Friction welding of Al–Mg–Si alloy to Ni–Cr–Mo low alloy steel

Abstract

It is difficult to weld the dissimilar material combination of aluminium alloys and low alloy steels using fusion welding processes, on account of the formation of a brittle interlayer composed of intermetallic compound phases and the significant difference in physical and mechanical properties. In the present work an attempt has been made to join these materials via the friction welding method, i.e. one of the solid phase joining processes. In particular, the present paper describes the optimisation of friction welding parameters so that the intermetallic layer is narrow and joints of acceptable quality can be produced for a dissimilar joint between Al-Mg-Si alloy (AA6061) and Ni-Cr-Mo low alloy steel, using a design of experiment method. The effect of post-weld heat treatment on the tensile strength of the joints was then clarified. It was concluded that the friction time strongly affected the joint tensile strength, the latter decreasing rapidly with increasing friction time. The highest strength was achieved using the shortest friction time. The highest joint strength was greater than that of the AA6061 substrate in the as welded condition. This is due to the narrow width of the brittle intermetallic layer generated, which progressed from the peripheral (outer surface) region to the centreline region of the joint with increasing friction time. The joints in the as welded condition could be bent without cracking in a bend test. The joint tensile strength in the as welded condition was increased by heat treatment at 423 K (150° C), and then it decreased when the heat treatment temperature exceeded 423 K. All joints fractured in the AA6061 substrate adjacent to the interface except for the joints heated at 773 K (500° C). The joints fractured at the interface because of the occurrence of a brittle intermetallic compound phase.     

Nd:YAG laser micro-welding of ultra-thin FeCo–V magnetic alloy: optimization of weld strength

The main aim of this research is to optimize the tensile strength of laser welded FeCo–V alloy. A mathematical relationship was developed to predict tensile strength of the laser beam welded FeCo–V foils by incorporating process parameters such as lamping current, welding speed, pulse duration and focused position. The procedure was established to improve the weld strength and increase the productivity. The results indicate that the pulse duration and welding speed have the greatest influence on tensile strength. The obtained results showed that the tensile strength of the weld joints increase as a function of increasing pulse duration reaching to a maximum at a pulse duration value of 2.25 ms. Moreover, the tensile strength of joints increases with decrease in welding speed reaching to a maximum at a welding speed of 125 mm/min. It has been shown that increase in pulse duration and decrease in welding speed result in increased effective peak power density and hence formation of more resistant welds. At higher pulse durations and lower welding speeds, the tensile strength of weld joints decreases because of formation of solidification microcracks in the fusion zone.     

Microstructure and mechanical properties of laser beam welding 6061 aluminum alloy with different states

With the diversification of manufacture methods,joining the same materials with different states becomes indispensable in practical application.In present work,6061 aluminum alloys with different states were welded by laser beam welding (LBW).The microstructures of welded joint,before and after heat treating,were investigated.The mechanical properties,such as the tensile properties and microhardness,were tested.And the fracture characteristic was observed by means of scanning electron microscope (SEM).The results show that the 6061 aluminum alloys have superior weldability and the microstructures are different significantly in different states.Besides,the grain boundaries of the joint microstructures become unclear after the heat treating.The strength and the elongations of welded joints could reach to those of the base metal.The tensile fracture occurs in the fusion zone and near 6061-0 alloy.And the fracture presents ductile rupture.Therefore,the LBW is an effective method for 6061 aluminum alloy.     

6061铝合金搅拌摩擦焊接头组织及性能

对厚度6 mm的6061铝合金进行了搅拌摩擦焊对接焊,采用光学显微镜、扫描电子显微镜、拉伸试验机及电化学工作站等设备对焊接接头的金相组织、断口形貌、拉伸性能和腐蚀性能进行了测试和分析.结果 表明,当焊接速度为80 mm/min、旋转速度在600 ～1500 r/min之间时,焊接接头的外观良好,无明显缺陷.随着旋转速度...     

6061铝合金FSW接头与MIG焊接头对比试验

采用搅拌摩擦焊(FSW)和MIG焊分别对6061铝合金板进行了焊接试验,测试了焊接接头的强度,观察了焊接接头的金相组织,并进行了接头的硬度分布测试.结果表明,搅拌摩擦焊接头抗拉强度高达212.05 MPa,是母材抗拉强度的86％,比MIG焊的接头强度略高.焊接接头软化区宽度比MIG焊接头软化宽度窄.6061铝合金母材为典型的轧制组织,焊核区为细小的等轴晶组织,MIG焊接头焊缝为柱状晶组织.     

Establishing empirical relationships to predict grain size and tensile strength of friction stir welded AA 6061-T6 aluminium alloy joints

AA 6061-T6 aluminium alloy(Al-Mg-Si alloy) has gathered wide acceptance in the fabrication of light weight structures requiring a high specific strength and good corrosion resistance.Compared with the fusion welding processes that are routinely used for joining structural aluminium alloys,friction stir welding(FSW) process is an emerging solid state joining process in which the material welded does not melt and recast.Joint strength is influenced by the grain size and tensile strength of the weld nugget region.Hence,an attempt was made to develop empirical relationships to predict grain size and tensile strength of friction stir welded AA 6061-T6 aluminium alloy joints.The empirical relationships are developed by response surface methodology(RSM) incorporating FSW tool and process parameters.A linear regression relationship was also established between grain size and tensile strength of the weld nugget of FSW joints.     

焊丝成分对6082-T6铝合金焊接接头组织和性能的影响

采用ER5356和ER5087焊丝对12 mm厚6082-T6铝合金进行熔化极惰性气体保护焊(MIG)后,通过显微硬度测试、拉伸力学性能测试、光学显微镜(OM)、扫描电镜(SEM)、电子背散射衍射(EBSD)和透射电镜(TEM)等研究焊丝成分对焊接接头力学性能与显微组织的影响。结果表明:采用ER5087焊丝焊接的6082-T6铝合金焊接接头焊缝区晶粒更细小;抗拉强度、屈服强度、断后伸长率以及焊接系数均高于ER5356焊丝焊接的6082-T6铝合金焊接接头的;两种焊丝焊接的6082-T6铝合金焊接接头的硬度最低区域与拉伸断裂位置均在距离焊缝中心10~15 mm处的热影响区,该区域β″强化相聚集长大、粗化,导致析出相强化作用减弱,成为焊接接头性能最薄弱区域。     

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.     

Comparative study on laser welding characteristics of aluminium alloy under atmospheric and subatmospheric pressures

Laser bead on plate welding of 10 mm thick aluminium alloy under atmospheric and subatmospheric pressures were comparatively investigated. With the decrease of ambient pressure, the penetration depth increased sharply at first and then gradually levelled off. The largest penetration depth could reach 8·7 mm when welded under the pressures of 10¹ Pa, while only 4·9 mm under atmospheric pressure. Weld bead without any porosity was produced under ambient pressures of 10^?1 Pa. The average tensile strength of joints welded under the pressure of 10¹ Pa was 300·2 MPa. The tensile strength remained constant as the ambient pressure decreased further. The shielding effect of plasma plume on laser beam was suppressed as the ambient pressure decreased. Therefore, the laser power deposition inside the keyhole was enhanced effectively. Under subatmospheric pressure, the porosity defects were eliminated effectively due to the keyhole stability and the change of liquid flow, i.e. moving upward along the rear wall of keyhole.     

Laser pressure welding of aluminium and galvannealed steel

Dissimilar metal joints of galvannealed steel and commercially available pure aluminium (A1050) sheets were produced by changing the laser power and the roller pressure by the laser pressure welding method. In this method, the YAG laser beam was irradiated into a flare groove made by these dissimilar metal sheets. In addition, the laser beam was scanned at various frequencies and patterns through the fθ lens using two-dimensional scanning mirrors. Then the sheets were pressed by the pressure rolls to be joined. The compound layers in the weld interface were observed by optical microscope, and the layer thicknesses were measured. The thicknesses were in the range of 7–20 μm. The mechanical properties of welded joints were evaluated by the tensile shear test and the peel test. In the tensile shear test, the strengths of the joints produced under the most welding conditions were so high that the fracture occurred through the base aluminium sheet. In the peel test of the specimens subjected to the laser beam of 1200–1400 W power under the roller pressure of 2.94 kN, the specimen fracture took place in the base aluminium sheet. Even if the compound layer was thick, high joint strength was obtained. In order to know the reason for such high strength of joints with thick compound layers and the joining mechanism, the compound layer was observed by the HR-TEM. The TEM observation results revealed that the main phase in the compound layer was the solid solution of Al + Zn. Moreover, the intermetallic compound was identified as FeAl, Fe₂Al₅, Fe₄Al₁₃, and Fe₂Al₅Zn_0.4 phase by electron diffraction. The Fe₃Zn₁₀ (Γ phase) of Fe–Zn intermetallic compound was confirmed on a Fe base material. It is assumed that the joining areas were heated in a range of 782°C more than 665°C, a melting point of Al, by laser irradiation because the δ_lk phase aspect was not confirmed. Because the surfaces of A1050 and Zn plated layer were melted thinly, the layer was over 10 μm thicker. The reason for the production of high strength joints with the relatively thick intermetallic compound layer was attributed to the formation of (Al + Zn) phase with finely dispersed intermetallic compounds.     

Optimizing pulsed current gas tungsten arc welding parameters of AA6061 aluminium alloy using Hooke and Jeeves algorithm

Though the preferred welding process to weld aluminium alloy is frequently constant current gas tungsten arc welding （CCGTAW）, it resulted in grain coarsening at the fusion zone and heat affected zone（HAZ）. Hence, pulsed current gas tungsten arc welding（PCGTAW） was performed, to yield finer fusion zone grains, which leads to higher strength of AA6061 （Al-Mg-Si） aluminium alloy joints. In order to determine the most influential control factors which will yield minimum fusion zone grain size and maximum tensile strength of the joints, the traditional Hooke and Jeeves pattern search method was used. The experiments were carried out based on central composite design with 31 runs and an algorithm was developed to optimize the fusion zone grain size and the tensile strength of pulsed current gas tungsten arc welded AA6061 aluminium alloy joints. The results indicate that the peak current （Ip） and base current （IB） are the most significant parameters, to decide the fusion zone grain size and the tensile strength of the AA6061 aluminum alloy joints.     

Mechanical properties of laser-pressure-welded joint between dissimilar galvannealed steel and pure aluminium

Dissimilar metal joints of Zn-coated Galvannealed steel (GA steel) and commercially available pure aluminium (A1050) sheets were produced by changing the laser power and the roller pressure by the laser pressure welding method. By this method, the YAG laser beam was irradiated into a flare groove made by these dissimilar metal sheets. In addition, the laser beam was scanned at various frequencies and patterns through the fθ lens using two-dimensional scanning mirrors. Then the sheets were pressed by the pressure rolls to be joined.

The compound layers in the weld interface were observed by an optical microscope and the layer thicknesses were measured. The thicknesses ranged from 7 to 20 μm. The mechanical properties of the welded joints were evaluated by the tensile-shear test and peel test. In the tensile-shear test, the strengths of the joints produced under the most welding conditions were so high that the fracture occurred through the base aluminium sheet. In the peel test of the specimens subjected to a laser beam of 1200–1400 W power under roller pressure of 2.94 kN, the specimen fracture took place in the base aluminium sheet. Even if the compound layer was thick, high joint strength was obtained. On the other hand, the specimen fractured in the weld interface at a laser power of 1500 W. The results of X-ray diffraction on the peel test specimen surface identified that the intermetallic compound on the GA steel side was Fe₂Al₅Zn_0.4. Moreover, the aluminium parts adhering to the GA steel side were confirmed. These results suggest that the fracture in the peel test occurred between the compound layer and A1050 and partly in the base aluminium. A micro-Vickers hardness test was performed to examine the hardness distribution in the compound layer. The hardness values near A1050 and GA steel were about 100 and 470 Hv, respectively, which suggests that the compound layer should not necessarily consist of brittle intermetallic compounds. It is therefore concluded that laser pressure welding could produce high strength joints of GA steel and A1050 dissimilar materials.     

激光焊接对SPF/DBTi-6Al-4V合金疲劳性能的影响

研究了SPF/DB Ti-6Al-4V合金及其激光焊接接头静态拉伸性能和疲劳性能,并获得S-N曲线.通过观察组织特征和疲劳断口形貌,分析了激光焊接对SPF/DB Ti-6Al-4V合金疲劳性能的影响.结果表明,SPF/DB T-6Al-4V合金激光焊接接头的抗拉强度略低于母材抗拉强度,而疲劳强度明显低于母材疲劳强度,约为其抗拉强度的40%.SPF/DB Ti-6Al-4V合金组织为α+β等轴细晶组织,其焊接接头组织为含α,针状马氏体α'和少量β相的魏氏组织结构.焊接接头组织结构的不均匀性,以及组织的粗大化是导致激光焊接接头疲劳性能下降的重要原因.SPF/DB Ti-6Al-4V合金疲劳断裂为塑性断裂,其焊接接头疲劳断裂为准解理断裂,这显著降低激光焊接接头的疲劳性能.而焊接气孔等焊缝表层微小几何不连续缺陷的存在往往成为激光焊接接头疲劳断裂的裂纹源.     

LF6/LD10铝合金搅拌摩擦焊工艺参数对接头性能的影响

通过LF6／LD10铝合金搅拌摩擦焊（FSW）的工艺试验研究，分析了工艺参数对其接头性能的影响。结果表明，当搅拌头的旋转速度值较低时，提高焊接速度有利于提高接头的抗拉强度值。当旋转速度值较高时，提高焊接速度对接头性能的影响不大。焊接速度较低时，改变旋转速度对于接头的力学性能影响不大；焊接速度较高时，提高旋转速度将会降低接头的力学性能。其它参数相同的条件下，材料所处的位置对接头拉伸性能的影响不大。其它条件相同，在焊接速度和旋转速度都较低时，使用无螺纹的搅拌头所得到的接头性能要优于带有螺纹的搅拌头施焊所得接头的性能；在焊接速度和旋转速度都较高时，搅拌针上的螺纹对于接头的力学性能的影响不大。     

Mechanical properties and microstructures of hybrid laser MIG welded dissimilar Mg–Al–Zn alloys

Abstract

Bead shape, microstructure changes and mechanical properties of laser metal inert gas (MIG) welded dissimilar Mg–Al–Zn alloys (from AZ31B to AZ61) are studied. The results show that heat ratio of arc to laser (HRAL) and welding speed are dominant parameters for achieving good tensile strength efficiency and elongation property. From AZ31B to AZ61, microstructure changes are observed as cellular dendrites to equiaxed dendrites and fish bone dendrites in the upper part of hybrid weld. Besides, at weld centreline, the solidification structure of lower part is finer than that of upper part. In this study, the maximum tensile strength efficiency and elongation reached 97·6 and 7% respectively. When the HRAL matches welding speed well, the joint achieves higher tensile strength with 45° shearing fracture at heat affected zone because of fewer defects. However, when utilising too low HRAL or fast welding speed, the joints show lower tensile strengths with nearly vertical fracture at fusion zone.     

Mechanical properties of friction stir welded Al alloys with different hardening mechanisms

The mechanical properties of precipitation hardened Al 6061-T651 and Al 7075-T6 and strain hardened Al 5083-H32, friction stir welded with various welding parameters, were examined in the present study. 4 mm thick Al 6061-T651, Al 7075-T6, and Al 5083-H32 alloy plates were used for friction stir welding (FSW) with rotating speed varied from 1000 to 2500 rpm (rotation per minute) and welding speed ranging from 0.1 to 0.4 mpm (m/min). Each alloy displayed slightly different trends with respect to the effect of different welding parameters on the tensile properties of the FSWed Al alloys. The tensile elongation of FSWed Al 6061-T651 and Al 7075-T6 tended to increase greatly, while the tensile strength decreased marginally, with increasing welding speed and/or decreasing rotating speed. The tensile strength and the tensile elongation of Al 6061-T651 decreased from 135 to 154 MPa and 10.6 to 17.0%, respectively, with increasing welding speed from 0.1 to 0.4 mpm at a rotating speed of 1,600 rpm. Unlike the age-hardened Al 6061-T651 and Al 7075-T6, the strain-hardened Al 5083-H32 showed no notable change in tensile property with varying welding parameters. The change in the strength level with different welding parameters for each alloy was not as significant as the variation in tensile elongation. It was believed that the tensile elongation of FSWed Al alloys with varying welding parameters was mainly determined by the coarse particle clustering. With respect to the change in tensile strength during friction stir welding, it is hypothesized that two competing mechanisms, recovery by friction and heat and strain hardening by plastic flow in the weld zone offset the effects of different welding parameters on the tensile strength level of FSWed Al alloys.     

Multi-objective optimization of friction stir welding parameters using desirability approach to join Al/SiCp metal matrix composites

Silicon carbide particulate (SiC_p) reinforced cast aluminium (Al) based metal matrix composites (MMCs) have gained wide acceptance in the fabrication of light weight structures requiring high specific strength, high temperature capability and good wear resistance. Friction stir welding (FSW) process parameters play major role in deciding the performance of welded joints. The ultimate tensile strength, notch tensile strength and weld nugget hardness of friction stir butt welded joints of cast Al/SiC_p MMCs (AA6061 with 20% (volume fraction) of SiC_p) were investigated. The relationships between the FSW process parameters (rotational speed, welding speed and axial force) and the responses (ultimate tensile strength, notch tensile strength and weld nugget hardness) were established. The optimal welding parameters to maximize the mechanical properties were identified by using desirability approach. From this investigation, it is found that the joints fabricated with the tool rotational speed of 1370 r/min, welding speed of 88.9 mm/min, and axial force of 9.6 kN yield the maximum ultimate tensile strength, notch tensile strength and hardness of 265 MPa, 201 MPa and HV114, respectively.     

TiNi形状记忆合金与不锈钢激光焊接头裂纹分析及防止措施

采用激光焊对TiNi形状记忆合金与不锈钢异种材料进行焊接,用扫描电镜和激光共聚焦显微镜研究了TiNi合金/不锈钢接头裂纹及断口特征,分析了焊缝裂纹的形成机理,并提出了防止裂纹的措施.结果表明,裂纹多以微裂纹的形式出现于焊缝中心和TiNi合金侧熔合区.焊缝中存在大量的脆性化合物是产生裂纹的内在原因,接头受到拉伸应力是产生裂纹的必要条件,焊缝裂纹是二者共同作用的结果.通过焊接区加镍和钴中间层材料、改变激光光斑位置、焊接区施加轴向力及优化激光焊接参数的方法均能在一定程度上改善焊缝金属的裂纹敏感性,其中加金属中间层效果更为明显,加镍和钴中间层后,接头抗拉强度分别达到372和347 MPa,比未加中间层的接头的抗拉强度分别提高98.9%和85.6%.     

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.     

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.