Effect of Cu on the Fracture and Exfoliation Corrosion Behavior of Al-Zn-Mg-xCu Alloy

Huibin Jiao,Songyi Chen,Peng Xie,Shanda Chen,Kanghua Chen,Zhen Yang

doi:10.3390/met8121048

Abstract

In the present work, the influence of Cu content on microstructure, mechanical properties and exfoliation corrosion behaviors of Al-Zn-Mg-xCu alloy extrusions has been investigated in longitudinal-transverse (L-T) and short-longitudinal (S-L) directions by means of mechanical tensile and exfoliation corrosion testing combined with optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that a higher Cu content significantly decreased the fracture toughness and ductility of the alloy in S-L direction compared with L-T direction. Concomitant with the increase in Cu content, a transition in fracture mode was observed from transgranular dimpled rupture to intergranular rupture in S-L direction. Moreover, the exfoliation corrosion (EXCO) resistance of the alloy decreased as the Cu content increased and the exfoliation corrosion resistance of the alloy in short-transverse (S-T) direction was better than that of L-T direction. These results were mainly associated with the large number of coarse intermetallics caused by high Cu content in the L-T direction of alloy.

Highlights

Nowadays, the 7xxx series of aluminum alloys have been widely applied in the aerospace industry, profiting from their excellent combination of low density, high specific strength and high toughness [1,2]
Hu et al showed that the occurrence of the anisotropy in over-aged 7050 aluminum alloy was mainly attributed to the microstructures, which were further characterized by visible precipitate free zones (PFZs) and coarse precipitates ingrain boundaries [13]
A small amount of Cu can promote the precipitation of strengthening phase but when the content of Cu increases to a certain extent (Cu > 1.45 wt.%), the formed S(Al2 CuMg) phase will the content of Cu increases to a certain extent (Cu > 1.45 wt.%), the formed S(Al2CuMg) phase will consume the Mg element, which would result in the decrease of the η0 phase formation and the adverse consume the Mg element, which would result in the decrease of the η′ phase formation and the effect on the alloy strength [20]

Summary

Introduction

The 7xxx series of aluminum alloys have been widely applied in the aerospace industry, profiting from their excellent combination of low density, high specific strength and high toughness [1,2]. With the rapid development of the aerospace industry and the innovation of science and technology, the demand for large-scale structural parts of high strength Al-Zn-Mg-Cu aluminum alloy is more urgent. Aiming at the requirements of large-scale, integrated, lightweight and high-reliability of aerospace aluminum alloy structural parts, it is urgent to develop high-strength, high-toughness and thick-section aluminum alloy materials with low anisotropy and high hardenability to realize the integration of large and complex aluminum structural parts [3,4]. With the development of aerospace industry, the demand for large-sized cross-section components (especially thick plates) is becoming more and more urgent and the requirements such as hardenability and mechanical property uniformity of the alloy are becoming stricter [8,9,10].

Objectives

Methods

Results

Discussion

Conclusion