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。     

下扎深度对7075铝合金搅拌摩擦点焊接头组织和性能的影响

对3 mm厚的7075-T6铝板进行搅拌摩擦点焊试验,研究下扎深度对接头组织和力学性能的影响。结果表明,搅拌区晶粒得到极大细化和均匀化,它的晶粒尺寸随下扎深度的增加而逐渐增大。随着下扎深度增加,接头畸变高度和畸变角度先减小后增大,变形区宽度先增大后减小,下扎深度为5.1 mm时,它的有效结合区宽度及变形区宽度最大,畸变高度和畸变角度最小。接头的拉剪载荷随下扎深度的增加先增大后减小,下扎深度5.1 mm的接头获得最大的拉剪载荷值,为12.44 kN,同时它的焊点表面成形良好,结合程度最佳。接头在拉伸试验中的失效方式为韧-脆混合型断裂。     

6061-T6铝合金回填式搅拌摩擦点焊疲劳性能分析

对6061-T6铝合金点焊接头进行单点疲劳试验,确定6061-T6铝合金回填式搅拌摩擦点焊的疲劳断裂原因,得出6061-T6铝合金的S-N曲线以及条件疲劳极限.通过对载荷水平为1.5 kN的6061-T6 RFSSW疲劳试样进行金相分析以及断口扫描分析,得到了6061-T6铝合金疲劳断裂原因以及疲劳断口特征.结果表明,6061-T6点焊接头中的钩状缺陷和上下板结合处缺口尖端的应力集中是造成疲劳破坏的主要原因,疲劳裂纹始于上下板搭接处焊点的钩状缺陷外边缘,即缺口尖端处;在焊接过程中,应通过优化工艺参数尽量减小钩状缺陷的尺寸以及降低缺口处的应力集中,从而提高焊点的疲劳寿命.     

6061-T6/7075-T6异种铝合金搅拌摩擦焊接头组织与性能

利用搅拌摩擦焊实现了2 mm厚7075-T6/6061-T6异种铝合金连接,并对材料放置位置和转速对接头成形与组织性能的影响进行了分析. 结果表明,7075-T6铝合金置于前进侧时更有利于焊接过程中材料的迁移行为,焊缝成形及接头性能更优.当焊接速度为150 mm/min、转速为1 000 r/min时,可获得内部无明显缺陷、外观良好的异种铝合金接头;相较于母材,热力影响区的小角度晶界含量增加,焊核区发生动态再结晶,小角度晶界转化为大角度晶界;接头拉伸性能随转速的增加,呈现先增加后减小的趋势.接头的平均抗拉强度和断后伸长率分别达到231 MPa和4.0%. 接头的断裂位置位于6061侧焊核区,与接头硬度最小位置相吻合.     

异种高强铝合金搅拌摩擦焊搭接接头的缺陷和拉伸性能

采用搅拌摩擦焊对5 mm厚2024/7075异种高强铝合金进行上下板交换位置的搭接焊试验,分析接头的缺陷特征和拉伸性能。结果表明:材料位置和焊接速度对缺陷和拉伸性能有较大影响。当2024铝合金为上板时,接头中存在大面积孔洞缺陷,焊缝表面粗糙,尤其在300 mm/min焊速下存在较严重的起皮缺陷;钩状缺陷为搭接接头的典型缺陷,低焊速(50和150 mm/min)下钩状缺陷向上扩展距离较大,7075铝合金为上板时高焊速(225和300 mm/min)下后退侧钩状缺陷水平向焊核区扩展距离较大;在低焊速下,7075铝合金为上板的接头强度较高;在高焊速下,2024铝合金为上板的接头强度较高;钩状缺陷严重减小接头的有效板厚和有效搭接宽度,是接头强度降低的主要因素,优化搅拌摩擦焊搭接工艺必须同时增大有效板厚和有效搭接宽度。     

2A12铝合金回填式搅拌摩擦点焊的工艺研究

采用回填式搅拌摩擦点焊(RFSSW)对上下板厚度分别为1.5 mm和2 mm的包铝2A12(LY12)铝合金进行焊接,主要对比套筒下扎式和搅拌针下扎式RFSSW接头组织与性能的不同。试验结果表明:工艺参数选择不当时,2种下扎方式分别产生位于热机影响区/焊核区(TMAZ/WZ)界面和WZ中心的未充分回填缺陷。虽然呈现同种断裂方式,套筒下扎式RFSSW接头因更宽的搭接区面积而拉剪强度更高。除此之外,套筒下扎式RFSSW接头WZ的硬度也更高。     

钛/铝异种合金FSLW接头的成形与组织研究

以Ti-6Al-4V钛合金和7075-T6铝合金为对象,将钛合金作为搭接上板,研究了钛/铝异种合金搅拌摩擦搭接焊接头的成形与显微组织。结果表明,当搅拌头转速较高时,搭接界面处会产生因材料填充不及时而形成的孔洞缺陷;随着转速的降低,孔洞缺陷的尺寸逐渐减小,当转速为190 r/min时可获得缺陷极小的接头,连接界面处钛/铝合金结合良好。在本文所使用的焊接工艺中,整个焊接过程在β相变点以下进行。     

不同下压量下TC4/A6061异种合金FSW接头成形及显微硬度研究

对2.5 mm厚的TC4钛合金板和A6061-T6铝合金板进行了搅拌摩擦焊对接试验,研究了不同下压量下接头的表面成形和显微硬度。试验结果表明:当下压量为0.10 mm时,焊缝表面出现沟槽缺陷;当下压量增大到0.26 mm时,焊缝两侧的飞边较多,且试件背部的铝合金与垫板发生粘连。当下压量为0.18 mm时,接头的表面成形良好且内部无缺陷,钛侧搅拌区的边界处出现了Ti-Al金属间化合物层,其厚度约为3μm。焊接接头的显微硬度最大值位于金属间化合物层处。     

7075-T6铝合金板温热成形极限图实验

研究7075-T6铝合金板在温热状态下成形性能,采用电化学腐蚀网格法,利用热力耦合条件下的通用板材成形性能实验机和网格应变自动测量分析系统,获得了7075-T6铝合金板在温热状态下(室温~200℃)的成形极限图(FLD)。实验表明,7075-T6铝合金板的成形极限曲线受温度影响显著,并随温度的升高而上升。基于实验数据,建立了不同温度下7075-T6铝合金板成形极限图的计算模型。     

铝合金低旋转速度回填式搅拌摩擦点焊接头组织及力学性能

采用低旋转速度制备1. 5 mm厚5182-O铝合金回填式搅拌摩擦点焊接头,并通过正交试验法对其表面成形、剪切拉伸、十字拉伸和疲劳性能进行分析,探究低旋转速度下5182-O铝合金点焊接头的综合性能。结果表明,焊接时间6. 5 s、旋转速度1 000 r/min、下扎深度1. 9 mm为最佳焊接参数;接头剪切拉伸力和十字拉伸力分别为6. 62 k N和3. 67 k N;疲劳寿命N为1×106时,疲劳极限载荷F为1 108 N;点焊接头剪切拉伸失效于上下板间的热机影响区,裂纹沿上板厚度方向扩展;接头疲劳显微裂纹同时起源于上下两板靠近载荷一侧,低旋转速度下热输入较低,氧化物不均匀性是裂纹源产生的主要原因。     

轴肩下压量对搅拌摩擦焊搭接接头力学性能的影响

采用表面为右螺纹圆柱型搅拌针的搅拌头对3mm厚LY12铝合金进行了搅拌摩擦焊搭接试验,研究了轴肩下压量对接头界面迁移和搭接接头力学性能的影响.结果表明,随轴肩下压量增大,焊缝两侧的搭接界面均向下迁移,其迁移量随下压量的增加而增加,焊缝返回侧的界面迁移量大于前进侧.控制轴肩下压量,当轴肩下压量合适时,焊缝两侧的界面仅发生较小的迁移.当焊缝两侧的界面仅发生较小的迁移量时,搭接接头有较高的抗剪强度,且断裂都发生在上板,呈正断.焊缝两侧的搭接界面向下迁移时,断裂都发生在下板,接头抗剪强度随界面迁移高度的增加而减小,且受拉侧在下板前进侧时,接头的抗剪强度较受拉侧在下板返回侧时的高.     

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.     

Effect of tool plunge depth on joint formation and mechanical performance of friction stir forming joints made between AA 5052-H32 and AA 6061-T6 sheet metals

The potential of friction stir forming for joining dissimilar grades of aluminum alloys namely, AA 5052-H32 and AA 6061-T6, was investigated. Study on the effect of tool plunge depth revealed that, lap shear load of 7.16 kN and cross-tensile load of 3.51 kN, recorded at medium tool plunge depth range from 0.5 to 0.7 mm, measured using a universal testing machine, were much larger than those of friction stir welded and friction stir spot welded joints fabricated on the same materials. Joint macrostructure observed with optical microscope revealed that joints were strengthened either by mechanical pin interlocking or by metallurgical bonding. The effect of tool plunge depth on the stir zone formation and the influence of frictional heat flux on the lower sheet were revealed through the microhardness measurement using Vickers hardness tester. Morphological studies revealed that tool plunge depth has a significant influence on the pin formation and the geometric features, generated in these joints. Occurrence of various failure modes such as pin pull-out, pin shear, partial bond delamination, and tear-off, were governed by the formation of critical weak zones at various tool plunge depths.     

Microstructure,static and fatigue properties of refill friction stir spot welded 7075-T6 aluminium alloy using a modified tool

ABSTRACT

Defect-free joints were produced in 2.0?mm thick 7075-T6 Al alloy by refill friction stir spot welding using a modified tool. Weld performance was evaluated in terms of microstructure, interfacial bonding, hardness, static and fatigue strength based on the experimental observations. The results indicated that grain size, interfacial bonding quality and lap shear strength significantly depend on sleeve penetration depth (SPD), with sufficient interfacial bonding and stable lap shear strength achieved when SPD?≥?1.8?mm. The SPD and applied load played a dominant role in determining the static lap shear and fatigue failure mechanisms, respectively. More precisely, the lap shear failure mode was an interfacial failure when SPD?≤?1.8?mm, and nugget pullout when SPD?≥?2.0?mm. The fatigue fracture mode involved nugget pullout under high applied load, while fracture through the parent sheet occurs under medium and lower applied loads.     

Effect of joint design on mechanical properties of AL7075 weldment

The effects of joint design on the mechanical properties of AL7075-T6 aluminum sheet were studied on the latest automated gas-tungsten arc-welding system. Using ER5356 filler metal, full-penetration welds were made on workpieces with various included joint angles. Testing of the mechanical properties of the joints was done in the as-welded, naturally aged, and postweld heat-treated conditions. The results show that by using crack-resistant filler, and by selecting the proper joint design and postweld heat treatment, strong, dependable welds can be produced on thin AL7075 sheet material. An elasticity model of the weld joint was established to help understand the mechanical behavior of the joints. An undermatched joint design is shown to be capable of achieving a joint strength that matches the strength of the base alloy.     

铝合金薄板搅拌摩擦焊搭接界面缺陷与接头性能

针对2A12–T4铝合金薄板进行了搅拌摩擦焊搭接试验,研究了焊接参数对缺陷形态与接头性能的影响规律. 结果表明,勾状缺陷具有更大的高度和弯曲角度,最大缺陷高度为上板厚度的12.7%. 随焊接速度增大,缺陷高度减小.随转速提高,勾状缺陷高度先增加后减小,冷搭接缺陷高度呈“V”形变化. 在950 r/min,200 mm/min下接头强度最高,接头系数可达84%. 维氏显微硬度分布呈“W”形,上板出现接头软化,焊核区下部硬度高于上部硬度. 冷搭接缺陷是影响接头性能的主要因素,由于有效搭接宽度较小,接头断裂方式为沿搭接面的剪切断裂.     

Novel dissimilar spot welding of aluminium alloy and steel sheets by friction stirring

Friction stir spot welding (FSSW) has been applied to a dissimilar metal lap joint of an aluminium alloy and steel by stirring only the upper aluminium alloy sheet. Therefore, FSSW cannot be used to weld a lap joint composed of three or more sheets and a lap joint with an adhesive interlayer. In the present work, we propose a novel spot welding process for dissimilar metal lap joints using a new tool with the tip made of spherical ceramics. When this process is applied to the lap joint of the aluminium alloy and steel, the tool can be plunged into the lower steel sheet, then a steel projection is formed in the aluminium alloy sheet. The height of this steel projection increases with the plunge depth, and accordingly, the weld strength increases; the tensile shear strength and the cross tensile strength reached about 3.6 and 2.3 kN/point, respectively.     

半螺纹搅拌针对2024铝合金搅拌摩擦搭接焊力学性能影响

作为影响搅拌摩擦焊（FSW）过程中塑性材料上下流动的重要因素,搅拌针螺纹形貌同样对搅拌摩擦搭接焊（FSLW）的材料流动和力学性能有着重要影响.为研究半螺纹搅拌针对FSLW接头显微组织和力学性能的影响,文中将全螺纹搅拌针和半螺纹搅拌针用于包铝2024铝合金FSLW试验,并对不同搅拌针作用下的FSLW接头的横截面形貌、剪切拉伸载荷、断裂位置等方面进行分析对比.结果表明,半螺纹搅拌针会使钩状缺陷向下弯曲,从而使FSLW接头具有较大的有效板材厚度以及搭接宽度.断裂模式同为剪切断裂,但半螺纹搅拌针作用下的FSLW接头拥有更大的拉断载荷.     

Study of top sheet thinning during friction stir lap welding of AZ31 magnesium alloy

Abstract

Friction stir lap welding was applied to AZ31 magnesium alloy sheets to investigate the effect of tool designs and welding variables on top sheet thinning. Three tools with different shoulder designs were used. Sheet thinning aroused by the hooking or cold lap feature was quantified, and the lap shear fracture load of the joints was evaluated and correlated with the effective top sheet thickness. The tool geometry has a significant effect on the morphology and extent of both hooking and cold lap features, as well as welding variables such as welding pitch and plunge depth. The morphology and extent of these features influenced the effective top sheet thickness, which exhibited a linear relationship with the unit width fracture load via the welded material strength. High fracture loads can be achieved by suppressing the hooking and cold lap features as well as by strengthening the material in the nugget.     

Development of friction stir spot welding using rotating tool without probe and its application to low-carbon steel plates

A friction stir spot welding process, in which a rotating tool without a probe was employed, was applied to a lap joint of low carbon steel plates with 0.5 mm thickness. In this process, the rotating tool of 3.6 mm diameter, rotating at 18,000 rpm, was plunged into the upper plate at a rate of 0.2 mm/s, and then kept at a maximum plunged depth of 0.05–0.25 mm for 0–1 s (dwell time). In the weld obtained by this process, a hole due to the impression of the plunged tool probe was not formed, although a slight depression by the tool plunging remained. At tool plunge depths of 0.05 mm or less, it was impossible to weld the plates. At tool plunge depths from 0.1 to 0.14 mm, joints were fractured at the interface in tensile test, and the failure load increased with tool plunge depth. At tool plunge depths from 0.16 to 0.22 mm, joints were fractured at an almost constant load along the periphery of the depression, leaving a part of the upper plate on the bottom plate surface. The maximum tensile failure load of 1.8 kN was obtained at a plunge depth of 0.2 mm. Based on the observation of the weld microstructure and measurement of the thermal cycle at various spots in the weld, controlling factors of the joint strength are discussed.