Luis Ricardo Jacobo

Grain refinement is one of the strategies for improving the mechanical properties of metal alloys, and one of the most effective methods is severe plastic deformation (SPD), particularly the extrusion process (ECAP), as it allows large deformations to be induced in the material. This study analyzed the microstructural and mechanical evolution of a ZINAG alloy (74%Zn-22%Al-4%Ag) processed by ECAP. The alloy was obtained by casting and then heat-treated at 350°C for 60 minutes, followed by quenching in water at room temperature. The ECAP process was carried out at room temperature following the B _c route, applying 2, 4, 6, and 8 deformation passes at a strain rate of 1.282×10⁻⁴ s⁻¹. The mechanical properties were evaluated using Vickers microhardness and tensile tests at a strain rate of 2.088×10⁻⁵ s⁻¹. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses showed significant grain refinement and the formation of AgZn₃ (ε) and Ag ₃ Al (δ) intermetallic compounds, which may contribute to superplasticity close to 600%. Likewise, the required deformation stress and microhardness decreased with increasing number of passes, while the maximum elongation was obtained with four deformation passes. The ECAP process proved to be effective in optimizing the microstructure and superplastic properties of the 74%Zn-22%Al-4%Ag alloy.

Purpose: The purpose of this paper is to study the effect of heat treatment (HT) applied to an API X60 steel in corrosion resistance and stress corrosion cracking (SCC) susceptibility through slow strain rate tests (SSRT) in NS4 solution and congenital water (CW) to assess external and internal SCC, respectively.Design/methodology/approach: API X60 steel was heat treated at a temperature of 1,200°C for 30 min followed by water quenching. Specimens from this steel were machined according to NACE TM 198. SSRT were performed in a constant extension rate tests (CERT) machine at room temperature at a strain rate of 1 × 10^–6s^–1. For this purpose, a glass cell was used. Corrosion behavior was evaluated through polarization curves (PCs).Findings: The SCC index obtained from SSRT indicates that the steel heat treated could be susceptible to SCC in CW and NS4 solution; the mechanism of SCC was hydrogen embrittlement. Thus, CW may promote the SCC phenomenon in pipelines. HT improves the steel corrosion resistance. Higher corrosion rate (CR) was observed when the steel is exposed to CW. The corrosion process in X60 steel shows that the oxidation reaction in the anodic branch corresponds to an activation process, and the cathode branches reveal a diffusion process.Originality/value: The purpose of the heat treatment applied to X60 steel was to generate a microstructure of acicular ferrite to improve the corrosion resistance and SCC behavior.