中国腐蚀与防护学报, 2023, 43(6): 1247-1254 DOI: 10.11902/1005.4537.2022.354

综合评述

2xxx系铝合金第二相对搅拌摩擦焊接头腐蚀行为的影响

钟嘉欣1, 关蕾,1, 李雨2, 黄家勇2, 石磊3

1.广东工业大学 省部共建精密电子制造技术与装备国家重点实验室 广州市非传统制造技术及装备重点实验室 广州 510006

2.中船黄埔文冲船舶有限公司 广东省舰船先进焊接技术企业重点实验室 广州 510715

3.山东大学 材料液固结构演变与加工教育部重点实验室 济南 250061

Effect of Second Phase on Corrosion Behavior of Friction-stir-welded Joints of 2xxx Series Al-alloy

ZHONG Jiaxin1, GUAN Lei,1, LI Yu2, HUANG Jiayong2, SHI Lei3

1.Guangzhou Key Laboratory of Nontraditional Machining and Equipment, State Key Laboratory of Precision Electronic Manufacturing Technology and Equipment, Guangdong University of Technology, Guangzhou 510006, China

2.CSSC Huangpu Wenchong Shipbuilding Company Limited, Guangdong Provincial Key Laboratory of Advanced Welding Technology for Ships, Guangzhou 510715, China

3.Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials (Ministry of Education), Shandong University, Jinan 250061, China

通讯作者: 关蕾,E-mail:lguan@gdut.edu.cn,研究方向为金属材料的腐蚀与防护

收稿日期: 2022-11-16   修回日期: 2022-12-21  

基金资助: 广东省自然科学基金.  2021A1515010967
广州市科技计划项目.  202102020723
广州市科技计划项目.  202102020626
中国博士后科学基金.  2020M682929

Corresponding authors: GUAN Lei, E-mail:lguan@gdut.edu.cn

Received: 2022-11-16   Revised: 2022-12-21  

Fund supported: Natural Science Foundation of Guangdong Province.  2021A1515010967
Science and Technology Program of Guangzhou.  202102020723
Science and Technology Program of Guangzhou.  202102020626
China Postdoctoral Science Foundation.  2020M682929

作者简介 About authors

钟嘉欣,女,1999年生,硕士生

摘要

搅拌摩擦焊 (FSW) 作为一种固态连接工艺,有效解决了工程应用上2xxx系铝合金的焊接难题。然而由于搅拌摩擦焊过程中接头各个区域所经历的热力作用不同,FSW接头显微组织在各个区域发生演化,进而导致接头腐蚀行为和机理存在明显差异。本文总结了2xxx系铝合金搅拌摩擦焊接头的腐蚀类型、腐蚀发生区域及诱因,并概述了改善焊接接头耐蚀性的方法。

关键词: 搅拌摩擦焊 ; 铝合金 ; 微观组织 ; 腐蚀行为

Abstract

Friction stir welding, as a solid state bonding process, can effectively solve the welding problems of 2xxx series Al-alloy in engineering applications. However, during friction stir welding process, every local area of the welded joint has experienced distinctive thermal cycling and material plastic flow, therefore, different local areas may exhibit obviously differences in their microstructure evolution, as well as in corrosion behavior and corrosion mechanism. In this paper, the corrosion types, positions of corrosion initiation and relevant inducing factors for friction stir welded joints of 2xxx series Al-alloy were reviewed, meanwhile, the relevant corrosion mechanism of weld joints and corresponding methods of improving corrosion resistance for the welded joints were also summerized.

Keywords: friction stir welding ; Al-alloy ; microstructure ; corrosion behavior

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本文引用格式

钟嘉欣, 关蕾, 李雨, 黄家勇, 石磊. 2xxx系铝合金第二相对搅拌摩擦焊接头腐蚀行为的影响. 中国腐蚀与防护学报[J], 2023, 43(6): 1247-1254 DOI:10.11902/1005.4537.2022.354

ZHONG Jiaxin, GUAN Lei, LI Yu, HUANG Jiayong, SHI Lei. Effect of Second Phase on Corrosion Behavior of Friction-stir-welded Joints of 2xxx Series Al-alloy. Journal of Chinese Society for Corrosion and Protection[J], 2023, 43(6): 1247-1254 DOI:10.11902/1005.4537.2022.354

2xxx系铝合金是一种典型的可热处理强化高强度铝合金。该类铝合金具有良好的力学性能,在航天航空、汽车以及造船中得到广泛的应用,然而由于其熔点低、热导率高、线膨胀系数大、和氧的亲和力大等特点,采用传统的熔焊方法连接该类铝合金容易形成开裂、残余应力和孔隙等缺陷,使焊接接头性能降低。搅拌摩擦焊 (FSW) 作为一种固态连接工艺,有效地减少上述缺陷的发生,基本上解决了2xxx系铝合金因特殊物理性质造成的焊接难题。因此,搅拌摩擦焊目前已经成为铝合金的优选焊接工艺。然而,2xxx系高强铝合金搅拌摩擦焊接头耐腐蚀性能母与材存在差异,整个焊接接头的耐蚀性不一致。毋庸置疑,铝合金发生腐蚀的本质原因在于其第二相种类多、成分复杂。搅拌摩擦焊接头在工艺过程中同时受到强烈塑性变形以及摩擦热循环作用,而机械作用以及热输入量的不均匀分布势必会造成各区域微观组织差异,从而导致各区域的腐蚀敏感性也明显不同。

近些年来国内外针对2xxx系铝合金搅拌摩擦焊接头各区域的微观组织、腐蚀行为的研究已经取得一定进展,然而目前并没有研究明确揭示微观组织与焊接接头腐蚀行为之间系统性的关系。因此,本文在介绍2xxx系铝合金微观组织及其腐蚀机理的基础上,根据国内外学者相关研究,总结归纳搅拌摩擦焊接头各区域发生的腐蚀类型与腐蚀诱发源以及提高接头耐蚀性的方法,为揭示搅拌摩擦焊接头腐蚀机理及其耐蚀性调控工艺提供指导。

1 铝合金搅拌摩擦焊概述

FSW是一种新型的固态焊接技术,在该过程中旋转的搅拌头插入对接的表面,直到轴肩接触到工件表面,随后使用具有特定设计的搅拌头沿焊缝线连接相同或者不同材料。如图1所示,搅拌头会先停留一定的时间,当预热搅拌头前面的材料后,搅拌头会沿着焊缝线同时向前移动和旋转,在这过程中被软化的金属材料从焊缝的前进侧 (AS) 移动到后退侧 (RS)。FSW过程中的软化、局部变形和材料混合所需的热量是由工具的摩擦和搅拌作用产生[1~3]

图1

图1   搅拌摩擦焊过程示意图[2]

Fig.1   Schematic diagram of the friction stir welding process[2]


FSW过程中的温度及其分布是决定微观结构演化的主要因素。随着与焊缝中心距离的增加,温度随着降低;焊缝两侧的温度为不对称分布,前进侧的温度通常要比后退侧温度高20 ℃左右;焊缝温度随着旋转速度的增加以及焊接速度的降低而升高。Benavides等[4]通过观察30 ℃下2024铝合金FSW过程前后再结晶晶粒尺寸的变化用以计算焊缝中心区的温度变化,焊接区最高温度为330 ℃。Jonckheere等[5]根据析出物演化模型预测,温度的升高会导致析出物半径的增加,析出物体积分数的降低。通过得到焊缝中的温度分布情况,从而能更加深入研究焊缝中微观组织的分布,进而对焊缝不同区域的腐蚀性能有更深的理解。

2 2xxx铝合金典型微观组织及其腐蚀机理研究

2.1 2xxx系铝合金中典型第二相

根据第二相的特点及其形成的温度范围,铝合金中的第二相可以大致分为3类:组分相、弥散相和析出相[6, 7]。一般来说,组成相比较粗大,尺寸从一微米到几十微米不等。在一些应用于结构方面的铝合金中,弥散相主要目的是在高温热处理以及热机械处理过程中控制晶粒的结构以及抗再结晶能力。组成弥散体的主要元素Mn、Zr和Cr的溶解度较低,因此在后续固溶热处理中结构和成分会变得十分稳定,溶解程度不大[8]。而析出相是指在时效过程中产生的细小的相或者团簇,包括晶内析出相以及晶界析出相。

Al-Cu-Mg系合金以何种相为主要强化相视合金中的铜含量及铜和镁的比值来决定。2024铝合金Cu含量为3.8%,Cu和Mg质量比为2.8,在这种含量及比值下合金的析出相应以S相为主[9, 10]。如表1能谱分析结果以及图2所示,可大体将第二相分成两类,1-7为边界圆滑的较为细小的Al-Cu-Mg颗粒,8-15为不规则形状的Al-Cu-Mn-Fe颗粒[11~15]

表1   两类第二相的EDS分析结果[15] (atomic fraction / %)

Table 1  EDS analysis of two second phases[15]

ElementIntermetallic 1Intermetallic 2
Al59.9576.32
Cu19.4912.99
Mg20.40-
Fe-5.63
Mn-4.36
Si-0.19

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图2

图2   抛光后的2024铝合金SEM图像[12]

Fig.2   SEM image of 2024 aluminum alloy after polishing,1-7 are Al-Cu-Mg particles while 8-15 are Al-Cu-Mn-Fe particles (a), magnified Al-Cu-Mg particles (b) and magnified Al-Cu-Mn-Fe particles (c)[12]


2.2 2xxx系铝合金典型第二相腐蚀机理

2xxx系铝合金中主要合金元素可分两大类,即含Mg、Li等的阳极性元素以及含Cu、Mn、Fe、Si等的阴极性元素。它们与基体Al形成电化学性质不同的第二相组织,其与铝基体相比,可能作为阳极或阴极相,导致点蚀等局部腐蚀的发生。当晶界存在沉淀相析出时,晶界两侧往往伴随形成宽度为100~300 nm的贫溶质区,称为无沉淀析出带 (PFZ)。PFZ与基体击穿电位 (Ebr) 差异是2xxx系铝合金晶间腐蚀的主要诱因之一。此外,析出相的存在导致了钝化膜的不连续,也降低了抗应力腐蚀性能。国内外学者[16~20]对2xxx系铝合金的点蚀、电偶腐蚀、应力腐蚀和晶间腐蚀等进行的大量研究表明,此类铝合金的耐蚀性取决于成分组成、热处理工艺、晶粒尺寸和形态、析出相的分布、环境条件和施加的载荷,但不同的腐蚀形式之间存在某种关联。

当2xxx铝合金处于含氯离子的腐蚀介质中时,典型活性第二相—S相呈现出两种不同的腐蚀形貌:一种是S相自身的腐蚀;另一种是S相边缘基体腐蚀[12]。点蚀的初始电偶建立在S相颗粒和其相邻的铝基体之间。S相自身的电化学行为较为活泼,相关文献[21]表明,在3.5% NaCl腐蚀介质中,S相的电位约为-0.94 VSCE,而2024铝合金电位为-0.81~-0.86 VSCE,因此S相将优先作为阳极被溶解,产生S相自身的腐蚀。随着浸泡时间的增加,S相颗粒变得越来越小,这意味着在初始阶段,S相中的Al和Mg被持续溶解。随着S相中Al和Mg含量的减少,Cu在颗粒中从边缘到中心的分布变化导致S相的自腐蚀电位提高。因此,S相反过来充当阴极,导致相邻的铝基体的阳极溶解。针对S相边缘基体的腐蚀,还有另一种观点认为铝基体的溶解可能是由局部碱化引起的[22]。当S相在发生溶解的同时,其边缘基体上发生两种阴极还原反应,使得S相附近局部发生碱化。由于Al2O3存在的平衡pH值为9,因此当S相附近局部pH>9时,S相边缘基体上的氧化膜将发生溶解,而后通过电化学过程又形成新的氧化膜。当这种过程不断进行,同样将导致S相附近基体的腐蚀。

关于Al-Cu-Mn-Fe颗粒,含有Mn以及Fe的这些颗粒通常在腐蚀介质中表现得很稳定,但当它们碎化后分布在铝基体中却可诱发点蚀。Kang等[12]研究表明富Fe相粒子在FSW过程中被碾碎,这些被碎化的粒子之间以铝基体填充,微区腐蚀原电池在该处建立,并且呈现阴极多而阳极少的状态,这将进一步导致缝隙中的铝基体加速溶解。

3 2xxx系铝合金搅拌摩擦焊接头微观组织

搅拌摩擦焊过程中接头各个区域所经历的热循环和材料塑性流动的作用不同,因此FSW接头各个区域的显微组织随之发生演变,接头腐蚀行为和机理也存在明显差异。根据FSW过程中经历的热力作用不同,可以将焊缝分为3个区域[23]:由中心向母材区 (BM) 过渡分别是焊核区 (NZ),热影响区 (HAZ),热机械影响区 (TMAZ),如图3所示。由于受到焊接热循环和搅拌针的机械搅拌双重作用程度不同,接头各区域的晶粒取向、晶粒度及第二相尺寸、数量、分布均存在差异。NZ区晶粒尺寸远小于母材以及其他区域,是由均匀细小的等轴晶组成且大角度晶界比例高。HAZ不发生塑性变形,仅受到热循环的作用,因此晶粒尺寸与母材相比有所长大[24, 25]。与NZ相比,TMAZ中的晶粒长且窄,相较于焊缝的其他区域小角度晶界的百分比大幅升高。康举等[26]利用差示扫描量热法 (DSC) 揭示2024铝合金FSW过程中析出相相对于母材回溶或粗化的相对值。证明在FSW过程中相对于BM,NZ有23.3%的S相发生回溶,HAZ有6.1%的S相发生回溶;利用TEM分析可以看出HAZ与NZ的第二相粒子尺寸均变小,数量也变少,尤其NZ的第二相粒子发生明显细化。

图3

图3   FSW过程中生成的宏观结构,后退侧的TMAZ结构和HAZ结构及前进侧的TMAZ结构[28]

Fig.3   Macrostructure presenting the regions generated during the FSW process (a), TMAZ on the RS (b), HAZ on the AS (c) and TMAZ on the AS (d)[28]


有研究者[24]对各区域的第二相进行能谱成分分析,在BSE模式下观察到第二相主要为Al-Cu-Mn-Fe (富Fe相) 以及Al-Cu-Mg颗粒 (S相)。第二相颗粒的尺寸变化主要由两个因素造成:一种是FSW过程中由于搅拌作用引起的塑性变形导致脆性富铁相颗粒被碎化,搅拌作用越厉害,第二相颗粒的尺寸越小。沿着BM、HAZ、TMAZ到NZ,塑性变形的增加导致了第二相颗粒尺寸不断减小以及颗粒数量不断增加;另一种是S相颗粒在热循环的作用下被溶解以及再沉淀[27]

4 2xxx系铝合金搅拌摩擦焊接头腐蚀行为

针对焊接接头各个区域对腐蚀的敏感性以及发生腐蚀的类型,出现了几种不同的观点,见表2所示,由此归纳3种主要结论: (1) NZ耐蚀性更差,腐蚀类型以点蚀为主。研究认为这与S相和残留杂质粒子的尺寸和分布状态有关,搅拌头轴肩作用区 (SAZ) 中的S相比HAZ和BM中的要更小更均匀,这与点蚀坑成核的地方增加有关系,点蚀易萌生于S相。(2) HAZ或靠近热机械影响区 (TMAZ) 的HAZ耐蚀性更差,腐蚀类型包括晶间腐蚀和点蚀。HAZ中晶内粗大S相 (Al2CuMg) 的数量增加,诱发点蚀。在靠近TMAZ的HAZ中为硬度弱区,在晶界析出的连续板状 S’ (S) 相或T1相是均匀晶间腐蚀的有利位置,故在该区域最易发生点蚀和晶间腐蚀。(3) 焊接接头耐蚀性优于母材。由于FSW过程中的温度升高,晶内晶界析出诱发点蚀和晶间腐蚀的Al2Cu或T1相发生回溶,从而减少了局部腐蚀发生概率。

表2   2xxx系铝合金搅拌摩擦焊接头腐蚀行为总结

Table 2  Summary of corrosion behaviour of FSWed joints of 2xxx series aluminum alloy

Al-alloyCorrosion typeCorrosion areaCorrosion inducing sourceReference
2024PittingNZUniformly distributed fine S phase[27]
2060-T8Intergranular corrosion

NZ&TMAZ

HAZ

The Cu rich phase at grain boundary[29, 30]
2024-T351PittingHAZ, located near to the TMAZThe coarse S phase in the grain[14, 31~33]
Intergranular corrosionThe continuous S phase at grain boundary
2098-T351, 2050-T3Exfoliation & intergranular corrosionHAZT1 phase at grain boundary、 sub-grain boundary[34, 35]
2014,2198-T851,2219Corrosion resistance is better than the base metalDissolution of Al2Cu/T1 phase[36~39]

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大多数文献表明,随着晶粒尺寸的减小,合金中的晶粒越细小,合金的强度越高,腐蚀敏感性减低,晶界的耐腐蚀性能越好。抗腐蚀性的提高通常归因于高晶界密度表面更容易钝化的能力或第二相的物理分解从而防止这些第二相作为发生局部腐蚀的萌生源。然而,也有相反的观点认为随着晶粒尺寸的减小,高晶界密度可能会提高整体表面活性,从而提高腐蚀速率。有学者[40]提出在没有氧化膜的情况下,当溶解速率>10 μA/cm2时,晶粒尺寸减小则腐蚀速率增加。另有实验表明,晶粒尺寸对腐蚀速率的影响结果取决于晶粒为等轴晶或柱状晶。晶粒细化的过程中也会影响第二相的分布情况,因此关于晶粒尺寸对腐蚀性能的影响,仍需结合其他关键因素进行分析。

由此可见,焊接接头各个区域的耐蚀性与其对应的晶粒和第二相特征均密切相关,但目前研究并未分别建立晶粒和第二相特征与各区域耐蚀性的定量关系。

5 提高2xxx系铝合金搅拌摩擦焊接头耐蚀性方法

部分学者对2xxx系铝合金搅拌摩擦焊接头腐蚀行为进行研究,试图找出最佳的腐蚀防护方法并揭示其机理。研究表明,在焊接过程中以及焊接后能在一定的程度上改善接头的抗腐蚀性能,例如降低焊接热输入量、焊后热处理、表面处理等,总结如表3所示。

表3   提高2xxx系铝合金搅拌摩擦焊接头耐腐蚀性的方法总结

Table 3  Summary of methods employed to improve the corrosion resistance of FSWed joints of 2xxx series aluminum alloy

MethorAl-alloyResultReference
Reduce heat input during weldingReduce the welding speed2024-T4The second-phase particles were dissolved and became smaller in size with segregation of the Cu elements at the grain boundary decreased[41]
Reduce the rotational speed2219-T87-[42]
Water cooling2219-T62, 2014θ(Al2Cu) phase was refined and the PFZ region was absent[39, 43]
Post welding heat treatmentartificial ageing of 8 and 9 h2014-T6-[44]
Surface treatmentSurface coating2024-T351, 2219-T87The grain had refined and the residual stress had reduced[45, 46]
Laser shock peening2024-T351The grain had refined, the phase had increased and the high density dislocation appeared[47]
ultrasonic impact treatment2A12[48]
2219-T6The grain had refined,the precipitated phase had dissolved[49]
laser surface melting2219The surface S phase had dissolved and the second phase was uniformly distributed[50]
in situ shot-peening-assisted cold spray coatingCoated porosity had reduced[51]

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5.1 降低焊接热输入量

改变搅拌头旋转速度、焊接速度以及提高焊接过程冷却速率等方法可以有效改善FSW焊缝微观组织,从而在一定程度上提高焊缝的耐腐蚀性能。在焊接过程中采用水冷的方法,提高焊缝冷却速率降低焊接过程的热输入量,获得了更细小以及更均匀的析出相,焊缝腐蚀性能得到改善[39]。转速在控制腐蚀攻击的位置方面起着重要作用[31],对于低转速焊缝,在焊缝区观察到局部的晶间腐蚀,而对于高转速焊缝,腐蚀主要发生在热影响区。Wang等[52]认为由于移动速度的增加导致析出相尺寸的增加,FSW接头的SCC敏感性随之增加。

从根本上说,改变旋转速度和移动速度实质上也是改变焊接过程中的热输入量。焊缝的具体能量输入可以利用该公式计算[53]

E=Tωvt

其中,E代表具体的能量输入,J/mm;T是测得的扭矩,N·m;ω是搅拌工具的角速度,rad/s;vt是搅拌工具的移动速度,mm/s;该公式忽略热量通过夹具或从焊接板顶表面对流产生的损失。从该公式可以获得,焊接过程的热输入量随着旋转速度的提高以及移动速度的减低而增加。因此,相关研究表明降低焊接过程中的热输入量为有效提高焊缝耐蚀性的方法之一[39, 41~43]。一方面,焊接过程摄入过高的热输入量会促进合金晶内以及晶界析出相的形成,从而降低焊缝的电位,提高其腐蚀敏感性。另一方面,晶粒尺寸能影响焊缝的腐蚀电流密度,晶粒尺寸越小,晶界密度越大,导致钝化层的形成越快,当提高焊缝热输入量时,焊缝温度提高促进晶粒生长,导致焊缝耐腐蚀性能降低。

5.2 焊后热处理

通过对FSW接头进行不同的焊后热处理工艺,可以改变析出相的大小、数量以及分布情况。FSW接头的电化学行为通常是由不同区域之间界面内的粗化沉淀物控制的。因此,可以通过重新溶解接头内的粗化析出相,或通过控制析出相的尺寸、位置和分布来改变焊缝微观组织,从而提高接头的耐腐蚀性能[54]。目前对于2xxx系铝合金FSW焊缝,焊后热处理对其微观组织的影响与腐蚀性能之间关系的研究不足。同时,焊后热处理只适用于整个构件并且对尺寸有一定的限制,因此该方法在实际应用上有诸多限制。

5.3 表面处理

相关表面处理通过改变焊缝第二相分布情况、晶粒特征分布、位错密度、残余应力等可以达到提高FSW焊缝耐蚀性的目的。激光表面熔化 (LSM) 是一种提高搅拌摩擦焊接头耐蚀性的表面改性方法,Ma等[50]使用LSM技术在FSW焊缝表面形成熔体区,研究表明焊缝表面的抗点蚀性明显提高。将腐蚀介质与焊缝隔离,表面制备涂层是改善FSW焊缝腐蚀性能最为可靠的技术之一。目前,国内外学者利用冷喷涂技术在2xxx铝合金焊缝表面制备较为致密的纯Al涂层,发现制备成的冷喷涂涂层出现大量的晶粒细化,经过相关腐蚀实验测试发现FSW接头的腐蚀敏感性显著降低[45, 46]。除此之外,利用微弧氧化表面改性技术在铝合金表面原位生成陶瓷涂层能明显地提高FSW焊缝耐蚀性[55~57]。由于残余应力常存在于FSW焊缝中,在特定腐蚀条件下极易引发SCC的发生,通过激光喷丸以及超声冲击处理可以很好降低残余压应力,改善焊耐蚀性。邓云发等[48]对2A12铝合金FSW焊缝表面进行超声冲击,表明其表面晶粒得到细化,位错密度增加,焊缝耐腐蚀性能得到提高。为了更进一步提高焊缝的耐蚀性,相关学者研发了原位喷丸辅助冷喷涂技术,该技术有效提高了涂层的孔隙率,提高FSW焊缝的耐蚀性[51]

6 总结

2xxx系铝合金因具有轻质、高强度以及较好的耐腐蚀性能在航天航空、汽车等工程领域有着广阔的应用前景,搅拌摩擦焊是广泛应用于该类合金或该合金与其他合金固态连接的最佳焊接方法之一。目前关于FSW接头微观组织的定性研究已成熟,但却未从定量的角度比较和分析各个区域微观特征 (如晶粒和第二相) 的差异。研究表明焊接接头四个区域的耐蚀性与其对应的晶粒和第二相特征均密切相关,但影响各区域腐蚀性能的主控因素尚不明确。因此,为了能更有效指导以及规范焊接工艺,亟需定量揭示焊接接头组织的局部差异性,以及建立2xxx系铝合金搅拌摩擦焊接头组织结构及电化学本征参数与腐蚀敏感性之间的定量关系。

提高搅拌摩擦焊接头耐蚀性可采用降低焊接过程的热输入量、焊后热处理、焊接接头表面处理等方法。值得注意的是,近年来为了获得更高的焊接质量以及提高焊接速率,外加高能场辅助搅拌摩擦焊工艺受到研究学者们的格外关注,且多着眼于对焊接接头力学性能以及微观组织两方面的研究,鲜有针对其腐蚀性能的相关研究。经分析,外加高能场对耐蚀性的影响也应源于其对接头晶粒和第二相特征的改变。因此,为有效降低该类搅拌摩擦焊接头的腐蚀敏感性,需要提出外加高能场后的焊接接头晶粒尺寸与第二相特征对其腐蚀性能影响的一般规律,进而指导焊接工艺的优选及焊接接头耐蚀性评价方法的优化。

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