铝合金搅拌摩擦焊接头微观组织和力学性能分析

目的 研究7020铝合金搅拌摩擦焊(FSW)的结构和机械性能。方法 采用搅拌摩擦焊对铝板进行对接焊试验,具体形式为单面焊双面成型。采用拉伸机和显微维氏硬度仪对试样进行力学性能测试;利用蔡司金相、光谱仪、扫描电子显微镜、X射线衍射仪研究母材和焊接接头的微观组织。结果 在硬度上,母材>热影响区>焊核区,热影响区平均硬度约为94HV,母材平均硬度为99HV,焊核区平均硬度最低为78HV,焊核区出现“S”缺陷,在一定程度上弱化了焊核区性能;7020铝合金搅拌摩擦焊接头的抗拉强度为235 MPa,屈服强度为158 MPa,屈强比为0.67,伸长率为7%,焊接系数可以达到73.8%;母材的抗拉强度为325 MPa,屈服强度为278 MPa,屈强比为0.86,伸长率为25%;焊接接头中心显微组织主要由胞状树枝晶体组成,显微结晶依次呈现为平面晶、胞状晶、树枝状晶、等轴晶;铝合金母材和焊接接头的金属相组成均为α?Al+Mg2Si;焊接接头断口呈现比较明显的韧性断裂特征。结论 铝合金搅拌摩擦焊可以获得性能比较优良的焊接接头,为其他铝合金材料的FSW焊接提供技术参考。     

转速对6061铝合金搅拌摩擦搭接焊接头组织和力学性能的影响

目的 研究不同转速条件下6061铝合金搅拌摩擦搭接焊接头组织和力学性能的变化规律,为工程实践应用提供参考。方法 在不同旋转速度（800、1 200、1 500 r/min）下对4 mm厚的6061铝合金进行搅拌摩擦搭接焊实验,固定进给速度和轴肩下压量,研究搅拌头转速对接头宏观组织、微观组织和力学性能的影响。结果 所有接头均没有出现明显缺陷,当转速为1 500 r/min时,搅拌区晶粒尺寸细化明显,最大失效载荷达到母材的75%,上板和下板的硬度曲线都呈“W”形;当转速为800 r/min和1 200 r/min时,下板硬度曲线呈“V”形。随着转速的增大,有效搭接宽度逐渐增大,接头的平均拉剪强度也在增大,所有接头都在前进侧断裂,断裂形式均为拉伸断裂。结论 转速的提升增加了焊接热输入量和机械搅拌作用,促进了有效搭接宽度的增大和晶粒尺寸的细化,但未能改变钩状缺陷的形成及延伸方向。当转速为1500r/min时,热输入量较大,搅拌区范围相对较大,下板存在更大面积的搅拌区,其硬度规律与上板的相似。所有接头均为拉伸断裂,断裂位置在热影响区附近,说明搭接接头连接良好。     

7050铝合金回填式搅拌摩擦点焊组织与性能研究

目的 研究2.5 mm厚的7050-T74511铝合金回填式搅拌摩擦点焊工艺参数,焊点组织与力学性能之间的关系。方法 通过显微组织观察和断口扫描,分析接头形貌特征和缺陷对断裂模式的影响。通过拉伸剪切测试,分析工艺参数与力学性能之间的关系。采用三因素三水平BBD响应面法进行工艺优化,建立拉剪失效载荷与工艺参数之间的二阶响应模型并求得最优工艺。结果 工艺优化的最佳参数为扎入深度2.7 mm,焊具转速为1500 r/min,焊接时间为8 s,在此参数下接头拉剪失效载荷为8.294 kN。当焊接工艺参数选择恰当时,可得到无缺陷接头。结论 焊接工艺窗口较窄;在高热输入条件下（扎入深度3.1 mm,转速2100 r/min）易产生孔洞、弱连接等缺陷,且这些缺陷主要分布在搅拌区与热力影响区界面上;在低热输入条件下（扎入深度2.7 mm,转速1500 r/min）,接头拉剪载荷较高,这与焊点在低热输入情况下组织缺陷较少有关。     

铝合金厚板静止轴肩搅拌摩擦焊接头组织及性能

采用8.5 mm厚度2A14-T4铝合金和自主研制搅拌工具进行静止轴肩搅拌摩擦焊（stationary shoulder friction stir welding,SSFSW）实验,探讨焊接工艺参数对接头组织和力学性能的影响规律。结果表明：只有在低转速工艺参数范围内（转速ω=400~600 r/min与焊接速率v=60~120 mm/min）可获得焊缝表面光滑、无缺陷厚板铝合金SSFSW焊接接头。SSFSW焊缝区主要由焊核区（NZ）组成,周围热力影响区（TMAZ）及热影响区（HAZ）宽度明显减小,焊核区与搅拌针形状类似且由两种不同尺寸细小等轴晶构成,前进侧NZ晶粒比后退侧NZ更为细小。接头显微硬度呈"W"状分布,NZ硬度值可达到母材硬度80%~90%,TMAZ与HAZ交界处存在软化区,硬度最低为母材硬度72%左右。在给定ω=500 r/min,v=140 mm/min焊接参数下,SSFSW接头抗拉强度可达到母材的88%,断裂位置多位于后退侧TMAZ与HAZ交界处软化区,具有韧性断裂特征。     

铝合金搅拌摩擦对接焊接头组织与性能研究

研究了5083铝合金搅拌摩擦焊(FSW)焊接接头组织与性能,采用金相显微镜观察焊接接头各区域的微观组织,并对接头显微硬度和力学性能进行了测定。结果表明,5083铝合金搅拌摩擦焊焊核组织为动态再结晶生成的细小组织,强化相均匀分布;热机影响区由于动态再结晶和焊接热循环的双重作用,组织变化较大,晶粒有一定程度的长大,强化相有所细化;热影响区仅仅受到热循环作用,使得晶粒粗化和强化相出现聚集现象。搅拌摩擦焊接接头中心硬度与母材基本相当,热机影响区和热影响区由于焊接热输入的原因,使得硬度有所降低。搅拌摩擦焊室温拉伸性能和冲击性能不低于母材的,其中拉伸试样均断裂于母材,焊核室温冲击值达到母材的1.5倍以上,热影响区冲击值与母材的相当。     

5083铝合金搅拌摩擦焊搭接接头研究

采用搅拌摩擦焊方法对5083铝合金进行搭接实验。用万能试验机对接头进行拉剪试验,对其断口利用SEM电镜进行观察和分析,并使用光学显微镜对其接头横截面进行组织观察。结果表明:即使搅拌针长度短于上层铝板的厚度,上、下层铝板在搅拌针作用的区域,晶粒都发生了一定细化,其尺寸都小于母材。而且焊缝横截面的显微硬度分布也显示出两板在搅拌针作用区域的硬度均与母材相当。在拉剪试验时,界面结合处没有出现断裂现象,断裂位置均在上层铝板前进侧的热影响区。接头强度系数最高可达80%,接头的断裂形式为韧性断裂。     

搅拌针偏移量对A356/6061铝合金搅拌摩擦焊的影响

对6mm厚的A356-T6/6061-T6异种铝合金的搅拌摩擦焊工艺进行了试验研究,采用OM、SEM、万能拉伸试验机、显微硬度仪等分析了搅拌针偏移量对搅拌摩擦焊接头组织和性能的影响。研究结果表明:搅拌针的偏移量在-0.4~0.4mm范围内均可获得外表美观、内部无明显缺陷的搅拌摩擦焊接头;焊核区两种材料的分界线非常清晰,分别由焊核区、热机影响区和热影响区组成,混合区主要分布在前进侧的焊核区;焊核区由晶粒细致的等轴晶组成,随厚度方向从上而下细化程度逐渐增加。搅拌针向6061侧偏移,有利于焊核区面积、接头强度以及延伸率的增加。当搅拌针向6061偏移0.4mm时,焊核区较-0.4mm时面积增大10%,接头强度和延伸率分别达到210MPa和8.8%,分别为A356母材的74.6%和65.2%;同时,接头断裂位置由返回侧逐渐向前进侧转移,断口位置与焊缝区最低硬度区相吻合;向A356侧偏移时,两侧的热影响区宽度变窄,硬度值增大。     

6061铝合金无倾角搅拌摩擦焊工艺及性能

目的 为了适应空间曲面构件的搅拌摩擦焊,开展6061铝合金无倾角搅拌摩擦焊工艺及性能的研究。方法 采用无倾角搅拌摩擦焊用的搅拌头,对5 mm厚6061-T6铝合金板材进行试验,研究焊缝成形及接头力学性能,并分析接头组织特征。结果 零倾角搅拌摩擦焊接头从组织上可区分为5个不同区域：焊核区(WNZ)、热力影响区(TMAZ)、热影响区(HAZ)、轴肩影响区(SAZ)和母材(BM);随着搅拌头转速增加,焊缝宽度和焊核尺寸均先变大后变小;随焊接速度增加,焊缝宽度和焊核尺寸均逐渐变小;当焊接速度固定时,随搅拌头转速增加,接头拉伸强度先增加后减小;当搅拌头转速固定时,随焊接速度增加,接头拉伸强度逐渐增大。结论 采用无倾角搅拌摩擦焊接方法,能够实现对5 mm厚6061-T6铝合金板材的有效焊接。     

2060搅拌摩擦焊对接接头显微组织与析出相分析

选用Al-Li-Cu-Mg系铝锂合金2060,开展搅拌摩擦焊对接接头显微组织与析出相演变规律研究.搅拌摩擦焊对接接头,呈现典型的母材、热影响区、热机影响区和焊核区四区分布特点.母材为双向板条组织,在α板条中有大量三角形AlCu2Mn化合物析出,但在其它相区,当受到热影响时,该相消失;热影响区组织粗大,热机影响区晶粒受到机械力作用,前进侧拉长,后退侧破碎;焊核区为等轴晶组织,出现了高温析出相AlxCuxMn,均布于整个焊核区域.接头显微硬度在母材区最高,热影响区最低,焊核区低于母材,稳定在115 HV.     

2060搅拌摩擦焊对接接头显微组织与析出相分析

本文选用Al-Li-Cu-Mg系铝锂合金2060,开展搅拌摩擦焊对接接头显微组织与析出相演变规律研究.搅拌摩擦焊对接接头,呈现典型的母材、热影响区、热机影响区和焊核区四区分布特点.母材为双向板条组织,在α板条中有大量三角形AlCu2Mn化合物析出,但在其它相区,当受到热影响时,该相消失;热影响区组织粗大,热机影响区晶粒受到机械力作用,前进侧拉长,后退侧破碎;焊核区为等轴晶组织,出现了高温析出相AlxCuxMn,均布于整个焊核区域.接头显微硬度在母材区最高,热影响区最低,焊核区低于母材,稳定在115 HV.     

工艺参数对AA2524回填式搅拌摩擦点焊接头成形及力学性能的影响

目的 改善2 mm厚AA2524回填式搅拌摩擦点焊（RFSSW）接头的成形和力学性能。方法 采用不同扎入深度和不同转速进行焊接,焊后对接头的孔洞大小、套筒退出线上的裂纹长度和拉剪强度进行对比,获得扎入深度和转速对接头成形和拉剪强度的影响规律。结果 扎入深度为2.6 mm时,接头孔洞较小,断裂载荷较高。随着转速的增加,接头孔洞逐渐减小,套筒退出线的裂纹减少,拉剪强度逐渐升高。扎入深度2.6 mm,焊接时间6 s,转速为2600 r/min时,获得了无孔洞和无退出线裂纹的接头,断裂载荷最大,为9.4 kN。结论 合适的扎深和转速匹配,可以获得成形良好,高断裂载荷的接头。     

Microstructure and failure mechanisms of refill friction stir spot welded 7075-T6 aluminum alloy joints

In this paper, the microstructure and mechanical properties of 7075-T6 aluminum alloy joints joined by refill friction stir spot welding (RFSSW) were investigated. The keyhole was refilled successfully, and the microstructure of the weld exhibited variations in the grain sizes in the width and the thickness directions. There existed defects (hook, voids, bonding ligament, etc.) associated to the material flow in the weld. Mechanical properties of the joint have been investigated in terms of hardness and tensile/shear and cross-tension test, and the fracture mechanisms were observed by SEM (scanning electron microscope). The hardness profile of the weld exhibited a W-shaped appearance in the macroscopic level, which reached the minimum at the boundary of the sleeve and the clamping ring. The variation laws between tensile/shear and cross-tension strength and processing parameters were rather complicated. The void in the weld played an important role in determining the strength of the joint. On the whole, the preferable strength can be obtained at lower rotational speed. Shear fracture mode was observed under tensile–shear loadings, and nugget debonding, plug type fracture (on the upper sheet) and plug type fracture (on the lower sheet) modes were observed under cross-tension loadings. It was also observed that the main feature affecting the mechanical properties of the joint is the alclad between the upper and lower sheets and the connecting qualities between the stir zone and thermo-mechanically affected zone.     

Identification of the pin offset effect on the friction stir welding (FSW) via Taguchi – Grey relational analysis: A Case study for AA 7075 – AA 6013 alloys

The aim of this work is to present a case study relating to the dissimilar friction stir welding (FSW) ability of AA 7075‐T651 and AA 6013‐T6 by applying pin offset technique. An orthogonal array L18 was conducted to perform the overlapped weld seams using three different values of pin offset, welding speed and tool rotational speed along with two different pin profiles determine the impact of welding parameters on the tensile properties of friction stir welded joints. The nugget zone for each of overlapped weld seams exhibited a complex structure and also, the pin offset and profile also were found to have a great impact on the microstructural evolution of the nugget zone. The ultimate tensile strength, elongation at the rapture and bending strength of welded joints were measured in the ranges of 194–215 MPa, 1.79–3.34 % and 203–352 MPa. From the Taguchi based Grey relational analysis, the optimum welding condition was determined for the welded joint performed using a single fluted pin profile with the zero pin offset, tool rotational speed of 630 min^?1 and welding speed of 63 mm/min. Microstructural and macro‐structural observations revealed that welded joints exhibiting lower tensile strength are consistent of various types of defects (e. g. cracks, tunnels and cavities). The fracture location of welded joints was found to be on the heat affected zone and between the heat affected zone and AA 6013‐base metal. The tool and pin wear was not observed during the welding applications     

The optimisation of process parameters for friction stir spot-welded AA3003-H12 aluminium alloy using a Taguchi orthogonal array

The aim of the present work is to optimise the welding parameters for friction stir spot welded non-heat-treatable AA3003-H12 aluminium alloy sheets using a Taguchi orthogonal array. The welding parameters, such as the tool rotational speed, tool plunge depth and dwell time, were determined according to the Taguchi orthogonal table L9 using a randomised approach. The optimum welding parameters for the peak tensile shear load of the joints were predicted, and the individual importance of each parameter on the tensile shear load of the friction stir spot weld was evaluated by examining the signal-to-noise ratio and analysis of variance (ANOVA) results. The optimum levels of the plunge depth, dwell time and tool rotational speed were found to be 4.8 mm, 2 s and 1500 rpm, respectively. The ANOVA results indicated that the tool plunge depth has the higher statistical effect with 69.26% on the tensile shear load, followed by the dwell time and rotational speed. The tensile shear load of the friction stir spot welding (FSSW) joints increased with increasing plunge depth. Additionally, examination of the weld cross-sections, microhardness tests and fracture characterisation of the selected friction spot welded joints were conducted to understand the better performance of the joints. All the fractures of the joints during tensile testing occurred at stir zone (SZ), where the bonded section was minimum. The tensile shear load and tensile deformation of the FSSW joints increased linearly with increasing the bonded size. The finer grain size in the SZ led to the higher hardness, which resulted in higher fracture strength. When the tensile shear load of the joints increased approximately 3-fold, the failure energy absorption of the joints increased approximately 15-fold.     

Microstructure and mechanical properties of dissimilar friction stir welding of 6061-to-7050 aluminum alloys

In this work, the microstructure and mechanical properties of friction stir welded dissimilar butt joints of 6061-to-7050 aluminum alloys were evaluated. Microstructure analysis of the cross-section of the joints revealed distinct lamellar bands and various degrees of intermixing that were correlated with tool rotational speed. Due to the distinct mechanical properties of the two alloys, microhardness measurements showed a consistent asymmetric hardness distribution profile across the weld nugget, regardless of tool rotational speed. Under monotonic tensile loading, an increase in the joint strength was observed with the increase in the tool rotational speed. Regarding fracture, the joints consistently failed on the 6061 aluminum alloy side. Furthermore, two modes of failure were observed, one through the stir zone and the other through the heat-affected zone. Inspection of the fracture surfaces suggested that inadequate material intermixing produced at low tool rotational speeds was the cause for the low mechanical strength and failure through the stir zone. On the other hand, the failure observed through the heat-affected zone at high rotational speeds was produced due to the material softening as confirmed by the microhardness measurements.     

Friction stir lap welded advanced high strength steels: Microstructure and mechanical properties

Friction stir welding was carried out under different heat input and cooling rates to produce lap joints between high strength martensitic steel sheets. The microstructure of the welds was characterized, and microhardness was evaluated. Joint efficiency was determined by lap shear test. Variation in processing conditions governed total heat input, peak temperature and cooling rate during friction stir welding. Weld nugget microstructure depended principally on cooling rate. The slowest cooling rate promoted ferrite-pearlite and the fastest cooling rate resulted in martensite formation in the weld nugget. The weakest region of all the joints was the heat affected zone, which consists of ferrite with small quantities of pearlite. Fracture during shear testing occurred along the heat affected zone of welded joints. The width and grain size of ferrite in heat affected zone controlled the joint efficiency.     

水下搅拌摩擦焊对铝/铜接头组织与性能的影响

目的 采用搅拌摩擦焊,对比分析大气环境和水下环境下铝/铜接头的组织与性能,以期获得力学性能更优异的铝/铜焊接接头。方法 利用搅拌摩擦焊,在焊接速度为40 mm/min、旋转速度为1 000 r/min的条件下,分别在大气环境和水下环境下对厚度为9 mm的6061铝合金板和T2纯铜板进行焊接。然后,对铝/铜界面、焊核区进行扫描电镜及能谱分析,并对铝/铜界面及焊核区进行物相分析,确定产物相组成。最后,对铝/铜试样进行拉伸及硬度检测。结果 铝/铜接头均无裂纹、气孔等缺陷。铜颗粒弥散分布在焊核区,铝/铜界面形成金属间化合物层。水下搅拌摩擦焊下界面元素扩散距离明显变短,且金属间化合物厚度更薄。铝/铜接头的金属间化合物为AlCu和Al4Cu9。大气环境焊接下接头的抗拉强度为130.6 MPa,断裂方式为脆性断裂;水下焊接下接头的抗拉强度为199.5 MPa,断裂方式为韧性断裂。水下环境下的接头硬度值更高,其中热影响区的硬度最低值约为65HV。结论 水下搅拌摩擦焊铝/铜接头无裂纹、气孔等缺陷。组织上,水下搅拌摩擦焊的铝/铜接头界面元素扩散距离更短,硬脆的金属间化合物更少;性能上,水下搅拌摩擦焊的铝/铜接头强度更高,抗拉强度达到199.5 MPa,达到母材的74.4%。     

Effect of FSW parameters on microstructure and mechanical properties of AM20 welds

This paper aims to demonstrate the successful friction stir welding (FSW) conditions of AM20 magnesium alloy. The maximum yield strength and ultimate tensile strength of weld were found to be 75% and 65% of the base metal strength, respectively. The maximum bending angle of the welded joint was 45°. Observations revealed that less plunging depth, high shoulder diameter, and low tool rotational speed and welding speed give better tensile properties. Maximum temperature was observed at 1?mm away from the tool shoulder toward the advancing side. Micro-hardness variation is found to be decreasing along the depth of the weld, and nugget zone (NZ) gives the higher hardness values when compared with base material (BM) and other welded zones. Needle-like grains of the BM became equiaxed grains due to grain recrystalized by the FSW process. The grains in the NZ were finer than thermo-mechanically affected zone and almost same size of grains observed at bottom, middle, and top of the NZ.     

Conventional and in situ tensile test of friction stir welded steel – Optimization of processing parameters

In the present investigation, steel plates were joined at different tool traversing speed by friction stir welding keeping other parameters same. Microstructural characterization was carried out with optical and scanning electron microscopes. At weld nugget pearlite and bainite were present within ferrite matrix. Thermo‐mechanically and heat affected zones microstructure consisted of pearlite and ferrite. Second phase area fraction and matrix grain size at different regions were varied depending on welding parameters. Weld nugget exhibited substantial improvement in microhardness with respect to base metal. In this respect heat affected zone revealed minimum microhardness and was below base metal value. Tensile tests were carried out on standard and miniature specimens in scanning electron microscope. Highest joint efficiency to the tune of ～82 % and ～120 % of that of base metal obtained for standard and miniature specimens, respectively machined from weld fabricated at lowest welding speed. With increment in welding speed assembly strength was reduced for both types of specimens. Standard specimens failed from heat affected zone and miniature specimens failed through centre of weld nugget. Apart from matrix grain size and second phase area fraction, precipitation of microalloyed carbide / carbonitride was responsible for altering the joint strength.