Friction Stir Welding of Aluminum Alloys

Friction stir welding( FSW ), a new solid-state welding technology invited in the early 1990s,enables us weld aluminum alloys and titanium alloys etc. The processing of FSW, the microstractare in FSW alloys and the factors influencing weld quality are introduced. The complex factors affecting the properties are researched.     

搅拌摩擦焊接过程的非稳态流场及影响因素

分析了搅拌摩擦焊洋葱圆环的非稳态流场形成过程和工艺参数对洋葱圆环的影响。在焊接过程中流入孔腔的金属流（特别是与焊针旋转方向相反的金属流）破坏了焊针未运动时产生的原始流动场，形成了复杂的涡状流动，并且在纵向呈现不均匀性，叠加后最终形成洋葱状形貌，实验表明搅拌工具的尺寸和焊接速度是影响洋葱圆环形貌的主要因素。     

搅拌摩擦焊研究最新进展

搅拌摩擦焊(Friction Stir Welding．简称FSW)是一种新型固相连接工艺．它不仅能实现其他连接方式能够实现的接头，且能实现在熔焊条件下焊接性能差、易产生焊接缺陷的材料的连接，如高强铝合金、铝锂合金，使焊接接头的性能大大提高．本文分析了近年来搅拌摩擦焊技术的发展和最新进展，涉及搅拌摩擦焊机理即塑性流体运动情况适用母材、力学性能和焊接工具．     

LF2铝合金搅拌摩擦连接研究

对厚度为3mm的LF2铝合金板成功地进行了搅拌摩擦连接．金相组织观察显示焊核区晶粒由原始母材的扁平状转变为更加细小的等轴晶粒，力学性能测试表明热影响区的强度为最薄弱区域．当焊接速度、工具旋转速度、轴向压力分别为60mm／min、1200r／min、400N时，焊缝区的抗拉强度为245 MPa，是母材抗拉强度的92％，延伸率可达到母材的80％以上．     

6082-T6铝合金薄板双轴肩搅拌摩擦焊温度场

采用热电偶对4 mm厚6082-T6铝合金薄板双轴肩搅拌摩擦焊不同工艺焊接过程中各特征点的温度进行测定,绘制各点的热循环曲线,分析焊接过程中接头各区域温度场分布特征。研究表明:6082-T6铝合金薄板双轴肩搅拌摩擦焊时,后退侧各点的峰值温度均高于前进侧,温度差值在20℃左右;当热影响区温度超过250℃时出现β'相溶解,硬度开始呈现下降趋势;焊速不变、转速增大时,热输入量呈先增大后减小的趋势,在转速为1000 r/min时各测温点温度均达到最大值,当转速为1200 r/min时出现下降;转速不变、焊速增大时,单位热输入量降低,前进侧与后退侧的峰值温度差值由小变大,温度场250℃等温线分布宽度明显缩小。     

Prediction and optimization of process parameter of friction stir welded AA5083-H111 aluminum alloy using response surface methodology

A systematic approach was presented to develop the empirical model for predicting the ultimate tensile strength of AA5083-H111 aluminum alloy which is widely used in ship building industry by incorporating friction stir welding (FSW) process parameters such as tool rotational speed, welding speed, and axial force. FSW was carried out considering three-factor five-level central composite rotatable design with full replications technique. Response surface methodology (RSM) was applied to developing linear regression model for establishing the relationship between the FSW process parameters and ultimate tensile strength. Analysis of variance (ANOVA) technique was used to check the adequacy of the developed model. The FSW process parameters were also optimized using response surface methodology (RSM) to maximize the ultimate tensile strength. The joint welded at a tool rotational speed of 1 000 r/min, a welding speed of 69 mm/min and an axial force of 1.33 t exhibits higher tensile strength compared with other joints.     

Comparison of fatigue property between friction stir and TIG welds

The alloy 5052 was welded by friction stir welding （FSW） and tungsten inert gas （TIG） welding. The effect of welding processes （FSW and TIG） on the fatigue properties of 5052 aluminum-welded joints was analyzed based on fatigue testing, and the S-N curve of the joints were established. The results show that the fatigue properties of FSW welded joints are better than those of TIG welded joints. The fatigue strength is determined as 65 MPa under 106 cycling of fatigue life. The microstructure of joints is fine grains and narrow HAZ zone in FSW welds, which inhibit the growth of cracks and produce high fatigue life compared with that of TIG welds. Fracture morphologies also show that the fatigue fracture results from weld defects.     

Optimization of process parameters to maximize ultimate tensile strength of friction stir welded dissimilar aluminum alloys using response surface methodology

Aluminium alloys generally present low weldability by traditional fusion welding process. Development of the friction stir welding （FSW） has provided an alternative improved way of producing aluminium joints in a faster and reliable manner. The quality of a weld joint is stalwartly influenced by process parameter used during welding. An approach to develop a mathematical model was studied for predicting and optimizing the process parameters of dissimilar aluminum alloy （AA6351 T6-AA5083 Hlll）joints by incorporating the FSW process parameters such as tool pin profile, tool rotational speed welding speed and axial force. The effects of the FSW process parameters on the ultimate tensile strength （UTS） of friction welded dissimilar joints were discussed. Optimization was carried out to maximize the UTS using response surface methodology （RSM） and the identified optimum FSW welding parameters were reported.     

硬铝合金焊接性能的研究

为了有效地使用热处理强化变形铝合金制造各种结构材料和零部件。研究其焊接性能指标．以Al-Cu-Mn系铝合金(2A16)为对象，采用交流钨极氩弧焊焊接工艺及同质和异质焊丝，制备了2A16硬铝合金焊接试样．通过测试力学性能、金相组织和扫描电镜断口分析等方法，对其焊接性能进行了研究．结果表明：2A16硬铝合金有较好的抗结晶裂纹形成能力，影响其焊接性能的主要问题是过时效软化区的强度下降：当填充金属中Mg／Cu质量比比较大时，焊缝出现脆断倾向，欲进一步提高焊接接头强度，一方面可采用能量密度更高的热源，同时减小焊接线能量，以减少过时效软化区的不利影响；另一方面，限制填充金属中Mg／Cu的质量比，避免出现对焊接接头强化不利的β相和T相．     

铝合金电阻点焊预压接触分析

为了探究铝合金电阻点焊的接触压力分布及初始导电区域,利用ABAQUS软件建立球面形电极条件下的预压接触二维轴对称有限元模型并对模型施加不同的电极压力.在可视化模块中得到了各个接触面上接触压力随载荷变化曲线、电极上的轴力分布云图及工件内的有效塑性应变云图.有限元分析结果表明,各接触面上的接触压力分布是不均匀的,电极-工件间的接触压力受电极球形端面轴向应力分布影响;工件间接触压力与材料所处状态有关;随着电极压力的增大,工件间接触半径呈线性增长.说明电阻点焊时可以通过选取不同截面的电极来改善接触压力的分布,进而改变初始导电区域的大小.     

Damage prediction of 7025 aluminum alloy during equal-channel angular pressing

Equal-channel angular pressing （ECAP） is a prominent technique that imposes severe plastic deformation into materials to en- hance their mechanical properties. In this research, experimental and numerical approaches were utilized to investigate the mechanical prop- erties, strain behavior, and damage prediction of ECAPed 7025 aluminum alloy in various conditions, such as die channel angle, outer comer angle, and friction coefficient. Experimental results indicate that, after the first pass, the yield strength, ultimate tensile strength, and hardness magnitude are improved by approximately 95%, 28%, and 48.5%, respectively, compared with the annealed state, mainly due to grain re- finement during the deformation. Finite element analysis shows that the influence of die channel angle is more important than that of outer comer angle or friction coefficient on both the strain behavior and the damage prediction. Also, surface cracks are the main cause of damage during the ECAP process for every die channel angle except for 90°; however, the cracks initiated from the neighborhood of the central re- gions are the possible cause of damage in the ECAPed sample with the die channel angle of 90°.     

Effects of the types of overlap on the mechanical properties of FSSW welded AZ series magnesium alloy joints

The effects of the types of overlap on the mechanical properties of the friction stir spot welding(FSSW) welded AZ series magnesium alloy joints were investigated by microstructural observations,microhardness tests,and tensile tests.The results show that the micro-structure of the stir zone adjacent to the periphery of the rotating pin is mainly composed of the upper sheet.The average distance D between the longitudinal segment of the curved interface and the keyhole periphery,the tensile shear force,and the microhardness of the stir zone of the FSSW welded AZ61 alloy joint are the highest in all samples.During FSSW of AZ31 and AZ61 dissimilar magnesium alloys,the ir-regular deformation of the longitudinal segment of the curved interface appears,while the microhardness of the stir zone is higher when AZ61 alloy is the upper sheet.Moreover,the microhardness of the stir zone increases initially and then decreases sharply in the longitudinal test position.     

Effects of low-frequency electromagnetic field on the surface quality of 7050 aluminum alloy ingots during the hot-top casting process

To improve the quality of 7050 aluminum alloy ingots, low-frequency electromagnetic (LFE) field was applied during the conventional hot-top casting process. Macrostructures and microstructures of the ingots by the conventional and LFE hot-top casting processes were studied. The experimental results show that when the LFE field is turn off during the hot-top casting process, cold folding appears, and the as-cast structure becomes very coarse. Additionally, the thickness of the shell zone is much thinner duri...     

Investigation on inductive heating of A356 alloy for thixo-forming

To meet the demands of continuous stream-line for component production in the thixo-forming industry, billet heating should be of high quality and in a controllable way. A 4-step inductive heating strategy for aluminum alloy A356 was performed. Thixotropic testing and microstructure analysis showed that a homogenous temperature distribution was achieved after tempera-ture-power-time optimization. Theoretical analysis was given concerning the thermal conductivity and heat capacity of A356 be-tween conventional and semisolid casting microstructures. The experimental results show that the optimized 4-step strategy could bethe best strategy for billet heating during the thixo-forming of aluminum alloy A356.     

镁合金双弧焊接过程研究与分析

研究了镁合金MIG-TIG双弧焊接方法,通过工艺实验获得了影响焊接过程的工艺参数(电流、弧长、焊丝末端与钨极末端的间距、焊接速度等)。在总电流为140 A,旁路电流为115 A,电弧电压为21 V,焊丝末端与钨极末端间距为3 mm时获得了成形较为美观的焊缝。分析了工艺参数对焊接过程及焊缝成形的影响,为进一步提高镁合金双弧焊接过程稳定性,获得质量高成形好的焊缝提供了一定的理论基础。     

铝合金电阻点焊焊接参数选择的智能化

通过深入分析点焊工艺过程,结合基于事例推理的特点,将铝合金点焊工艺事例属性划分为事例特征Ⅰ和事例特征Ⅱ两类。设计了铝合金相似点焊工艺事例的检索策略:在事例特征Ⅰ的约束下,以事例特征Ⅱ中包含的材质的热物理性质和板厚作为检索相似事例的依据。用模糊推理方法对检索到的相似事例库中的工艺知识、规则进行提取、总结,进而指导对新的点焊工艺事例的求解,较好地解决了铝合金点焊工艺设计中,基于事例推理时难以建立合适的模型对检索到的相似事例进行修正的难题,使点焊焊接参数的智能求解过程更符合专家的思维,过程更加灵活,具有开放性。系统应用实例及工艺实验证明此方法是可行的。     

7A52铝合金搅拌摩擦焊接头第二相的形貌及相组成

为进一步研究高强铝合金搅拌摩擦焊接头的性能,必须对接头中的第二相进行明确表征.采用光学显微镜、扫描电镜及能谱、透射电镜对7A52铝合金搅拌摩擦焊接头第二相的种类、数量、形状、大小、分布进行了观察.结果表明,基材的第二相组成主要为沿轧制方向分布的粗大Al₆（Mn,Fe）和Mg₂Si,细小的η′相（MgZn₂）和η相（MgZn₂）,其他各区均弥散分布αAl₁₂（Fe,Mn）3Si和Mg₂Si.动态再结晶区主要包含T相（Mg₃₂（Al,Zn）49）、Al₆Mn、S相（Al₂CuMg）.热机影响区晶界处连续分布条带状A_l6Mn,η相发生粗化,分布在晶粒内部,由原来的长条状破碎成椭球状,晶界有无沉淀析出带.热影响区与基材相比,η′相形貌和分布状况并无明显变化,η相明显粗化;与热机影响区相比,Al₆Mn仍然在晶界处呈条带状分布,晶内有S相存在.     

ZL114A高强铸造铝合金的焊接

ZL114A高强铸造铝合金用于生产导弹壳体等零件。由于铸造工艺的影响，铸造存在气孔、疏松、夹渣、裂纹、偏析、缺损等缺陷，用焊接的方法修复铸造缺陷可以取得显著的经济效益，对交流氩弧焊补ZL114A高强铸铝件的工艺过程加以介绍。