铝合金回填式搅拌摩擦点焊组织及力学性能分析

采用回填式搅拌摩擦点焊技术对7075-T6铝合金进行了点焊试验.对接头进行了显微组织、显微硬度、剪切和十字形拉伸测试.结果表明,接头显微组织可分为焊核区、热力影响区、热影响区及母材;在焊缝中发现了钩状缺陷、孔洞、未焊合、未完全回填及粘连韧带等缺陷;焊缝区显微硬度呈W形分布,焊点中心呈V形分布;在旋转频率为1 400 r/min,焊接时间为4s时,接头的抗剪强度达到最大值125.6 MPa,为母材强度的39.6％;接头的十字形拉伸载荷随工艺参数的变化规律比较复杂,最大十字形拉伸强度可达43.9 MPa.     

A newly developed tool without probe for friction stir spot welding and its performance

A newly developed tool for friction stir spot welding (FSSW) has been proposed, which has no probe, but a scroll groove on its shoulder surface (scroll tool). By use of this tool, FSSW has been performed on aluminium alloy 6061-T4 sheets and the potential of the tool was discussed in terms of weld structure and static strength of welds. The experimental observations showed that the scroll tool had comparable or superior performance to a conventional probe tool. It was confirmed that sound welding could be achieved without a probe hole, in which the scroll groove played significant roles in the stirring of the material and the shoulder plunge depth was the important processing variable. The maximum tensile-shear strength of the welds made by the scroll tool was found to be 4.6 kN that was higher than that of the welds made by the probe tool and two different fracture modes, shear fracture and plug fracture, appeared depending on processing condition. The shear fracture took place at smaller shoulder plunge depths or at shorter tool holding times, while the plug fracture occurred at larger shoulder plunge depths or at longer tool holding times. It was indicated that the tensile-shear strength and associated fracture modes were determined by two geometrical parameters in the weld zone.     

Influence of FSSW parameters on fracture mechanisms of 5182 aluminium welds

The influence of the tool rotational speed, the probe plunge depth and the shoulder penetration depth on weld microstructure and on the weld strength have been studied. The shear tests showed that the friction stir spot welds fail by nugget pullout. Three microstructural factors play a determinant role on the weld's strength: the size and location of the stir zone, and the unwelded interface tip slope. With increasing rotational speed, the shear strength increases because of the larger size of the stir zone. By changing the probe plunge depth the location of the stir zone can be controlled in order to maximize the bonded distance between the interface tip and the central hole left by the probe. The shoulder penetration depth must be sufficient to ensure a horizontal interface tip and therefore avoid fracture by the opening mode (mode I) during shear loading.     

Effect of hook characteristics on the fracture behaviour of dissimilar friction stir welded aluminium alloy and mild steel sheets

ABSTRACT

Under tensile shear loading, fracture modes of dissimilar lap welds produced by friction stir scribe technology were studied. Three fracture modes were observed. For zone A fracture, the initial crack was restrained, and the joint ultimately fractured in the base mild steel. For zone B fracture, the initial crack progressed through the aluminium sheet just above the Al/steel interface. For zone C fracture, the initial crack proceeded along the steel hook to the aluminium sheet surface. Fracture mode and joint strength were greatly influenced by steel hook size, and the steel hook size was affected by welding parameters and tool scribe height. In this study, the experimental joint strength achieved the calculated joint load limit.     

Influences of welding parameters on mechanical properties of AZ31 friction stir spot welds

Abstract

In this study, the influence of welding parameters, including tool rotational speed, plunge rate and dwell time, on the overlap tensile shear properties of AZ31 friction stir spot welds was investigated. The microstructures in stir zones and fracture surfaces were observed using optical microscope and scanning electron microscope respectively. The bonded width and h value (the distance from the tip of the partially bonded region to the top of the weld surface) were measured. The results indicated that larger bonded width and higher h value of the AZ31 weld result in better mechanical property. It is proposed that high tensile shear loads are produced when the tool rotational speed range of 1500–2250 rev min^?1 and 1 s dwell time are applied during the friction stir spot welding of AZ31. The plunge rate range from 2·5 to 10 mm s^?1 has insignificant influence on the tensile shear load of AZ31 joints under the present conditions. The failure mode changes from interfacial to pullout when the tool rotational speed is >2250 rev min^?1. The fracture feature of AZ31 welds is brittle fracture.     

Development of processing windows for friction stir spot welding of aluminium Al5052 /copper C27200 dissimilar materials

Friction stir spot welding technique was used to join dissimilar combinations of aluminium alloy (Al5052) with copper alloy (C27200) and friction stir spot welding windows such as tool rotational speed–dwell time and tool rotational speed–plunge depth diagrams for effective joining of these materials were developed. Using a central composite design model, empirical relations were developed to predict the changes in tensile shear failure load values and interface hardness of the joints with three process parameters such as tool rotational speed, plunge depth and dwell time. The adequacy of the developed model was verified using ANOVA analysis at 95% confidence level. Response surface methodology was used to optimize the developed model to maximize tensile strength and minimize interface hardness. A high tensile shear failure load value of 3850 N and low interface hardness value of HV 81 was observed for joints made under optimum conditions, and validation experiments confirmed the high predictability of the developed model with error less than 2%. The operating windows developed shall act as reference maps for future design engineers in choosing appropriate friction stir spot welding process parameter values to obtain good joints.     

Al-Mg合金填充式搅拌摩擦点焊性能

为了确定Al-Mg铝合金填充式搅拌摩擦点焊性能,以Al-Mg铝合金中2 mm的5A06为研究对象,对填充式搅拌摩擦点焊接头进行了剪切拉伸、十字形拉伸、显微组织和疲劳性能等测试,并建立了焊点组织区模型.结果表明,接头显微组织可以分为焊核区、热影响区、热力影响区和母材区部分;旋转频率为2000 r/min时,剪切载荷均值7865 MPa,十字形拉伸载荷均值3480 N;通过SEM和OM分析,点焊接头疲劳裂纹均起始于上下板结合面的焊点边缘,该区域的环沟槽、孔洞及包铝层等缺陷和应力集中是造成疲劳破坏的主要原因.     

根部未焊合对AZ31B镁合金搅拌摩擦焊接头性能的影响

针对厚4.3 mm的AZ31B镁合金短针设计搅拌摩擦焊接,研究工艺参数对根部未焊合率的影响,并通过接头组织与拉伸断口形貌分析,分析了根部未焊合对接头抗拉强度的影响。结果表明:焊接速度一定时,当搅拌头旋转速度超过临界值950 r/min时,随着转速的增加,接头根部未焊合率降低。当旋转速度一定时,焊接速度对接头未焊合率几乎无影响。所有拉伸试样均在根部未焊合界面处起裂并发生断裂,而焊合区断口呈现典型的韧脆混合断裂特征。此外,接头抗拉强度随着根部未焊合率的降低而升高,当旋转速度为1 180 r/min、焊接速度120 mm/min时,接头的抗拉强度达到最大值188 MPa,为母材强度的76.4%。     

Analysis of process parameters effects on dissimilar friction stir welding of AA1100 and A441 AISI steel

Abstract

A prominent benefit of friction stir welding process is to join plates with dissimilar material. In this study, an attempt is made to find effects of tool offset, plunge depth, welding traverse speed and tool rotational speed on tensile strength, microhardness and material flow in dissimilar friction stir welding of AA1100 aluminium alloy and A441 AISI steel plates. Here, one factor at a time experimental design was utilised for conducting the experiments. Results indicated the strongest joint obtained at 1·3?mm tool offset and 0·2?mm plunge depth when the tool rotational speed and linear speed were 800?rev min^??1 and 63?mm min^??1 respectively. The maximum tensile strength of welded joints with mentioned optimal parameters was 90% aluminium base metal. Fracture locations in tensile test at all samples were in aluminium sides. Owing to the formation of intermetallic compounds at high tool rotational speed, the microhardness of joint interface goes beyond that of A441 AISI steel.     

搅拌摩擦焊修复ZL210铸造铝合金组织与性能分析

鉴于铸件中存在不可避免的缺陷,以ZL210合金为研究对象,对搅拌摩擦焊修复技术进行试验研究,重点分析转速对修复接头微观形貌和力学性能的影响. 结果表明,当转速过低时,修复区容易出现孔洞缺陷;在合理的焊接参数组合下可得到无缺陷的焊核区,其由细小的等轴晶组成. 修复区的显微硬度呈“W”分布,热影响区的宽度随转速增加而增加. 另外,随着转速的增加,修复区的抗拉强度先增加后减小;当转速为1 500 r/min,修复区的抗拉强度和断后伸长率达到最大值,分别为318 MPa和11.8%. 断裂形貌表明修复后材料呈现典型的韧性断裂.     

Investigation on friction stir lap welding of aluminium to aluminium clad steel sheets

Abstract

In this work, the feasibility of friction stir lap welding an aluminium alloy (Al-5083) to the aluminium clad steel sheet was studied. The welded joints were characterised by various methods including shear–tensile test and optical microscopy and scanning electron microscopy. The results indicated that sound and defect free joints were obtained. The fracture loads of the samples reached up to 94% compared with that of the steel base metal. Moreover, the joint strength linearly increased with the decrease in thickness of the aluminium layer roll bonded on the steel sheet. It was also shown that welding rotation and travel speed variation did not considerably impact the fracture loads in the studied range.     

Development of solver system for FEM analysis of solder joints

This study was aimed at establishment of a model that can predict tensile shear strength and fracture portion of laser-welded lap joints in the tensile test. To clear the influence of bead length and bead width on them, the joints that used steel sheets with a thickness in the range of 0.8–1.2 mm were evaluated. It was found that the tensile shear strength increases with the bead size, and the fracture occurs at base metal (BM), weld metal (WM) or a portion between them with a curvature heat-affected zone (HAZ), in the tensile test. Also to clarify the rotational deformation process around WM during the tensile test, cross-sections of joints were observed, which were applied to several loads in the tensile test. This observation derived the relationship between the radius, R_i, at the inner plane of the HAZ and the rotational angle at the centre of the sheet thickness. Furthermore, the relationship between Ri and the applied load was obtained by linear regression. A plastic analysis for deformation of the joints was carried out based on these functions and some assumptions. These assumptions consider that the joint consists of BM, WM and HAZ, which are under a simplified stress mode. Finally, estimation of the tensile shear strength and the fracture portion of the joints was achieved. This estimation made good accordance with the experimental results.     

The influence of refill FSSW parameters on the microstructure and shear strength of 5042 aluminium welds

Refill friction stir spot welding (FSSW-Refill) was used to produce solid-state joints in an automotive 5042 aluminium alloy. The influence of plunge depth, rotational speed, plunge rate and time on the microstructure and shear strength was investigated. The Statistica software package was used to correlate process parameters with the mechanical properties of the joints. The most significant variables are plunge depth and tool rotational speed, while volumetric defects have a small influence on the mechanical performance of the welds. Reducing the rotational speed from 1900 rpm to 900 rpm increased the bonding ligament length. For joints produced at a higher tool rotational speed (1900 rpm) the material flow was more vertical, i.e., towards the surface of the joint, the bonding ligament length was reduced and the shear strength was impaired.     

Process parameters optimization for friction stir welding of RDE-40 aluminium alloy using Taguchi technique

Taguchi approach was applied to determine the most influential control factors which will yield better tensile strength of the joints of friction stir welded RDE-40 aluminium alloy. In order to evaluate the effect of process parameters such as tool rotational speed, traverse speed and axial force on tensile strength of friction stir welded RDE-40 aluminium alloy, Taguchi parametric design and optimization approach was used. Through the Taguchi parametric design approach, the optimum levels of process parameters were determined. The results indicate that the rotational speed, welding speed and axial force are the significant parameters in deciding the tensile strength of the joint. The predicted optimal value of tensile strength of friction stir welded RDE-40 aluminium alloy is 303 MPa. The results were confirmed by further experiments.     

转速对2060铝锂合金RFSSW接头成形及拉剪性能的影响

以2060铝锂合金为研究对象，进行了回填式搅拌摩擦点焊试验，研究了不同转速下接头内部成形及其与拉伸性能的关系. 结果表明，点焊接头在不同转速下出现了未完全回填缺陷、孔洞缺陷及向下弯曲的钩状结构. 未完全回填缺陷与孔洞缺陷在低转速与高转速下易出现，钩状结构向下弯曲且随转速的增加其高度先增加再减小. 拉剪载荷随转速的提高先增加再降低；在转速为2 200 r/min时，接头拉剪载荷达到9 800 N. 拉剪试样的断裂方式均为剪切断裂，断裂位置可分为三类:沿搭接界面断裂、沿套筒作用区底部断裂及沿包含两者的混合断裂.     

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.     

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.     

铱片的显微组织与室温拉伸断裂机制研究

采用辉光放电质谱法(GDMS)、光学显微镜(OM)、扫描电镜(SEM)和力学试验机等测试手段,对不同加工状态的铱片杂质元素含量、金相组织、断口形貌和室温力学性能进行了研究。结果表明:加工状态对铱片的力学性能有重要影响,1 mm厚的热轧态铱片平均抗拉强度为213.6 MPa,延伸率为2.52%,主要为脆性沿晶断裂,部分为脆性穿晶解理断裂;而0.1 mm厚的冷加工态铱片平均抗拉强度为954.1 MPa,延伸率为0.55%,断裂模式主要为脆性穿晶断裂;两者在断裂之前均未发生明显的塑性变形,表现为脆性断裂模式。     

Friction stir lap welding of plastic to metal using adjustable tool

An OX horn type interlocking joint of MC Nylon-6 (top sheet) and AMXS6020 Mg alloy (bottom sheet) with satisfactory mechanical properties had been obtained by friction stir lap welding (FSLW) using an adjustable tool. The adjustable tool produced the good surface appearances and mechanical interlocking interfaces with low shoulder rotation speeds and high probe rotation speeds. The Mg alloy around the probe was stirred into the melted MC Nylon-6 zone during the FSLW process to form OX horn shape which bended toward the joint centre. The influences of welding parameters on Mg alloy horns formation, tensile shear strength and fracture morphology were investigated. Mechanical interlocking induced by the Mg alloy horns contributed to the main joining mechanism.     

搅拌头旋转频率对静止轴肩搅拌摩擦焊接头力学性能的影响规律

利用自行设计的静止轴肩装置对6005A-T6铝合金进行了静止轴肩搅拌摩擦焊的试验研究.结果表明,当焊接速度为200 mm/min时,表面光滑且无缺陷的焊接接头抗拉强度与断后伸长率随着搅拌头旋转频率的增加呈现先增加后减小的趋势;焊接接头的正背弯180°无裂纹;当旋转频率为1800 r/min时,抗拉强度达到最大值234 MPa,接头强度系数达到79%.静止轴肩搅拌摩擦焊接头的显微维氏硬度呈W形分布,最小值出现在前进侧的热影响区;接头的软化程度随搅拌头旋转频率的增加而增加.焊接接头的断裂位置位于热力影响区,断口呈韧性断裂.