<strong>7055</strong>铝合金的非等温双级时效行为

doi:10.11900/0412.1961.2020.00039

金属学报

2020, Vol. 56

Issue (11): 1495-1506 DOI: 10.11900/0412.1961.2020.00039

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7055铝合金的非等温双级时效行为

李吉臣¹, 冯迪¹^,²(

), 夏卫生², 郭为民³(

), 王国迎¹

1 江苏科技大学材料科学与工程学院镇江 212003
2 华中科技大学材料科学与工程学院武汉 430074
3 洛阳船舶材料研究所海洋腐蚀与防护重点实验室青岛 266237

The Non-Isothermal Double Ageing Behaviour of 7055 Aluminum Alloy

LI Jichen¹, FENG Di¹^,²(

), XIA Weisheng², GUO Weimin³(

), WANG Guoying¹

1 School of Materials Science and Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, China
2 School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
3 State Key Laboratory for Marine Corrosion and Protection, Luoyang Ship Material Research Institute, Qingdao 266237, China

引用本文:

李吉臣, 冯迪, 夏卫生, 郭为民, 王国迎. 7055铝合金的非等温双级时效行为[J]. 金属学报, 2020, 56(11): 1495-1506.
Jichen LI, Di FENG, Weisheng XIA, Weimin GUO, Guoying WANG. The Non-Isothermal Double Ageing Behaviour of 7055 Aluminum Alloy[J]. Acta Metall Sin, 2020, 56(11): 1495-1506.

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摘要:

采用硬度测试、电导率测试、室温拉伸实验、剥落腐蚀实验、DSC分析以及TEM观察，研究了非等温双级时效对7055铝合金组织及性能的影响。结果表明：在第二级时效的连续升温阶段，晶内由GP区、η′和α-Al三相共存状态逐渐演变为η′、η和α-Al三相共存态。在第二级时效的连续降温阶段，晶内二次析出GP区和η′相，合金硬度再次升高。晶界η相在时效过程中不断粗化并呈断续分布，合金电导率持续增加。非等温双级时效的第二级升温速率和最高时效温度(T_p)决定了合金的性能。在相同性能水平下，快速升温对应相对更高的T_p。以电导率22 MS/m为标准，1 ℃/min升温速率对应的T_p为215 ℃，而3 ℃/min升温速率下T_p则为225 ℃。经过105 ℃、24 h预时效并包含升降温的非等温二级时效，7055铝合金的抗拉强度和剥落腐蚀等级可达610 MPa和EB级别，表现出比T6和T73态更加优异的综合性能，且取消等温保温阶段实现了热处理工艺的短流程操作。

关键词 ： 7055铝合金, 非等温时效, 强度, 剥落腐蚀

Abstract：

Thick plates of 7055 aluminum alloy are widely used as structural components, especially in the aerospace industry, due to their high strength, low density, excellent hot workability, and high stress-corrosion resistance, which are dependent on the type of thermal treatment the alloy is subjected to. Because of the heating and cooling stages in such components, non-isothermal ageing has attracted a lot of research interests. Replacing isothermal ageing with non-isothermal ageing is needed for higher efficiency and practicability. Herein, a novel isothermal-ageing technique based on double ageing is developed. Hardness test, electrical conductivity test, room-temperature tensile test, exfoliation corrosion test, DSC, and TEM analyses were employed to study the influence of non-isothermal double ageing on microstructure and properties of the 7055 aluminum alloy. The results showed that in the heating stage of the second ageing treatment, inner grains of the microstructure evolved from a three-phase coexistence state containing the GP zone, η′ phase, and α-Al to that containing η′ phase, η phase, and α-Al. On the other hand, in the continuous cooling stage of the second ageing, GP zone and η′ phase re-precipitated, resulting in improved hardness. The η phase on the grain boundary became coarse and discontinuously distributed, which resulted in a progressive improvement of the electrical conductivity. The heating rate and highest ageing temperature (T_p) of the second ageing stage determined the final properties. With a standard electrical conductivity of 22 MS/m, 1 ℃/min heating rate corresponds to the T_p of 215 ℃, while T_p of 225 ℃ is needed when heating by 3 ℃/min. After pre-aged by 105 ℃, 24 h and non-isothermal ageing including heating and cooling stages, the strength and exfoliation corrosion resistance of approximately 610 MPa and EB level were achieved, respectively. The alloy showed a better comprehensive performance than the T6 and T73 state ones. Additionally, the non-isothermal ageing removing the heat preservation stage realized the short process preparation.

Key words： 7055 aluminum alloy non-isothermal ageing strength exfoliation corrosion

收稿日期: 2020-02-10

ZTFLH:

TG146.2

基金资助:国家自然科学基金项目(51801082);海洋腐蚀与防护重点实验室开放研究基金项目(KF190409)

作者简介: 李吉臣，男，1997年生，硕士生

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https://www.ams.org.cn/CN/10.11900/0412.1961.2020.00039 或 https://www.ams.org.cn/CN/Y2020/V56/I11/1495

图1 7055铝合金非等温时效工艺示意图

图2 1和3 ℃/min加热速率下7055铝合金升温时效和随后炉冷时效(部分温度点)过程的电导率演变曲线

图3 1和3 ℃/min加热速率下7055铝合金升温时效和随后炉冷时效(部分温度点)过程的硬度演变曲线

表1 不同时效状态下7055铝合金的性能

图4 不同时效状态试样的剥落腐蚀形貌

图5 不同时效状态试样晶内析出相的TEM像及选区电子衍射(SAED)谱Color online

图6 不同时效状态下晶界的TEM 像

图7 第一级时效以及升温时效过程中沉淀相的TEM像及其SAED谱 (3 ℃/min)

图8 不同升温时间点试样的DSC曲线(升温速率为3 ℃/min)

图9 不同降温时间点试样的DSC曲线(Tp=225 ℃)

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