Influence of Rolling Conditions on the Microstructure and Mechanical Properties of Magnesium Sheet AZ31

Abstract

The main reason for using lightweight metals in the automotive industry is the potential saving of natural energy resources simply by weight reduction. Magnesium, as the lightest available construction metal, offers a wide range of opportunities for use in automobiles. At present mostly cast parts are used and the use of wrought magnesium alloys is still well below the potential. [1] There are two main reasons for this: a lack of sufficient cold formability and the anisotropy of the properties of the finished sheets. [2,3] Also, the rolling process is not adequately developed and still needs a lot of improvement to produce material with the required properties.Generally, mechanical properties are affected by grain size, microstructural homogeneity, and texture. [4] In a plastic deformation process such as rolling, the process parameters cause changes in the microstructure, which determine the mechanical properties. It is important to understand the complex mechanisms of deformation, recovery, and recrystallization during plastic deformation at elevated temperatures in order to achieve process development. [5] This Communication describes two aspects of the deformation behavior of magnesium sheets. First, we give a brief mechanical characterization of a commercial magnesium with a focus on the anisotropy and the possible microstructural causes of this behavior. Second, we discuss the rolling process and its influence on the sheets. The aim is to show the influence of the parameters on the microstructure and texture and how this could affect the anisotropy in the rolled sheets.Experimental: We examined commercial rolled sheet, and specimens rolled to 3 mm thickness in our laboratory from various starting materials. Commercial AZ31B rolled sheet (with nominal composition 3 wt.-% Al, 1 wt.-% Zn, balance Mg) was provided in the stress-relieved H24 temper and 1.6 mm thick. Tensile tests at room temperature were conducted on a Zwick Z050 universal testing machine with a constant strain rate of 10 ±3 s ±1 . The commercial sheet tensile samples were 125 mm 20 mm 1.6 mm in size; samples taken from our rolled material had a cross section of 3 mm 6 mm. Owing to the limited material available, the specimen shape was freely chosen, taking the standard ISO specifications into consideration. Texture was measured by X-ray diffraction in reflection geometry on a Brukers AXS diffractometer. [6,7] Metallography was performed after picric acid etching.A laboratory mill was used for all rolling experiments. The rollers were kept at room temperature and operated at a speed of 3 m/min rolling rate. The specimens for stepwise rolling had a size of roughly 100 mm 50 mm 10 mm (l 0 b 0 h 0 ). The specimens for one-step rolling experiments had different starting dimensions in order to reach a final sheet thickness of 3 mm. All rolling was done at a specimen temperature of 400 C on withdrawal from the furnace, which was located directly next to the mill.The first part of the experimental processing consisted of stepwise rolling by reducing t...

Magnesium sheet production by using the extrusion process

“…The anisotropy in the mechanical behaviour is caused by the crystallographic texture that is developed during the forming process and can be influenced by the process method as well as the process conditions. So the values of the tensile yield stress (TYS) and the ultimate tensile strength (UTS) of rolled as well as extruded profiles differ significantly depending on the loading direction [1,4]. The present study discusses the microstructure and mechanical properties depending on the process temperature of extruded thin flat profiles using the common commercial magnesium wrought alloy AZ31.…”

A crystal plasticity FE model for deformation with twin nucleation in magnesium alloys

“…A complicating phenomenon of magnesium and its alloys (e.g., AZ31) is their deformation induced anomalous mechanical behavior (Kaiser et al, 2003;Bohlen et al, 2007;Barnett, 2007a,b;Brown et al, 2007;Ma et al, 2011;Kadiri et al, 2013). These materials possess low-symmetry hexagonal closed packed (hcp) crystallographic structure, an attribute that leads to pronounced anisotropy in mechanical properties, e.g.…”

Mechanical Characteristics of Superplastic Deformation of AZ31Magnesium Alloy

“…Microstructural evolution in terms of grain growth and cavitation has also been studied, due to its strong influence on the limiting fracture strain, and the post forming attributes of the alloy ( Kaiser et al (Ref 31,32) was one of few to highlight the issue of initial anisotropy exhibited by the AZ31 alloy, both at room temperature and temperatures up to 250°C. No comprehensive data has been published on the initial state of anisotropy, and more importantly, the deformation-induced anisotropy in the AZ31 at elevated temperatures.…”