淬火速率对<strong>7136</strong>铝合金应力腐蚀开裂敏感性的影响

doi:10.11900/0412.1961.2021.00053

金属学报

2022, Vol. 58

Issue (9): 1118-1128 DOI: 10.11900/0412.1961.2021.00053

研究论文

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淬火速率对7136铝合金应力腐蚀开裂敏感性的影响

马志民¹^,²^,³, 邓运来¹^,³, 刘佳², 刘胜胆¹^,³(

), 刘洪雷⁴

^1.中南大学材料科学与工程学院长沙 410083
^2.包头职业技术学院包头 014030
^3.中南大学有色金属材料科学与工程教育部重点实验室长沙 410083
^4.东北轻合金有限责任公司哈尔滨 150060

Effect of Quenching Rate on Stress Corrosion Cracking Susceptibility of 7136 Aluminum Alloy

MA Zhimin¹^,²^,³, DENG Yunlai¹^,³, LIU Jia², LIU Shengdan¹^,³(

), LIU Honglei⁴

^1.School of Materials Science and Engineering, Central South University, Changsha 410083, China
^2.Baotou Vocational and Technical College, Baotou 014030, China
^3.Key Laboratory of Non-Ferrous Metal Materials Science and Engineering, Ministry of Education, Central South University, Changsha 410083, China
^4.Northeast Light Alloy Company Ltd., Harbin 150060, China

引用本文:

马志民, 邓运来, 刘佳, 刘胜胆, 刘洪雷. 淬火速率对7136铝合金应力腐蚀开裂敏感性的影响[J]. 金属学报, 2022, 58(9): 1118-1128.
Zhimin MA, Yunlai DENG, Jia LIU, Shengdan LIU, Honglei LIU. Effect of Quenching Rate on Stress Corrosion Cracking Susceptibility of 7136 Aluminum Alloy[J]. Acta Metall Sin, 2022, 58(9): 1118-1128.

全文: PDF(3932 KB) HTML

摘要:

针对7xxx系铝合金的抗应力腐蚀性能对淬火速率敏感的问题,通过浸入式末端淬火和慢应变速率拉伸实验研究了淬火速率对7136铝合金应力腐蚀开裂(SCC)敏感性的影响规律。结果显示,随着淬火速率的减小,合金的SCC敏感性先增高后降低,淬火速率约为5.3℃/s时的SCC敏感性最高；SCC裂纹扩展方式由穿晶扩展转变为沿晶扩展。淬火速率越小淬火析出相越多,尺寸越大,晶界和亚晶界附近的无沉淀析出带越宽。淬火速率大于5.3℃/s时,晶界析出相中Zn、Mg元素含量随淬火速率减小迅速增加,而淬火速率小于5.3℃/s后,Cu元素含量迅速增加。晶界和亚晶界析出相形貌特征以及晶界析出相化学成分的变化是SCC敏感性随淬火速率减小先增加后降低的主要原因。

关键词 ：铝合金, 应力腐蚀开裂, 淬火速率, 微观组织

Abstract：

7xxx series aluminum alloys are well-known structural materials, and they have been used in various fields, such as aerospace and vehicle, owing to their low density, high strength, and good formability. However, they are susceptible to stress corrosion cracking (SCC). SCC reduces the service life of these alloys and limits their application. With the development of the aerospace and vehicle industries, high-strength 7xxx series aluminum alloys are manufactured as semiproducts with large sections, such as thick plates, to avoid welding and jointing defaults. Quenching is a critical step for producing thick plates because their properties, such as SCC susceptibility, are sensitive to the quenching rate, and the quenching rate is generally lower at the center layer than at the surface layer during quenching. In this study, the effect of quenching rate on the SCC susceptibility of 7136 aluminum alloy was investigated using immersion end-quenching technique and slow strain rate tensile (SSRT) test. The strength, elongation, and fracture time of the samples after SSRT in oil and NaCl solution were obtained, and the crack features on and near the fracture surface were examined using SEM. SCC susceptibility was evaluated using the reduction rates of strength, elongation, fracture time, and stress corrosion sensitivity index (I_SSRT). The mechanism is discussed herein based on microstructural examination using SEM, EBSD, STEM in a HAADF mode, and EDS. Results show that the SCC susceptibility of the alloy first increases and then decreases with the decrease in the quenching rate. The SCC susceptibility is the highest at the quenching rate of approximately 5.3°C/s with the Ithe number and size of quench-induced precipitates increase gradually, and the precipitate free zones (PFZs) near grain boundary (GB) and subgrain boundary (SGB) widen; and the contents of Zn and Mg in precipitates at grain boundaries increase rapidly when the quenching rate is greater than 5.3^oC/s, and Cu content increases rapidly when the quenching rate is lower than 5.3^oC/s. The quench-induced changes in the morphology and chemical composition of precipitates at GB/SGB are the main reasons for the SCC susceptibility to increase first and then decrease with the decrease in the quenching rate.

Key words： aluminum alloy stress corrosion cracking quenching rate microstructure

收稿日期: 2021-01-29

ZTFLH:

TG146.2

基金资助:国家重点研发计划项目(2016YFB0300901);内蒙古自治区高等学校科学研究项目(NJZY21092)

作者简介: 马志民,男,1981年生,博士生

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图1 末端淬火示意图及慢应变速率拉伸试样尺寸

图2 7136铝合金试样不同位置的时间-温度曲线与平均淬火速率

图3 淬火速率为263.0、5.3和1.8℃/s时7136铝合金试样的应力-应变曲线

图4 不同淬火速率下7136铝合金试样的强度、伸长率及断裂时间及相应的下降率(KR、KA、Kt)

图5 不同淬火速率下7136铝合金试样的应力腐蚀敏感指数(ISSRT)

图6 在NaCl溶液中的不同淬火速率下7136铝合金试样断口形貌的SEM像

图7 在NaCl溶液中不同淬火速率下7136铝合金试样断口附近的SEM像

图8 不同淬火速率7136铝合金试样纵截面晶粒取向分布图

图9 不同淬火速率7136铝合金试样的SEM像

图10 不同淬火速率7136铝合金试样的STEM-HAADF像

图11 不同淬火速率7136铝合金试样晶界和亚晶界上析出相的特征参数

图12 淬火速率为263.0℃/s时7136铝合金试样晶界处的STEM-HAADF像和EDS面扫描图

图13 不同淬火速率7136铝合金试样晶界析出相中Zn、Mg、Cu元素的含量

图14 不同淬火速率下7136铝合金应力腐蚀开裂裂纹扩展示意图

图15 淬火速率为5.3和1.8℃/s时7136铝合金试样中不同无沉淀析出带宽度的晶界和亚晶界的比例

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