Effect of various non-isothermal aging on properties and microstructure of 7055 aluminum alloy

Abstract

This study investigated the effect of various non-isothermal aging processes on the mechanical properties and corrosion resistance of 7055 aluminum alloy extruded bars. The investigation utilized electrical conductivity, mechanical properties, local corrosion resistance and slow strain rate tensile test combined with microstructure characterization techniques such as metallographic microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that the NIA-2 (120 °C→200 °C/30 min→120 °C, v = 30 °C/h) process significantly improves the strengths of the alloy compared to the T73 temper, the tensile strength and yield strength increase by 53.0 MPa–632.5 MPa and by 64.7 MPa–605.4 MPa respectively. Additionally, the maximum depths of intergranular corrosion (IGC) and exfoliation corrosion (EXCO) decrease from 80.6 μm to 97.7 μm–71.4 μm and 89.5 μm respectively. Therefore, the NIA-2 process can achieve both high strength and excellent corrosion resistance. Furthermore, the study shows that the sizes of grain boundary precipitates (GBPs) and matrix precipitates (MPs) increase with the sequence of NIA-1 (120 °C→200 °C→120 °C, v = 30 °C/h), NIA-2, and NIA-3 (120 °C→200 °C→120 °C, v = 20 °C/h) processes. The atomic percentages of Zn, Mg, and Cu in GBPs also vary with the different processes. The increases in the sizes of GBPs, MPs, and the widths of precipitation-free zones (PFZs), as well as the segregations of GBPs components, are primarily responsible for the improved mechanical properties and corrosion resistance of the alloy.

Keywords

• 7055 aluminum alloy
• Non-isothermal aging
• Microstructure
• Mechanical properties
• Local corrosion performance
• Stress corrosion cracking