Effect of temperature on the suppression of twinning in textured magnesium
- PDF / 524,915 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 81 Downloads / 163 Views
Research Letter
Effect of temperature on the suppression of twinning in textured magnesium Roshan Plamthottam and Steven Lavenstein, Department of Mechanical Engineering, Whiting School of Engineering, The Johns Hopkins University, Baltimore, MD 21218-2682, USA Jaafar A. El-Awady, Department of Mechanical Engineering, Whiting School of Engineering, The Johns Hopkins University, Baltimore, MD 21218-2682, USA; Department of Materials Science and Engineering, Whiting School of Engineering, The Johns Hopkins University, Baltimore, MD 21218-2682, USA Address all correspondence to Steven Lavenstein at [email protected] and Jaafar A. El-Awady at [email protected] (Received 17 June 2019; accepted 24 July 2019)
Abstract In this work, the effect of temperature, in the range of 25 to 250 °C, on deformation twinning in textured polycrystalline pure magnesium (Mg) was investigated. Compression loading was applied perpendicular to the c-axis texture direction. The yield strength and strain hardening rate are shown to drastically decrease with increasing temperature with total suppression of twinning at 200 °C. This behavior is attributed to the decrease in the critical resolved shear stress for prismatic slip and temperature insensitivity of tensile twinning. These results provide a first step in fundamentally understanding the deformation of Mg at elevated temperatures and quantify the mechanisms that lead to their improved formability at elevated temperatures.
Magnesium (Mg) alloys have great potential as structural materials in many applications due to their light weight and high specific strength.[1–3] However, Mg and its alloys display poor corrosion resistance and low formability at room temperature, relative to their aluminum counterparts. They also exhibit a tension–compression asymmetry with the compressive strength being significantly less than the tensile strength.[4–6] This greatly inhibits the widespread use of Mg alloys at the industrial scale. The low formability of Mg at low temperature can be attributed to its hexagonal close-packed (HCP) crystal structure.[7] Furthermore, the stress states induced by forming are often complex, which generally necessitate the accommodation of plastic deformation in multiple directions. Although basal slip in Mg provides easy plastic flow, it is not active when the applied load is parallel or perpendicular to the c-axis. As a result, non-basal slip systems (e.g., prismatic and pyramidal) and deformation twinning are the only nonzero Schmid factor systems that can facilitate deformation in these directions. However, the critical resolved shear stresses (CRSS) of nonbasal slip systems are relatively high and are hard to activate during deformation at low temperatures. Thus, deformation twinning generally dominates at room temperature. Furthermore, since fracture in Mg typically initiates at double twin boundaries,[8] the ductility of Mg at room temperature is accordingly low. The suppression of twinning is generally desirable to improve the formability and ductility of Mg since fracture
Data Loading...
