Effect of Initial Grain Size on Microstructure and Mechanical Properties of Extruded Mg-9Al-0.6Zn Alloy

Abstract

The effect of initial grain size on the microstructural evolution and tensile properties of an extruded Mg-9Al-0.6Zn alloy was investigated using homogenized billets with grain sizes of 411 and 87 lm. It is found that although dynamically recrystallized (DRXed) grains remain the same size regardless of the initial grain size, a finer-grained billet results in a significant reduction of the size and area fraction of un-DRXed grains through an increase in grain boundaries capable of acting as nucleation sites for DRX during hot extrusion. This increase in the fraction of DRXed grains, combined with more precipitates, improves the tensile yield strength of the extruded alloy. The elongation is also significantly improved, as the reduction in unDRXed grains suppresses the formation of twins that cause micro-cracks. This increased ductility subsequently results in an increase in ultimate tensile strength through continuous strain hardening.

Investigation into the Extrudability of a New Mg-Al-Zn-RE Alloy with Large Amounts of Alloying Elements

“…%) with UTS varying from 397.8 to 418.6 MPa and elongation values over 12%. Park et al [37] reported that the UTS of the Mg-9Al-0.6Zn alloy reached 375 MPa after extrusion at a billet temperature of 523 K (250 °C), extrusion speed of 1 mm/s and a reduction ratio of 7.35. Bu et al [38] developed a new magnesium alloy containing large amounts of alloying elements, including La and Gd (Mg-Al-Zn-RE).…”

Research Progress on Microstructure Evolution and Strengthening-Toughening Mechanism of Mg Alloys by Extrusion

“…Magnesium alloys with high alloying content will dynamically precipitate a large number of fine, second-phase particles during extrusion, which will affect the DRX behavior of the alloy through its grain boundary pinning effect [ 100 , 101 , 102 ]. In addition to dynamically formed precipitates, the original microstructure of the magnesium alloys before extrusion also affects DRX behavior during the extrusion process, for instance, smaller original grains provide more high-angle grain boundaries and more points for DRX nucleation and promote DRX behavior during extrusion [ 103 ]. The extrusion parameters also affect DRX behavior, for instance, small extrusion ratio and low extrusion temperature can lead to incomplete recrystallization behavior, which can promote strength at the expense of ductility.…”

Feasibility of grain refinement method for AZ91 alloy using commercial Al-SiC composite

“…In particular, it is more effective in cast Mg alloys, where more than 90% are used as cast products, because it can suppress hot cracking during casting and ensure a fine and uniform distribution of solute elements and second-phase particles, thereby improving the mechanical strength and ductility of the as-cast component [5][6][7]. This technique is also very important in reducing product cost because feedstock materials with a fine and homogeneous structure can reduce heat treatment times and process sequences owing to their improved formability, encompassing rollability and extrudability [8,9].…”