Mechanical Properties and Microstructure of the Magnesium Alloy Mg-6.8Y-2.5Zn-0.5Al Produced by Casting and Hot Rolling

Abstract

In recent years, magnesium alloys have been received much attention as important structural materials for lightweight components in automotive, electronic and space industries because of the low density, high specific strength, high damping capacities and good casting properties. Among various magnesium alloys, rare earth (RE) containing alloys are known to show high strength, excellent creep resistance, and good thermal stability. Long period stacking ordered structures (LPSO) being responsible for the improved property profile in some Mg–RE alloys. One promising system are the Mg-Y-Zn alloys, which are predominantly processed via extrusion. Only a few studies are focused on hot rolling. However, these works are confined to rolling temperatures between 350 °C and 420 °C. The present paper summarizes the development of a rolling technique including pass schedule and heat treatment for the magnesium alloy Mg-6.8Y-2.5Zn-0.5Al in as-cast condition in order to produce sheets with a final thickness of 2.5 mm. The investigations are accompanied by the characterization of the microstructure as well as the determination of the mechanical properties.

Microstructure and Texture Evolution during Twin-Roll Casting and Annealing of a Mg–6.8Y2.5Zn–0.4Zr Alloy (WZ73)

“…Similar results were achieved after conventional casting of the same ingots, as described in [32]. The important difference between the as-cast and the TRC state is that after conventional casting, fine lamellar structures could be observed within the magnesium matrix [18,33]. Lamellas of the LPSO structure within the Mg matrix did not occur after TRC.…”

“…XRD results indicate that the transformation from the 18R to the 14H phase has occurred, as described in Liu et al [21]. These lamellae are known from microstructures of LPSO-containing magnesium alloys after conventional casting [18,33]. It was therefore assumed that annealing at high temperatures resulted in the dissolution of the network-shaped LPSO phase during the holding time.…”

Hot Deformation Behaviour and Processing Maps of an as-Cast Mg-6.8Y-2.5Zn-0.4Zr Alloy

“…This result indicates that the data in the instability regime are beyond the validity of PLB regime that can be described by Sellars and Tegart's sinh formula, e.g. (8). ).…”

“…This result indicates that the data in the instability regime are beyond the validity of PLB regime that can be described by Sellars and Tegart's sinh formula, e.g. (8). Based on the DMM, the processing map of the as-cast Mg-6.8Y-2.5Zn-0.4Zr alloy that was deformed at logarithmic strain value of 0.4 was established.…”