Modeling the strength and ductility of magnesium alloys containing nanotwins
- PDF / 648,302 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 26 Downloads / 226 Views
Modeling the strength and ductility of magnesium alloys containing nanotwins S.B. Gorti and B. Radhakrishnan Computer Science and Mathematics Division Oak Ridge National Laboratory Oak Ridge, TN 37831-6114, U.S.A. ABSTRACT Magnesium alloys have been receiving much attention recently as potential lightweight alternatives to steel for automotive and other applications, but the poor formability of these alloys at low temperatures has limited their widespread adoption for automotive applications. Recent work with face centered cubic (FCC) materials has shown that introduction of twins at the nanometer scale in ultra-fine grained FCC polycrystals can provide significant increase in strength with a simultaneous improvement in ductility. This objective of this work is to explore the feasibility of extending this concept to hexagonal close packed (HCP) materials, with particular focus on using this approach to increase both strength and ductility of magnesium alloys. A crystal plasticity based finite element (CPFE) model is used to study the effect of varying the crystallographic texture and the spacing between the nanoscale twins on the strength and ductility of HCP polycrystals. Deformation of the material is assumed to occur by crystallographic slip, and in addition to the basal and prismatic slip systems, slip is also assumed to occur on the {1 0 1 1} planes that are associated with compression twins in these materials. The slip system strength of the pyramidal systems containing the nanotwins is assumed to be much lower than the strength of the other systems, which is assumed to scale with the spacing between the nanotwins. The CPFE model is used to compute the stress-strain response for different microstrucrutral parameters, and a criterion based on a critical slip system shear strain and a critical hydrostatic stress is used to compute the limiting strength and ductility, with the ultimate goal of identifying the texture and nanotwin spacing that can lead to the optimum values for these parameters. INTRODUCTION In recent years, there has been much interest in developing magnesium alloys as lightweight materials to replace steel and aluminum alloys for automotive and other applications. However, the poor formability of magnesium alloys at low temperatures has limited their use to some specialized parts in the automotive industry. The poor formability is related mainly to a strong basal texture that develops in these alloys during hot rolling or extrusion, which restricts the available modes of deformation. Metallic polycrystals generally exhibit an inverse relationship between strength and ductility. However, recent research has shown that the introduction of nanotwins within ultra-fine grains can lead to significant enhancement in strength without loss of ductility [1]. The strength level is dictated by the mean spacing between the twins and the ductility is determined by the ability of the twin-matrix interface to allow dislocations to glide. In the case of ultra-fine grained copper, the yield strength level increas
Data Loading...
