Abstract
Extruded Al-Zn-Mg-Cu alloy samples with grains aligned parallel to the extrusion direction were subjected to high-pressure annealing. The effects of annealing pressure on the microstructure, hardness, and corrosion properties (evaluated using potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS)) were investigated. Phase analysis showed the presence of MgZn2 and α-Al phases, the MgZn2 phase dissolved into the matrix, and its amount decreased with the increasing annealing pressure. The recrystallization was inhibited, and the grains were refined, leading to an increase in the Vickers hardness with increasing the annealing pressure. The corrosion resistance was improved after high-pressure treatment, and a stable passivation layer was observed. Meanwhile, the number of corrosion pits and the width of corrosion cracks decreased in the high-pressure annealed samples.
Highlights
The degree of recrystallization decreases with increasing annealing pressure
Strengthening due to grain refinement and solid solution strengthening leads to an increase in the Vickers hardness of the Al-Zn-Mg-Cu alloy from 132 to 180 HV
Eb increases and Ipass decreases with the increases in the annealing pressure
Summary
Al-Zn-Mg-Cu-based alloys are widely applied in the aerospace and automobile sectors due to their excellent properties, such as high specific strength, formability, and corrosion resistance [1,2,3]. As a liquid-phase process, casting is capable of producing lightweight bulk components and is conventionally used to fabricate Al-Zn-based alloys [4,5]. Casting is a simple and relatively low-cost process. It may lead to large dendritic microstructures, shrinkage during solidification, etc. The drawback of employing the conventional casting process is that the Zn content is restricted to 8 wt.% due to the presence of possible solidifying problems, such as microstructural coarsening, the macrosegregation of elements, and cracking [12,13,14]
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