Zn/Cu regulated critical strain and serrated flow behavior in Al-Mg alloys

Next-generation high performance aluminum alloys are required for lightweight strategies and advanced automotive applications. A current challenge for 5xxx series alloys is their poor strength and dreadful surface appearance caused by serrated yielding behavior during plastic deformation. Here we show that the serrated yielding behavior can be eliminated in Zn/Cu modified novel alloys, while simultaneously achieving above 100 MPa improvement of the strength at a pre-aging temper. The formation of GP zones of the precursor of T-Mg-32(AlZnCu)(49) phase during pre-aging treatment and the depletion of vacancies are mainly attributed to the elimination of dynamic strain aging. The critical strain shows a transformation from normal to inverse behavior with an increase of Zn content in the high-strength novel alloys. Such inverse behavior is because of the impediment of GP zones and solute atoms to the dislocations at lower strain rates. These results provide insight into the serrated yielding behavior of the aluminum alloys.