Yasin Mehdizadeh, Saeed Reza Allahkaram, Mohammad H.mohammad-Ebrahimi, Majid Shamsarjmand,
Volume 22, Issue 4 (December 2025)
Abstract
The present work deals with the corrosion behavior and mechanical properties of a coted AZ31 magnesium alloy through plasma electrolyte oxidation (PEO) coating process in different alkaline electrolytes based on sodium silicate (Si-coating), sodium polyphosphate (P-coating) and sodium aluminate (Al-coating). The scanning electron microscopy (SEM) equipped with the energy dispersive x-ray spectroscopy (EDX) plus x-ray diffraction were recruited to investigate the morphology, chemical composition, and phase structure of coatings, respectively. Microscopic scrutiny revealed that the coating in the phosphate electrolyte was twice as thick and the relative porosity percentage was higher than those formed in the other electrolytes. The phase analysis indicated that the MgO was present as the prevailing phase in the Al-coating and P-coating. However, the dominant phase in the Si-coating was Mg2SiO4. Electrochemical testing was examined in a solution containing 3.5.wt% sodium chloride, showing improvements in corrosion resistance of coated alloys. These investigations confirmed that the corrosion resistance of Si-coating was dramatically higher than others which could be attributed to the presence of the dense and stable Mg2SiO4 phase as well as its relatively low porosity. According to the results of tensile tests, the coated samples had lower tensile strength and elongation than the uncoated one. The tensile strength and elongation diminished upon changing the electrolyte from Al-coating to P-coating, while the yield strength was almost similar. Further analyses indicated that the drop of tensile strength and elongation could be attributed to the presence of cracks and pores in the brittle ceramic PEO coating as stress concentration regions during deformation. Those areas are created due to thermal stress during the coating process and deformation in the elastic stage.
Sahar Ziraki, Amir Moghaddam Kia, Ramin Ebrahimi,
Volume 22, Issue 4 (December 2025)
Abstract
In this study, an existing approach for estimating fatigue life using tensile data was extended and applied to 4340 steel under different temperature. The S-N and strain-life curves were plotted at 25, 200, and 350 ˚C. The Basquin and Coffin-Manson equation constants were determined based on the corrected true fracture stress and strain values. Moreover, the b constants were approximated as -0.065, -0.072, and -0.073 at 25, 200, and 350 ˚C, respectively. This was achieved by setting the alternating stress equal to the fatigue limit in an infinite number of cycles when b leveled off. The transition fatigue life of 1000 cycles was considered for 4340 steel to determine the c constants, which were determined to be -0.69, -0.7, and -0.699, at 25, 200, and 350 ˚C, respectively and the strain-life curves were plotted. Comparison of S-N curves obtained from both fatigue and tensile data revealed strong agreement, indicating that the tensile test is a simple and cost-effective method capable of providing a quick estimate of high- and low-cycle fatigue behavior and serving as a suitable alternative to conventional fatigue testing.
