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The 7B85 aluminum alloy is one of the Al-Zn-Mg-Cu alloy series with light weight, high specific strength and good machinability that are extensively used in the transportation and aerospace industries.[1] However, aluminum (Al) alloys suffer from different forms of corrosion such as pitting corrosion, stress corrosion cracking and intergranular corrosion due to the aging strengthening of the alloys.[2–4] The surface structure affects the comprehensive performance of the alloys such as corrosion resistance, fatigue and wear performance.[5–7] Surface nanocrystallization (SNC) techniques can significantly change the surface microstructure of the

CHUNMING WANG, GUANMING XU, LUMING ZENG, XUEHUI ZHANG, and TONGXIANG LIANG are with the Faculty of Materials Metallurgy and Chemistry, Jiangxi University of Science and Technology, Ganzhou 341000, P.R. China. ZHENGHUA TANG is with the School of Materials Science and Engineering, Sichuan University, Chengdu 610064, P.R. China. Contact e-mail: [email protected] Manuscript submitted December 8, 2019.

METALLURGICAL AND MATERIALS TRANSACTIONS A

alloy through severe plastic deformation such as surface mechanical attrition,[5,6] laser/ultrasonic shot peening[3,7–9] and USRT.[10,11] The nanostructured surface layer induced by SNC methods can improve the microhardness, residual stress, friction resistance and corrosion resistance of the alloys. The surface roughness, compressive residual stress, microstrain and dislocation density play vital roles in the corrosion of the alloys.[3] Among these methods, the USRT has become increasingly popular in recent years because of the remarkable reduction of the surface roughness and damage of the alloys, which can be applied to improving the surface integrity, corrosion resistance, wear and fatigue performance of the materials such as stainless steel,[12–14] Ti alloy,[15–17] Mg alloy[18] and Al alloys.[10,11,19] In this study, to overcome the pressing issue regarding corrosion, we report an outstanding enhancement of the corrosion resistance and mechanical properties of 7B85 sheet alloy through USRT. The effects of USRT on the microstructure, corrosion behavior and mechanical properties of the 7B85-T6 alloy are investigated. The chemical compositions (wt pct) of the 7B85-T6 plate measured by X-ray fluorescence spectroscopy (XRF) were 7.33 pct Zn, 1.54 pct Mg, 1.09 pct Cu, 0.11 pct Zr, 0.04 pct Si, 0.03 pct Fe and balanced Al. The tensile specimens were machined from a 20-mmthick 7B85-T6 plate along the rolling direction, as shown in Figure 1. The USRT of the tensile samples was conducted by a numerical control machine with ultrasonic surface rolling equipment with the ultrasonic vibration frequency of 28 kHz. The basic experimental USRP parameters of the samples are shown in Table I. The phase constitution and texture analysis of the 7B85-T6 alloys before and after USRT were performed by X-ray diffraction (XRD) with Cu-Ka radiation at 40 kV and 25 mA. The pole figures were measured by the Schulz back-reflection method, and data were analyzed by the Textool