异种铝合金回填式搅拌摩擦点焊的组织与性能

选用6061-T6与7075-T6铝合金为研究对象,研究异种合金回填式搅拌摩擦点焊接头的组织和拉剪性能. 将7075铝合金作为上板,主要讨论套筒下扎深度对接头成形和性能的影响. 结果表明,当套筒刚扎透上板时,接头内部无缺陷产生. 随着套筒下扎深度的增大,接头内部会出现孔洞、撕裂和未充分回填等缺陷. 当使用较小的套筒扎入量时,决定接头性能的关键位置,即钩状缺陷处和焊点中心搭接面处的结合情况良好. 接头的断裂载荷随着套筒下扎深度的增大先增大后减小,最大载荷在深度为3.4 mm时达到7 236 N.     

A6N01-T5铝合金焊接接头的组织与疲劳性能

为了确定A6N01-T5铝合金挤压型材MIG焊接接头发生疲劳断裂的原因,本文采用高频疲劳试验机对A6N01-T5铝合金MIG焊接试样进行低周疲劳拉伸试验,研究了A6N01-T5铝合金焊接接头低周疲劳行为、疲劳裂纹表面和断口表面以及缺陷对疲劳性能的影响。结果表明:在热影响区存在一个明显的软化区,该软化区在疲劳拉伸实验中变形较严重;A6N01铝合金焊接试样的疲劳裂纹源萌生于气孔及夹杂等缺陷产生应力集中处;焊缝近表面的气孔及内部的夹杂是裂纹快速扩展的诱因。     

铝合金搅拌摩擦点焊疲劳性能研究

研究了2mm厚的6082-T6铝合金搅拌摩擦点焊接头的疲劳性能。在最优的焊接工艺参数和良好的焊接接头的基础上,完成了点焊接头的疲劳实验,观察分析点焊接头薄弱环节的微观组织和疲劳断口的形貌,并测试接头显微硬度,得到了在一定范围内预测疲劳寿命的表达式。结果表明:疲劳裂纹在上下板间的接头根部起裂,在热影响区和热力影响区的交界处扩展直至断裂;微量元素形成的强化相在很大程度上影响点焊接头的疲劳性能;点焊接头的疲劳寿命随着应力强度因子的变小呈增大趋势。     

6N01-T5铝合金焊接接头疲劳断裂分析

为了确定6N01-T5铝合金挤压型材焊接接头发生疲劳断裂的原因,对6N01-T5铝合金型材及其焊接接头分别进行了疲劳试验,获得了它们的S-N曲线及条件疲劳极限.分析了接头的显微组织与力学性能,并对疲劳断口进行分析,得到了6N01-T5铝合金焊接接头的疲劳断口特征.结果表明,接头显微组织为α-Al与α-Al和Mg2Si的伪共晶,主要缺欠为气孔;在热影响区与母材交界处存在一软化区,该软化区会引起静载断裂,但不是构件发生疲劳断裂的主要原因;位于焊缝表面焊接缺欠以及构件的表面状态是影响接头疲劳性能的主要原因.     

6061/7075异种铝合金回填式搅拌摩擦点焊接头的组织与性能研究

以6061/7075异种铝合金为研究对象进行回填式搅拌摩擦点焊试验,研究了板材相对位置对接头成形和性能的影响。试验结果表明,当7075铝合金作为上板时,套筒最大下扎深度处和焊点中心处均会产生孔洞缺陷;当6061铝合金作上板时,可获得无缺陷的接头且上下板的冶金结合效果明显较好,其接头的最大拉断载荷为11502 N。     

7N01S-T5铝合金焊接接头疲劳性能

对MIG焊接得到的板厚为10 mm的7N01S-T5铝合金焊接接头进行疲劳试验,研究其疲劳性能,通过对疲劳试验后的试样进行金相组织观察和断口SEM观察,分析其疲劳试验前后显微组织变化以及断裂的原因。结果表明,7N01铝合金焊接接头的疲劳极限为111.6 MPa,经过疲劳试验的焊接接头断裂在硬度值最低的焊缝处,裂纹沿垂直于焊缝柱状晶的方向扩展。疲劳源处未见明显的夹渣、气孔等缺陷。焊缝处析出相聚集在晶界,部分区域出现了液化裂纹。     

汽车用双相钢/铝合金异种材料电阻点焊过程数值模拟研究

基于SORPAS软件,对1.8 mm的DP590双相钢板和1.2 mm的6061-T6铝合金板材点焊过程进行了模拟,并将模拟熔核形貌与试验结果进行对比。结果表明,随着焊接过程的进行,工件与电极接触界面处温度迅速升高,而上下电极附近温度并没有迅速升高,接头在铝合金侧和双相钢侧形成双熔核;在整个焊接过程中,铝合金侧的应变明显比双相钢侧大,变形主要集中在熔核附近,熔核边缘应变大于心部;模拟的熔核直径为4.3 mm,实测值为4.6 mm,模拟结果与实测结果较为吻合,所建立的模型可以用于DP590钢及6061-T6铝合金板异种材料电阻点焊过程模拟。     

镁/钢无匙孔搅拌摩擦点焊接头连接机理与断裂方式研究

采用最新研制的无匙孔搅拌摩擦点焊设备对AZ31B镁合金和DP600镀锌钢板进行搭接点焊试验。通过对点焊接头宏观、微观组织形貌及断口分析表明,接头搅拌区结合界面处镁钢呈"楔状"与"弯钩状"相互嵌入对方基体中,形成牢固的机械互锁结构,而轴肩作用区结合界面平整,生成了厚度约6~9μm的"竹节状"中间层,其长度各不相同,且中间层之间存在裂纹;点焊接头拉伸断口有两种断裂方式,轴肩作用区为解理断裂,搅拌区为韧脆混合断裂;原位拉伸试验结果表明,应力集中最大的部位在镁钢两板之间点焊接头的焊点边缘处;接头的拉伸断裂面靠近镁侧,断裂时脆性中间层基本上留在了钢侧。     

6005铝合金手工MIG-背面水冷焊接头高周疲劳性能的研究

为了测定6005-T6铝合金焊接接头的疲劳极限,对4 mm厚6005-T6铝合金采用手工MIG焊焊接,并且焊后在试板背面进行通水冷却,使用高频疲劳试验机对焊接试件进行疲劳试验,并绘制了S-N曲线。对疲劳断口形貌和焊接接头的显微组织进行分析,研究了疲劳断裂的原因。结果表明:铝合金手工MIG焊接头在50%存活率情况下,其高周(10~7)疲劳极限应力为125 MPa,S-N拟合曲线为σ_(max)=701N_f~(-0.127)。不同应力状态下疲劳裂纹均萌发于试样的表面。高应力状态下,断口中很难发现扩展辉纹,与静态拉伸断口相似。低应力状态断口扩展区存在大量扩展辉纹。热影响区的粗晶区和晶界聚集的第二相对疲劳性能不利。     

6061-T6铝合金激光-MIG复合焊广域环境下疲劳性能研究

以磁悬浮列车底架地板用6061-T6铝合金为对象,研究了6061-T6铝合金激光-MIG复合焊焊接接头在低高温(-40℃、常温、70℃)的疲劳性能,为广域环境条件下磁悬浮列车设计提供基础实验数据。结果表明:常温条件下的疲劳极限为67.1 MPa,焊缝断口具有明显的劳源区、疲劳扩展区和瞬时断裂区,疲劳扩展区存在明显的疲劳辉纹,局部存在不同族簇疲劳辉纹,瞬时断裂区有明显的韧窝结构,瞬断区为韧性断裂;低温(-40℃)条件疲劳极限为61.3 MPa,焊缝断口疲劳辉纹细而致密,存在大量的二次裂纹,焊缝韧塑性降低;高温(70℃)条件疲劳极限为56.2 MPa,焊缝疲劳断口呈现准解理断裂特征,大量脆性疲劳辉纹分布于断口且瞬断区为典型的聚集型韧窝特征。     

Effect of Sleeve Plunge Depth on Interface/Mechanical Characteristics in Refill Friction Stir Spot Welded Joint

Refill friction stir spot welding was employed to produce 6061-T6 aluminum alloy joints with different sleeve plunge depths.The interface characteristics of joint-line remnant and hook are investigated by optical and scanning electron microscopy.The joint-line remnant consists of primary bonding region and secondary bonding region,and two types of hook can be identified as downward hook and upward hook.Tensile shear results demonstrate that joint-line remnant and hook make interaction effects on tensile shear properties.The optimal joint is achieved when sleeve plunge depth was 2.0 mm with the corresponding failure load of 8673.4 N.Three different types of fracture mode are exhibited in joints produced at different sleeve plunge depths,which are closely related with the morphology of interface characteristics.     

Fatigue lives of friction stir spot welds in aluminum 6061-T6 sheets

The fatigue lives of friction stir spot welds in aluminum 6061-T6 lap-shear specimens under cyclic loading conditions are investigated in this paper. The paths of fatigue cracks near friction stir spot welds in lap-shear specimens are first examined. The experimental observations suggest that under cyclic loading conditions, the fatigue crack is initiated near the possible original notch tip in the stir zone and propagates along the circumference of the nugget, then through the sheet thickness and finally grows in the width direction to cause final fracture. A fatigue crack growth model based on the Paris law for crack propagation and the local stress intensity factors for kinked cracks is then adopted to predict the fatigue lives of friction stir spot welds. The global and local stress intensity factors are used to estimate the local stress intensity factors of kinked cracks with experimentally determined kink angles. The results indicate that the fatigue life predictions based on the Paris law and the local stress intensity factors as functions of the kink length agree well with the experimental results.     

7075铝合金FSW接头腐蚀疲劳性能及断裂特征

以7075-T6铝合金搅拌摩擦焊接头为研究对象,对其显微组织结构、3.5% NaCl(质量分数)溶液腐蚀疲劳寿命和腐蚀疲劳断裂特征进行了研究,分析了7075铝合金搅拌摩擦焊接头的腐蚀疲劳性能及断裂过程.结果表明,7075-T6铝合金搅拌摩擦焊接头腐蚀疲劳S-N曲线方程为lgN=5.845-0.014S,随着应力幅增大,腐蚀疲劳寿命大幅度降低;腐蚀疲劳裂纹起源于接头的热影响区,逐渐扩展最终断裂于接头的焊核区.腐蚀疲劳断口存在多个裂纹源,且受到应力集中作用的影响,裂纹源萌生于腐蚀坑处.高应力作用加剧了试样边角部分的腐蚀损伤,导致边角比平面位置腐蚀程度更严重.裂纹扩展区出现了明显的晶间断裂和疲劳辉纹;在腐蚀介质和交变载荷的共同作用下,裂纹扩展区腐蚀程度最重,晶界处产生了阳极溶解现象并产生了“冰糖块状”和“蚁巢状”的形貌特征;瞬断区产生了大量解理台阶和二次裂纹,为脆性断裂,在第二相粒子分布区域存在孔洞形貌特征.     

Static shear strength and fatigue life of refill friction stir spot welded AA 6061-T6 sheets

This study was aimed at evaluating the static shear strength and fatigue properties of the newly developed refilled friction stir spot welded AA 6061-T6 joints. The keyhole, the process disadvantage of conventional friction stir spot welding, was refilled successfully, using an additional filler plate, with specially designed tools. Two different tool profiles, namely, convex and concave, were used for the refilling process. Sound and defect free joints were obtained by the refilling process. Joints refilled with convex tools showed better static shear strength than those with the concave ones. The variation of microhardness in different regions of the weld was analysed. Fatigue tests were conducted on the lap shear specimens at a stress ratio of R?=?0·1. The optical micrographs of the welds after fatigue failure in both the conventional and refilled processes were examined to study the fatigue crack propagation and failure modes.     

ABS塑料与6082铝合金搅拌摩擦点焊工艺及机理

针对2 mm厚的ABS塑料板和6082-T6铝合金进行搅拌摩擦点焊可焊性试验,并将成形较好的试件的横截面的形貌进行了观察分析,并对其进行力学性能的测试.结果表明,将铝合金板放在上,塑料板放在下的搭接方式可以实现良好的连接;最优工艺参数为搅拌头旋转速度为400 r/min,焊接时间为30 s,所得焊接接头的抗拉剪载荷最大为3.31 kN;点焊接头有两种断裂模式.     

Removing approach for flashes of friction stir spot welds

A friction stir spot welding tool with a threaded probe and a flat shoulder was made to join 6061-T6 aluminum sheets under various indentation depths, rotational speeds, indentation rates and dwelling times. Two types of flashes, ring-shape and petal-shape, were found and their forming processes were identified. A concept of combining friction stir spot welding and end milling was proposed to make welds and remove flashes simultaneously. Pictures and micrographs were examined to study the effects of processing parameters on the flash thickness, height, and type, and to obtain the maximum flash thickness/cutter width for tool design. Based on experimental results, a welding tool with two flash-removing cutters was developed to remove flashes during welding. The mechanical properties of friction stir spot welds with and without flashes are further examined to evaluate the performance of the proposed welding tool.     

基于响应面法的钛铝异种金属搅拌摩擦点焊工艺参数优化

为同时满足减轻质量和降低成本的需求,钛/铝复合结构具有很好的应用前景,但由于钛合金与铝合金之间的物化性能差异巨大,采用传统焊接方式很难形成可靠的连接,而搅拌摩擦点焊技术在连接异种金属方面优势明显,目前针对钛/铝合金的搅拌摩擦点焊研究较少.因此采用回填式搅拌摩擦点焊对2 mm厚的TC4钛合金和6061铝合金进行点焊试验,...     

Fatigue Life of 6061 Aluminium Alloy Welding Samples both in Atmosphere and Water

名义厚度为0.04英寸（1.02 mm）的6061-O和6061-T4铝合金板材在航空工业里广泛使用。将这些板材在氩弧焊后淬火时效热处理至T62态后制成标准试样。在频率为60 Hz、应力比为0.1条件下,分别在大气和潮湿环境中进行疲劳试验,且施加载荷方向垂直于焊缝。断裂形貌通过扫描电子显微镜（SEM）观察。结果表明：与大气环境中相比,焊缝在潮湿环境下疲劳性能急剧下降,而且疲劳带也不是很明显。焊缝在潮湿环境下断裂表面含氧量比在大气中高是可能的原因。     

超声振动对6061-T4铝合金搅拌摩擦焊接头组织和性能的影响

利用自主研制的试验装置,通过工具头将超声振动能量施加在搅拌头前方的待焊工件上,研究了超声振动能量对减少焊接缺陷、改善搅拌摩擦焊接头组织和力学性能的影响.对6 mm厚度6061-T4铝合金板进行了超声振动强化搅拌摩擦焊工艺试验,并与相同工艺条件下的常规搅拌摩擦焊进行了对比.结果表明,超声振动能够减小焊速/转速比较大时的焊缝内部隧道型缺陷,增大材料对接混合区宽度和焊核区体积,细化焊核区和热力影响区微观组织,提高接头抗拉强度和焊核区显微硬度.     

Mechanical characterization of friction stir spot microwelds

Microstructures and failure mechanisms of friction stir spot microwelds in 300-μm thin sheet of aluminum 1050 alloy were investigated. As an alternative to conventional soldering and welding in joining thin metals for electronic, medical and microdevices, friction stir welding may be utilized in order to limit the excessive heat damage. Transmission electron microscopy micrographs of the cross sections of friction stir spot microwelds in lap-shear specimens were examined. These microwelds showed the failure mode of nugget pullout under lap-shear loading conditions. The experimental observations suggested that under lap-shear loading conditions, the failure was initiated near the possible original notch tip in the stir zone and the failure propagated along the circumference of the nugget to final fracture. Microindentation hardness data of base metal, heat affected zone, thermal-mechanical affected zone and stir zone were obtained. The interface between the heat affected zone and the thermal-mechanical affected zone was the softest region, where the cracks of friction stir spot microwelds in the lap-shear specimens under the loadings initiated and leaded to fracture of the specimens.