Materials flow and phase transformation in friction stir welding of Al 6013/Mg

Material flow and phase transformation were studied at the interface of dissimilar joint between Al 6013 and Mg, produced by stir friction welding (FSW) experiments. Defect-free weld was obtained when aluminum and magnesium were placed in the advancing side and retreating side respectively and the tool was placed 1 mm off the weld centerline into the aluminum side. In order to understand the material flow during FSW, steel shots were implanted as indexes into the welding path. After welding, using X-ray images, secondary positions of the steel shots were evaluated. It was revealed that steel shots implanted in advancing side were penetrated from the advancing side into the retreating side, whereas the shots implanted in the retreating side remained in the retreating side, without penetrating into the advancing side. The welded specimens were also heat treated. The effects of heat treatment on the mechanical properties of the welds and the formation of new intermetallic layers were investigated. Two intermetallic compounds, Al₃Mg₂ and Al₁₂Mg₁₇, were formed sequentially at Al6013/Mg interface.     

Numerical studies on controlling of process parameters in friction stir welding

A thermo-mechanical model is developed to predict the material deformations and temperature histories in the friction stir welding (FSW) process. Based on this model, the effects of the welding parameters on temperatures and material behaviors are investigated. Numerical results indicate that the maximum temperature in the FSW process can be increased with the increase of the rotating speed. The increase of the welding speed can lead to the obvious increase of the efficient input power for FSW system. The material particles on the top surface do not enter into the wake and just pile up at the border of the wake at the retreating side and this is the reason for the formation of the weld fash in FSW. Both the increase of the rotating speed and the decrease of the welding speed can lead to the increase of the stirring effect of the welding tool, which can improve the friction stir weld quality. But when the rotating speed is increased, the weld fash becomes more obvious. When the welding speed becomes higher, the rotating speed must be increased simultaneously to avoid any possible welding defects such as void. The simultaneous increase of the rotating and the translating speeds of the welding tool can lead to the increase of the residual stress.     

7075铝合金搅拌摩擦焊接头变形及失效行为

使用搅拌摩擦焊（FSW）设备对厚度为6mm的7075高强度铝合金平板进行对接试验。设计出双径试样,采用液压伺服试验机对7075铝合金搅拌摩擦焊接头进行拉伸试验,并借助奥林巴斯显微镜和扫描电镜观察接头的变形及失效过程。结果表明,7075铝合金搅拌摩擦焊接头在拉伸过程中出现双颈缩现象,颈缩首先在后退侧出现,随着加载的进行,前进侧也出现颈缩现象。微裂纹在接头中的前进侧和后退侧颈缩区内晶界处由微孔洞聚集产生。随着应变的增加,微孔洞数量明显增加,当应变足够大时,微孔洞连接形成微裂纹。微裂纹沿着与加载方向成45°向焊核区进行扩展,导致接头断裂,断裂位置位于接头中的焊核区,断裂方式为剪切断裂混合着微孔聚集型断裂。     

Effect of tool rotation rate on microstructure and mechanical properties of friction stir welded copper

Abstract

Defect free copper welds were achieved by friction stir welding (FSW) carried out at a constant welding speed of 100 mm min^?1. The influence of tool rotation rate on microstructure, mechanical properties and fracture location was investigated. As the tool rotation rate increased, the grains of nugget zone grew significantly, the thermomechanically affected zone became indistinct and the grain size increased, but the effect of tool rotation rate on the grain size of heat affected zone was limited. Both ultimate tensile strength (UTS) and elongation increased first and then decreased with increasing rotation rate and the UTS achieved a highest value of 282 MPa at the rotation rate of 400 rev min^?1 together with the welding speed of 100 mm min^?1, which was on the level of the base metal. The fracture occurred at the cavity defect on the advancing side of the joint when the FSW was performed at a low tool rotation rate, while it occurred on the retreating side when the tool rotation rate was relatively high.     

搅拌摩擦焊待焊界面消失模型

提出了一种搅拌摩擦焊接过程中待焊界面消失并形成焊缝的二维模型,阐述了搅拌摩擦焊接过程中待焊界面在焊接热、焊接作用力及搅拌作用下形成焊缝的过程,并把焊缝划分成晶粒长大区、界面氧化区、待焊界面消失区、塑性金属流动区、S线等区域,同时描述了待焊界面冶金熔合后在搅拌摩擦焊缝内部的分布形态.该模型对晶粒长大区、待焊界面消失区、S线3个特定区域进行了试验验证和说明.结果表明,待焊界面在搅拌针后退侧的前方区域已经达到冶金熔合状态,并在搅拌针的搅拌作用下扭曲并进入焊缝形成S线特征.     

Non-destructive inspection for weld joint of steel structure

Friction stir welding (FSW) succeeded in producing high quality dissimilar welds with AA5083 and A6N01 by evaluation of the microstructure and the root bend testing. A6N01 with a wide optimum range of welding condition should be placed on the retreating side to weld a sound joint between AA5083 and A6N01. The optimum welding condition of FSW for the dissimilar alloys between AA5083 and A6N01 was wider than that of AA5083. In the opposite orientation, A6N01 on the advancing side can hardly flow into AA5083 on the retreating side in front of the tool. As the pores on inappropriate welding conditions were observed, large pores on a lower tool rotation speed were different from small discontinuous pores on a higher tool rotation speed.     

ODS钢搅拌摩擦焊接头的微观组织及其高温力学性能

采用搅拌摩擦焊(friction stir welding,FSW)技术对氧化物弥散强化(oxide dispersion strengthen,ODS)铁素体钢进行了焊接,并对焊接工艺进行了优化. 当转速为150 r/min,焊接速度为30 mm/min时可以获得无焊接缺陷的ODS钢焊接接头. 结果表明,采用FSW焊接的ODS钢接头的微观组织出现明显的洋葱环结构,搅拌区为等轴再结晶晶粒,前进侧热机影响区表现出明显的塑性流动的特征,热影响区的晶粒较母材也发生了明显改变. 接头的高温拉伸性能偏低,但经过温度1 150 ℃,时间1 h的热处理后,其高温拉伸性能得到大幅提高,与母材拉伸性能接近.     

Friction stir welding of AZ31 magnesium alloys processed by equal channel angular pressing

Equal channel angular pressing (ECAP) is an effective thermo-mechanical process to make ultrafine grains.An investigation was carried out on the friction stir welding (FSW) of ECAPed AZ31 magnesium alloys with a thickness of 15 mm.For different process parameters,the optimum FSW conditions of ECAPed AZ31 magnesium alloys were examined.The basic characterization of weld formation and the mechanical properties of the joints were discussed.The results show that the effect of welding parameters on welding quality was evident and welding quality was sensitive to welding speed.Sound joints could be obtained when the welding speed was 37.5 mm/min and the rotation speed of the stir tool was 750 r/min.The maximum tensile strength (270 MPa) of FSW was 91% that of the base materials.The value of microhardness varied between advancing side and retreating side because of the speed field near the pin of the stir tool,which weakened the deformed stress field.The value of microhardness of the welding zone was lower than that of the base materials.The maximum value was located near the heat-affected zone (HAZ).Remarkable ductile character was observed from the fracture morphologies of welded joints.     

The effect of material arrangement on mechanical properties in Friction Stir Welded dissimilar A5052/A5J32 aluminum alloys

The joining of dissimilar A5052 and A5J32 alloy sheets with thicknesses of 1.5mm and 1.6mm, respectively, was carried out using the Friction Stir Welding (FSW) technique. The tool rotated at a speed in a range of 1000 rpm to 1500 rpm with a welding speed ranging from 100 mm/min to 400 mm/min. The hardness and tensile properties of the friction stir welded A5052/A5J32 joint were investigated according to the fixing location. In the case where the A5J32 aluminum alloy was fixed on the retreating side, defect-free welds were obtained under all welding conditions. However, in the case where the A5052 aluminum alloy was fixed on the retreating side, some welding defects were observed at the joint under certain welding conditions with a lower heat input. However, the welding defects had no effect on the mechanical properties. A good correlation between the hardness distribution and the welding zones was observed. The experimental results showed that the tensile properties differed depending on the fixing location of the materials and were also affected by the welding conditions.     

Residual stresses simulation for friction stir welded joint

Abstract

As a solid state joining technique, friction stir welding (FSW) can produce high strength, low distortion joints efficiently. Compared to fusion welding, residual stresses in FSW joints are expected to be low due to a relatively low heat input. However, apart from the heat input, the force from the tool also plays an important role in the development of welding stresses. In the present paper, a semicoupled thermomechanical finite element model containing both thermal load and mechanical load was established to simulate the development of welding stresses during FSW process; an autoadapting heat source model was employed in the thermal analysis; the fixture was also included in the mechanical analysis model. The simulation results showed that due to the effect of the tool force, the longitudinal residual tensile stresses became smaller and were asymmetrically distributed at different sides of the weld centre; the peak of the tensile residual stresses at the retreating side was lower than that at the advancing side. Calculated and experimental results were compared.     

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.     

铝合金搅拌摩擦焊物理场三维数值模拟

基于热物理模拟构建的2024-T3铝合金Arrhenius本构关系,使用Deform-3D软件建立了搅拌摩擦焊三维热-力耦合模型,模拟焊接过程温度、应力、应变等物理场在塑性变形区的分布状态. 结果表明,各物理场受焊速和转速的影响均呈不对称分布,其中材料在前进侧表现为压应力状态,在后退侧出现受拉应力状态;此外,在前进侧材料分别向焊缝表面和根部流动,当材料由后退侧向前进侧的流动速度小于在厚度方向上的流动速度时,在焊缝内产生缺陷,并通过试验验证了这一现象.     

7N01铝合金搅拌摩擦焊接头力学性能

研究了在不同焊接参数的条件下,7N01铝合金搅拌摩擦焊接头的力学性能.结果表明,在特定的旋转频率和前进速度匹配条件下,下压量在0.3～1.0 mm范围波动,7N01铝合金搅拌摩擦焊接头的抗拉强度均能够稳定在340 MPa以上,达到母材的80%左右.通过扫描电镜观察断口发现,搅拌摩擦焊接头断口以韧窝型为主,在低倍下部分断口呈现出明显的分层现象,两层间分界部分呈现出阶梯状形貌.接头硬度测试表明,后退侧的平均硬度略高于前进侧,这也与拉伸测试中接头普遍断于前进侧的现象吻合.     

搅拌摩擦焊接Al-Li合金接头的微观组织及力学性能

采用锥形带螺纹搅拌头搅拌摩擦焊接5mm厚的Al—Li合金轧制板材，并对接头组织、力学性能及断裂特性进行了研究．结果表明，焊核区组织发生动态再结晶，形成细小的等轴晶晶粒，在等轴晶的晶界处析出大量的偏析相．热影响区组织发生回复和粗化反应，形成粗大的棒状回复晶粒；热机影响区组织发生弯曲变形，但整体上仍保留带状组织形貌，前进侧热机影响区组织变形程度高于后退侧，该区同时还发生回复反应，且后退侧热机影响区内的回复晶粒数量多于前进侧．拉伸实验结果表明，焊接速度v=40mm／min时，接头强度达到最大值，为345MPa；v=60mm／min时，接头延伸率达到最大值，为9．6％．硬度测试结果表明，搅拌摩擦焊接头发生软化，前进侧的软化区宽度大于后退侧．断口形貌分析表明，接头断裂模式为韧-脆混合型断裂．     

5mm厚铝合金双面搅拌摩擦焊接

对5mm厚的1050-H24铝合金板材进行了双面搅拌摩擦焊接(FSW)，重点研究了接头的拉伸性能和断裂部位及其影响因素。研究结果表明，一次焊接参数、二次焊接参数和焊接方向对双面FSW接头的拉伸性能和断裂部位有不同程度的影响。一次焊接参数的影响较小，而二次焊接参数的影响显著并且存在最佳取值。同向焊接的接头强度较高且断在前进侧(AS)或后退侧(RS)，而异向焊接的接头强度较低且只断在AS。在文中的试验条件下，1500r／min的旋转速度、400mm／min的二次焊速和同向焊接方式是最佳的工艺组合，接头最高强度达到母材强度的78％。     

MIG焊叠加对6A01-T5铝合金FSW焊接头组织及性能的影响

研究了MIG焊叠加对6A01-T5铝合金FSW焊接头组织及性能的影响. 结果表明, MIG/FSW叠加焊缝熔合良好,叠加位置未出现气孔等缺陷,FSW焊核区及热影响区组织发生粗化,叠加位置附近微观组织出现明显改变;叠加区域硬度明显降低,尤其是FSW焊缝热力影响区和热影响区. FSW、中心叠加、前进侧热力影响区叠加和后退侧热力影响区叠加MIG焊接头的抗拉强度分别为219.8, 188.0, 195.4和191.4 MPa,MIG焊叠加降低了接头的抗拉强度,断口均表现韧性断裂特征;FSW焊接头及带有MIG叠加焊缝余高的三种接头中值疲劳强度分别为76.7, 65.0, 67.5和65.0 MPa,MIG焊叠加也使FSW接头的疲劳性能有所下降.     

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.     

AA5083铝合金的搅拌摩擦焊接工艺参数对搅拌头受力和热输入的影响(英文)

采用系统实验设计方法研究AA5083铝合金搅拌摩擦焊接工艺参数对搅拌头受力和热量输入的影响,得到了用来设计搅拌摩擦焊搅拌头和焊机的经验模型。当采用计算机来控制搅拌摩擦焊接时,这些模型可用来确定AA5083这类铝合金的摩擦焊接工艺参数、编制焊接程序及工艺参数控制。结果表明:影响轴向力和热量输入的重要参数是搅拌头转速、焊接速度和搅拌头轴肩直径,而影响纵向应力的重要参数是焊接速度和探头直径。     

Numerical modelling of 3D plastic flow and heat transfer during friction stir welding of stainless steel

Abstract

Three-dimensional (3D) viscoplastic flow and temperature field during friction stir welding (FSW) of 304 austenitic stainless steel were mathematically modelled. The equations of conservation of mass, momentum and energy were solved in three dimensions using spatially variable thermophysical properties using a methodology adapted from well established previous work in fusion welding. Non-Newtonian viscosity for the metal flow was calculated considering strain rate and temperature dependent flow stress. The computed profiles of strain rate and viscosity were examined in light of the existing literature on thermomechanical processing of alloys. The computed results showed significant viscoplastic flow near the tool surface, and convective transport of heat was found to be an important mechanism of heat transfer. The computed temperature and velocity fields demonstrated strongly 3D nature of the transport of heat and mass indicating the need for 3D calculations. The computed temperature profiles agreed well with the corresponding experimentally measured values. The non-Newtonian viscosity for FSW of stainless steel was found to be of the same order of magnitude as that for the FSW of aluminium. Like FSW of aluminium, the viscosity was found to be a strong function of both strain rate and temperature, while strain rate was found to be the most dominant factor. A small region of recirculating plasticised material was found to be present near the tool pin. The size of this region was larger near the shoulder and smaller further away from it. Streamlines around the pin were influenced by the presence of the rotating shoulder, especially at higher elevations. Stream lines indicated that material was transported mainly around the pin in the retreating side.     

强制冷却搅拌摩擦焊接工艺

搅拌摩擦焊接在工业生产中应用的主要问题之一,是焊接硬化状态材料时接头强度系数较低.简要分析了焊接热对接头强度的影响,提出了在搅拌摩擦焊接过程中进行强制冷却的工艺方法.对比了强制冷却对紫铜搅拌摩擦焊接头表面状况、硬度分布和接头性能的影响,建立了强制冷却搅拌摩擦焊接过程中焊接区温度的近似表达式.结果表明,在紫铜搅拌焊接过程中进行强制冷却,可以降低焊接过程中焊缝及热力影响区变形金属的温度,减小接头软化的程度和范围,提高搅拌摩擦焊接接头的性能.采用转速1 500 r/min、移动速度0.3 mm/s的强制冷却的工艺方法,得到的紫铜搅拌摩擦焊接头抗拉强度达269 MPa.