Effect of friction welding conditions on mechanical properties of A5052 aluminium alloy friction welded joint

Abstract

The present paper describes the mechanical properties of Al–Mg aluminium alloy (A5052) friction welded joints. Two types of A5052 with different tensile properties were used, namely, H112 base metal with 188 MPa tensile strength and H34 with 259 MPa tensile strength. Similar metal specimens were joined using a continuous drive friction welding machine with an electromagnetic clutch to prevent braking deformation. That is, the joints were welded using the 'low heat input' friction welding method developed by the present authors, in which the heat input is lower than in the conventional method. An A5052–H112 joint produced using a friction speed of 27·5 s^?1, friction pressure of 30 MPa, friction time of 2·0 s (just after the initial peak torque), and forge pressure of 60 MPa had approximately 95% joint efficiency. It fractured at the welded interface and in the A5052–H112 base metal. To improve the joint efficiency, an A5052–H112 joint was produced at a forge pressure of 75 MPa, which was the same as the yield strength of the A5052–H112 base metal. It had 100% joint efficiency and fractured in the A5052–H112 base metal. In contrast, an A5052–H34 joint was made using a friction speed of 27·5 s^?1, friction pressure of 90 MPa, friction time of 0·3 s (just after the initial peak torque), and forge pressure of 180 MPa. It had approximately 93% joint efficiency and fractured in the A5052–H34 base metal. This joint also had a softened region at the welded interface and in the adjacent region. To improve the joint efficiency, an A5052–H34 joint was made at a forge pressure of 260 MPa, which was the same as the ultimate tensile strength of the A5052–H34 base metal. Although this joint had a slightly softened region at its periphery, it had approximately 93% joint efficiency. The failure of the A5052–H34 joint to achieve 100% joint efficiency is due to a slight softening at the periphery and the difference in the anisotropic properties of the A5052–H34 base metal between the longitudinal and radial directions.     

Properties and improvement of super fine grained steel friction welded joint

Abstract

This paper describes friction welded joint properties of super fine grained steel (SFGS) and discusses improvements in these joint properties. The average grain size diameter of the SFGS base metal is ～0·6 μm, and its ultimate tensile strength is 660 MPa. The joint, made by a continuous drive friction welding machine (conventional method), fractured at the welded interface even though it possessed 100% joint efficiency. This was due to both the coarsening of the grain size and the softening of the welded interface with its adjacent region caused by heat input during braking times. The authors developed a joining method using a continuous drive friction welding machine that has an electromagnetic clutch to eliminate heat input during braking time, which was called the 'low heat input friction welding method' (LHI method). The joint obtained by the LHI method had the same tensile strength as the base metal at the friction time when the friction torque reached the initial peak. That is, the joint obtained 100% joint efficiency and fractured at the base metal, although the adjacent region of the welded interface softened only slightly. The grain size of this joint was smaller than that obtained by the conventional method. It was clarified that the optimum friction welded joint of the SFGS could be obtained by the LHI method in comparison with the conventional method.     

Mechanical properties of friction welded joint between Ti–6Al–4V alloy and Al–Mg alloy (AA5052)

Abstract

The present paper describes the mechanical properties of a friction welded joint between Ti–6Al–4V alloy and Al–Mg alloy (AA5052). The Ti–6Al–4V/AA5052–H112 joint, made at a friction speed of 27.5 rev s^?1, friction pressure of 30 MPa, friction time of 3.0 s, and forge pressure of 60 MPa, had 100% joint efficiency and fractured in the AA5052–H112 base metal. The Ti–6Al–4V/AA5052–H34 joint, made under the same friction welding conditions, did not achieve 100% joint efficiency and it fractured in the AA5052–H34 base metal because the AA5052–H34 base metal had softened under friction heating. The joints made at low friction speed or using short friction time showed fracture at the welded interface because a sufficient quantity of heat for welding could not be produced. However, the joints made at high friction speed or using long friction time were also fractured at the welded interface: in this instance, the welded interface also had an intermetallic compound layer consisting of Ti₂Mg₃Al₁₈. The Ti–6Al–4V/AA5052–H34 joint made at a friction speed of 27.5 rev s^?1 with friction pressure of 150 MPa, friction time of 0.5 s, and forge pressure of 275 MPa had 100% joint efficiency and fractured in the AA5052–H34 base metal, although the AA5052–H34 side softened slightly. In conclusion, the Ti–6Al–4V/AA5052–H112 joint and Ti–6Al–4V/AA5052–H34 joint had 100% joint efficiency and fractured in the AA5052 base metal when made under the friction welding conditions described above.     

Joining phenomena and joint strength of friction welded joint between pure aluminium and low carbon steel

Abstract

This paper describes the joining phenomena and joint strength of friction welded joints between pure aluminium (P-Al) and low carbon steel friction welds. When the joint was made at a friction pressure of 30 MPa with a friction speed of 27·5 s^?1, the upsetting (deformation) occurred at the P-Al base metal. P-Al transferred to the half radius region of the weld interface on the low carbon steel side, and then it transferred toward the entire weld interface. When the joint was made at a friction time of 0·9 s, i.e. just after the initial peak of the friction torque, it had ～93% joint efficiency and fractured on the P-Al side. This joint had no intermetallic compound at the weld interface. Then, the joint efficiency slightly decreased with increasing friction time. The joint had a small amount of intermetallic compound at the peripheral region of the weld interface when it was made at a friction time of 2·0 s. When the joint was made at a friction time of 0·9 s, the joint efficiency decreased with increasing forge pressure, and all joints were fractured at the P-Al side. Although the joint by forge pressure of 90 MPa had hardly softened region, it had ～83% joint efficiency. To clarify the fact of decreasing joint efficiency, the tensile strength of the P-Al base metal at room temperature was investigated, and the tensile test was carried out after various compression stresses and temperatures. The tensile strength of the P-Al base metal has decreased with increasing compression stress at any temperature. Hence, the fact that the joint did not achieve 100% joint efficiency was due to the decrease in the tensile strength of the P-Al base metal by the Bauschinger effect. To obtain higher joint efficiency and fracture on the P-Al side, the joint should be made without higher forge pressure, and with the friction time at which the friction torque reaches the initial peak.     

Joining phenomena during friction stage of A7075-T6 aluminium alloy friction weld

Abstract

This paper describes the effect of friction welding conditions on joining phenomena during the friction stage of type 7075-T6 aluminium alloy (A7075) friction welds. The friction torque had wear and seizure stages until the initial peak torque when A7075 was welded under high friction speed and low friction pressure, i.e. 27 · 5 rev s^?1 and 30 MPa. Initial seizure and joining began at the central region (centre axis) of the welded interface, and extended towards the peripheral region (outer surface). On the other hand, when A7075 was welded under high friction speed and high friction pressure, i.e. 27 · 5 rev s^?1 and 90 MPa, almost no wear stage existed before the initial peak torque. Initial seizure and joining began at the peripheral region of the welded interface and extended towards the central region. Then, the friction torque reached an initial peak torque when the welded interface was joined completely and upsetting of both base metals started. As a conclusion, the joining mechanism of A7075 friction welding was similar to that of low carbon steel.     

Effect of welding heat input and post-weld aging time on microstructure and mechanical properties in dissimilar friction stir welded AA7075–AA5086

The effects of welding heat input and post-weld heat treatment on the mechanical and microstructural aspects of dissimilar friction stir welds of age-hardened AA7075-T6 and strain hardenable AA5086-H32 aluminium alloys were investigated. X-ray diffraction (XRD) residual stress analysis and tensile testing together with optical metallography and transmission electron microscopy (TEM) were performed to assess the effects of process parameters on welded joints. It was discovered that joints produced without heat sink exhibited more homogeneous stir zones than other joints. Of the natural aging time studied, higher amount of solid solution during rapid cooling of welds produced higher driving force for increase in hardness in the AA7075 side during natural aging. Natural aging within stirring zone and thermo-mechanical affected zone of AA7075 side resulted in a 10 to 25 MPa reduction in the residual stress in these zones; its effect decreased considerably in the welds performed without heat sink. In addition, natural aging had no noticeable effect on the joint strength.     

Strength enhancement of autocompleting medium and high carbon steels friction welded joints

An autocompleting friction welding method, which was developed by the authors, is to weld with using a rotating insert piece set between fixed workpieces. The conditions to enhance the strength of the welded joint in an autocompleting friction welding method which involves a rotating insert between the fixed workpieces were determined. The weld faying surface of the fixed specimen had a 10 mm diameter. When MCS joint was made at an insert thickness of 4 mm through a friction pressure of 36 MPa, it did not achieve 100% joint efficiency because the weld interfaces were not completely joined. MCS joint had 100% joint efficiency and fractured on the MCS base metal although the crack was generated at the weld interface, when that was made at an inner groove diameter of 11 mm with the bottom of the grooves for the insert piece (groove bottom thickness) of 0.9 mm or more through a friction pressure of 90 MPa. To obtain a joint with no cracks, MCS joint was made with an inner groove diameter of 12 mm at a friction pressure of 90 MPa. When the groove bottom thickness was 0.75 mm, MCS joint had 100% joint efficiency and the MCS base metal fracture with no crack at the weld interface. When HCS joint was made with an inner groove diameter of 11 mm at friction pressures of 90 and 150 MPa, it did not achieve 100% joint efficiency because the weld interfaces were not joined completely. The weld interfaces of HCS joint at a friction pressure of 120 MPa were completely joined although it did not achieve 100% joint efficiency. To improve the joint efficiency, HCS joint was made with an insert thickness of 5 mm, a groove bottom thickness of 0.64 mm, and an inner groove diameter of 12 mm with a friction pressure of 120 MPa. HCS joint had 100% joint efficiency and fractured on the HCS base metal with no crack at the weld interface.     

Joint properties and its improvement of high-tensile strength steel joint by autocompleting friction welding method

This paper describes the improvement of properties of a high-tensile strength steel joint by an autocompleting friction welding method that was developed by the authors. The base metal was high-tensile strength steel of 800 MPa class. The weld faying surface of the fixed specimen had a 10 mm diameter, and the effect of the thickness and that at the bottom of the grooves (groove bottom thickness) for the insert piece on the joining phenomena and joint properties were investigated. The value of a circumferential shear fracture (CSF value) was defined and calculated by the ratio between the theoretical and the actual generated friction torques. When the CSF value was lower than 1, the insert piece had the CSF before the friction torque reached the initial peak. Also, when the CSF value was larger than 1, the insert piece had the CSF after the friction torque reached the initial peak. When the joint was made at the insert thickness of 5 mm with the CSF value of nearly 1, it had 100% joint efficiency although it had the softened region near the weld interfaces. The joint had cracks at the weld interface when it was made with friction pressures of 36 and 120 MPa. However, the joint had no crack at the weld interface when it was made with a friction pressure of 90 MPa. When the joint was made at the insert thickness of 4 mm with the CSF value of nearly 1, it had also 100% joint efficiency although it had the softened region near the weld interfaces. However, the softened region at the weld interface of the joint with the insert thickness of 4 mm was lower than that with 5 mm. Also, this joint had 90° bend ductility with no crack at the weld interface. In conclusion, it was possible to make a joint with no cracks for high-tensile strength steel by an autocompleting friction welding method.     

GH4169合金与FGH96合金惯性摩擦焊接头组织和力学性能

在主轴转速为650 r/min、转动惯量为340 kg·m2、焊接压力为450 MPa焊接参数下，实现GH4169与FGH96异质材料惯性摩擦焊接，并对焊后热处理的接头进行显微组织与力学性能分析.在焊接热-力耦合作用下，焊接接头不同区域的金相组织发生变化，晶粒出现不同程度的细化、变形，基体强化相出现不同程度的溶解、变形.焊接接头显微硬度呈"山峰"状分布特征，焊接接头室温抗拉强度平均值为1 366 MPa，高温抗拉强度平均值为1 176.7 MPa，在650℃，641 MPa条件下的平均持久寿命为215 h，焊接接头具有良好的综合力学性能.     

Development of autocompleting friction welding method

Abstract

This paper describes an autocompleting friction welding method that was carried out to weld with an insert piece set between fixed base metals. The base metal was low carbon steel, and the faying surface of the fixed specimen had a 10 mm diameter. The effect of the thickness of the insert piece (insert thickness) on the joining phenomena was investigated. When the insert thickness was 3˙2 mm and the friction welding conditions were a friction speed of 27˙5 s^–1 and friction pressure of 36 MPa, the insert piece had a shear fracture toward the circumferential direction in the peripheral portion of the weld interfaces by the initial peak produced during the friction process. The joint also had cracks at the adjacent region of the weld interfaces, although it had the same tensile strength as the base metal. On the other hand, the joint made using the insert piece with a groove on its peripheral portion had the same tensile strength as the base metal, where it fractured. This joint also had 90° bend ductility without cracks. In this case, the optimum insert thickness was 4˙0 mm, and the thickness at the bottom of the grooves (groove bottom thickness) was 1˙2 mm with an 11 mm inner groove diameter, and the friction welding conditions were a friction speed of 27˙5 s^–1 and friction pressure of 36 MPa. In conclusion, a sound friction welded joint was made by an autocompleting friction welding method.     

Effect of friction welding condition on joining phenomena and joint strength of friction welded joint between brass and low carbon steel

Abstract

This paper describes the effect of friction welding condition on joining phenomena and joint strength of friction welded joints between copper–zinc alloy (brass) and low carbon steel (LCS). When the joint was made at a friction pressure of 30 MPa with a friction speed of 27·5 s^?1, brass transferred to the half radius region of the weld interface on the LCS side. Then, transferred brass extended towards the almost whole weld interface with increasing friction time. The joint efficiency increased with increasing friction time, and then the joint obtained 100% and the brass base metal fracture when the joint was made with a friction time of 4·2 s or longer. However, the fact that all joints had some cracks at the periphery portion of the weld interface was due to a deficiency of transferred brass at the periphery portion on the weld interface of the LCS side. On the other hand, brass transferred to the peripheral region of the weld interface on the LCS side, and then transferred towards the entire weld interface when the joint was made at a friction pressure of 90 MPa with a friction speed of 27·5 s^?1. The joint efficiency increased with increasing friction time, and it reached 100% at a friction time of 1·5 s or longer. In addition, all joints fractured from the brass base metal with no cracking at the weld interface. To obtain 100% joint efficiency and the brass base metal fracture with no cracking at the weld interface, the joint should be made with opportune high friction pressure and friction time at which the entire weld interface had the transferred brass.     

Effect of post-weld heat treatment on joint properties of dissimilar friction stir welded 2024-T4 and 7075-T6 aluminum alloys

The effect of post-weld heat treatment on dissimilar friction stir welded AA7075 and AA2024 joints was studied. After welding in constant parameters, solution heat treatment and various aging treatments were given to the welded joints. Microstructural and phase characterizations were done using optical microscope, SEM, FE-SEM, XRD and EDS techniques. Finally, mechanical properties of post-weld heat treated joints were evaluated and compared with as-welded joints. Results show that both 2024-T6 and 7075-T6 post-weld heat treatment procedures considerably improve the mechanical strength of the welded joint, with higher strength obtained for the 7075-T6 procedure, in comparison with the as-welded joint. This is explained by the formation of fine precipitates during the aging process, despite the abnormal grain growth. Fracture occurs at the interface between thermo-mechanical affected zone (TMAZ) and heat affected zone (HAZ) on the retreating side (AA7075) of as-welded joint, while by applying post-weld heat treatment fracture location shifts towards the stir zone (SZ) of the welded joint. Also, for post-weld heat treated samples, fracture surface is predominantly inter-granular, while in as-weld joint, fracture surface is mostly trans-granular. This is explained by dissolution and coarsening of precipitates within grains in post-weld heat treated joints.     

Properties of as welded and heat treated pure titanium–7075 Al–Zn–Mg alloy friction weld joints

Abstract

The effects of joining conditions and an age hardening post­weld heat treatment (PWHT) at 120°C for 24 h on the tensile strength and metallurgical properties of dissimilar friction joints between pure titanium and age strengthened 7075 Al–Zn–Mg alloy were investigated. Highest strength was achieved using intermediate friction pressure (150 MPa), short friction time (0.5 s), and high upsetting (forging) pressure (400 MPa). The joint tensile strength decreased when the joint diameter was increased from 8 to 16 mm. The joint tensile strength of as welded (AW) dissimilar joints was similar to that of PWHT joints with diameters of 8, 12, and 16 mm. Detailed TEM confirmed that there was a negligible difference in the thickness of the intermetallic layer formed at the dissimilar joint interface for AW and PWHT joints. While the intermetallic phases formed at the joint interface comprised Al₃Ti, τ (Ti₂Mg₃Al₁₈), and Al in AW joints, they consisted of Al+τ or Mg₂Al₃+τ+Al in PWHT joints. Softened regions were generated in 7075 base material immediately next to the interface in AW joints. Post­weld heat treatment increased the hardness of the softened region almost to that of as received 7075–T6 base material in 12 and 16 mm diameter joints. In contrast, the hardness of the softened region in 8 mm diameter joints could not be recovered to that of the as received material. This was a result of overaging and coarse precipitates in the softened region produced during the friction welding operation.     

Influence of forge pressure on properties of friction welded pipelines using intermediate ring

Abstract

An innovative welding method for fully automatic joining of pipelines has been developed. The proposed welding procedure is a variant of the conventional friction welding process. A rotating intermediate ring is used to generate heat necessary to realise the weld. The working principles of the welding process are described. The influence of the forge pressure on the mechanical properties of the welds and the heat affected zone microstructure was experimentally investigated. It was found that the forge pressure had no influence either on the mechanical properties or on the weld microstructure, which is in contradiction with the published data in literature concerning conventional friction welding.     

异质钛合金线性摩擦焊接头微观组织

为了探明TC11与TC17异质钛合金线性摩擦焊接头微观组织形成机制,采用光学显微镜和扫描电镜研究接头不同区域的微观组织.结果表明,线性摩擦焊接头由TC11一侧的热力影响区(TMAZ)、TC11一侧的焊缝区、TC17一侧的焊缝区和TC17一侧的TMAZ所组成.在TMAZ未发现有动态再结晶发生,而材料的相变与变形是同时进行的.在焊缝区内发生了动态再结晶过程,摩擦停止后在摩擦界面上形成初生β共生晶粒.在振幅为3 mm、频率为40 Hz、摩擦压力为66.7 MPa条件下,随着摩擦时间的延长,初生β相动态再结晶晶粒尺寸和α相片层宽度增加.     

6082-T6铝合金无减薄搅拌摩擦焊接头组织与性能

为解决传统搅拌摩擦焊接过程中的焊缝减薄问题,以轨道交通领域常用的6082-T6铝合金作为研究对象,从轴肩下压量为零的角度出发,通过轴肩端面圆形内凹槽及搅拌针周向螺纹复合三铣平面的设计,获得了无减薄且成形良好的焊接接头. 结果表明,当焊接速度一定时,转速的增加可提高焊接热输入,抑制焊缝缺陷的产生. 相较于转速400, 600 r/min下的接头可焊区间得到了有效拓宽,焊接速度最高可达400 mm/min;焊接过程的热循环受焊接速度与转速的耦合作用. 焊接热循环过大,焊缝易出现粗大组织,影响焊接接头的强度. 在转速600 r/min、焊接速度500 mm/min的参数下,接头抗拉强度达254 MPa,为母材强度的80%.     

铝合金/合金钢异种金属摩擦焊接头组织与性能

针对油气资源勘探开发用钻杆轻量化的需求,以小尺寸试棒7075-T6铝合金和37CrMnMo合金钢利用连续驱动摩擦焊技术实现连接,探索开发铝合金/合金钢轻量化复合钻杆焊接制造的可能性和可行性,研究了焊接工艺参数对接头成形、微观组织及力学性能的影响. 结果表明,接头界面铝侧的晶粒受到力和热的作用发生完全动态再结晶,而在热力影响区发生了不完全动态再结晶. 界面沿径向热力分布的不均匀导致了在中心区域没有化合物产生,但在1/2半径区域有亚微米级的化合物层生成,接头抗拉强度最大可达240 MPa. 中心区域较为平整的断裂面说明该区域是接头的薄弱环节. 因此仍需进一步调控铝合金/合金钢摩擦焊接过程,促进中心区域冶金结合,以提升接头整体强度.     

600MPa级超细晶粒钢摩擦焊过程性能分析

利用摩擦焊对直径为13 mm的600 MPa级别的超细晶粒钢进行了焊接. 结果表明,严格控制摩擦焊工艺参数,超细晶粒钢具有良好的摩擦焊焊接性. 超细晶粒钢摩擦焊接头热影响区出现了轻微的晶粒长大,尺寸至9~11 μm. 接头性能分析表明,超细晶粒钢摩擦焊接头强度可达715 MPa,断面伸长率22%,断面收缩率68%,冲击韧性可达98 J,呈典型的韧性断裂. 急停试验表明,摩擦焊过程中变形区金属在摩擦扭矩和轴向压力大作用下,沿着轴向、切向、径向三个方向流动. 随摩擦时间的增加,不同区域的晶粒的尺寸都略有增加,其中以高温区增加最为明显.     

TC17钛合金线性摩擦焊接头组织及力学性能分析

针对固溶时效态TC17钛合金焊态及焊后热处理态线性摩擦焊接头,进行显微组织及力学性能对比分析. 结果表明,焊态时焊缝组织发生了回复与再结晶,由于焊后冷却速度较快,生成了亚稳定β相,焊缝区发生了软化;热力影响区组织沿受力变形方向拉长、细化、交替呈带状分布,加工硬化程度较高,显微硬度明显高于其它区域;热影响区由于二次次生α相基本溶解于亚稳定β相,导致显微硬度显著降低. 经过焊后热处理,亚稳定β相发生时效分解,析出了弥散程度更高的针状次生α相使得焊接区硬度大幅度提高. 由于亚稳定相的生成,焊态接头发生软化,拉伸均断裂在焊缝区,抗拉强度达到母材强度91.8%,断口呈脆性断裂形态;焊后热处理态接头由于二次次生α相的析出,起到弥散强化的作用,拉伸试验均断在母材,断口呈典型韧性断裂形态.     

铝合金搅拌摩擦焊缝摩擦塞补焊组织与力学性能

对2219-T87铝合金搅拌摩擦焊缝进行摩擦塞补焊工艺试验,对塞补焊接头的焊缝成形、显微组织、显微硬度和抗拉强度进行了观察和测试,对拉伸断口进行了扫描电镜观察.结果表明,在7 500 r/min的焊接转速和40~55 kN的焊接压力下可获得无缺陷摩擦塞补焊接头;塞补焊接头沿垂直于搅拌焊缝方向的最大抗拉强度和断后伸长率分别可以达到336 MPa和8%,分别相当于母材抗拉强度和断后伸长率的73.9%和66.7%;在母材和塞棒之间的底部结合面是最薄弱的区域,如何控制该区域的结合强度是影响摩擦塞补焊接头拉伸性能的关键因素.