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金属学报  2017, Vol. 53 Issue (9): 1075-1090    DOI: 10.11900/0412.1961.2017.00047
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高强7050铝合金超低温大变形加工与组织、性能调控
侯陇刚1(), 刘明荔1, 王新东2, 庄林忠1, 张济山1
1 北京科技大学新金属材料国家重点实验室 北京 100083
2 北京科技大学冶金与生态工程学院 北京 100083
Cryogenic Processing High-Strength 7050 Aluminum Alloy and Controlling of the Microstructures and Mechanical Properties
Longgang HOU1(), Mingli LIU1, Xindong WANG2, Linzhong ZHUANG1, Jishan ZHANG1
1 State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China
2 School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, China
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摘要: 

通过低温冷却+轧制变形的方法研究了高强7050铝合金的低温塑性变形及其对合金组织性能的影响。结果表明,高强7050铝合金经液氮冷却预处理后可实现与温/热轧相比较高的轧制变形加工量,并产生大量亚结构和高密度位错,使合金显著强化,其中低温下的高变形能力主要与合金在低温下具有高的加工硬化能力密切相关,而强度提升主要来自于固溶强化和变形位错强化的贡献。虽然超低温变形能够明显加快淬火态高强7050铝合金的时效进程,但直接时效处理可使超低温变形态7050铝合金保有较高的强度和一定延伸率,其中析出和位错强化是其强化主因,而时效引起的回复和强化相析出共同促进延伸率的改善。淬火态高强7050铝合金在室温变形过程中,形变热引起基体中析出的溶质原子团簇(或GP区)和η′相与变形位错发生交互作用,导致大量剪切带(失稳区)形成,从而易引发轧板开裂或边裂,而超低温变形过程中溶质扩散受阻以致强化相析出被抑制,从而明显降低了剪切失稳区的发生,使合金能够获得均匀、稳定的塑性变形或良好的加工硬化,确保获得较高质量的超低温轧板。高强铝合金在低温下所表现出来的优异塑性变形和加工能力有望成为改善高强铝合金难变形加工的有效途径。

关键词 高强铝合金超低温变形组织力学性能加工硬化    
Abstract

The high strength or flow stress as well as low plastic deformability of 7000 series Al alloys makes it difficult to improve their microstructures and mechanical properties by cold processing, and many advanced alloying methods and processing technologies are continually developed for higher mechanical properties and acceptable elongation. In this work, the cryogenic deformation (rolling) was applied to process high-strength 7050 Al alloys, and its effects on the microstructures and mechanical properties were studied. The results showed that after the pre-cooling with liquid nitrogen, the quenched 7050 Al alloy can obtain much higher rolling reduction, similar to that under warm or hot rolling, and a great number of substructures and high-density dislocations were formed which greatly increased the strength. The higher cryogenic deformability would be mainly related with the higher work-hardening ability at low temperature, while the strength enhancement would be largely attributed to the solution strengthening and dislocation strengthening. The cryogenic deformation can obviously stimulate the ageing process of the quenched 7050 Al alloy, but the direct ageing of the cryogenic-rolling 7050 Al alloy can assure higher strength and acceptable elongation, which would be greatly attributed to the precipitation strengthening and dislocation strengthening, while the recovery and ageing-induced precipitates help improving the tensile elongation. During room-temperature rolling, the formation of GP zones and η′ phases caused by the heats transformed from the deformation as well as their interaction with dislocations leads to the appearance of amounts of shear bands (instability areas), which will easily cause the cracking or edge-cracking of the rolling sheets. However, the cryogenic rolling with distinctly impeding the solute diffusion can result in the suppression of precipitation of the strengthening phases so as to decrease the occurrence of the shear instability areas, and uniform and stable plastic deformation or good work-hardening as well as high-quality rolling sheets are obtained. The excellent plastic deformability of high-strength Al alloys at cryogenic temperatures could be suggested as an effective way to improve the processing of high-strength Al alloys.

Key wordshigh-strength Al alloy    cryogenic deformation    microstructure    mechanical property    work-hardening
收稿日期: 2017-02-15     
ZTFLH:  TG146.2  
基金资助:国家自然科学基金项目No.51401016,中央高校基本科研业务费专项资金项目No;FRF-TP-12-137A,现代交通金属材料与加工技术北京实验室项目及新金属材料国家重点实验室基金项目No.2011Z-05
作者简介:

作者简介 侯陇刚,男,1982年生,博士

引用本文:

侯陇刚, 刘明荔, 王新东, 庄林忠, 张济山. 高强7050铝合金超低温大变形加工与组织、性能调控[J]. 金属学报, 2017, 53(9): 1075-1090.
Longgang HOU, Mingli LIU, Xindong WANG, Linzhong ZHUANG, Jishan ZHANG. Cryogenic Processing High-Strength 7050 Aluminum Alloy and Controlling of the Microstructures and Mechanical Properties. Acta Metall Sin, 2017, 53(9): 1075-1090.

链接本文:

https://www.ams.org.cn/CN/10.11900/0412.1961.2017.00047      或      https://www.ams.org.cn/CN/Y2017/V53/I9/1075

图1  淬火态7050铝合金板材经室温与超低温轧制后的形貌
图2  淬火态7050 铝合金板材经RTR和LN2R变形后的微观组织
图3  70%和91%LN2R态7050铝合金中存在的亚结构、位错胞及淬火态合金中的亚晶
图4  350 ℃、1 h过时效态7050铝合金经60%RTR、77%RTR及66%LN2R变形后的组织TEM像
Rolling process Heat treatment σy / MPa σb / MPa δ / %
Original T6 (120 ℃, 24 h) 507 565 11.6
80% hot rolling[30] T6 518 600 16.8
80%LN2R No 571 624 7.0
(10% per pass)
82.5%LN2R No About 625 676~682 8.6~9.4
(20% per pass)
91%LN2R
(10% per pass)
No 650 690 About 3.0
80 ℃, 24 h 578~583 639 11.5~13.6
80 ℃, 48 h 589 642 9.0
80 ℃, 72 h 591 650 12.0
100 ℃, 24 h 601 636 8.2
120 ℃, 24 h 570~573 601~606 5.3~8
475 ℃, 0.5 h+T6 498 590 15.3
PA 602~605 650~653 6.6~7.8
7050 T7651 455 524 8.0
表1  不同状态7050铝合金板材的室温拉伸性能
图5  LN2R态7050铝合金在不同状态下的室温拉伸曲线
图6  淬火态7050铝合金经63%RTR变形后的微观组织
图7  固溶态及91%LN2R态7050铝合金在不同时效态下的DSC曲线
图8  91%LN2R态7050铝合金在80 ℃时效24和48 h后的TEM像及HRTEM像
图9  91%LN2R态7050铝合金经不同时效处理后的TEM及HRTEM像
图10  淬火态7050铝合金经RTR变形、91%LN2R变形及时效处理后的XRD谱
图11  淬火态7050铝合金在不同温度和应变速率下单轴压缩真应力-应变曲线及应力幅值的变化
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