6061铝合金双轴肩搅拌摩擦焊接扭矩特征

为了揭示6061铝合金BTFSW过程中焊接扭矩的特征,对扭矩进行了检测,分析了扭矩信号的频谱特征、扭矩峰值的变化特点、扭矩振荡与焊缝表面成形的关系.研究表明扭矩具有周期性,主要频率接近于2倍主轴旋转频率值,频差的存在说明了焊接区域存在搅拌头与不同速率的金属流之间挤压摩擦的叠加行为;当接触点温度小于500℃时,扭矩峰值随着焊接速度的提高而变大,随着旋转速度的提高而变小;正常较小的扭矩振荡不影响表面成形,但当接触点温度大于550℃、上下轴肩间距过小或焊接速度过小或旋转速度过大等时,扭矩易发生异常振荡.对进一步揭示深入研究BTFSW焊接机理、搅拌头三维受力特征及其与焊接参数、焊接质量的关系有着重要的推动意义.     

铝合金搭接搅拌摩擦焊接头拉伸变形的数值模拟

通过对2A12铝合金搭接搅拌摩擦焊接头的强度试验,研究了搭接搅拌摩擦焊接头的断裂行为,应用有限元方法对2A12铝合金板材搭接搅拌摩擦焊接头的拉伸力学响应进行了模拟计算,获得了搭接搅拌摩擦焊接头在外载作用下的局部应力应变分布与变形规律.结果表明,在搭接接头的搭接面上存在两个类裂纹的未焊接区域,塑性变形首先在搭接界面裂纹尖端区域发生,上板受拉侧裂纹尖端周围区域的塑性变形最大,是导致搭接搅拌摩擦焊接头上板的前进侧热影响区断裂的主要原因.     

铝合金搅拌摩擦焊技术研究存在的问题及趋势

搅拌摩擦焊(Friction Stir Welding-FSW)是目前铝、镁、铜及有色金属等轻合金连接的最先进连接技术之一,FSW与传统熔焊相比,在工艺过程、接头性能等方面具有许多优势.在讨论FSW技术特征、工艺特点及应用研究的基础上,对目前国内外有关FSW技术的研究现状、发展趋势及存在问题进行了详细综述,所涉及的问题是在工业化铝合金结构制造领域(如飞机机身结构、高速客车及汽车车体结构等)大规模推广应用FSW技术必须解决的基础性问题;其次讨论基于FSW研究开发的新思路及新工艺,尤其是搅拌摩擦点焊技术(Friction Stir Spot Welding-FSSW)的原理、特点及在汽车车体轻量化开发中的巨大应用前景.     

6061铝合金搅拌摩擦焊工艺

采用搅拌摩擦焊方法对板厚6mm的6061铝合金板在不同参数下进行焊接,研究6061铝合金搅拌摩擦焊工艺以及主要参数对焊缝成形和接头力学性能的影响,观察焊接接头的金相组织,通过硬度分布测试分析焊接接头的力学不均匀性.结果表明:压入量过大或过小时容易造成焊接接头成形差等缺陷,压入量为0.3 mm时可以获得优质的焊缝成形;搅...     

GIL壳体5754铝合金FSW与GTAW接头组织和性能

针对GIL壳体材料5754铝合金,制备FSW和GTAW接头,并研究焊接接头的显微组织、拉伸性能、弯曲性能和冲击性能。结果表明,两种焊接方法下焊缝组织均为α-Al基体弥散分布着细小的β相(Al8Mg5),采用GTAW方法时,热影响区晶粒明显粗化;两种焊接接头的强度和弯曲性能均可以满足壳体的强度设计要求。由于FSW过程的搅拌作用,焊缝金属发生高温动态回复再结晶,因此FSW接头的抗拉强度和冲击性能更为优异。     

LY12铝合金搅拌摩擦焊接头残余应力分析

采用小孔法对不同焊接工艺参数下得到的LY12铝合金薄板搅拌摩擦焊对接接头的残余应力进行了测量和分析.为了消除孔边塑性变形对测量精度的影响,建立了三维有限元法模拟应变释放系数的测量试验,使用基于孔边形状改变比能的A,B系数修正法对盲孔释放系数进行修正.结果表明,接头残余应力呈不对称分布,前进侧应力高于返回侧;纵向残余应力总是高于横向残余应力,但是横向残余应力并非在零附近,而是有一定的大小,约为焊前母材强度的10.8%;在一定范围内,搅拌摩擦焊接头残余应力随旋转频率先增大后减小,随下压量和焊接速度的增加而增加.     

解决运载工具铝合金焊接难题的新途径--搅拌摩擦焊

阐述了采用铝合金焊接结构制造运载工具的必要性和效果，论述了铝合金焊接运载工具的机械性能试验结果并分析其焊接中的难题。介绍了用搅拌摩擦焊解决铝合金焊接难题的新途径及其主要原因。     

Material flow and core/multi-shell structures in a friction stir welded aluminum alloy with embedded copper markers

The objective of this study was to reveal the material flow and temperature distribution in a thick aluminum plate during friction stir welding and examine the subsequent microstructural change with particular attention to the reaction between copper marker and aluminum matrix. It is shown that the material adjacent to the threaded pin was transported from the top to bottom non-symmetrically, and then was forced to move upwards at a small distance from the pin due to the constraint of an extrusion-die-like configuration. The interaction between the copper marker and aluminum matrix led to the formation of (i) a unique core/multi-shell microstructure consisting of copper core, inner shell of AlCu and outer shell of Al₂Cu, and (ii) a composite band containing uniformly-distributed Al₂Cu particles with refined grains due to the lower stacking fault energy of copper and the pinning role of Al₂Cu particles.     

Fatigue crack growth in the welding nugget of FSW joints of a 6060 aluminum alloy

Friction stir welded butt joints were performed on 8 mm thick sheets made of AA6060 T6 aluminum alloy by means of a CNC machine tool, at feed rates between 117 and 683 mm/min and tool rotational speed between 838 and 1262 rpm. Tensile tests, metallographic analyses and micro-Vickers tests were carried out to evaluate the mechanical properties of the joints as a function of the process parameters. The fatigue behavior was studied by means of crack growth tests performed according to ASTM E647 standard on CT specimens, with propagation in the middle of joint along the weld nugget. The results show the influence of welding process parameters on mechanical properties and fatigue behavior. Reduction of UTS of about 20–30% with respect to base material occurred with rupture in the softened zone of welding, usually HAZ. In this range, slight variations of joint efficiency were observed with f/S ratio, while the width of the softening area increases for decreasing values of this parameter. Fatigue crack growth was always slower than that in the base material at low ΔK below 12 MPa m^1/2. The effect of non-optimal welding parameters was evident at intermediate and high ΔK, due to defects, such as tunnels, that cause dramatic increase of propagation rate up to five times higher than the base material.     

Experimental study on temperature distributions within the workpiece during friction stir welding of aluminum alloys

This study aims to experimentally explore the thermal histories and temperature distributions in a workpiece during a friction stir welding (FSW) process involving the butt joining of aluminum 6061-T6. Different types of thermocouple layout are devised to measure the temperature histories during FSW at different locations on the workpiece in the welding direction. Successful welding processes are achieved by appropriately controlling the maximum temperatures during the welding process. Regression analyses by the least squares method are used to predict the temperatures at the joint line. A second-order polynomial curve is found to best fit the experimental temperature values in the width direction of the workpiece. The Vickers hardness test is conducted on the welds to evaluate the hardness distribution in the thermal-mechanical affected zone, the heat affected zone, and the base metal zone. Tensile tests are also carried out, and the tensile strength of the welded product is compared with that of the base metal.     

7A52铝合金搅拌摩擦焊工艺优化

接头强度是搅拌摩擦焊接头性能的一个重要指标,通过搅拌头旋转频率、焊接速度和轴肩下压量等焊接工艺参数的不同组合制备了35个7A52焊接试板,对试板进行拉伸试验检测了接头的抗拉强度,建立并分析了焊接接头抗拉强度与焊接工艺参数之间的回归模型,搅拌头旋转频率n,焊接速度v和轴肩下压量d<,ta>单独变化时,接头抗拉强度都有峰值...     

7050铝合金搅拌摩擦焊接头超高周疲劳性能

采用超高周疲劳试验系统研究7050-T7451铝合金搅拌摩擦焊接头的超高周疲劳性能. 试验结果表明,焊接接头在10⁷周次以上仍然会发生疲劳失效,S-N曲线在10⁸周次左右出现转折点,呈折线型下降;通过SEM对超高周疲劳断口形貌进行观察发现,当应力范围较高时,试件的疲劳裂纹往往在表面萌生,随着应力范围的降低,裂纹有亚表面和内部萌生的倾向;裂纹萌生位置取决于表面起裂和内部起裂相互竞争的结果;试件的断裂位置多为焊接接头的热力影响区和热影响区,EBSD和接头硬度的分析结果表明断裂位置与接头组织不均匀密切相关.     

厚板铝合金FSW和MIG焊接接头疲劳性能

对厚度10 mm的6082-T6铝合金搅拌摩擦焊(FSW)和MIG焊接接头的疲劳强度进行了试验研究,并与6082-T6母材疲劳性能进行了对比分析.结果表明,6082-T6母材的疲劳S-N曲线最高、MIG焊接接头S-N曲线度最低,而FSW接头的疲劳S-N曲线近似位于两者之间;在高应力区FSW疲劳强度低于MIG焊接接头、而在低应力区高于MIG焊接接头.大部分FSW试样疲劳裂纹启始于焊缝根部的"弱连接"缺陷,采用机械加工去掉1.4 mm厚度焊缝根部材料后,FSW疲劳强度明显提高并接近母材数据.厚板6082-T6铝合金FSW焊缝根部质量控制是影响疲劳性能的关键因素.     

Influences of tool pin profile and welding speed on the formation of friction stir processing zone in AA2219 aluminium alloy

AA2219 aluminium alloy has gathered wide acceptance in the fabrication of light weight structures requiring a high strength to weight ratio. Compared to the fusion welding processes that are routinely used for joining structural aluminium alloys, friction stir welding (FSW) process is an emerging solid state joining process in which the material that is being welded does not melt and recast. This process uses a non-consumable tool to generate frictional heat in the abutting surfaces. The welding parameters and tool pin profile play major roles in deciding the weld quality. In this investigation, an attempt has been made to understand the effect of welding speed and tool pin profile on FSP zone formation in AA2219 aluminium alloy. Five different tool pin profiles (straight cylindrical, tapered cylindrical, threaded cylindrical, triangular and square) have been used to fabricate the joints at three different welding speeds. The formation of FSP zone has been analysed macroscopically. Tensile properties of the joints have been evaluated and correlated with the FSP zone formation. From this investigation it is found that the square pin profiled tool produces mechanically sound and metallurgically defect free welds compared to other tool pin profiles.     

铝合金平板搅拌摩擦焊接应力变形分析

针对6056-T6铝合金平板进行搅拌摩擦焊接和试板变形检测试验.并用数值方法对试板变形进行模拟,考察了模拟温度、应力场分布和试板变形情况,对试验和模拟温度、变形进行比较.结果表明,在文中条件下,沿焊缝长度方向试板产生下挠,最大变形量6.3 mm;沿试板宽度方向试板相对发生上拱,最大变形量4.5 mm,模拟与实测变形趋势非常吻合.纵向残余应力在焊缝中心线两侧非对称性分布,前进侧大于回转侧.     

Microstructure and mechanical properties of Al-6061-T6 alloy welded by a new hybrid FSW/SSW joining process

In this study for the first time, the effects of decrease in heat inflow to the weld metal in friction stir process by utilising semisolid processing and decreasing the pin rotational speed as well as increasing the pin transverse speed were examined. As a result, the characteristic loss of hardness and strength in the weld zone were eliminated. The results showed that by approaching the ultrafine microstructure in the weld zone through the hybrid FSW/SSW process, the hardness and elongation values reached to 90?Hv and 8.88%, respectively. These are only slightly different from those of the base metal of the welded samples. Furthermore, the ultimate tensile strength of the samples welded by the hybrid technique was found to be about 167?MPa that was higher than those of the samples welded by friction stir welding (151?MPa) and semisolid welding (114?MPa) techniques.     

2219铝合金FSW-VPPA交叉焊缝组织与力学性能

采用搅拌摩擦焊(FSW)和变极性等离子弧焊(VPPA),在2219铝合金6 mm板上沿着相互垂直的方向施焊以形成FSW-VPPA交叉焊缝.对交叉焊缝的组织形貌进行了观察分析,并对交叉焊缝和单一VPPA焊缝的拉伸力学性能及断口形貌进行了对比研究.结果表明,交叉焊缝微观组织呈现不对称、不均匀的特征,其焊缝区组织主要由α-Al基体和(α-Al+CuAl2)共晶组成,熔合区以及近熔合区的热影响区易于出现聚集性气孔;熔合区附近气孔发生率增加导致交叉接头抗拉强度及断后伸长率明显下降.     

超声表面机械研磨处理对6061铝合金FSW接头疲劳行为的影响

利用超声表面机械研磨处理(USMGT)方法对6061-T6铝合金搅拌摩擦焊(FSW)接头进行了表面晶粒细化处理,采用光学显微镜、显微硬度仪、扫描电镜等测试手段,对接头组织、力学性能及疲劳性能进行了分析。结果表明,USMGT处理后焊接接头表面形成了包含大量细化晶粒的梯度细晶层,表面细晶层的形成使接头表面硬度得到提高;接头的宏观断裂位置在热机影响区(TMAZ)和热影响区(HAZ)之间,滚压处理强化试样表层,FSW接头内部TMAZ和HAZ之间出现的软化现象无法消除,相比其他区域,该部分依然是疲劳薄弱区,承受载荷时微观裂纹源萌生位置由表面向内部迁移;滚压处理会使表层引入残余压应力,从而使得接头的疲劳性能得到提高,当应力幅值为150 MPa时,USMGT后的接头疲劳寿命达到未处理的3．5倍。     

Comparative study of fatigue behaviour in dissimilar Al alloy/steel and Mg alloy/steel friction stir spot welds fabricated by scroll grooved tool without probe

Abstract

Aluminium alloy A6061-T6 or magnesium alloy AZ31 sheet was welded to steel sheet by a friction stir spot welding technique using a scroll grooved tool without a probe. The material flow in the nugget of the Mg/steel weld was less than that in the Al/steel one. The Al/steel weld exhibited higher static tensile–shear strength than the Al/Al weld, while the strengths of Mg/steel and Mg/Mg welds were comparable. Tensile–shear fatigue tests were performed using lap shear specimens of both dissimilar and similar welds. The dissimilar welds exhibited nearly the same fatigue strengths as the similar ones. The effective nugget size in the dissimilar welds was defined as the area where Al or Mg alloy remained on the steel side after static fracture. When the fatigue strengths of dissimilar welds were evaluated based on the effective nugget size, the normalised fatigue strengths of Al/steel and Mg/steel welds were comparable.