低活化铁素体–马氏体钢搅拌摩擦焊接头组织和性能分析

文中对9% Cr低活化铁素体-马氏体钢搅拌摩擦焊接头的组织和性能进行了分析.结果表明,搅拌摩擦焊接头不同区域微观组织存在明显的差异.搅拌区内奥氏体的动态再结晶引起晶粒细化和马氏体转变,并且晶界M₂₃C₆相溶解,晶内M₃C相析出;热力影响区组织变化与搅拌区相似,但晶粒尺寸明显大于母材;热影响区和母材区均表现回火组织特征.搅拌区硬度显著提高,分布均匀;热力影响区硬度值变化较大;热影响区发生软化,其硬度值在接头区域最低.随着拉伸测试温度的增加,搅拌区的屈服强度单调降低,抗拉强度先增大后减小,而断后伸长率先减小后增大.     

C18000铜合金搅拌摩擦焊接头微观组织与性能

对3.5 mm厚的C18000铜合金板进行搅拌摩擦焊焊接试验. 在焊接速度120 mm/min,转速1 200 r/min工艺下获得无缺陷焊接接头. 在金相显微镜下对接头的宏观形貌、微观组织进行观察,用扫描电镜和透射电镜对母材和搅拌区组织进行观察分析. 结果表明,接头区大致分为母材区、热影响区、热力影响区和搅拌区,搅拌区晶粒细小均匀,热力影响区晶粒沿边界切线方向被拉长;搅拌区Cr₃Si相部分溶解,搅拌区组织中的Cr单质相和Ni₂Si相溶解导致接头硬度和抗拉强度下降. 搅拌区平均硬度为151.4 HV;接头抗拉强度为497 MPa,达到母材的72%;接头电导率下降为35%IACS.     

Microstructural analysis of stir zone of Al alloy produced by friction stir spot welding

Abstract

Friction stir spot welding (FSSW), which was recently developed as a spot joining technique, has been applied to a lap joint of Al alloy 6061 sheets, 1 mm in thickness, to clarify its microstructural features of the joint. A nugget shaped stir zone having finer grain size was observed around the exit hole of the probe. Crystallographic texture analyses using EBSD method suggested that the material flow occurred along the rotating direction of the FSSW tool in the wide region including the stir zone. In the periphery of the nugget shaped stir zone, which was characterised by finer grain size than the stir zone interior, no inclusions or precipitates were found on the SEM scale. A softened region was formed around the joint centre, which could be explained as resulting from dissolution and/or growth of the strengthening precipitates due to thermal cycle of FSSW.     

Microstructures and ion-irradiation behaviour of friction stir welded 12Cr-ODS steel

12Cr oxide dispersion strengthened steel was successfully joined by friction stir welding (FSW), and the joints were irradiated with 3?MeV Au ions at 500°C. The morphology of grains, dislocations, sizes and distributions of nano-sized oxide particles (NPs) in different zones of the FSW joints were analysed. It was found severe plastic deformation occurred and fine equixed grains were formed in stir zone (SZ). The NPs coarsen obviously in thermal-mechanically affected zone (TMAZ) on advancing side (AS) due to the relative movements of plastic materials with high-velocity gradient. The size distributions of the NPs in base metal (BM), heat affected zone (HAZ) and RS-TMAZ are concentrated in a smaller range than those in SZ and AS-TMAZ. Finer grains and high density of dislocations result in hardness increasing obviously in SZ. Irradiation introduced higher hardening in HAZ because of its less grain boundaries and dislocation density compared with SZ and BM.     

Development of novel heating tool friction stir spot welding (HT-FSSW) for AZ31 magnesium alloy

In this work, a new heating tool friction stir spot welding (HT-FSSW) process was developed, and its impacts on the microstructure and mechanical properties of the welded AZ31 magnesium alloy joints were investigated by microstructure observation, tensile tests and microhardness tests. An increase in the heating tool temperature resulted in a decrease in the grain size of the stir zone (SZ) and an increase in the grain size of the thermomechanically affected zone (TMAZ). The rising heating tool temperature also aggrandised the bonded zone width and enhanced the tensile shear load strength per unit area of the HT-FSSW welded joints. With an increase in the heating tool temperature, the microhardness of SZ increased while that of the TMAZ decreased. Moreover, the slope of the Hall–Petch relationship between microhardness and grain size of the TMAZ is larger than that of the SZ.     

Microstructural modification of cast Mg alloys by friction stir processing

Abstract

Cast Mg alloys were processed using friction stir processing (FSP) to acquire a fine grained structure and high strength. Actually, FSP is a novel grain refinement method for light metal alloys. Using FSP, a cast microstructure with coarse grain size was refined to equiaxial fine grain through dynamic recrystallisation; second phase particles were finely dispersed by FSP. Moreover, FSP is effective to eliminate cast defects such as microshrinkages or porosities. Commercial die cast Mg alloy (AZ91D) and high strength Mg–Y–Zn alloy plates were prepared for FSP. Heat input using a rotational tool during FSP closely affected the microstructure in the stirred zone. Actually, FSP with lower heat input produced a finer grain size and higher hardness. Changes in the friction stir processed microstructures affecting mechanical properties were not only grain refinement, but also second phase particle distributions. Results show that alloys with high hardness by FSP have finely dispersed second phase particles without dissolution during FSP.     

高镁铝合金搅拌摩擦交叉焊接头微观组织与力学性能

为满足大型铝合金船舶壁板的制造需求,对新一代高镁铝合金进行了搅拌摩擦交叉焊接试验. 结果表明,交叉焊接头成形良好,搅拌区晶粒尺寸最小,热力影响区晶粒形态没有明显方向性,与单道搅拌摩擦焊相比,交叉焊接头搅拌区晶粒组织更细. 显微硬度测试结果表明,交叉焊接头显微硬度变化范围较小,前进侧接头软化明显;拉伸试验测试结果表明,交叉焊接头抗拉强度为340 MPa,为母材强度的87%,对比搅拌摩擦焊接头抗拉强度358 MPa略微降低,在热影响区断裂,断裂方式为45°韧性断裂;疲劳裂纹萌生于焊缝底部,在最大应力150 MPa下循环超2 × 106次未断裂,疲劳性能良好,瞬断区断裂方式为韧性断裂.     

Fracture toughness of structural aluminium alloy thick plate joints by friction stir welding

Abstract

The fracture toughness in a friction stir welded joint of thick plates of structural aluminium alloy type A5083-O is investigated. A joint between two 25 mm thick plates is fabricated by one sided, one pass friction stir welding. The Charpy impact energy and critical crack tip opening displacement (CTOD) in the friction stir weld are much higher than those in the base metal or heat affected zone, whereas mechanical properties such as stress–strain curve and Vickers hardness are not conspicuously different. The effects of the microstructure on crack initiation and propagation are studied in order to clarify the difference in fracture toughness between the stir zone and base metal. The analyses of the fracture resistance curves and the diameters of dimples in the fracture surface after both tensile and bending tests show that the fine grained microstructure in the stir zone helps to increase ductile crack initiation and propagation resistance. It is found that the high fracture toughness value in the stir zone is affected by the fine grained microstructure in friction stir welds.     

Microstructure and Mechanical Properties of Low-Carbon Q235 Steel Welded Using Friction Stir Welding

This study focuses on the microstructure and mechanical properties of the joints of Q235 mild steel, which was formed by the friction stir welding (FSW). The results indicated that, after the FSW, the heat-affected zone (HAZ) of the retreating side (HAZ_RS) and the HAZ of the advancing side (HAZ_AS) recovered under the influence of the heating cycle. The transformation of the phases in the thermo-mechanically affected zone (TMAZ) of the retreating side (TMAZ_RS), the stir zone (SZ) and the TMAZ of the advancing side (TMAZ_AS) generated the pearlite and acicular ferrite. The continuous dynamic recrystallization occurred in all the three zones, whereas the grains were refined. The SZ mainly consisted of D₁, D₂ and F shear textures, while the TMAZ_AS was made up of only the F shear texture. The fine-grained structure, pearlite and the acicular ferrite improved the hardness and tensile strength of the joint. Its ultimate tensile strength was 479 MPa, which was 1.3% higher than that of the base metal. However, the uniform elongation was 16%, which showed a decrease of 33%. The fracture was a ductile fracture with the appearance of dimples. Besides, the joints of the FSW showed an excellent bending performance.     

Friction stir welding of DH36 steel

Abstract

Hot rolled DH36 carbon steel, 6.4 mm in thickness, was friction stir welded at speeds of 3.4 mm s^-1 (8 in min^-1), 5.1 mm s^-1 (12 in min^-1), and 7.6 mm s^-1 (18 in min^-1). Single pass welds free of volumetric defects were produced at each speed. The relationships between welding parameters and weld properties are discussed. Optical microscopy, microhardness testing, and transverse and longitudinal tensile tests have been performed. Bainite and martensite are found in the nugget region of the friction stir welds whereas the base material is comprised of ferrite and pearlite. The maximum hardness is observed in the weld nugget, and the hardness decreases gradually from the weld nugget, through the heat affected zone, to the base metal. Tensile testing also indicates overmatching of the weld metal relative to the base metal. Maximum hardness and longitudinal (all weld metal) tensile strengths increase with increasing welding speeds. Weld transverse tensile strengths are governed by the base metal properties, as all transverse tensile bars fail in the base metal.     

Tool design and stir zone grain size in AZ31 friction stir spot welds

Abstract

The influence of tool design and tool rotational speed variations on the torque, energy output, stir zone temperature and average grain size in the stir zones of AZ31 friction stir spot welds was investigated. The average stir zone grain size decreased by ～1 μm in AZ31 friction stir spot welds made using a three-flat/threaded tool design and tool rotational speeds of 2250 and 3000 rev min^?1. However, there was no statistically significant influence of tool design on the average grain sizes in friction stir spot welds made using tool rotational speeds of 1500 and 1000 rev min^?1. There was no evidence of grain growth in the stir zones of AZ31 friction stir spot welds. Similar torque, calculated energy output and stir zone temperature values were found in AZ31 friction stir spot welds made using threaded and three-flat threaded tool designs and tool rotational speeds from 1000 to 3000 rev min^?1.     

Development of friction stir welding of high strength steel sheet

Abstract

For friction stir welding (FSW) of advanced high strength steel (AHSS) sheets with tensile strength grades between 590 and 1180?N?mm^?2, the appropriate welding condition range and the influence of welding conditions on microstructures and mechanical properties of the welds were investigated. The appropriate welding conditions to avoid defects such as the incomplete consolidation at the bottom of the weld were obtained for the steel sheets up to 1180?N?mm^?2 grade. The higher tool rotation speed evidently resulted in the larger volume fraction of martensite and higher hardness in the stir zone (SZ), attributed to an increase in the peak temperature of its thermal cycle. The tensile strength of the weld joint was as high as that of the base metal for the steels up to 980?N?mm^?2 grade, but slightly lower than that of the base metal for the steel of 1180?N?mm^?2 grade due to the heat affected zone (HAZ) softening.     

Friction stir welding of dissimilar A319 and A356 aluminium cast alloys

Abstract

In the present investigation, the microstructure and mechanical characteristics of dissimilar A319 and A356 cast Al alloys plates joined by friction stir welding (FSW) were evaluated. The effect of tool rotational and welding speeds as well as the post-weld heat treatment (PWHT) on such properties was investigated. Post-weld heat treatment was carried out at a solutionising temperature of 540°C for 12 h followed by aging at 155°C for 6 h. For the as welded specimens, the welded zone (WZ) exhibited higher hardness values when compared with the A319 and A356 parent alloys. The peak hardness at the WZ was found to increase by increasing the tool rotational speed and/or reducing the welding speed. In contrast, the post-weld heat treated (PWHTed) specimens exhibited lower hardness values at the WZ than the parent alloys. For PWHTed specimens, the peak hardness at the WZ was found to decrease by increasing the tool rotational speed and/or reducing the welding speed. Tensile tests results demonstrate that, for the as welded specimens, the tensile fracture took place on A356 side where the hardness was minimal. While for PWHTed specimens, the fracture took place at the WZ. Increasing the tool rotational speed reducing both tensile and yield strengths, but increases the ductility of the joint.     

氧化物弥散强化材料的搅拌摩擦焊分析

为了探索搅拌摩擦焊技术应用于氧化物弥散强化材料的可焊接性及其基本特点,文中对厚度为4 mm的氧化物弥散强化铜合金进行了焊接试验,并对焊接接头的宏观形貌、微观组织、显微维氏硬度进行了分析. 发现焊接接头横截面由搅拌区、热力影响区、热影响区和母材区4部分组成. 前进侧热影响区与热力影响区形成明显的分界线,后退侧则相对模糊. 搅拌区的组织为细小的等轴晶粒,出现了洋葱环和L线,热力影响区晶粒沿一定方向发生形变,热影响区组织粗化. 沿焊缝横截面的显微维氏硬度呈V形分布,其中搅拌区硬度值最低.     

Friction stir weld nugget temperature asymmetry

Abstract

Two different hardness distributions were observed to result from the friction stir welding of an Al–Mg–Si alloy using identical welding speeds but different heat inputs. In one case, the distribution was relatively symmetric about the weld centreline and in the other, the hardness declined continuously from the advancing to the retreating sides of the weld nugget. Based on in-probe temperature measurements, full-field grain size mapping, and response to post-weld heat treatment, it has been ascertained that under low heat input conditions, the weld nugget attained a higher temperature on the advancing side than on the retreating side. Such a temperature asymmetry has often been proposed and has been predicted by simulation but, has not been convincingly demonstrated before this time.     

Friction stir welding of pure titanium lap joint

Abstract

The effects of welding parameters on friction stir welding of pure titanium lap joint were investigated together with the microstructural characteristics of the sound joint. Three kinds of welding defects were found under the condition of tool load control, namely, the groove-like defect, the inner cavity defect and the overheating rough surface and tool penetration defect with increasing heat input. The tool plunge depth control effectively increased the lap width compared with the tool load control, so the sound joints fractured in the base metal were acquired at 250 rev min^–1–75 mm min^–1 and 200 rev min^–1–50 mm min^–1. The sound joint consisted of the thermomechanically affected zone, the stir zone, the lap zone and the top layer. The microstructure was fined obviously after welding, and finer grains were observed in the lap zone and top layer.     

搅拌摩擦对接焊6061铝合金的高周疲劳行为

对6061铝合金进行搅拌摩擦对接焊,其焊接工艺参数为：旋转速度600、800、1000、1200 r/min,前进速度80、100 mm/min,探针插入深度1.85 mm。基于搅拌摩擦焊参数计算得到的能量输入结果表明,在输入能量为196～405 kJ的情况下,接头在297～354 kJ的输入能量范围内有最大的抗拉强度。在不同的应力比（R=0.5,0.3,0.1,-0.3,-0.5）下,将高强度、低强度2种焊接头进行疲劳测试。结果表明,对于这2种焊接头,显微组织特征明显影响其疲劳性能,比如搅拌区、热力影响区（TMAZ）和热影响区。从接头的显微组织、裂纹扩展路径和断裂表面观察等方面对其疲劳强度进行讨论。     

Friction stir butt welding of A5052-O aluminum alloy plates

Friction stir butt welding (FSW) between A5052-O aluminum alloy plates with a thickness of 2 mm was performed.The rotation speeds of the welding tool were 2000 and 3000 r/min,respectively.The traverse speed was ranged from 100 mm/min to 900 mm/min.The defect-free welds with the very smooth surface morphology were successfully obtained,except for at the welding condition of 3000 r/min and 100 mm/min.The onion ring structure was observed in the friction-stir-welded zone (SZ) at the condition of 2000 r/min and 100 mm/min.For all the welding conditions,the grain size of the SZ was smaller than that of the base metal,and was decreased with the decrease of the tool rotation speed and with the increase of the tool traverse speed.The stir zone exhibited higher average hardness than the base metal.The decrease of the tool rotation speed and the increase of the tool traverse speed resulted in the increase in the average hardness of the SZ.The tensile strength of the FSWed plates was similar to that of the base metal,except for at the welding condition of 3000 r/min and 100 mm/min.The total elongation of the FSWed plates was lower than that of the base metal.     

Relationships between weld parameters,hardness distribution and temperature history in alloy 7050 friction stir welds

Abstract

Aluminium alloy 7050 was friction stir welded using three different ratios of tool rotation rate to weld travel speed. Welds were made using travel speeds of between 0·85 and 5·1 mm s^?1. Weld power and torque were recorded for each weld. An FEM simulation was used to calculate the time–temperature history for a subset of the welds. For each weld the hardness distribution with and without post-weld heat treatment was determined. The hardness distributions within the welds are rationalised based on the friction stir welding parameters and the resulting temperature histories. The analysis provides a basis for manipulation of weld parameters to achieve desired properties.     

Comparison of formability of friction stir welded and laser welded dual phase 590 steel sheets

Abstract

The formability of welded dual phase 590 (DP 590) steel sheets was investigated, using both friction stir welding and laser welding. Similar and dissimilar gauge sheets were joined using both processes. The laser welded sheets were produced under process conditions typical of industrial production of tailor welded blanks. The friction stir welded specimens were produced in a lab, where different tool rotational speeds and translation speeds were investigated in order to obtain good weld properties. The formability of the welded sheets was evaluated using a series of mechanical tests, including transverse tension and plane strain formability testing. Friction stir welded specimens performed about the same as laser welded specimens in transverse tension testing; however, hardness profiles showed that the laser welds had greater peak hardness than the friction stir welds. Therefore plane strain formability tests were performed with the welds oriented along the major strain direction. When this type of weld stretching was performed the friction stir welded sheets were shown to be ～20% more formable than the laser welded sheets.