Reaching improved surface quality and strength in highly formable AlMg-based alloysWednesday (06.11.2019) 17:20 - 17:40 Part of:
The global need to reduce CO2 emissions and to save energy is putting enormous pressure on utilizing materials oriented lightweight design. Hence, the automotive industry is increasingly using aluminium alloys to reduce the total car weight. Unfortunately, aluminium alloys show a limited formability and strength compared to steels. Nowadays, alloys of the 6xxx and 5xxx series are frequently used, but the first show limited formability and the second exhibit low strength and, after forming, poor surface quality due to the appearance of stretcher-strain marks. Here we address improvements of the surface quality of the highly formable AlMg-based 5xxx-series alloys via a processing-controlled suppression of Lüders elongation. The decisive measure for suppressing Lüders-strain marks is based on the formation of non-aged dislocations. We demonstrate that these can be created intrinsically by utilization of the difference in the thermal expansion of matrix and certain primary constituents upon quenching. Moreover, we discuss the effect of alloying elements. The phenomena of 5xxx series alloys having fully suppressed dynamic strain aging and extended plastic deformation at cryogenic temperatures is discussed as a future perspective to enable the production of complex light-weight parts. Finally, a novel design strategy to produce high strength 5xxx series alloys by utilizing precipitation hardening is discussed.