A study on the phase transformation of γ2-Al8Mn5 to LT-Al11Mn4 during solutionizing in AZ91 alloy

• Published in: Journal of alloys and compounds 2021-08, Vol.873, p.1, Article 159836
• Main Authors: Sarvesha, R., Ghori, Ubaid-ur-Rehman, Thirunavukkarasu, G., Chiu, Yu Lung, Jones, Ian P., Jain, J., Singh, S.S.
• Format: Article
• Language: English
• Subjects: Alloys; Aluminum base alloys; Atom probe tomography; AZ91; Corrosion resistance; Electron microscopes; Low temperature; LT-Al11Mn4; Magnesium base alloys; Mechanical properties; Morphology; Phase stability; Phase transitions; Stability analysis; Transmission electron microscopy; γ2-Al8Mn5
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2021.159836

•γ2-Al8Mn5 phase transformed to LT -Al11Mn4 phase due to uphill diffusion of Al.•Shell type structure developed where LT -Al11Mn4 shell encapsulated γ2-Al8Mn5 phase.•Higher volume of LT-Al11Mn4 phase resulted in cracks in the shell.•Si, Fe and Mg content decreased in the LT-Al11Mn4 during solutionizing. [Display omitted] γ2-Al8Mn5 intermetallic particles are generally present in commercial Mg-Al-Zn alloys. The present study is concerned with the effect of solutionizing on the morphology and phase stability of the γ2-Al8Mn5 particles in an as-cast AZ91 alloy. Analysis using energy dispersive spectroscopy (EDS) and electron back scattered diffraction (EBSD) in a scanning electron microscope (SEM), transmission electron microscopy (TEM) and atom probe tomography (APT) suggests that solutionizing resulted in uphill diffusion of Al from the α-Mg matrix resulting in the phase transformation of γ2-Al8Mn5 to Low Temperature (LT) -Al11Mn4 phase. This leads to a shell type structure of LT-Al11Mn4 encapsulating γ2-Al8Mn5 and the formation of cracks in the LT-Al11Mn4 phase. These can propagate during external loading, affecting the mechanical properties. Additionally, the content of Fe and Si decreased in the LT-Al11Mn4, which could potentially decrease locally the corrosion resistance.