Abstract
Laboratory-scale sheets of 5182-type AlMgMn alloys with varying Mg and Mn contents and additions of different amounts of Zn, Cu, Zr and Er were studied. The sheets were produced using two different cold-rolling degrees and two soft-annealing treatment procedures: air-circulated furnace annealing at 370 °C with subsequent furnace cooling, and salt-bath annealing with subsequent water quenching. Mechanical properties and deformation surface quality were studied via tensile tests with simultaneous visual surface characterization. The influence of the chemical composition and the processing route on grain size, mechanical properties, and surface quality is discussed in the study. A reduction in the Mg content improves the surface quality after plastic deformation, but at the expense of the mechanical properties. The results suggest the presence of an optimum Mn content in terms of optical appearance and mechanical properties. Adding Zr largely inhibits recrystallization, which is reflected in a textured microstructure. Adding Er affects neither the surface quality nor the mechanical properties. Specific combinations of Zn or Cu addition, cold-rolling degree, and heat treatment generate significant improvements in the mechanical and optical properties. In general, annealing at high temperature with subsequent quenching leads to enhanced surface quality and mechanical properties, and adding Zn enables further noteworthy improvements.
Highlights
AlMgMn alloys have a wide field of application, ranging from beverage cans to structural components [1]
Investigations into the influencing factors and underlying mechanisms have been conducted for some time to understand, reduce or eliminate the Lüders elongation and dynamic strain ageing (DSA), which cause these various kinds of SSM
Because of inconsistencies in the straightforward d−0.5 dependence of the Lüders elongation, the authors of this study recently proposed a new interpretation of this dependence [36]
Summary
AlMgMn alloys have a wide field of application, ranging from beverage cans to structural components [1]. Because of their well-balanced properties and favourable production costs, 5xxx series alloys have become a field of special interest in the automotive industry, complementing or even replacing 6xxx series alloys. The major drawback to using AlMgMn alloys in visible car parts, e.g., fenders or bonnets, is their non-decorative surface effects (Lüders lines and stretcher strain marks (SSM). Investigations into the influencing factors and underlying mechanisms have been conducted for some time to understand, reduce or eliminate the Lüders elongation and dynamic strain ageing (DSA), which cause these various kinds of SSM. The first concept involves the pinning of dislocations by Cottrell-like clouds of Mg atoms
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