Orientation imaging microscopy and microhardness in a ZK60 magnesium alloy processed by high-pressure torsion

Abstract

An extruded ZK60 magnesium alloy was processed by high-pressure torsion (HPT) at room temperature for up to 5 turns under a constant compressive pressure of 2.0 GPa with a rotation speed of 1 rpm. This processing produced an average grain size of ~700 nm. The grain size distributions and textures were examined by electron backscatter diffraction (EBSD) and this revealed some multi-modality in the microstructure at different stages of straining with fractions of both coarse grains and ultrafine grains. EBSD analysis at the mid-radius positions of unprocessed and HPT-processed materials revealed a gradual evolution from a prismatic {101 ത 0} fiber to an ultimate basal {0001} fiber texture with the c-axis parallel to the normal direction.The majority of grain boundaries had misorientations larger than 15 o throughout the processing.The strain hardening tended towards a reasonable hardness homogeneity with a hardenability exponent, η, of 0.07 up to strains of ~20 and with a subsequent hardness saturation at Hv ≈ 125.

The Effect of High‐Pressure Torsion on Microstructure, Hardness and Corrosion Behavior for Pure Magnesium and Different Magnesium Alloys

“…The AZ91 and the ZK60 alloys present a broader hardening stage up to strains of >20. Previous reports described strain hardening up to strains of ≈20 in ZK60 and a broad strain hardening in the AZ91 alloy . It is known that hardening is effective in preventing deformation localization and this agrees with the higher homogeneity of the hardness distribution in these alloys compared to the AZ31 alloy.…”

“…Homogeneous corrosion in simulated body fluid was also reported in a Mg–Zn–Ca alloy processed by HPT . The processing technique of HPT increases the hardness of diverse magnesium alloys to values over 100 Hv which are higher than the hardnesses observed after conventional thermo‐mechanical processing.…”

Using Post‐Deformation Annealing to Optimize the Properties of a ZK60 Magnesium Alloy Processed by High‐Pressure Torsion

“…It is apparent from Figure a and 2a that the processing by 5 turns of HPT produces a majority of fine grains although some limited numbers of coarser grains also remain within the microstructure. This result matches earlier reports describing the application of HPT to this alloy and also to the AZ31 magnesium alloy . There is some evidence in Figure a for a bi‐modality in the grain size distribution with a peak around ≈0.3 μm and another broader peak at ≈1.0 μm.…”

“…Based on the data available to date it appears that, in order to increase the ductility at low temperatures after SPD processing, the simplest approach is probably to make use of post‐deformation annealing and some limited data are already available demonstrating the feasibility of this approach for nanostructured titanium . Earlier studies on the magnesium ZK60 alloy confirmed the development of excellent high temperature ductility through the formation of a UFG structure after processing by HPT and, therefore, the present research was initiated to provide a first comprehensive analysis of the effect of post‐deformation annealing on the strength properties of the ZK60 alloy.…”

Effect of Initial Annealing Temperature on Microstructural Development and Microhardness in High‐Purity Copper Processed by High‐Pressure Torsion

“…However, with increasing number of turns, the microstructures usually evolve toward homogeneity and many metals exhibit a complete homogeneity at high numbers of turns. Materials showing this behavior include Al, [3,[8][9][10][11][12][13] Cu, [14][15][16] Ti, [17][18][19] Mg, [20][21][22][23] Fe, [24][25][26] Ni, [27,28] and numerous others metals and alloys. [29,30] Nevertheless, some materials show a different type of behavior when processed by HPT.…”