Influence of Surface Nanocrystallization and Partial Amorphization Induced by Ultrasonic Shot Peening on Surface Propert
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Influence of Surface Nanocrystallization and Partial Amorphization Induced by Ultrasonic Shot Peening on Surface Properties of 7075 Aluminum Alloy Lihua Zhu, Yanjin Guan, Zongshen Wang, Hongyu Zheng, Jun Lin, Jiqiang Zhai, and Zhendong Xie Submitted: 9 May 2020 / Revised: 16 September 2020 / Accepted: 23 September 2020 This paper investigates the influence of ultrasonic shot peening (USP) on the surface microstructure, hardness, roughness, and corrosion resistance of 7075 aluminum alloy. After the USP treatment, both surface nanocrystallization and partial surface amorphization of 7075 aluminum alloy were observed by XRD, SEM, and TEM methods. The results showed that the average surface grain size was refined to about 30 nm, while maximal surface amorphization percentage reached 43.68%. Both surface hardness and roughness increased with the peening duration, and their interplay was discussed. The maximal surface hardness achieved in this work was 249.60 HV, which is 46% higher compared to the original specimen. Besides, corrosion resistance initially increased with the peening duration and then decreased when the peening duration exceeded 200 s. The influence of both surface microstructure and roughness on the corrosion resistance was also analyzed. Keywords
aluminum alloy, corrosion resistance, partial amorphization, surface hardness, surface roughness, ultrasonic shot peening
1. Introduction Aluminum alloys have a wide range of applications, and they are a golden standard in aviation, aerospace, shipbuilding, nuclear, and weaponry industry due to their high specific strength, excellent corrosion resistance, and formability (Ref 1, 2). However, the fast development of industry placed new, higher demands in terms of strength, hardness, corrosion resistance, and other properties in front of aluminum alloys. Surface nanocrystallization (SNC) is a useful and practical approach to enhance surface properties and decrease failures that originate from the surface, improving the integral performance of the material (Ref 3). Many SNC methods were developed so far, like surface mechanical attrition treatment (SMAT) (Ref 4), severe shot peening (Ref 5), ultrasonic shot peening (USP) (Ref 6), ultrasonic impact treatment (Ref 7, 8), surface rolling (Ref 9), laser peening (Ref 10), etc. USP, a mechanical surface treatment that uses ultrasonic vibrations as an energy source to accelerate shots to strike materialsÕ surface consecutively (Ref 11, 12), was considered as one of the most effective SNC treatments (Ref 13), successfully realized SNC Lihua Zhu, Zongshen Wang, and Hongyu Zheng, School of Mechanical Engineering, Shandong University of Technology, Zibo 255000, PeopleÕs Republic of China; Yanjin Guan, Jun Lin, and Jiqiang Zhai, Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials (Ministry of Education), Shandong University, Jinan 250061, PeopleÕs Republic of China; Zhendong Xie, School of Aeronautics, Shandong JiaoTong University, Jinan 250357, PeopleÕs Republic
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