铝合金与镀锌钢脉冲旁路耦合电弧GMAW熔钎焊搭接工艺及接头性能的研究

采用脉冲旁路耦合电弧GMAW熔钎焊方法,以ER4043焊丝为填充材料,实现了铝合金与镀锌钢异种金属的熔钎焊接,得到外观成形良好、变形小的搭接接头。通过SEM、EPMA、EDS、显微硬度计和拉伸实验机对搭接接头的微观组织及力学性能进行了研究。结果表明:在搭接接头界面中心区的铝侧形成针状或锯齿状的FeAl3金属间化合物,而在钢侧形成平齐的Fe2Al5和Fe0.7Al3Si0.3金属间化合物。显微硬度测试分析进一步证明了铝合金与镀锌钢界面中心区由硬度高的金属间化合物组成。搭接接头的平均拉剪强度达到144.85MPa,最高拉剪强度达到186.73MPa,达到了铝合金母材强度的88.5%,且断裂方式为韧性断裂。     

铝合金与镀锌钢薄板熔钎焊接头组织与力学性能

为了对铝合金和镀锌钢板进行优质高效焊接,采用Fronius冷金属过渡焊接机对锻铝6061和SPCC镀锌钢板进行了熔钎焊实验。焊接实验结果表明可以采用专家系统提供的参数进行焊接获得成型良好的接头;组织分析表明接头界面可以分为边缘富锌区、铝熔化区和铝钢界面反应层三个反应区。能谱分析结果表明边缘富锌区主要组成元素是锌和铝,铝钢之间的反应层主要是Fe2Al5反应相;接头上的缺陷主要有气孔、冷隔和低熔共晶缩孔。力学性能测试结果表明:铝、钢熔钎焊接头强度达到80MPa;Fe2Al5反应相平均硬度HV410,镀锌钢母材的平均显微硬度HV130,铝熔化区的平均显微硬度HV55。     

铝/钢异种材料钎焊研究现状与发展趋势

"低碳环保,节能减排"已经成为国家实现可持续发展的重要环节,而如何实现汽车轻量化、减少温室气体的排放则成为汽车行业的前沿课题。采用高强度铝合金材料部分代替结构钢,是减轻汽车质量的一种有效途径,而铝合金与钢之间焊接接头的质量是衡量铝/钢结构可靠性的重要指标。实现铝合金与钢之间可靠连接的主要难点是两种材料的物理化学性能差异很大,常温下两者几乎不互溶,且容易发生反应生成Fe-Al脆性金属间化合物,严重影响铝/钢焊接接头的质量。而铝合金与钢的钎焊可通过调节钎料成分或改变焊接工艺等方法来控制接头脆性金属间化合物的形成,近年来受到了国内外学者的广泛关注并取得了突破性进展。目前,铝/钢钎焊的研究主要集中在钎焊材料改性和钎焊工艺优化两个方面。钎剂的改性就是向Nocolok钎剂中加入活性剂,增强钎剂对铝合金和不锈钢两种材料表面氧化膜的同时去除作用,改善钎料在母材上的润湿性;钎料的改性主要是通过微合金化的方法向钎料中添加微量的合金元素,通过改变钎料的化学成分来改善钎料基体的组织和性能,近年来取得了大量的研究成果并在工业生产中得到广泛应用,如添加Cu、Ag等元素均可以显著改善钎料的力学性能和可靠性。在钎焊工艺方面,钎焊温度和保温时间直接影响钎料的填缝和钎料与母材的相互作用,并决定钎焊接头的质量。除此之外,在不锈钢表面预镀一层中间相也是相关学者研究的重点课题,镀层金属可以限制Fe原子与钎料中Al原子的相互扩散,降低界面脆性金属间化合物层的厚度,从而提高钎焊接头的力学性能。本文综合评述了铝与钢异种材料钎焊的研究进展。首先介绍了铝合金与钢常用的几种钎焊方法,以及每种钎焊方法各自的特点和应用范围;然后综述了钎焊材料的改性及钎焊工艺的优化对铝/钢钎焊接头性能的影响,并对其作用机理进行了分析;最后整理了目前铝/钢异种金属钎焊存在的问题及相应的解决措施,并对其未来的研究和发展趋势进行了展望,以期为铝/钢连接技术的发展以及最终在汽车行业的广泛应用提供有益的参考。     

钢-铝激光焊接的关键技术与未来趋势展望

汽车车身多材料结构要求两种不同类型的材料进行连接(如钢-铝、铸铁-铝、铝-镁等).激光焊热量集中,热源能准确控制,应力应变小,与其他焊接方法相比,更适合于钢、铝异种材料的焊接.在分析钢-铝焊接难点的基础上,总结了当前钢-铝激光焊接中常见的焊接缺陷、接头连接形式、表面处理及填加焊料,着重概括了激光焊接工艺参数对焊缝质量的影响,指出钢-铝激光焊接技术未来的发展趋势是设计与开发柔性化夹具,加强钢-铝激光焊接工艺参数优化、焊接缺陷控制、合金元素填料筛选、FeAl脆性金属间化合物与延塑性较好金属间化合物的形成条件、Fe/Al界面结合机理等方面的基础研究,期望为激光焊接多材料车身结构提供重要的技术参考.     

铝/镁搅拌摩擦焊-钎焊焊接接头微观组织结构

目的研究不同工艺参数下钎料Zn的添加对Al/Mg异种金属搅拌摩擦焊-钎焊焊接接头组织和性能的影响。方法以厚度为0.05 mm的纯Zn作为钎料,对3 mm厚的2A12-T4态铝合金和4 mm厚的AZ31变形镁合金,进行搅拌摩擦焊-钎焊的复合焊接,分析锌夹层的添加对接头微观组织与力学性能的影响。结果当添加Zn中间层时,接头钎焊区缓解了拉伸断裂趋势,在焊接速度为23.5 mm/min,旋转速度为375 r/min时,接头抗拉剪力达到5.5 k N,复合焊接接头的钎焊焊缝由搭接区、固相扩散区、钎焊区组成。结论钎料的添加有效阻止了Al-Mg系金属间化合物的形成。     

钢/铝添加粉末激光焊接头界面组织与性能

基于密度泛函理论的第一性原理,利用层技术构建钢/铝激光焊接的Fe/Al界面模型,研究金属原子X(X=Sn,Sr,Zr,Ce,La)置换Fe/Al界面模型中Fe(Al)原子的合金形成热及其体系电子结构。结果表明:Sn,Sr,Ce优先置换Fe/Al界面处的Al原子,而La,Zr优先置换Fe/Al界面处的Fe原子,合金化促进Fe/Al界面电子在不同轨道之间的转移,增强Fe-Al的离子键性能,提高Fe/Al界面结合能力,改善Fe/Al界面的脆性断裂,其中Sn的合金化效果最显著。在此基础上,进行1.4mm厚DC51D+ZF镀锌钢和1.2mm厚6016铝合金试件添加Sn,Zr粉的激光搭接焊实验,结果显示:添加粉末可促进焊接熔池的流动性,改变接头界面成分和显微组织,添加Sn粉激光焊钢/铝接头的抗拉强度327.41MPa,伸长率22.93%,较添加Zr粉和未添加粉末有了明显提高。     

激光熔-钎焊镀锌钢/铝异种金属的接头性能影响因素及改善措施

激光熔-钎焊是实现镀锌钢板/铝合金异种金属理想连接方式的重要焊接方法。对于焊接多材料车身结构,镀锌钢-铝激光异种金属焊接工艺可提供重要的技术参考。在介绍激光熔-钎焊方法优异性的基础上,综述了影响焊接接头性能的主要因素,并总结了改善接头性能采取的优化措施。     

铝合金／铜／不锈钢接触反应钎焊接头微观组织分析

采用接触反应钎焊对6063铝合金／镀铜层／1Cr18Ni9Ti不锈钢进行焊接,借助扫描电子显微镜和电子探针对接头的微观组织及Fe—Al国金属间化合物生长情况进行测试和分析。结果表明：钎缝中靠近不锈钢一侧为Fe—Al金属间化合物层,靠近铝合金一侧主要是Cu（Al）固溶体,中心区域由Cu-Al化合物和Cu（Al）固溶体混俞而成;随着保温时间的延长,化合物层厚度随之增加,Cu在铝合金一侧富集出现晶界渗透现象;钎缝中首先产生Cu—Al金属间化合物,之后共晶液相中的Al原于穿越Cu—Al金属间化合物层和残余镀铜层扩散至不锈钢侧,与Fe原子生成少量Fe—Al金属间化合物。     

电弧作用下AlSi5钎料在镀锌钢板上铺展及界面行为研究

采用 TIG 电弧钎焊试验方法,主要研究了电流大小、电弧加热时间以及弧长对 AlSi5钎料在镀锌钢板上润湿铺展及界面行为的影响。实验结果表明：随着电流、燃弧时间和某一范围内弧长的增加,钎料在镀锌钢板上的润湿角逐渐减小,铺展面积逐渐增加,并在某一特定范围时润湿铺展性能达到最佳;随着燃弧电流的增加,界面金属间化合物的厚度呈现先增加后减小的趋势,靠近母材一侧有 Fe2 Al5相生成,钎料一侧则生成 FeAl3相;Al 元素扩散到界面处与 Fe 元素发生扩散反应形成 Fe-Al 金属化合物颗粒,在钎缝中弥散分布着 Si 元素,对钎缝有强化作用。     

喷丸预处理对铝合金与钢TIG熔-钎焊的影响

为了使铝合金与钢的连接更加牢固,以Al-Si(6%~8%)为钎料,采用TIG熔-钎焊对5052铝合金和镀锌钢板进行连接,并对铝合金板的熔-焊区进行表面喷丸预处理,研究了表面喷丸对接头界面组织及力学性能的影响.研究表明:喷丸预处理能细化接头熔焊区柱状晶晶粒并使其分布更均匀,促进钢/熔池金属间的界面反应;表面喷丸明显改变了钢/铝扩散层厚度,厚度由6.0μm增加到9.5μm.力学性能测试结果表明,表面喷丸显著改善了连接质量,接头拉剪强度达到238.6 N/mm.     

Dissimilar metals TIG welding-brazing of aluminum alloy to galvanized steel

Dissimilar metals TIG welding-brazing of aluminum alloy to galvanized steel was investigated, and the wettability and spreadability of aluminum filler metal on the steel surface were analyzed. The resultant joint was characterized in order to determine the brittle intermetallic compound (IMC) in the interfacial layer, and the mechanical property of the joint was tested. The results show that the zinc coated layer can improve the wettability and spreadability of liquid aluminum filler metal on the surface of the steel, and the wetting angle can reach less than 20°. The lap joint has a dual characteristic and can be divided into a welding part on the aluminum side and a brazing part on the steel side. The interfacial IMC layer in the steel side is about 9.0 μm in thickness, which transfers from (α-Al + FeAl₃) in the welded seam side to (Fe₂Al₅+ FeAl₂) and (FeAl₂+ FeAl) in the steel side. The crystal grain of the welded seam is obviously larger in size in the aluminum side. The local incomplete brazing is found at the root of the lap joint, which weakens the property of the joint. The fracture of the joint occurs at the root and the average tensile strength reaches 90 MPa.     

Friction stir weld assisted diffusion bonding of 5754 aluminum alloy to coated high strength steels

In the present paper friction stir-induced diffusion bonding is used for joining sheets of 5754 aluminum alloy to coated high strength steels (DP600 and 22MnB5) by promoting diffusion bonding in an overlap configuration. Mechanical performance and microstructures of joints were analyzed by overlap shear testing, metallography, and X-ray diffraction. Our results show that the strength of joint is dependent upon tool travel speed and the depth of the tool pin relative to the steel surface. The thickness and types of intermetallic compounds formed at the interface play a significant role in achieving a joint with optimum performance. That is, the formation of high aluminum composition intermetallic compounds (i.e. Al₅Fe₂) at the interface of the friction stir lap joint appeared to have a more negative effect on joint strength compared to the presence of high iron composition intermetallic phases (i.e. FeAl). This is in agreement with previously reported findings that FeAl intermetallic can improve the fracture toughness and interface strength in Al/St joints.     

热输入对AZ31B镁合金/PRO500超高强钢TIG熔-钎连接特性的影响

利用TIG电弧作为热源开展了AZ31B镁合金与超高强钢PRO500熔-钎连接试验,研究了不同焊接热输入条件对接头微观结构及力学性能的影响。结果表明:利用TIG电弧能够实现AZ31B镁合金/PRO500钢的有效熔-钎连接,强度可达镁合金母材的85%,接头界面区形成由Fe-Mg-O化合物、金属间化合物AlFe_3相和基体Fe元素、熔敷金属中扩散过来的Mg元素等共同组成的过渡区;随着焊接电流的增大,AZ31B镁合金/PRO500钢熔-钎焊接头断裂模式由包含了延性断裂和准解理断裂的混合断裂模式转化为准解理断裂主导的脆性断裂模式,结合强度显著下降。     

Analysis of process parameters effects on friction stir welding of dissimilar aluminum alloy to advanced high strength steel

Thin sheets of aluminum alloy 6061-T6 and one type of Advanced high strength steel, transformation induced plasticity (TRIP) steel have been successfully butt joined using friction stir welding (FSW) technique. The maximum ultimate tensile strength can reach 85% of the base aluminum alloy. Intermetallic compound (IMC) layer of FeAl or Fe₃Al with thickness of less than 1 μm was formed at the Al–Fe interface in the advancing side, which can actually contribute to the joint strength. Tensile tests and scanning electron microscopy (SEM) results indicate that the weld nugget can be considered as aluminum matrix composite, which is enhanced by dispersed sheared-off steel fragments encompassed by a thin intermetallic layer or simply intermetallic particles. Effects of process parameters on the joint microstructure evolution were analyzed based on mechanical welding force and temperature that have been measured during the welding process.     

Fine structures in Fe3Al alloy layer of a new hot dip aluminized steel

The fine structure in the Fe-Al alloy layer of a new hot dip aluminized steel (HDA) was examined by means of X-ray diffractometry (XRD), electron diffraction technique, etc. The test results indicated that the Fe-Al alloy layer of the new aluminized steel mainly composed of Fe₃Al, FeAl and α-Fe (Al) solid solution. There was no brittle phase containing higher aluminum content, such as FeAl₃ (59.18% Al) and Fe2Al7 (62–93% Al). The tiny cracks and embrittlement, formerly caused by these brittle phases in the conventional aluminum-coated steel, were effectively eliminated. There was no microscopic defect (such as tiny cracks, pores or loose layer) in the coating. This is favourable to resist high temperature oxidation and corrosion of the aluminized steel.     

Oxidation Resistance of the Aluminide Coating Formed on Carbon Steels

Low and medium carbon steels were aluminized by the pack aluminizing technique using halideactivated pure-Al and Fe-Al packs. The effect of mixture composition, aluminizing temperatureand time and C content of the steel substrate on the structure and thickness of the aluminidelayer, and on the oxidation resistance was investigated. The optimum oxidation resistance canbe achieved with a low carbon steel substrate when the intermetallic phases Fe3Al and FeAlform the surface of the aluminide layer. In this case, the Al concentration at the surface of thealuminide coating is at least ≥15 wt pct. Formation of high Al concentration phases (FeAl3 andFe2Al5) during aluminizing should be avoided as they tend to embrittle the aluminide layer andreduce its oxidation resistance.     

钢基铝镀层转化为陶瓷层的演变规律研究

热浸镀铝钢经等离子体电解氧化(Plasma Electrolytic Oxidation, PEO)处理后, 表面铝镀层转化为陶瓷层. 实验对阳极电压变化、陶瓷层生长规律、涂层截面形貌和成分等进行了研究. 结果表明: 在PEO初期, 热浸铝试件的阳极电压变化趋势与纯铝试件相同, 在PEO后期电压有下降趋势. 铝镀层消耗和陶瓷层厚度增长近似为线性变化. 当铝镀层完全陶瓷化后, FeAl层参与PEO反应, 但陶瓷层生长速率变慢, 在界面处出现大量裂纹; 陶瓷层主要成分为Al、Si、O元素, 相结构主要为γ-Al₂O₃与莫来石相, 在PEO后期出现α-Al₂O₃相. 复合陶瓷层硬度呈区域性分布, 陶瓷层最高硬度可达HV1800.     

Study of the Interface between Steel Insert and Aluminum Casting in EPC

The effective surface treatment method for steel insert composited with Al base metal by expendable pattern casting （EPC） process and the bonding interface between steel insert and Al base metal were investigated.It was found that Zn plating on steel insert was effective on improving the bonding property between steel insert and Al base metal in EPC process.Zn is thought to promote the formation of diffusion layer.But almost none content of Zn was observed in the boundary which had been plated on the steel insert.A diffusion layer consisting of Al,Si and Fe was formed at the insert/alloy interface and its hardness was higher than the steel insert as matter of course Al base metal.This layer turned out to be intermetallic compounds of Al-Si-Fe system.Higher pouring temperature promoted the diffusion of Fe into Al alloy,so Fe content in intermetallic layers increased at higher pouring temperature.The layer nearest to steel disappeared due to applied pressure.     

Effect of heat treatment on the microstructure and property of cold-sprayed nanostructured FeAl/Al2O3 intermetallic composite coating

It is difficult to deposit dense intermetallic compound coatings by cold spraying directly using compound feedstock powders due to their intrinsic low temperature brittleness. A method to prepare intermetallic compound coatings in-situ employing cold spraying was developed using a metastable alloy powder assisted with post heat treatment. In this study, a nanostructured Fe(Al)/Al₂O₃ composite alloy coating was prepared by cold spraying of ball-milled powder. The cold-sprayed Fe(Al)/Al₂O₃ composite alloy coating was evolved in-situ to FeAl/Al₂O₃ intermetallic composite coating through a post heat treatment. The effect of heat treatment on the phase formation, microstructure and microhardness of cold-sprayed Fe(Al)/Al₂O₃ composite coating was investigated. The results showed that annealing at a temperature of 600 °C results in the complete transformation of the Fe(Al) solid solution to a FeAl intermetallic compound. Annealing temperature significantly influenced the microstructure and microhardness of the cold-sprayed FeAl/Al₂O₃ coating. On raising the temperature to over 950 °C, diffusion occurred not only in the coating but also at the interface between the coating and substrate. The microhardness of the FeAl/Al₂O₃ coating was maintained at about 600HV_0.1 at an annealing temperature below 500 °C, and gradually decreased to 400HV_0.1 at 1100 °C.