Effect of Er on Microstructure and Corrosion Behavior of Al–Zn–Mg–Cu–Sc–Zr Aluminum Alloys

Abstract

In this study, the influence of Er addition on the microstructure, type transformation of second phases, and corrosion resistance of an Al–Zn–Mg–Cu alloy were explored. The results revealed that the added Er element could significantly refine the alloy grains and change the second-phase composition at the grain boundary of the alloy. In the as-cast state, the Er element significantly enhanced the corrosion resistance of the alloy due to its refining effect on the grains and second phases at the grain boundary. The addition of the alloying element Er to the investigated alloy changed the type of corrosion attack on the alloy’s surface. In the presence of Er, the dominant type of corrosion attack is pitting corrosion, while the alloy without Er is prone to intergranular corrosion attack. After a solution treatment, the Al8Cu4Er phase was formed, in which the interaction with the Cu element and the competitive growth relation to the Al3Er phase were the key factors influencing the corrosion resistance of the alloy. The anodic corrosion mechanism of the Al8Cu4Er and Al3Er phases evidently lowered the alloy corrosion rate, and the depth of the corrosion pit declined from 197 μm to 155 μm; however, further improvement of corrosion resistance was restricted by the morphology and size of the Al8Cu4Er phase after its formation and growth; therefore, adjusting the matching design of the Cu and Er elements can allow Er to improve the corrosion resistance of the Al–Zn–Mg–Cu aluminum alloy to the greatest extent.

Investigating the effects of deformation-induced densification on the constitutive behavior and corrosion resistance of Al–Zn–Mg powder metallurgy alloy during hot deformation

“…Therefore, OCP can be a thermodynamic indicator for a relative driving force for the reaction and be a kinetics indicator for a relative corrosion rate. It can be observed from Table 2 that the OCP values are lower than those reported in previously mentioned literature: −0.89 V versus SCE for Al-Zn-Mg-Cu-Sc, 16 −0.93 V versus SCE for deformed Al-Mg, 38 −1.0 V Ag/AgCl for Al-Mg-Sc, 39 and −0.96 V Ag/AgCl for Al-Mg, 40 even though the alloys share a similar composition, despite variations in composition and alloying elements. However, in our study, the majority of OCP values are notably low, exceeding −1 V versus SCE.…”

“…Plastic deformation via cold rolling, 13 extrusion, 14 and equal channel angular pressing 15 decreased the corrosion resistance of the material as demonstrated by the increase in corrosion current (i corr ) and lowered critical pitting potential (E pit ). Xing et al 16 investigated the impact of Er addition on the microstructure and corrosion resistance of an as-cast Al–Zn–Mg–Cu alloy by traditional metal mold casting, revealing that Er refines grains, alters second-phase composition, and shifts corrosion from intergranular to pitting, with Al8Cu4Er phase enhancing corrosion resistance, but with limitations due to phase morphology and size. Wang et al 17 studied the enhancement of corrosion resistance and strength in Al–4.5Cu–3.5Zn–0.5Mg cast alloy through a novel non-isothermal aging (NIA) treatment, which leads to improved mechanical properties and reduced corrosion depth, whereas plastic deformation via high-pressure torsion increases the corrosion resistance of Al–Mg–Sc alloy due to the creation of a more surface-protective oxide layer.…”

Improving the Thermal Stability of the Fine-Grained Structure in the Cu-15Ni-8Sn Alloy during Solution Treatment by the Additions of Si and Ti

“…High temperature solution treatments are able to promote the formation of supersaturated solid solutions, providing a chemical driving force for Spinodal decomposition and ordering transformation [ 11 , 12 ], but they often lead to uncontrollable grain coarsening, encroaching on the superior ductility induced by the fine-grain structure via the hot extrusion process. A large number of studies have shown that the addition of trace elements can result in the development of the drag effect on solid solution atoms and the pinning effects on the insoluble second phase, which shows an important role of the suppression of grain boundary migration during solution treatment [ 13 , 14 , 15 , 16 ]. At present, a thorough investigation of the effect of trace elements on the grain growth kinetics and the thermal stability of grains is lacking and is critical to seek a way to realize the synergy of superior strength and high ductility of the Cu-15Ni-8Sn alloy.…”

Effect of Sm + Er and Heat Treatment on As-Cast Microstructure and Mechanical Properties of 7055 Aluminum Alloy

“…In contrast, Sm and Er could form rare earth phases in aluminum alloy and were cheaper than Sc. The rare earth phase could fix the grain boundary during solid solution treatment, and the rare earth atoms could provide more nucleation sites for the precipitation of the η’ phase, which make it smaller during the aging treatment, thus refining the grain [ 16 , 17 , 18 ]. At the same time, the strongest strengthening effect was present in Er, which effectively prevented grain boundary displacement during its melting process and significantly raised the tensile strength and yield strength of aluminum alloy [ 19 ].…”