Aravindha R. Antoniswamy

Static recrystallization and grain growth in AZ31B-H24 magnesium alloy sheet

The effects of static annealing on recovery, recrystallization and grain growth in a magnesium alloy sheet are investigated at 50°C to 450°C. Full recrystallization is observed after annealing at 250°C or higher temperatures. Recrystallized grain size increases with temperature through normal grain growth. Room-temperature hardness drops abruptly following recrystallization and then decreases with increasing grain size. Predictive relationships are proposed for recrystallized grain size as a function of temperature and time and for hardness as a function of recrystallized grain size.

Hot Forming of Mg AZ31B Alloy Sheet Processed by Warm Rolling

Mg alloy AZ31B is of interest for hot forming because it can achieve a superplastic response at high temperatures and slow strain rates. As temperature decreases and forming rate increases, its strain-rate sensitivity decreases and significant plastic anisotropy can arise. These effects are the result of a transition in deformation mechanisms from grain-boundary-sliding (GBS) to dislocation-climb (DC) creep. However, sheet production using warm rolling can produce a material with a smaller grain size and weaker basal texture. These microstructural changes promote GBS creep and decrease the degree of anisotropy under DC creep. Microstructural and tensile data are presented to show these effects at 350 and 450C through comparisons to a similar material having a more usual microstructure.

The Effects of Plastic Anisotropy in Warm and Hot Forming of Magnesium Sheet Materials

Mg alloy sheet materials often exhibit plastic anisotropy at room temperature as a result of the limited slip systems available in the HCP lattice combined with a commonly strong basal texture. Less well studied is plastic anisotropy developed at the elevated temperatures associated with warm and hot forming. At these elevated temperatures, particularly above 200°C, the activation of additional slip systems significantly increases ductility. However, plastic anisotropy is also induced at elevated temperatures by a strong crystallographic texture, and it can require an accounting in material constitutive models to achieve accurate forming simulations. The type and degree of anisotropy under these conditions depend on both texture and deformation mechanism. The current understanding of plastic anisotropy in Mg AZ31B and ZEK100 sheet materials at elevated temperatures is reviewed in this article. The recent construction of material forming cases is also reviewed with strategies to account for plastic anisotropy in forming simulations.

The Influence of Deformation Mechanisms on Rupture of AZ31B Magnesium Alloy Sheet at Elevated Temperatures

Gas-pressure bulge tests were conducted on Mg alloy AZ31B wrought sheet until rupture at temperatures from 250 to 450°C. The rupture orientation was observed to change with forming pressure, which controls the forming strain rate, at 350 to 450°C. This phenomenon is a result of associated changes in the mechanisms of plastic deformation. At slow strain rates (≤ 3 × 10−2 s−1), cavity interlinkage associated with grain boundary sliding (GBS) creep induced rupture along the sheet rolling direction (RD). At fast strain rates (≥ 3 × 10−2 s−1), flow localization (necking) associated with dislocation-climb-controlled (DC) creep induced rupture along the long-transverse direction (LTD), a result of mild planar anisotropy. Biaxial bulge specimens tested at 250 to 300°C ruptured explosively, hence preventing any further analysis.