Microstructural and Mechanical Characteristics of AZ61 Magnesium Alloy Processed by High-Pressure Torsion

Abstract

Experiments were conducted on an AZ61 magnesium alloy to evaluate the microstructural characteristics and the mechanical properties after processing by High-Pressure Torsion (HPT). The results show that processing by HPT produces excellent grain refinement with average grain sizes of $0:22 and $0:11 mm after processing at 423 K and room temperature, respectively. Tensile testing after HPT revealed the potential for achieving superplastic elongations with a maximum recorded elongation of 620% when testing at a temperature of 473 K. Using microhardness measurements, it is demonstrated that the the microstructure gradually evolves with increasing torsional straining in HPT so that ultimately there is a reasonably homogeneous structure across the disk.

Evolution of microstructure and mechanical properties of an as-cast Mg-8.2Gd-3.8Y-1.0Zn-0.4Zr alloy processed by high pressure torsion

“…This is related to the much enhanced grain refinement in the present alloy (down to 55 nm) as compared to the grain refinement achieved in pure Mg (typically down to 1 μm). Also for HPT processed conventional Mg alloys such as AZ31 (grain size typically refined down to 1 or 0.5 μm, depending on conditions [41]), AZ61 (grain size typically refined down to 0.2 μm [27]) and ZK60 (grain size typically refined down to 1 μm [42]), the grain refinement is more limited and grain size strengthening will be substantially less than for the present HPT processed Mg-Gd-Y-Zn-Zr alloy.…”

“…These observations show that the microstructure refinement initially develops at the edge (where the strain is highest), and then spreads to the centre of the disk, but the microstructure still remains non-uniform over the disk even after 16 turns, particularly in the immediate vicinity of the central area. This is mainly due to the dependency of strain on distance to the centre of the disk: accumulated strain introduced by HPT decreases from periphery to the centre of the disk (see [27,28] and Discussion). 5(d)), and the corresponding SAED pattern further supports this (inset in Fig.…”

The Strength–Grain Size Relationship in Ultrafine-Grained Metals

“…Effect of grain size on superplastic strain rate in Mg alloys; [7] datum points for ECAP [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] and HPT. [46][47][48][49] Figure 2. Microhardness-grain size relation in commercial purity Ti; [76] the H-P relationship holds down to 9 nm using experimental data.…”

“…1[a] are taken from various reports for Al alloys, [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] and in Fig. 1 [b] there are similar sets of data for a range of Mg alloys [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] where the upper solid lines in Figs 1[a] and [b] show the predicted normalized strain rates derived using eq. [2].…”

Development of High-Pressure Sliding Process for Microstructural Refinement of Rectangular Metallic Sheets

“…[3][4][5] It has an advantage over other SPD processes that the grain refinement is more effective as it is possible to introduce very large strain and it is applicable to rather less ductile materials. [6][7][8][9] It is also capable of consolidating powders and machining chips without relying on sintering process. [10][11][12][13][14] Major limitation of the HPT process is that the sample size is small because it is used in a form of thin disk with typically the size of 10-20 mm in diameter and $1 mm in thickness.…”