Role of dislocation density on the onset and intensity of stretcher strain marks in novel Al–Mg alloys with high Mg content

Abstract

The formation of stretcher strain marks (SSMs), or Portevin-Le Chatelier (PLC) bands, poses challenges in high Mg content Al–Mg alloys, affecting surface quality and mechanical performance. This study explores the role of dislocation density and recrystallization behavior in influencing the onset and characteristics of SSMs in Al-6Mg, Al-7.5Mg, and Al-8.5Mg alloys in the annealed condition. These alloys were prepared using an innovative casting method where Mg was alloyed with a Mg + Al2Ca master alloy (Eco-Al processing) to protect the melt. Tensile testing, digital image correlation (DIC), and electron backscatter diffraction (EBSD) were employed to investigate mechanical behavior and microstructural evolution. The findings indicate that higher Mg content increases dislocation density post-annealing, delaying the onset of SSMs by promoting uniform strain distribution and enhanced strain hardening, which reduces early and intense localized deformation. The presence of higher Mg also retards recrystallization due to the solute drag effect, restricting grain boundary movement and contributing to a more heterogeneous microstructure with stronger texture and a higher proportion of low-angle grain boundaries (LAGBs). These findings emphasize the complex interaction between Mg content, dislocation density, and microstructural evolution, offering strategies to optimize processing and alloy design to minimize SSMs formation and enhance alloy performance in demanding applications such as automotive and aerospace.

Keywords

• Al–Mg alloys
• Stretcher strain marks (SSMs)
• Portevin-le chatelier effect (PLC)
• Dislocation density
• Digital image correlation (DIC)
• Electron backscatter diffraction (EBSD)