Effect of PWHT on microstructure and corrosion resistance of the nugget zone in AZ31 friction stir weld

• Published in: International journal of advanced manufacturing technology 2022-12, Vol.123 (7-8), p.2757-2769
• Main Authors: Amara, Khawla, Badji, Riad, Bouabdallah, Mabrouk, Cheniti, Billel, Aissani, Mouloud, Haddad, Ahmed, Ziouche, Aicha
• Format: Article
• Language: English
• Subjects: CAE) and Design; Computer-Aided Engineering (CAD; Corrosion; Corrosion effects; Corrosion rate; Corrosion resistance; Electrochemical impedance spectroscopy; Engineering; Friction stir welding; Grain boundaries; Grain size; Industrial and Production Engineering; Intermetallic compounds; Internal energy; Magnesium base alloys; Mechanical Engineering; Media Management; Metal compounds; Metal sheets; Microstructure; Original Article; Post-weld heat treatment
• ISSN: 0268-3768; 1433-3015
• DOI: 10.1007/s00170-022-10379-w

In the present work, the friction stir welding technique was employed to join AZ31 magnesium alloy sheets. The study aims at assessing the effect of post-weld heat treatment (PWHT) on the microstructural evolution and the corrosion behavior of the nugget zone (NZ) in the temperature range of 200—400 °C for 1 and 4 h. The results indicated that above 300 °C, increasing PWHT temperature resulted in a remarkable increase in the NZ grain size due to the reduction of the stored energy accumulated during the FSW process. It was found that the size and the fraction of Al 11 Mn 4 , inter-metallic compounds (IMCs), formed around the Al 8 Mn 5 particles increase with PWHT temperature and holding time. The electrochemical impedance spectroscopy (EIS) measurements performed in 3.5% NaCl solution revealed that the corrosion rate in the NZ decreases with increasing PWHT temperature up to 300 °C. This was confirmed by Kelvin probe force microscopy (KPFM) measurements where the grain boundaries exhibited a cathodic behavior and high Volta potential values with respect to the matrix values.