Realization of high strength and high ductility for AZ61 magnesium alloy by severe warm working

Abstract

Extruded Mg-6%Al-1%Zn (AZ61) alloy bar was subjected to 4-pass Equal Channel Angular Extrusion (ECAE) processing at 448-573 K. At the processing temperature of 448 K, extremely fine grains with the average grain size of 0.5 mm are formed as a result of dynamic recrystallization originated by fine Mg 17 Al 12 (b) phase particles having 50-100 nm diameter dynamically-precipitated during ECAE processing. The sizes of both a matrix and b phase decrease with decreasing processing temperatures. In tensile test at room temperature under the strain rate of 1!10 K3 s -1 , tensile strength increases with decreasing ECAE processing temperatures due to fine grains, fine precipitates and residual strain hardening. Especially, highest strength of 351 MPa was achieved in the specimen ECAE-processed at 448 K. In addition to such high strength, elongation reaches 33% in that specimen. This specimen exhibits clear strain rate dependencies of both flow stress and elongation even at room temperature. As a result, higher elongation of 67% is obtained under low strain rate of 1!10 K5 s K1. In such specimen, non-basal slip and grain boundary sliding occur in addition to basal slip. Furthermore, there are grains with no dislocations, suggesting the occurrence of dynamic recovery. The contribution of all the deformation mechanisms would cause high ductility in finegrained AZ61 alloy specimen with high strength. q

Effect of differential speed rolling on microstructure and mechanical properties of an AZ91 magnesium alloy

“…This is possible because the DSR processing temperature was considerably lower than that for the ARB (473 K versus 648 K) and repeated reheating between the ARB passes, possibly causing grain coarsening, was absent in the DSR process. Achievement of high strength and high ductility was also realized in the ECAPed AZ61 alloys, as the ECAP temperature could be lowered below 473 K [14] such that submicron grain size was obtained in addition to development of new texture formed for easy slip in basal planes. Likewise, DSR with a highspeed ratio processed at 473 K can produce high strength and high ductility in the AZ91 sheets by significantly enhancing the degree of grain refinement to submicron size with reducing the basal texture intensity.…”

Influence on the microstructure and properties of AZ61 magnesium alloy at warm deformation

“…Due to wrought magnesium alloy manufactured by the plastic forming process has excellent mechanical properties, magnesium and its alloys are attractive for many engineering structural applications [2,3], However, due to magnesium is hexagonal close-packed lattice (HCP), the symmetric is low and the glide system is little, its alloy has poor workability at room temperature. In order to expand the magnesium alloy product market, severe plastic deformation has been studied to improving the mechanical properties of magnesium alloy [4,5], such as equal channel angular pressing (ECAP), but commercial availability is little. In this article compression deformation behavior of AZ61 alloy has been investigated at different temperature and strain rate, mean- * Corresponding author.…”

Grain Refinement of Extruded AZ31 Magnesium Alloy by Ecap Process

“…While models have hitherto been proposed based on studies on ductile materials like Al and Cu at room temperature [8], the limitations of such models on Mg processed above room temperatures have been highlighted in the earlier sections. Fig.…”

“…Fig. 5 is a schematic illustration of the model proposed for the grain refinement of Mg during ECAP [8]. The illustration applies to the grains in the centre portion of the billet [7 -9].…”