Effect Of Microstructure And Texture On The Formability And Serrated Deformation Behavior Of5xxx Series Aluminum Alloy

Al-Mg alloys have been considered for use in a wide variety of automotive applications due to their high strength to weight ratio and good formability. The formability is closely related to plastic anisotropy, which is intrinsically determined by crystallographic textures. Presently, by optimizing the Mg and the content of other alloying elements and rolling and annealing processes, the mechanical properties and formability of the alloy can be improved simultaneously. The effects of alloying elements, such as Mg, Zn and Cu, and cold rolling and recrystallization annealing processing parameters on the microstructure, mechanical properties anisotropy and texture of Al-Mg alloys developed for auto body sheets were investigated by OM, SEM, TEM, EBSD and tensile testing in detail. Moreover, the influences of alloy composition, strain rate and processing parameters on the serrated deformation behavior are studied. A qualitative explanation is made according to the mechanism of dynamic strain aging. The conclusions should be as follows:A newly developed5xxx series aluminum alloy having higher strength and formability was designed, which containing a composition of Al-6.1Mg-0.15Cu-0.2Mn-0.1Si-0.2Fe(wt%). After two times of cold rolling, intermediate annealing and recrystallization annealing at450℃for1h, compared to the standard5182alloy, mechanical properties of the newly developed alloy was greatly improved while maintaining its good formabilityFormability of the alloy showed a "^" type change with increasing Mg and Cu content. Alloying elements content does not change the texture components of the alloy, but it has a greater impact on the density and volume fraction of the textures. The texture density of the alloy was greatly reduced by particle stimulated nucleation and the rolling textures were retained by strain induced boundary migration after recrystallization annealing. These two aspects could improve the formability of the alloy. Formability of the alloy decreased with increasing final cold rolling reduction. The high formability was obtained under the condition of higher intermediate annealing temperature and higher final annealing temperature.The serrated deformation behavior happens in a wide range of loading strain rate. With decreasing strain rate, serrations in the stress-strain curve become more intense. The stress drop and reloading time of serrations increase with increasing plastic strain, and exhibit a common linear relationship. The increase rates of stress drop and reloading time increase with increasing Mg content. The stress drop and reloading time of serrations decrease with increasing grain size in the case of annealed samples. The cold-rolled sample exhibits the most severe serrations because it initially contains a large number of grain boundaries and dislocations.