that the fatigue strength of welded material (weld deposit and heat affected zone) is much lower than that of the plain material.     

Zr58Nb2.76Cu15.46Ni12.74Al10.34Y0.5非晶合金激光焊接接头微观结构及显微硬度表征

目的 探究激光焊接参数对非晶合金焊接接头的组织演变、焊缝成形、晶化程度等的影响规律,以及控制接头晶化的有效途径.方法 采用碟片激光器对Zr58Nb2.76Cu15.46Ni12.74Al10.34Y0.5非晶合金进行激光焊接,对比分析不同激光功率下,焊接速度对接头熔宽和晶化组织形成的影响规律,并对接头各区域微观组织特征...     

Effects of mechanical heterogeneity on the tensile and fatigue behaviours in a laser-arc hybrid welded aluminium alloy joint

The effects of mechanical heterogeneity on the tensile and high cycle fatigue (10⁴–10⁷ cycles) properties were investigated for laser-arc hybrid welded aluminium alloy joints. Tensile–tensile cyclic loading with a stress ratio of 0.1 was applied in a direction perpendicular to the weld direction for up to 10⁷ cycles. The local mechanical properties in the tensile test and the accumulated plastic strain in the fatigue test throughout the weld’s different regions were characterized using a digital image correlation technique. The tensile results indicated heterogeneous tensile properties throughout the different regions of the aluminium welded joint, and the heat affected zone was the weakest region in which the strain localized. In the fatigue test, the accumulated plastic strain evolutions in different subzones of the weld were analyzed, and slip bands could be clearly observed in the heat affected zone. A transition of fatigue failure locations from the heat affected zone caused by accumulated plastic strain to the fusion zone induced by fatigue crack at pores could be observed under different cyclic stress levels. The welding porosity in the fusion zone significantly influences the high cycle fatigue behaviour.     

Fatigue strength of steel and aluminium welded joints based on generalised stress intensity factors and local strain energy values

Weld bead geometry cannot, by its nature, be precisely defined. Parameters such as bead shape and toe radius vary from joint to joint even in well-controlled manufacturing operations. In the present paper the weld toe region is modelled as a sharp, zero radius, V-shaped notch and the intensity of asymptotic stress distributions obeying Williams’ solution are quantified by means of the Notch Stress Intensity Factors (NSIFs). When the constancy of the angle included between weld flanks and main plates is assured and the angle is large enough to make mode II contribution non-singular, mode I NSIF can be directly used to summarise the fatigue strength of welded joints having very different geometry. By using a large amount of experimental data taken from the literature and related to a V-notch angle of 135°, two NSIF-based bands are reported for steel and aluminium welded joints under a nominal load ratio about equal to zero. A third band is reported for steel welded joints with failures originated from the weld roots, where the lack of penetration zone is treated as a crack-like notch and units for NSIFs are the same as conventional SIF used in LEFM. Afterwards, in order to overcome the problem related to the variability of the V-notch opening angle, the synthesis is made by simply using a scalar quantity, i.e. the mean value of the strain energy averaged in the structural volume surrounding the notch tips. This energy is given in closed form on the basis of the relevant NSIFs for modes I and II and the radius R_C of the averaging zone is carefully identified with reference to conventional arc welding processes. R_C for welded joints made of steel and aluminium considered here is 0.28 mm and 0.12 mm, respectively. Different values of R_C might characterise welded joints obtained from high-power processes, in particular from automated laser beam welding. The local-energy based criterion is applied to steel welded joints under prevailing mode I (with failures both at the weld root and toe) and to aluminium welded joints under mode I and mixed load modes (with mode II contribution prevailing on that ascribable to mode I). Surprising, the mean value of ΔW related to the two groups of welded materials was found practically coincident at 2 million cycles. More than 750 fatigue data have been considered in the analyses reported herein.     

X70大变形管环焊接头及断裂机制研究

目的基于应变设计大变形管线环焊接头热影响区的软化问题,解决制约管线安装质量和服役寿命等难题。方法通过显微硬度测试、微观组织分析,研究了X70大变形管接头热影响区的软化原因,并利用数字相关法研究了焊接接头拉伸过程中的断裂机制,还对焊接接头热影响区进行了激光增强探索。结果 X70焊接接头热影响区粗晶区的最大硬度损失达HV0.239;软化区最大应变达到37%以上;经过热影响区激光重熔后,X70钢焊接接头抗拉强度可提高10%以上,断裂位置均位于母材。结论 X70焊接接头热影响区粗晶区存在明显的软化;拉伸过程中在软化区出现了明显的应变集中,是X70焊接接头断裂于近缝区的主要原因;焊接接头热影响区粗晶区粗大的粒状贝氏体和铁素体导致了焊接接头热影响区的软化。     

热输入对Q1100钢焊接接头低温韧性及耐蚀性能的影响

采用10 kJ/cm和15 kJ/cm两种焊接热输入对Q1100超高强钢进行熔化极气体保护焊,研究焊接接头的组织性能及局部腐蚀行为。结果表明：两种热输入焊接接头的焊缝组织主要为针状铁素体和少量的粒状贝氏体,粗晶区组织均为板条贝氏体,细晶区组织均为板条贝氏体和粒状贝氏体,临界相变区组织为多边形铁素体、马奥岛和碳化物的混合组织。两种热输入焊接接头中电荷转移电阻均为母材>热影响区>焊缝区,母材耐蚀性最好,热影响区次之,焊缝区耐蚀性最差。在腐蚀过程中,焊缝区作为阳极最先被腐蚀,当腐蚀一定时间后,腐蚀位置发生改变,阳极腐蚀区域转移到母材区,而焊缝区作为阴极得到保护。热输入为10 kJ/cm时,焊接接头具有更好的低温韧性和耐蚀性,其焊缝和热影响区-40℃冲击功分别为46.5 J和30.2 J。     

Effect of microstructural features on the failure behavior of hybrid laser welded AA7020

Detailed investigations of microstructural feature, mechanical property, fatigue strength, and damage mechanism were conducted on hybrid laser welded 7020‐T651 aluminum alloys used into high‐speed railway vehicles. The results show that the hybrid laser welding process can induce significant changes of microstructures and alloying elements, together with numerous gas pores. Such local modifications degrade the fatigue performance. The tensile strength of welded joints was approximately 74% with respect to the base metal, thus satisfying the design standard. The fatigue property was determined in the low and high cycle regimes. It was found that the fatigue strength of welded joints was fairly inferior to that of the base metal, but far higher than the IIW recommended value. Furthermore, welding defects were well believed to contribute to the shorter fatigue life. The small fatigue crack growth presented highly discontinuous and inhomogeneous due to microstructure and porosity. By contrast, the crack stable growth stage was less sensitive to microstructural features of hybrid welded joints.     

Schwingfestigkeitseigenschaften von Schweißverbindungen hochfester,schweißgeeigneter Baustähle

Fatigue strength properties of welded joints of high-strength weldable structural steel. Particularly with regard to weld joints, high-strength and super high-strength structural steels under unfavourable boundary conditions is hardly superior to normal-strength characteristics of butt joint and cruciform joint samples can be improved by optimizing the weld seam geometry and by subsequent mechanical treatment by shot peening with ceramic balls or with steel scraps, and at determining which difficulties may occur during this process. The practical tests were supported and completed by theoretical calculations according to the FE-method. A final comparison with the standards will illustrate the difficulties in determining admissible fatigue strength values of weld joints.     

Combined effect of strength & sheet thickness on fatigue behaviour of resistance spot welded joint

Fatigue performance of spot welded lap shear joint is primarily dependent on weld nugget size, sheet thickness and corresponding joint stiffness. Two automotive steel sheets having higher strength lower thickness and lower strength higher thickness are resistance spot welded with established optimum welding condition. The tensile‐shear strength and fatigue strength of lap shear joint of the two automotive steel sheets are determined and compared. Experimental fatigue life of spot welded lap shear joint of each steel are compared with predicted fatigue lives using different stress intensity factor solutions for kinked crack and spot weld available in literature. Micrographs of fatigue fractured surfaces are examined to understand fracture micro‐mechanisms.     

DP590双相钢点焊接头的正交试验及超声检测分析

对DP590双相钢点焊接头进行正交试验,研究不同工艺因素对点焊接头失效载荷和焊核直径的影响,确定最优点焊工艺参数,并探讨点焊接头压痕深度的超声测量方法.采用超声波水浸聚焦入射法对1.5 mm厚的DP590双相钢点焊接头进行超声C扫描,获得接头焊核直径,利用超声A扫信号,计算点焊接头压痕深度,并与实际测量结果对比.研究表明:焊接参数对DP590点焊接头的失效载荷与焊核直径的显著性影响一致,从大到小依次为焊接电流、焊接时间、电极压力;DP590点焊接头最优的焊接工艺参数为:焊接时间70 ms,焊接电流15.0 k A,电极压力6.5 k N,在此参数下接头的抗拉强度为9 521.4 N;超声A扫信号计算得到的点焊接头表面压痕率与实际压痕率的误差在2.5%~9.7%,超声计算所得压痕深度与实际测量压痕率较为接近.     

搅拌摩擦与氩弧焊铝合金接头疲劳性能的比较

建立了铝合金焊接接头的S-N曲线,对比分析了搅拌摩擦和氩弧焊两种工艺对其焊接接头疲劳性能的影响,结果表明:在载荷相同的条件下,铝合金搅拌磨擦焊接接头的疲劳性能优于氩弧焊接头,搅拌摩擦焊接头的疲劳寿命N=106次的疲劳强度为59-65 MPa,搅拌摩擦焊接接头具有比氩弧焊接头更为细小的晶粒和狭窄的焊接热影响区,阻碍了滑移带的形成和裂纹的扩展,从而提高了接头的疲劳性能,铝合金焊接接头的缺陷是主要的疲劳裂纹源.