异种材料搅拌摩擦焊接接头金相试样的制备技术

通过对搅拌摩擦焊接接头金相试样制备技术的经验总结,介绍了异种材料搅拌摩擦焊接接头金相试样制备过程中磨光、抛光和浸蚀等关键操作,提出在金相试样的制备过程中的注意事项和技术要点,对搅拌摩擦焊接接头的微观组织分析、工艺制定等具有一定的参考价值。

7A04-T6铝合金水下搅拌摩擦焊接接头的组织和性能

在循环水冷和空气条件下对7A04-T6铝合金进行搅拌摩擦焊接（FSW）,分析强制冷却对7A04-T6铝合金FSW接头组织性能的影响。结果表明：循环水冷具有明显的瞬时快冷作用,显著抑制再结晶晶粒和析出相的长大,焊核区的平均晶粒尺寸为0.8μm,析出相尺寸为30-150nm,均小于空气条件下接头的晶粒尺寸（2.8μm）及析出相尺寸（80-400nm）。与空气条件下相比,强制水冷条件明显改善接头的力学性能。焊核区的平均硬度值提高11.9HV,接头抗拉强度提高43.2MPa,达到母材抗拉强度的87.6%;接头的应变硬化能力增强,拉伸断口呈现出微孔聚合型断裂特征。

6005A铝合金搅拌摩擦焊接头耐腐蚀性能

为了研究高速列车车体用T6时效6005A铝合金型材的搅拌摩擦焊接头耐工业性环境及海洋性气候腐蚀的性能.通过人造气氛腐蚀试验盐雾试验方法(GB/T10125-2012)、金属和合金的腐蚀电化学试验方法恒电位和动电位极化测量导则(GB/T24196-2009),对6005A-T6铝合金型材搅拌摩擦焊接头的耐盐雾腐蚀性能及耐电化学点蚀性能进行了研究.盐雾试验搅拌摩擦焊接头腐蚀率低于母材,说明接头耐盐雾腐蚀性能更好;腐蚀后形貌保持最好的是热机影响区,其次是焊核.电化学试验搅拌摩擦焊热机影响区极化曲线在最左上方,腐蚀电流密度为3.005μA/cm2,腐蚀电位为-682.953 mV,说明耐酸性点蚀性能最好,其次是焊核,热影响区电化学参数较差,母材最差.研究结果表明:6005A-T6铝合金型材搅拌摩擦焊接头整体耐腐蚀性能优于母材,尤其是热机影响区耐蚀性能很好,但热影响区耐蚀性能差.

6005A铝合金搅拌摩擦焊接头耐腐蚀性能

为了研究高速列车车体用T6时效6005A铝合金型材的搅拌摩擦焊接头耐工业性环境及海洋性气候腐蚀的性能。通过人造气氛腐蚀试验盐雾试验方法(GB/T10125-2012)、金属和合金的腐蚀电化学试验方法恒电位和动电位极化测量导则(GB/T24196-2009),对6005A-T6铝合金型材搅拌摩擦焊接头的耐盐雾腐蚀性能及耐电化学点蚀性能进行了研究。盐雾试验搅拌摩擦焊接头腐蚀率低于母材,说明接头耐盐雾腐蚀性能更好;腐蚀后形貌保持最好的是热机影响区,其次是焊核。电化学试验搅拌摩擦焊热机影响区极化曲线在最左上方,腐蚀电流密度为3.005μA/cm2,腐蚀电位为-682.953mV,说明耐酸性点蚀性能最好,其次是焊核,热影响区电化学参数较差,母材最差。研究结果表明:6005A-T6铝合金型材搅拌摩擦焊接头整体耐腐蚀性能优于母材,尤其是热机影响区耐蚀性能很好,但热影响区耐蚀性能差。

Interface characteristic of friction stir welding lap joints of Ti/Al dissimilar alloys

Lap joints of TC1 Ti alloy and LF6 A1 alloy dissimilar materials were fabricated by friction stir welding and corresponding interface characteristics were investigated. Using the selected welding parameters, excellent surface appearance forms, but the interface macrograph for each lap joint cross-section is different. With the increase of welding speed or the decrease of tool rotation rate, the amount of Ti alloy particles stirred into the stir zone by the force of tool pin decreases continuously. Moreover, the failure loads of the lap joints also decrease with increasing welding speed and the largest value is achieved at welding speed of 60 mm/min and tool rotation rate of 1500 r/min, where the interracial zone can be divided into 3 kinds of layers. The microhardness of the lap joint shows an uneven distribution and the maximum hardness of HV 502 is found in the middle of the stir zone.

Comparison of FSW and TIG welded joints in Al-Mg-Mn-Sc-Zr alloy plates

In order to study the welding process,microstructure and properties of Al-Mg-Mn-Sc-Zr alloy,comparative methods of friction stir welding（FSW） and tungsten inert gas（TIG） were applied to the two conditions of this alloy,namely hot rolled plate and cold rolled-annealed plate.The relationships between microstructures and properties of the welded joints were investigated by means of optical microscopy and transmission electron microscopy.Compared with the base metal,the strength of FSW and TIG welded joints decreased,and the FSW welding coefficients were higher than the TIG welding coefficients.The loss of substructure strengthening and a very little loss of precipitation strengthening of Al3（Sc,Zr） cause the decreased strength of FSW welded joint.But for the TIG welded joint,the disappearance of both the strain hardening and most precipitation strengthening effect of Al3（Sc,Zr） particles contributed to its softening.At the same time,the grains in weld nugget zone of FSW welded joints were finer than those in the molten zone of TIG welded joints.

Corrosion evaluation of friction stir welded lap joints of AA6061-T6 aluminum alloy

Corrosion behavior of friction stir lap welded AA6061-T6 aluminum alloy was investigated by immersion tests in sodium chloride + hydrogen peroxide solution. Electrochemical measurement by cyclic potentiodynamic polarization, scanning electron microscopy, and energy dispersive spectroscopy were employed to characterize corrosion morphology and to realize corrosion mechanism of weld regions as opposed to the parent alloy. The microstructure and shear strength of welded joint were fully investigated. The results indicate that, compared with the parent alloy, the weld regions are susceptible to intergranular and pitting attacks in the test solution during immersion time. The obtained results of lap shear testing disclose that tensile shear strength of the welds is 128 MPa which is more than 60% of the strength of parent alloy in lap shear testing. Electrochemical results show that the protection potentials of the WNZ and HAZ regions are more negative than the pitting potential. This means that the WNZ and HAZ regions do not show more tendencies to pitting corrosion. Corrosion resistance of parent alloy is higher than that for the weldments, and the lowest corrosion resistance is related to the heat affected zone. The pitting attacks originate from the edge of intermetallic particles as the cathode compared with the Al matrix due to their high self-corrosion potential. It is supposed that by increasing intermetallic particle distributed throughout the matrix of weld regions, the galvanic corrosion couples are increased, and hence decrease the corrosion resistance of weld regions.

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.

Effect of tool tilt angle on strength and microstructural characteristics of friction stir welded lap joints of AA2014-T6 aluminum alloy

Friction stir welding(FSW)has been extensively adopted to fabricate aluminium alloy joints by incorporating various welding parameters that include welding speed,rotational speed,diameters of shoulder and pin and tool tilt angle.FSW parameters significantly affect the weld strength.Tool tilt angle is one of the significant process parameters among the weld parameters.The present study focused on the effect of tool tilt angle on strength of friction stir lap welding of AA2014-T6 aluminium alloy.The tool tilt angle was varied between 0°and 4°with an equal increment of 1°.Other process parameters were kept constant.Macrostructure and microstructure analysis,microhardness measurement,scanning electron micrograph,transmission electron micrograph and energy dispersive spectroscopy analysis were performed to evaluate the lap shear strength of friction stir lap welded joint.Results proved that,defect-free weld joint was obtained while using a tool tilt angle of 1°to 3°.However,sound joints were welded using a tool tilt angle of 2°,which had the maximum lap shear strength of 14.42 kN and microhardness of HV 132.The joints welded using tool tilt angles of 1°and 3°yielded inferior lap shear strength due to unbalanced material flow in the weld region during FSW.

Mechanism of corrosion fatigue fracture of friction stir welding joints of 7075 aluminium alloy in 3.5% NaCl solution

The corrosion fatigue fracture mechanism of friction stir welding(FSW) joints of 7075 aluminium alloy in3.5% NaCl solution is investigated. The corrosion fatigue crack source originates from the junction of nugget zone(NZ)and thermo-mechanical affected zone(TMAZ). Multiple crack sources are developed at the same time, and they merge into large cracks along the boundary line of NZ and TMAZ during the propagation stage. Furthermore, a mutual reinforcement coupling always exists between corrosion and cyclic loading during the initiation and propagation of corrosion fatigue crack. It is necessary to consider the effect of welding residual stress for understanding the mechanism of corrosion fatigue fracture of FSW joints.

Microstructures and microhardness for sheets and TIG welded joints of TA15 alloy using friction stir spot processing

Effects of friction stir spot processing(FSSP)on the microstructures and microhardness of tungsten inert gas(TIG)welded TA15titanium alloy joints were investigated.The macro/micro structural observation and microhardness evaluation of the TA15alloy sheets and TA15TIG welded joints were carried out using optical microscope and microhardness tests.The results show that FSSP effectively improves the microstructure and increases the microhardness of the TA15sheets.As for the TIG welded joints,FSSP also effectively improves the microstructure of joints.And the average microhardness value in weld nugget zone is improved significantly,while a small increase of this value in heat affected zone is observed.The hardness in stirring zone is significantly higher than that in the base metal.Two peak values of hardness appear along the width direction in stirring zone.After FSSP,the average hardness of the weld zone of TA15TIG welded joint is significantly higher than that before FSSP.Under the present process parameters,both the surface oxidation in TA15sheets and in TIG welded joints after FSSP are not evident,while the surface forms the bright white layer,which is composed of a great multitude of fine grains.

三层复合板铝/镁合金/铝FSW接头的微观组织与抗拉强度

在不同焊接速度下进行了三层复合板Al/AZ31/Al搅拌摩擦焊接(FSW)工艺试验,并观察分析其接头成形显微组织和拉伸性能。结果显示:在实验优化的工艺参数下,焊缝接头成形较好,其内部呈层状分布且未发现缺陷;焊核区(NZ)晶粒细化明显,大角晶界(HAGBs)和再结晶晶粒占比达80%;在焊缝前进侧带状组织区(BS)和镁、铝界面处存在金属间化合物(IMC),主要为Al_(3)Mg_(2)和Al_(12)Mg_(17);随焊速的增加,焊接接头的抗拉强度先增大后减小,在v=100 mm/min时焊核区铝层晶粒平均尺寸为1.75μm,接头抗拉强度达到最大87.3 MPa,是母材的50.8%。