焊后热处理对7055-0.1Sc铝合金搅拌摩擦焊接头的组织与力学性能的影响

Al-Zn-Mg-Cu(7000系)高强铝合金具有高比强度、比刚度和良好的耐腐蚀性能，在航空航天、船舶制造、轨道交通等领域得到了广泛的应用[1,2] 添加稀土元素Sc对铝合金有显著的改性作用，使其具有高强度、高耐热性和良好的抗蚀性[3,4] 在传统7055、7075等高强铝合金中加入微量Sc元素的Al-Zn-Mg-Cu-Sc铝合金可使其具有更加优异的综合力学性能[5,6]，但是用熔焊焊接高强7000系(包括含Sc)铝合金时产生的气孔和热裂纹等缺陷使接头的力学性能严重降低[7] 搅拌摩擦焊(Friction Stir Welding，FSW)是一种固相连接技术，特别适于焊接Al-Zn-Mg-Cu-Sc铝合金 [8]

虽然FSW的热输入明显小于熔焊，但是其接头仍出现软化现象 先前的研究表明，提高时效强化铝合金接头力学性能的三种方式，分别是提高焊接速度[9,10]、采用冷却介质增加FSW过程的冷却速率[11]和焊后热处理[12~15] 焊后热处理是最有效的方式 对5.4 mm厚2219-T6铝合金FSW接头的研究表明[12]，焊后人工时效热处理能显著提高焊速接头的力学性能 对6 mm厚2014-T6铝合金FSW接头的研究表明[12]，焊后固溶＋人工时效(T6)热处理可将接头硬度恢复到母材的水平，但是接头焊核区(Nugget zone, NZ)的晶粒发生了异常长大[13] Robert等[14]对2519-0.36Sc铝合金进行FSW，发现焊后T6热处理使接头的整体硬度明显提高，但是NZ区的晶粒异常长大，且在NZ与热机影响区(Thermal-mechanically affected zone, TMAZ)的界面出现了孔洞，使接头的疲劳性能大幅降低 以上研究表明，焊后热处理能提高时效强化铝合金FSW接头的硬度，但是T6热处理使某些合金接头NZ出现晶粒异常长大和孔洞 在焊后T6热处理过程中FSW接头的晶粒是否异常长大，与接头的原始晶粒尺寸有密切的关系[15]，而工艺参数是影响FSW接头晶粒尺寸的关键因素 Sc能抑制晶粒长大 基于此，本文对11 mm厚7055-0.1Sc-T4铝合金进行FSW，研究焊后人工时效和T6热处理对接头的组织和性能的影响

1 实验方法

实验用母材(Base material, BM)为11 mm厚的7055-0.1Sc-T4轧制板材，其化学成分和力学性能分别列于表1和表2

Table 1

表1

表17055-0.1Sc-T4轧制板材的化学成分

Table 1Chemical composition of 7055-0.1Sc-T4 plate (mass fraction, %)

Zn	Mg	Cu	Sc	Zr	Si	Fe	Mn	Al
7.6~8.4	1.8~2.3	2.0~2.6	0.1	0.08~0.25	≤0.1	≤0.15	≤0.05	Bal.

Table 2

表2

表27055-0.1Sc-T4轧制板材的拉伸性能

Table 2Tensile properties of 7055-0.1Sc-T4

Yield Strength / MPa	Tensile Strength / MPa	Elongation / %
595±28	635±36	9±5

进行FSW前，用砂纸将试板表面打磨以除去表面的氧化膜，再用酒精清除表面的油污 用FSW-SDLM 50型焊机对100 mm×300 mm板材进行对焊，搅拌头的主轴倾角为2.75°，转速为500 r/min，焊速分别为100 mm/min和250 mm/min，焊后的接头在空气中自然冷却至室温

将接头在室温下放置20 d后，切取试样分别进行焊后人工时效(120℃×24 h)和T6(470℃×1.5 h+水淬+120℃×24 h)热处理 分别将焊态(As welded, AW)接头、焊后人工时效态(Artificial aging, AA)接头和固溶＋人工时效态(T6)接头简称AW接头、AA接头和T6接头 例如，500-100-AW表示转速为500 r/min，焊速为100 mm/min的焊接态接头

在垂直于焊接方向切取金相样品，将其磨抛后用Keller试剂(2 mL HF+3 mL HCl+5 mL HNO3+190 mL H2O)腐蚀，然后分别用体视显微镜和Leica DMI光学显微镜观察其宏观和微观组织

沿焊接样品板厚的中线，使用Leco LM-247AT型硬度仪测试样品的显微硬度，载荷为300 g，保压时间15 s，各点间距为1.5 mm 将TEM试样预减薄至约60 μm，然后将其冲成直径为3 mm的圆片，再将其在30% HNO3＋70% CH3OH溶液中双喷减薄，用液氮冷却后使用JEOL JEM-2100F型透射电镜(TEM)观察和分析接头各区域的第二相特征，加速电压为200 kV

在垂直于焊接方向切取室温拉伸样品，其尺寸在图1中给出 用INSTRON 5982型拉伸机测试拉伸性能，应变速率为1×10-3 s-1，测试3个标准试样，取其结果的平均值 用Quanta 450型扫描电镜(SEM) 观察拉伸后断口的形貌



图1拉伸试样的尺寸

Fig.1Configuration and sizes of tensile specimen

2 结果和讨论2.1 接头的形貌

图2给出了各种FSW 7055-0.1Sc-T4接头横截面的宏观形貌 可以看出，焊接态接头均没有出现任何焊接缺陷(图2a和b)，可分为NZ、TMAZ和热影响区(Heat affected zone, HAZ)三个区域 焊后T6热处理没有改变低焊速接头500-100-T6的宏观形貌(图2c)，但是高焊速接头500-250-T6底部的颜色发生明显的改变(图2d)且出现了晶粒异常长大 接头500-100-T6中心和接头500-250-T6底部(图2c和d中黑色箭头所示)的抛光态局部放大图显示，在两个区域均出现了微小孔洞(图3a和b)，其位置均位于接头“S”线上 与AW接头相比，人工时效热处理的FSW接头宏观和微观形貌没有变化



图2FSW 7055-0.1Sc-T4焊接态和T6态接头横截面的宏观形貌

Fig.2Cross-sectional macrostructure of FSW 7055-0.1Sc-T4 joints (a) 500-100-AW, (b) 500-250-AW, (c) 500-100-T6, (d) 500-250-T6



图3图2c, d中黑色箭头所示位置的放大图

Fig.3Magnified of zones marked by the black arrows in Fig.2c, d

温度较低(120℃)的人工时效热处理后，FSW接头的宏观和微观形貌与焊接态接头的组织基本相同，而FSW铝合金接头在焊后T6热处理过程中晶粒异常长大[13~15] 铝合金的晶粒稳定性与晶粒尺寸和第二相分布有关[15~17] 在FSW过程中较高的热输入和剧烈塑性变形使NZ发生动态再结晶，NZ晶粒为等轴细小的再结晶晶粒，此时晶界处于高自由能状态，焊后晶界仍保持较高的能量状态，NZ底部晶粒越细其晶界能越高[18] 本文的研究中，低焊速接头500-100-AW的晶粒较大 NZ中Al3(Zr, Sc)等难溶颗粒对晶粒长大的抑制，使焊后T6热处理没有改变低焊速接头500-100-T6的晶粒形貌 但是，高焊速500-250-AW接头的晶粒更加细小，高角晶界能给二次再结晶极大的驱动力，细小晶粒与周围晶粒合并以降低晶界能，达到更稳定的组织状态[19]；Al3(Zr, Sc)等相对晶界的钉扎已不能抑制其晶粒长大，因此在接头500-250-T6 NZ底部晶界能最高的位置发生晶粒异常长大(图2d和图4e)



图4FSW 7055-0.1Sc-T4焊接态和T6态接头不同位置的微观组织

Fig.4OM of different regions in the FSW joints (a) BM, (b)~(e) magnified NZ of position B~E in Fig.2

图5给出了FSW 7055-0.1Sc-T4接头中的“S”线分布 “S”线源自于板材原始面，由高密度的Al2O3颗粒组成[20] 从图5可以看出，转速为500 r/min、焊接速度为100 mm/min时“S”线从NZ的底部开始偏向后退侧，最后呈弧状向上曲折延伸到接头上部(图5a) 焊速由100 mm/min提高到250 mm/min，NZ材料的流动弱化[21]，使后退侧更多的金属材料参与NZ成型，使接头“S”线的弯曲程度提高且集中在NZ中心区域(图5b) 与AW态相比，T6热处理的接头其“S”线形状不变，但更加直观、易于观察(图5c和d)，“S”线上分布着许多黑点 本研究中的黑点形貌分布与Ren等[22]对FSW 7075-T651铝合金接头的报道类似 该报道称，T6热处理后接头沿“S”线开裂，周围有许多小孔洞 Hu等[23]观察了T6热处理后FSW接头“S”线周围出现的小孔洞，认为FSW接头的残余应力和氧化物与基体之间线膨胀系数的差异产生的热应力，是T6热处理后“S”线周围产生小孔洞的原因 这可用于解释本文实验中T6热处理后接头出现孔洞缺陷(图3a和b)



图5FSW 7055-0.1Sc-T4焊接态和T6态接头的“S”线分布

Fig.5Pattern of “S” line in FSW 7055-0.1Sc-T4 joints (a) 500-100-AW, (b) 500-250-AW, (c) 500-100-T6, (d) 500-250-T6

2.2 硬度分布

图6给出了各个状态FSW 7055-0.1Sc-T4接头横截面中心线的硬度分布 可以看出，对于各焊接参数，AW态和AA态接头的硬度呈“W”型分布，最低硬度区(Low hardness zone，LHZ)位于HAZ，随着焊速由100 mm/min提高到250 mm/min，LHZ的硬度随之提高，位置内移(图6a和b) 焊后人工时效热处理明显提高了500~100和500~250两种接头NZ和BM的硬度，但是没有改变LHZ的硬度 而焊后T6处理使两个接头各区硬度的提高相同(约195 Hv)，明显高于BM(T4态)的硬度



图6FSW 7055-0.1Sc-T4接头横截面中心线的显微硬度分布

Fig.6Microhardness profile of FSW 7055-0.1Sc-T4 joints

沉淀强化铝合金FSW接头的硬度分布，主要受各区域沉淀强化相演变的影响 7000系(Al-Zn-Mg-Cu)铝合金是可热处理强化铝合金，在T6热处理过程中这种合金的析出相序列为SSSS→GP Zone(I or II)→η'(MgZn2)→η(MgZn2)[9] 在7055铝合金中添加微量Sc元素，生成的Al3(Zr, Sc)与基体保持良好的共格关系[4]，弥散分布在基体中有稳定晶界和弥散强化的作用 Al-Zn-Mg-Cu-Sc铝合金在较低的温度(25~100℃)时效GP区和Al3(Zr, Sc)是主要强化相[9]，而在高于120℃[9]的温度时效则η'相、η相和Al3(Zr, Sc)相是主要强化相

图7给出了FSW 7055-0.1Sc-T4接头BM、NZ、LHZ的典型TEM明场像 BM沉淀相为球状Al3(Zr, Sc)和GP区[24]，对基体有弥散强化作用(图7a和b) 在FSW过程中NZ经历了峰值温度>475℃的热循环[25]，使GP区溶解，板条状的η相基于Al3(Zr, Sc)颗粒相形核并析出(图7c)，在后续自然时效过程中NZ中的GP区重新析出[24]，使NZ的硬度略比BM低但是远高于LHZ



图7FSW 7055-0.1Sc-T4焊接态和T6接头沉淀相的分布

Fig.7TEM micrographs (a) BF and (b) associated diffraction patterns of BM; (c) NZ and (d) LHZ of 500-100-AW; (e) NZ and (f) LHZ of 500-100-T6

在FSW过程中HAZ经历峰值温度为360~370℃的热循环[26]，使GP区溶解并析出粗化的η'相和η相(图7d)，粗化沉淀相破坏了与基体之间的共格关系[27]，使硬度降低，因此HAZ的硬度最低 470℃×1.5 h固溶处理使500~100接头各区的沉淀相重新溶进Al基体中，提高了基体中溶质原子的浓度、相变驱动力和形核率，在随后的人工时效过程中接头各区的沉淀相均匀析出细小且高密度的η'和η相(图7e和f)，因此T6处理后接头的硬度分布呈“一”字分布，硬度整体提高

2.3 拉伸性能和断裂特征

表3列出了各FSW 7055-0.1Sc-T4接头的拉伸性能 可以看出，FSW各接头的抗拉强度明显低于BM；焊后人工时效热处理使500~100和500~250接头的抗拉强度分别小幅度提高了15.9 MPa和9.1 MPa，塑性小幅度降低；而焊后T6处理使500-100-T6和500-250-T6接头的抗拉强度分别大幅度提高了156.6 MPa和86.5 MPa，其最高强度系数可达87.6%，但是接头几乎没有塑性而直接脆断

Table 3

表3

表3FSW 7055-0.1Sc-T4的接头热处理前后的拉伸性能

Table 3Transverse tensile properties of FSW 7055-0.1Sc-T4 joints under AW, AA and T6 states

Number	Sample	Tensile Strength / MPa	Elongation / %	Strength coefficient / %
1	500-100-AW	399.9±1.4	8.9±0.5	63.0%
2	500-250-AW	468.5±7.8	6.3±0.5	73.8%
3	500-100-AA	415.8±2.1	4.3±0.4	65.5%
4	500-250-AA	477.6±3.5	3.8±0.4	75.2%
5	500-100-T6	556.5±1.5	Brittle fracture	87.6%
6	500-250-T6	555.0±2.0	Brittle fracture	87.4%

图8给出了各FSW 7055-0.1Sc-T4接头拉伸断裂的位置，黑色箭头所指为接头断裂时产生的裂纹 AW态和AA态FSW接头的断裂位置均位于LHZ，断裂路径呈“之”字形，中部路径与接头的拉伸方向呈45°夹角，上部和下部路径与中部垂直(图8a) 而T6态FSW接头的断裂位置均位于NZ(图8b和c) 进一步观察可以发现，500-100-T6接头断裂路径的中下部与“S”线基本重合(图8b)，500-250-T6接头的断裂路径只在根部与少量“S”线重合(图8c)



图8FSW 7055-0.1Sc-T4焊接态和T6接头的断裂位置

Fig.8Fracture locations of FSW 7055-0.1Sc-T4 joints (a) 500-100-AW, (b) 500-100-T6, (c) 500-250-T6

焊后T6热处理后，接头都在NZ断裂 低焊速的T6态接头“S”线上的微孔洞(图3a)在拉伸过程中成为裂纹源且沿着与基体结合强度较弱的“S”线扩展[23]，因此500-100-T6接头的断裂路径与“S”线部分重合 高焊速的500-250-T6接头根部的断裂路径(图8c中红框位置)与图3b中的根部“S”线对应，表明该位置为接头拉伸时先断裂的部位 与低焊速接头相比，高焊速接头的“S”线分布更加弯曲，使500-250-T6接头的断裂路径只有少部分与“S” 线重合[22]

图9给出了FSW 7055-0.1Sc-T4 接头的典型断口形貌 从图9可见，500-100-AW接头断口的宏观形貌较为平坦(图9a)，而500-100-T6接头的宏观断口上、下明显不同 图9b中左侧黑色箭头一侧为接头下部，呈台阶状，而上部凹凸不平 500-100-AW断口中心位置C放大后的微观形貌表明，其断裂形式主要是穿晶断裂，可观察到明显的韧窝组织，韧窝底部有沉淀相颗粒，是典型的铝合金断口形貌(图9c) 在500-100-T6接头的拉伸过程中，其NZ中部“S”线上的孔洞成为裂纹源，裂纹沿“S”线向接头上下扩展 因此，位置D和E放大后的微观形貌为解理断裂，没有明显的韧窝组织特征，为典型的脆性断裂特征(图9d和e) 需要强调的是，接头500-250-AW、500-100-AA和500-250-AA与接头500-100-AW断口的形貌类似，接头500-250-T6与接头500-100-T6的断口形貌类似



图9FSW 7055-0.1Sc-T4焊接态和T6接头断口的形貌

Fig.9Fracture morphologies of FSW 7055-0.1Sc-T4 joints, macrographic of (a) 500-100-AW, (b) 500-250-T6; magnified micrographs of positions C-E: (c) position C, (d) position D, (e) position E

3 结论

(1) 在转速为500 r/min、焊接速度为100~250 mm/min条件下，7055-0.1Sc-T4的FSW接头没有焊接缺陷，其最低硬度区位于热影响区

(2) 焊后人工时效热处理使焊核区和母材区域的硬度提高，但是低硬度区的硬度没有明显变化，接头的抗拉强度小幅提高而塑性降低

(3) T6热处理后低焊速接头焊核区的晶粒没有异常长大，但是高焊速接头焊核区底部的晶粒异常长大；T6热处理将FSW 7055-0.1Sc-T4接头各区的硬度提高到均一水平，使其强度大幅提高、强度系数提高到87.6%，但是其塑性极低

(4) 焊接态“S”线不影响FSW 7055-0.1Sc-T4接头的拉伸性能，但是T6热处理使接头出现沿“S”线分布的孔洞，拉伸时接头沿“S”线脆断

参考文献

View Option 原文顺序文献年度倒序文中引用次数倒序被引期刊影响因子

[1]

Schuster P A, ?sterreicher J A, Kirov G, et al.

Characterization and comparison of process chains for producing automotive structural parts from 7xxx aluminum sheets

[J]. Metals, 2019, 9(3): 305

DOIURL [本文引用: 1]

Due to their high specific strength, EN AW-7xxx aluminium alloys are promising materials for reducing the weight of automotive structural parts. However, their formability at room temperature is poor due to pronounced natural ageing. Therefore, we investigated hot stamping and W-temper forming for EN AW-7075 and a modified variant of EN AW-7021. For hot stamping of the modified EN AW-7021, a low-temperature stabilisation heat treatment (pre-aging at 80 °C for 1 h) was incorporated into the process chain design to inhibit natural ageing after forming. The process chains were compared with respect to dimensional accuracy, mechanical properties, microstructure, precipitation status (assessed by differential scanning calorimetry) and crashworthiness. It was found that hot stamping is suitable to form failure-free parts with good dimensional accuracy for both alloys while W-temper forming suffers from springback. Within a time-span of 21 days after forming, hardness values of hot stamped and stabilised parts did not increase significantly. Compared to non-stabilised parts, stabilised parts also showed significantly improved folding behaviour in quasi-static compression testing and absorbed approximately 15% more energy.

[2]

Peng X Y, Guo Q, Liang X P, et al.

Mechanical properties, corrosion behavior and microstructures of a non-isothermal ageing treated Al-Zn-Mg-Cu alloy

[J]. Mater. Sci. Eng. A, 2017, 688: 146

DOIURL [本文引用: 1]

[3]

Yu L B, Wang W Y, Wang J, et al.

The effects of Sc addition on the microstructure and mechanical properties of Be-Al alloy fabricated by induction melting

[J]. J. Mater. Eng. Perform., 2019, 28(4): 2378

DOI [本文引用: 1]

[4]

Zhang J Y, Gao Y H, Yang C, et al.

Microalloying Al alloys with Sc: a review

[J]. Rare Met., 2020, 39(6): 636

DOI [本文引用: 2]

[5]

Teng G B, Liu C Y, Li J, et al.

Effect of Sc on microstructure and mechanical property of 7055 Al-alloy

[J]. Chin. J. Mater. Res., 2018, 32(2): 112

DOI [本文引用: 1]

The effect of Sc addition on the microstructure and mechanical properties of 7055 Al-alloy as-cast, as well as after homogenization-, rolling-, solution- and aging-treatment was investigated. The addition of 0.25%(mass fraction) Sc could lead to the formation of Al3(Sc, Zr) phase, which can promote the heterogeneous nucleation during casting. Therefore, the microstructure of the as cast 7055 Al-alloy was refined. The precipitation of nano-sized Al3(Sc, Zr) phase occurred during the homogenization treatment of the 7055-Sc Al-alloy, and this nano-sized Al3( Sc, Zr) phase could effectively inhibit the coarsening of Al grains during homogenization treatment, and play a role in pinning the grain boundaries, therewith inhibiting the recovery and recrystallization, thus retaining the fiber-like structure during subsequent rolling and solution treatments. Compared to the plain 7055 Al-alloy, the 7055-Sc Al alloy exhibited much higher fine grain strengthening effect due to finer grain size and showed higher tensile strength and hardness as high as 642 MPa and 218 HV, respectively.

滕广标, 刘崇宇, 李 剑 等.

添加Sc对7055铝合金微观结构和力学性能的影响

[J]. 材料研究学报, 2018, 32(2): 112

DOI [本文引用: 1]

研究了添加Sc元素对7055铝合金铸造、均匀化处理、轧制和固溶时效过程的微观结构演化以及力学性能的影响 结果表明,向7055溶液中添加质量分数为0.25%的Sc导致在铸造过程中形成初生Al₃(Sc,Zr)相 这个相能促使合金发生非均质形核,显著细化合金的铸造组织 在7055-Sc铝合金的均匀化处理过程中析出高密度纳米Al₃(Sc, Zr)相,不但能抑制晶粒粗化,而且在后期轧制变形和固溶时效处理过程中还起钉扎晶界、抑制回复与再结晶、保留纤维组织的作用 与7055铝合金相比,7055-Sc铝合金的晶粒尺寸更小,因此具有更有效的细晶强化效应 添加Sc的时效处理态7055铝合金的最大抗拉强度和显微硬度,分别提高到642 MPa和218 HV

[6]

Mo Y F, Liu C Y, Teng G B, et al.

Fabrication of 7075-0.25Sc-0.15Zr alloy with excellent damping and mechanical properties by FSP and T6 treatment

[J]. J. Mater. Eng. Perform., 2018, 27(8):4162

DOI [本文引用: 1]

[7]

Verma R P, Kumar Lila M.

A short review on aluminum alloys and welding in structural applications

[J]. Mate. Today: Proc., 2021, 46: 10687

[本文引用: 1]

[8]

Mishra R S, Ma Z Y.

Friction stir welding and processing

[J]. Mater. Sci. Eng. R, 2005, 50(1-2): 1

DOIURL [本文引用: 1]

[9]

Gupta S, Haridas R S, Agrawal P, et al.

Influence of welding parameters on mechanical, microstructure, and corrosion behavior of friction stir welded Al 7017 alloy

[J]. Mater. Sci. Eng. A, 2022, 846: 143303

DOIURL [本文引用: 4]

[10]

Zhang H, Qin H L, Wu H Q.

Effect of process parameters on mechanical properties of friction stir welded 2195 Al-Li alloy joints

[J]. Trans. China Weld. Inst., 2016, 37(4): 19

[本文引用: 1]

张 华, 秦海龙, 吴会强.

工艺参数对2195铝锂合金搅拌摩擦焊接头力学性能的影响

[J]. 焊接学报, 2016, 37(4): 19

[本文引用: 1]

[11]

Liu J, Chen H G, Wei J X, et al.

Micro-softening behavior and its control of 7N01-T5 Al alloy friction stir welded joint

[J]. Light Alloy Fabrication Technol., 2021, 49(11): 58

[本文引用: 1]

刘 建, 陈辉刚, 韦景勋 等.

7N01-T5铝合金搅拌摩擦焊接头微区软化行为及控制

[J]. 轻合金加工技术, 2021, 49(11): 58

[本文引用: 1]

[12]

Zhang Z, Xiao B L, Ma Z Y.

Enhancing mechanical properties of friction stir welded 2219Al-T6 joints at high welding speed through water cooling and post-welding artificial ageing

[J]. Mater. Charact., 2015, (106): 255

[本文引用: 3]

[13]

Zhang Z, Xiao B L, Ma Z Y.

Influence of post weld heat treatment on microstructure and mechanical properties of friction stir-welded 2014Al-T6 alloy

AMR, 2012, (409): 299

[本文引用: 2]

[14]

Kosturek R, ?nie?ek L, Wachowski M, et al.

The influence of post-weld heat treatment on the microstructure and fatigue properties of Sc-modified AA2519 friction stir-welded joint

[J]. Materials, 2019, 12(4): 583

DOIURL [本文引用: 1]

The aim of this research was to investigate the influence of post-weld heat treatment (PWHT, precipitation hardening) on the microstructure and fatigue properties of an AA2519 joint obtained in a friction stir-welding process. The welding process was performed with three sets of parameters. One part of the obtained joints was investigated in the as-welded state and the second part of joints was subjected to the post-weld heat treatment (precipitation hardening) and then investigated. In order to establish the influence of the heat treatment on the microstructure of obtained joints both light and scanning electron microscopy observations were performed. Additionally, microhardness analysis for each sample was carried out. Fatigue properties of the samples in the as-welded state and the samples after post-weld heat treatment were established in a low-cycle fatigue test with constant true strain amplitude equal to ε = 0.25% and cycle asymmetry coefficient R = 0.1. Hysteresis loops together with changes of stress and plastic strain versus number of cycles are presented in this paper. The fatigue fracture in tested samples was analyzed with the use of scanning electron microscope. Our results show that post-weld heat treatment of AA2519 friction stir-welded joints significantly decreases their fatigue life.

[15]

Hassan K A A, Norman A F, Price D A, et al.

Stability of nugget zone grain structures in high strength Al-alloy friction stir welds during solution treatment

[J]. Acta Mater., 2003, 51(7): 1923

DOIURL [本文引用: 4]

[16]

Zhang J H, Hu Z L.

Microstructural thermal stability of aluminum alloy friction stir welding joint

[J]. Chin. J. Mech., 2022, 58(5): 73

张嘉恒, 胡志力.

铝合金搅拌摩擦焊接头组织热稳定性

[J]. 机械工程学报, 2022, 58(5): 73

[17]

Zuiko I S, Mironov S, Betsofen S, et al.

Suppression of abnormal grain growth in friction-stir welded Al-Cu-Mg alloy by lowering of welding temperature

[J]. Scr. Mater., 2021, 196: 113765

DOIURL [本文引用: 1]

[18]

Hu Z L, Dai M L, Pang Q.

Influence of welding combined plastic forming on microstructure stability and mechanical properties of friction stir-welded Al-Cu alloy

[J]. J. Mater. Eng. Perform., 2018, 27(8): 4036

DOI [本文引用: 1]

[19]

Li N J.

Characterizations on microstructures and properties of 7075 aluminum alloy after friction stir processing and subsequent heat treatment

[D].

Chongqing:

Chongqing University, 2017

[本文引用: 1]

李念军.

7075铝合金搅拌摩擦加工及热处理后的组织性能表征研究

[D].

重庆:

重庆大学, 2017

[本文引用: 1]

[20]

Zhang Z, Xiao B L, Ma Z Y.

Effect of segregation of secondary phase particles and "S" line on tensile fracture behavior of friction stir-welded 2024Al-T351 joints

[J]. Metall. Mater. Trans. A, 2013, 44(9): 4081

DOIURL [本文引用: 1]

[21]

Zeng X H, Xue P, Wang D, et al.

Effect of processing parameters on plastic flow and defect formation in friction-stir-welded aluminum alloy

[J]. Metall. Mater. Trans. A, 2018, 49(7): 2673

DOI [本文引用: 1]

[22]

Ren S R, Ma Z Y, Chen L Q.

Effect of initial butt surface on tensile properties and fracture behavior of friction stir welded Al-Zn-Mg-Cu alloy

[J]. Mater. Sci. Eng. A, 2008, 479(1): 293

DOIURL [本文引用: 2]

[23]

Hu Z L, Pang Q, Dai M L.

Microstructure and mechanical properties of friction stir welding joint during post weld heat treatment with different zigzag lines

[J]. Rare Met., 2018, 38(11): 1070

DOI [本文引用: 2]

[24]

Lin H Q, Wu Y L, Liu S D.

Impact of initial temper of base metal on microstructure and mechanical properties of friction stir welded AA 7055 alloy

[J]. Mater. Charact., 2018, 146: 159

DOIURL [本文引用: 2]

[25]

Kang J, Feng Z C, Frankel G S, et al.

Friction stir welding of Al alloy 2219-T8: part I-evolution of precipitates and formation of abnormal Al2Cu agglomerates

[J]. Metall. Mater. Trans. A, 2016, 47(9): 4553

DOIURL [本文引用: 1]

[26]

Liu F C, Ma Z Y.

Influence of tool dimension and welding parameters on microstructure and mechanical properties of friction-stir-welded 6061-T651 aluminum alloy

[J]. Metall. Mater. Trans. A, 2008, 39(10): 2378

DOIURL [本文引用: 1]

[27]

Chen Z W, Yan K, Ren C C, et al.

Precipitation sequence and hardening effect in 7A85 aluminum alloy

[J]. J. Alloys Compd., 2021, 875: 159950

DOIURL [本文引用: 1]

Characterization and comparison of process chains for producing automotive structural parts from 7xxx aluminum sheets

1

2019