Corrosion behavior of aluminum/steel dissimilar metals friction stir welding joint

The corrosion performance of aluminum/steel contact and aluminum/steel FSW joint in 3.5 wt.%NaCl solution were analyzed using potentiostatic tests.The post-corrosion microstructure of the welding joint was characterized by optical microscope(OM),scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS).The results showed that the localized corrosion of FSW joint of Al/steel dissimilar metals mainly initiated at the interface transition zone(ITZ).Precipitation of intermetallic compounds(IMCs)and Fe-rich phase particles in ITZ accelerated the corrosion of the FSW joint.This phenomenon has been attributed to distinct corrosion potentials between IMCs and steel,aluminum base metal.The corrosion resistance sequence of IMCs in ITZ is Fe_(3)Al>FeAl>Fe_(2)Al_(5).

Dissimilar welding of high nitrogen stainless steel and low alloy high strength steel under different shielding gas composition:Process,microstructure and mechanical properties

Ar-N_(2)-O_(2)ternary shielding gas is employed in dissimilar welding between high nitrogen steel and low alloy steel.The effect of O_(2)and N_(2)is investigated based on the systematical analysis of the metal transfer,nitrogen escape phenomenon,weld appearance,nondestructive detection,nitrogen content distribution,microstructure and mechanical properties.There are two nitrogen sources of the nitrogen in the weld:high nitrogen base material and shielding gas.The effect of shielding gas is mainly reflected in these two aspects.The change of the droplet transfer mode affects the fusion ratio,N2in the shielding gas can increase nitrogen content and promote the nitrogen uniform distribution.The addition of 2%O_(2)to Ar matrix can change the metal transfer from globular transfer to spray transfer,high nitrogen base material is thereby dissolved more to the molten pool,making nitrogen content increase,ferrite decrease and the mechanical properties improve.When applying N2-containing shielding gas,arc stability becomes poor and short-circuiting transfer frequency increases due to the nitrogen escape from droplets and the molten pool.Performance of the joints is improved with N_(2)increasing,but internal gas pores are easier to appear because of the poor capacity of low alloy steel to dissolve nitrogen,The generation of pores will greatly reduce the impact resistance.4-8%N2content in shielding gas is recommended in this study considering the integrated properties of the dissimilar welded joint.

Effect of process parameters on microstructure and properties of laser welded joints of aluminum/steel with Ni/Cu interlayer

The effects of laser parameters and interlayer material on the microstructure and properties of the welded joint between 6061 aluminum alloy and stainless steel were studied.The results show that the density and microstructure of the welded joint can be optimized by changing the laser power with 0.05 mm Cu foil and 0.1 mm Ni foil as interlayer.A large number of new Cu-Al binary phases were found near the aluminum alloy,which effectively inhibited the formation of the binary brittle phase of Fe-Al.The maximum shear force of 1350.96 N was obtained with laser power of 2200 W.The shear force of the welded joint increased to 1754.73 N when the thickness of the Cu foil thickness changed to 0.02 mm.

Influence of Creep Strength of Weld on Interfacial Creep Damage of Dissimilar Welded Joint between Martensitic and Bainitic Heat-Resistant Steel

The mechanical properties, creep rupture strength, creep damage and failure characteristics of dissimilar metal welded joint （DMWJ） between martensitic （SA213T91） and bainitic heat-resistant steel （12Cr2MoWVTiB（G102）） have been investigated by means of pulsed argon arc welding, high temperature accelerated simulation, mechanical and creep rupture test, and scanning electronic microscope （SEM）. The results show that there is a marked drop of mechanical properties of undermatching joint, and low ductility cracking along weld/G102 interface is induced due to creep damage. Creep rupture strength of overmatching joint is the least. The mechanical properties of medium matching joint are superior to those of overmatching and undermatching joint, and creep damage and failure tendency along the interface of weld/G102 are lower than those of overmatching and undermatching joint after accelerated simulation for 500 h, 1 000 h, 1 500 h, and the creep rupture strength of medium matching joint is the same as that of undermatching joint. Therefore, it is reasonable that the medium matching material is used for dissimilar welded joint between martensitic and bainitic steel.

Interfacial microstructure evolution of 12Cr1MoV/TP347H dissimilar steel welded joints during aging

The interfacial microstructure evolution of 12Cr1MoV/TP347H dissimilar steel welded joints with a nickel-based filler metal during aging was studied in detail to elucidate the mechanism of premature failures of this kind of joints.The results showed that not only a band of granular Cr_(23)C_(6)carbides were formed along the fusion boundary in the ferritic steel during aging,but also a large number of granular or plate-like Cr_(23)C_(6)carbides,which have a cube-cube orientation relationship with the matrix,were also precipitated on the weld metal side of the fu-sion boundary,making this zone be etched more easily than the other zone and become a dark etched band.Stacking faults were found in some Cr_(23)C_(6)carbides.In the as-welded state,deformation twins were observed in the weld metal with a fully austenitic structure.The peak micro-hardness was shifted from the ferritic steel side to the weld metal side of the fusion boundary after aging and the peak value increased signific-antly.Based on the experimental results,a mechanism of premature failures of the joints was proposed.

Microstructural Evolution on the T91 Dissimilar Metal Joints during Creep Rupture Tests

T91 steel is one of the new materials presently employed in power plant pipe components. The creep rupture strength and microstructure of the T91+10CrMo910 and T91+13CrMo44 welded joints were analyzed during creep rupture tests. Creep transgranular ductile rupture occurred at the 10CrMo910 matrix in the T91+10CrMo910 welded joints and creep intergranular brittle rupture occurred at the 13CrMo44 HAZ in the T91+13CrMo44 joints. Microhardness measurements showed high hardness at the heat affected zone (HAZ) of T91 and a sharply drop at the 13CrMo44 HAZ during creep rupture. The metallographic tests showed that no obvious microstructure degradation was observed in the 10CrMo910 HAZ and matrix, while creep cracks appeared at the 13CrMo44 HAZ. T91 steel had relatively high creep resistant strength in the welded joints tested. Recovery occurred in the T91 HAZ with the growth of subgrain size and the decrease of dislocation density during creep. It was concluded that the dissimilar joints of T91 and low alloy heat-resistant steel should have close creep strength matching to increase the service life of the overall joints at elevated temperature.

Effect of joining temperature on microstructure and properties of diffusion bonded Mg/Al joints

The joining of AZ31B Mg alloy to 6061 Al alloy was investigated at different joining temperatures by vacuum diffusion bonding method. The microstructures of Mg/Al dissimilar joints were studied by means of optical microscopy （OM）, scanning electron microscopy （SEM） and energy dispersive X-ray （EDX）. The results show that the thickness of each layer in the diffusion zone increases with the increase of joining temperature, and the microstructure changes obviously. At joining temperature of 440 °C, the diffusion zone is composed of Mg2Al3 layer and Mg17Al12 layer. At joining temperatures of 460 and 480 °C, the diffusion zone is composed of Mg2Al3 layer, Mg17Al12 layer, eutectic layer of Mg17Al12 and Mg-based solid solution. The width of high-hardness zone in the joint increases with increasing joining temperature, and the micro-hardnesses at different locations in the diffusion zone are significantly different. The joining temperature of 440 °C offers the highest tensile strength of 37 MPa, and the corresponding joint exhibits brittle fracture at the intermetallic compound layer of Mg17Al12.

Microstructure characteristics and mechanical properties of steel stud to Al alloy by CMT welding-brazing process

Cold metal transfer （CMT） welding of nickel-coated Q235 steel studs with 606l Al alloy was carried out using ER4043 as filler metal. The welding process was stable, and appearance of weld formed well without surface defect under the parameters of welding current 121 A, welding voltage 15.4 V and welding speed 6 r/min. The microstructure of fiUer metal was analyzed by means of scanning electron microscopy. The filler metal and 6061 Al alloy were fused to form fusion welding interface, the fusion zone had a good bonding without any micro defect. The steel stud did not melt and brazing interface was formed between the filler metal and steel stud. Two different reaction layers existed in the brazing interface, the Fe2Al5 layer about 10 -12 p^m formed near the steel stud side, and the other layer was mainly composed of FeAl3. Nickel-rich zone was formed in the root toe area of the fillet weld, which was mainly composed of Al3Ni2. The tensile tests showed that the maximum shearing strength of the joints was 129 MPa. The joint was brittle fractured in the intermetallic compound layer where plenty of FeAl3 were distributed continuously.

基于Ni/Zn中间层的6061铝合金/Q355钢电阻点焊接头组织与性能

【目的】采用预置Ni/Zn中间层的方法进行Q355钢/6061铝合金异种金属的电阻点焊研究。【方法】在不同焊接时间、焊接电流及电极压力下分别对6061铝合金与Q355钢的电阻点焊工艺进行对比分析并获得最优电阻点焊工艺参数,然后采用在铝合金板与钢板之间添加Ni/Zn箔片作为中间层的方法来研究Ni/Zn中间层对铝/钢电阻点焊接头组织与性能的影响,并利用光学显微镜、扫描电镜、能谱分析及拉伸试验机等方法对含Ni/Zn中间层的铝/钢电阻点焊接头微观组织、元素占比、第二相的变化及抗拉剪力进行了研究。【结果】结果表明,铝/钢点焊接头由铝一侧熔核,钢一侧熔核和结合界面处的金属间化合物组成,具有典型的双熔核特征。通过在6061铝合金与Q355钢的中间分别增加Ni与Zn箔片来阻碍脆硬的Al-Fe金属间化合物的生成量。添加Ni中间层的接头界面区生成了韧性较好的Al3Ni,从而阻碍了硬而脆的Al-Fe金属间化合物的形成。添加Zn中间层的接头界面区生成了一定量的Fe2Al5Zn0.4,使Al-Fe金属间化合物层的厚度减小至2.88μm,最大抗拉剪力达到4.69 kN。【结论】添加Ni/Zn中间层后,铝/钢电阻点焊接头的熔核直径与抗拉剪力均有所提升,同时Ni元素的添加会在铝/钢界面处生成韧性较好的Al3Ni相,从而阻碍了Al-Fe金属间化合物的生成。

6A01-T5铝合金/304不锈钢的缝隙腐蚀行为研究

目的 研究6A01-T5铝合金和304不锈钢异种金属间的缝隙腐蚀行为规律。方法 采用常温常压浸泡腐蚀方法,结合SEM、EDS、XRD和白光干涉检测,对6A01-T5铝合金/304不锈钢缝隙结构在碱性Na Cl溶液中的腐蚀行为进行研究。结果 6A01-T5铝合金/304不锈钢缝隙腐蚀表现为在缝口处产生沿缝口方向的凹陷渠,在缝内,以局部减薄和腐蚀坑为主,并随着腐蚀时间的延长,腐蚀程度逐渐加重。不同区域腐蚀产物的形貌和成分组成不尽相同,缝外暴露区的腐蚀产物表现为晶体颗粒状,主要成分为Ca CO3和Al(OH)3等铝的腐蚀产物。缝口附近沿缝口方向形成一层有明显界线的腐蚀产物覆盖层,缝隙内部的腐蚀产物相对较少,表现为尺寸相对较小的结块,主要成分为Al(OH)3等铝的腐蚀产物。结论 在6A01-T5铝合金与304不锈钢非电连接情况下,6A01-T5铝合金/304不锈钢缝隙内2种金属分别独立发生缝隙腐蚀,因2种金属在腐蚀过程中争夺O2,使得304不锈钢对6A01-T5铝合金的缝隙腐蚀起到抑制作用。

铝/钢异种金属焊接接头腐蚀行为及其影响因素综述

铝/钢异种金属焊接接头结合了两种材料优异的性能,在各行各业具有较为广泛的应用.由于铝、钢两种金属之间理化性能的巨大差异以及极小的固溶度,导致铝/钢接头容易出现脆性金属间化合物、气孔等缺陷,严重影响着接头的力学性能.然而,随着铝/钢接头越来越广的应用范围和复杂多样的应用环境,接头的耐腐蚀性能也得到了更多的关注.对近些年铝/钢异种金属焊接接头的耐腐蚀方面研究工作做了系统的汇总,旨在从接头腐蚀机理出发,提升接头的耐腐蚀性.综述了接头腐蚀形式规律,并从焊接工艺、腐蚀环境、微观组织和金属间化合物等影响因素的角度出发,详细地讨论了腐蚀行为与各因素之间的关系及影响机理.同时,指出了接头腐蚀机理,从各影响因素方面提出了改善接头耐腐蚀性能的措施,减小铝/钢接头实际服役过程中腐蚀所带来的影响.

铝/钢异种金属搅拌摩擦焊性能改善方法及其研究现状

铝合金与钢的复合结构具有质量轻、强度高、成本低等特点,广泛应用于航空航天、船舶重工、汽车制造等领域。搅拌摩擦焊(Friction stir welding,FSW)作为一种新型固相连接技术,具有高效、节能、环保等优势,但利用传统搅拌摩擦焊获得的铝/钢异种接头仍然存在诸多缺陷。基于铝/钢异种金属搅拌摩擦焊的优化,本文对目前已经在铝/钢搅拌摩擦焊方面取得成果的辅助方式进行总结归纳,将其划分为机械结构式辅助FSW、中间过渡层辅助FSW、温度控制型外源辅助FSW和超声振动辅助FSW,并在此基础上进一步展望了铝/钢异种金属搅拌摩擦焊优化方法的发展方向。

焊接速度对铝合金/铜激光熔钎焊接头组织及性能的影响

采用激光熔钎焊在不同焊接速度(4,5,6,7,8 mm·s^(-1))下对5052铝合金和T2铜进行对接焊,研究了焊接速度对接头宏观形貌、显微组织、显微硬度、抗拉强度及拉伸断裂机理的影响。结果表明:随着焊接速度增加,激光熔钎焊接头的焊缝成形先变优后变差,当焊接速度为6 mm·s^(-1)时焊缝成形最佳;随着焊接速度增加,接头中树枝状Al-Cu共晶组织变少,Zn-Al共晶组织变多,当焊接速度为6 mm·s^(-1)时接头铜侧界面反应区出现Al_(4)Cu_(9)和Al_(2)Cu金属间化合物,熔焊区由α-Al固溶体、η-Zn固溶体、Al-Cu共晶组织和Zn-Al共晶组织组成;随着焊接速度增加,铝合金/铜激光熔钎焊接头熔焊区硬度变化不大,铜侧界面反应区硬度下降,接头抗拉强度先增大后减小,拉伸断裂模式按照解理断裂、准解理断裂、韧性断裂、准解理断裂顺序依次变化,当焊接速度为6 mm·s^(-1)时抗拉强度(212 MPa)最大,接头发生韧性断裂。

6061铝合金/DP600钢CMT熔钎焊接头的组织及力学性能

铝合金/钢异种金属连接结构有着广阔的应用前景。采用ER4043焊丝对6061铝合金与DP600钢异种金属进行CMT焊和脉冲电弧焊,并用高速摄影仪研究了焊接过程,分析了焊接模式和工艺参数对搭接接头的组织、界面层及力学性能的影响。试验结果表明,与脉冲电弧焊相比,CMT焊接能在低热输入下实现铝合金与钢的熔钎焊,有效控制金属间化合物的生成,焊接过程稳定,焊缝成型连续美观,焊接效率更高。随着CMT焊和脉冲电弧焊热输入的增加,界面层厚度均逐渐增加,当CMT焊的电流为65 A,热输入为1.97 kJ/cm时,钢侧界面层的厚度约为3μm,搭接接头强度最高。

基于不同焊材的超高强钢与BS700高强钢焊接接头裂纹的试验研究

采用熔化极活性气体保护焊对抗拉强度大于1600 MPa的超高强钢与抗拉强度大于760 MPa的BS700高强钢进行焊接时,组合接头焊缝易出现焊接裂纹,为解决该问题,使用直径1.0 mm的ER70-G焊材或ER307Mo焊材,在打底焊接电流160~180 A、电压21~24 V,盖面焊接电流190~210 A、电压23~26 V条件下开展了焊接对比试验。工艺性和焊接性试验结果表明,使用ER307Mo焊材焊接的试样弯曲性能明显优于使用ER70-G焊材焊接的试样;使用ER70-G焊材焊接的试样焊缝存在未贯穿的微裂纹,焊缝断面裂纹率达到35.29%;使用ER307Mo焊材焊接的试样焊缝断面未发现裂纹。ER307Mo焊材更适合超高强钢与BS700高强钢的焊接。试验解决了超高强钢与BS700高强钢组合接头的开裂问题,为抗拉强度相差较大的异种高强钢的焊接提供了解决方案。

不同热源作用下钢/铝异种金属对接接头的焊缝成形和性能分析

采用三种热源(激光-MIG复合、单MIG、单激光)实现2 mm厚的SUS304不锈钢板和6061铝合金板的对接连接,对比了不同热源下钢侧的湿润铺展情况、焊缝中心组织、钢/铝界面层化合物和接头的拉伸性能。结果表明,激光-MIG复合热源下焊缝的正背面铺展效果最好,而单激光热源下熔融金属很难铺展到钢侧。激光-MIG复合热源和单MIG热源下,焊缝中心组织为α-Al基体上分布着短棒状的Al-Si共晶体,钢/铝界面处有连续分布的锯齿状金属间化合物,界面层厚度分别约为3.6、3.3μm;单激光热源下焊缝中心组织为等轴晶上弥散分布着很多小块状的析出相,钢/铝界面层化合物呈针叶状并沿着铝焊缝生长,厚度约为5.7μm。复合热源下接头的抗拉强度最高,为226.5 MPa,达到铝合金母材的53.8%,断口有少量河流花样;单激光热源下的焊接接头的抗拉强度最低(67 MPa),断口大部分区域呈河流花样,属于典型的脆性断裂。

铝/钢异种金属电弧熔钎焊研究现状

铝合金和钢在高温下易反应生成多种金属间化合物,使铝/钢的焊接一直是焊接领域的一大难题。控制接头界面处金属间化合物的生成及其尺度,是成功进行铝/钢焊接的关键。电弧熔钎焊是解决铝/钢异种金属焊接全面走向工程应用的最具希望的几种焊接方法之一。文中综述了近年来铝/钢电弧熔钎焊研究的发展现状,分析了铝/钢电弧熔钎焊焊接性,重点探讨了控制金属间化合物生长的方法,包括减小焊接热输入、降低热源能量密度、添加具有抑制金属间化合物生长的合金元素、采用中间层等;总结了改善液态金属润湿性和铺展性的方法,包括采用镀层/覆层、采用钎剂、采用辅助磁场、进行预热或辅助加热等。最后提出了若干铝/钢电弧熔钎焊需要进一步解决的问题。

钢/铝薄板热无铆连接接头力学性能研究

目的针对目前车用高强钢和高强度铝合金板料在无铆连接工艺上出现的成形接头效果不佳及接头强度难以满足实际工况等问题,提出一种钢/铝异种材料热无铆塑性连接工艺,以有效提高22MnB5高强钢与7050铝合金铆接接头性能。方法通过软件Abaqus建立钢/铝异种材料无铆塑性连接有限元模型,对塑性连接接头尺寸特性进行分析;进一步通过仿真分析研究高强钢初始铆接温度对接头截面颈厚与自锁值的影响,并采用拉伸试验研究铝板在不同初始温度下及成形接头在不同冷却方式下对无铆塑性连接接头性能的影响。结果将有限元仿真分析结果与试验的金相图进行了对比研究,得出二者成形接头的尺寸基本吻合,并产生了有效的机械自锁,证明了仿真模型的准确性。随后,经仿真分析确定,钢加热至700℃时,接头颈厚值与自锁值均最大,分别为0.402、0.357 mm,该成形温度下接头特征尺寸最佳。最后,通过试验分析发现,常温铆接、阀冷、室冷、水冷的拉力峰值分别为2.0763、5.3140、2.4111、2.0240 kN。由此可得,热处理后接头的抗剪切强度较常温铆接提高了28.5%,在3种冷却方式处理下,阀冷的接头强度最佳,水冷的接头强度最差。结论通过对比分析,确定了22MnB5钢加热至700℃且铝仅经热传导并采用阀冷时进行无铆塑性连接的接头强度最佳。

汽车用铝钢无匙孔搅拌摩擦点焊接头组织及界面特征研究

随着轻量化技术的发展,镀锌钢板与铝合金等异种金属连接在现代汽车工业中的应用越来越多,回抽式无匙孔搅拌摩擦点焊具有热输入低、焊缝晶粒细小、接头力学性能高等优点,在铝合金等轻金属焊接领域具有很大的优势。本工作使用回抽式搅拌摩擦点焊技术,成功实现了0.7 mm厚的镀锌钢板与2 mm厚的铝合金板的无匙孔搅拌摩擦点焊连接。在不同的焊接转速下,对铝钢异种金属进行无匙孔搅拌摩擦点焊实验研究,分析了无匙孔搅拌摩擦点焊接头的剪切性能、断口形貌、各区微观组织、界面区特征及连接机理。研究结果表明,转速为1 200 r/min、压入量为0.2 mm、焊接时间为15 s时焊接接头最佳,具有最好的力学拉伸性能,断裂位置为热机影响区;通过扫描电镜(SEM)和能谱分析(EDS)对接头的微观形貌以及断口形貌进行观察分析发现,在搅拌区接头界面形成了约6μm厚的金属间化合物,为AlFe_(3)、Al_(13)Fe_(4)、AlFe;各位置处金属间化物的形貌与厚度不同,断裂方式为混合断裂机制,界面处的连接为机械结合和冶金结合两种接合方式。

激光功率对铝/钢激光对接熔钎焊接头组织与性能的影响

以Er2319焊丝为钎料,在不同激光功率(1.0~1.4kW)下对6061-T6铝合金和Q235A镀锌钢进行激光对接熔钎焊,研究了激光功率对接头显微组织和拉伸性能的影响。结果表明:在1.1~1.3kW激光功率下均可实现铝合金和钢的有效连接,激光功率为1.2kW时的成形质量最好;1.1,1.2kW激光功率下焊缝区组织为大量的等轴晶以及少量的破碎枝晶,1.3kW激光功率下则以粗大的针状晶为主;1.2kW激光功率下接头界面处的金属间化合物层厚度小于1.1kW激光功率下;接头的抗拉强度随着激光功率的增加呈先升后降的趋势,1.2kW激光功率下的抗拉强度最大,为107.42 MPa,断裂类型为韧脆混合断裂。