Microstructure Evolution and Mechanical Properties of AZ80 Mg Alloy during Annular Channel Angular Extrusion Process and Heat Treatment

Abstract

Microstructure evolution and mechanical properties of AZ80 Mg alloy during annular channel angular extrusion (350 °C) and heat treatment with varying parameters were investigated, respectively. The results showed that dynamic recrystallization of Mg grains was developed and the dendritic eutectic β-Mg17Al12 phases formed during the solidification were broken into small β-phase particles after hot extrusion. Moreover, a weak texture with two dominant peaks formed owing to the significant grain refinement and the enhanced activation of pyramidal <c + a> slip at relative high temperature. The tension tests showed that both the yield strength and ultimate tensile strength of the extruded alloy were dramatically improved owing to the joint strengthening effect of fine grain and β-phase particles as compared with the homogenized sample. The solution treatment achieved the good plasticity of the alloy resulting from the dissolution of β-phases and the development of more equiaxed grains, while the direct-aging process led to poor alloy elongation as a result of residual eutectic β-phases. After solution and aging treatment, simultaneous bonding strength and plasticity of the alloy were achieved, as a consequence of dissolution of coarse eutectic β-phases and heterogeneous precipitation of a large quantity of newly formed β-phases with both the morphologies of continuous and discontinuous precipitates.

Effect of Microstructure on the Dimensional Stability of Extruded Pure Aluminum

“…The misorientation of these substructures was gradually increased as the number of thermal cycles increasing until equiaxed grains were formed. Furthermore, the average grain sizes in samples annealed at 150 • C, 350 • C and 400 • C after thermal cycling were reduced from 120.2 µm to 36.3 µm, from 82.4 µm to 28.5 µm and from 58.7 µm to 35.4 µm, respectively, indicating that the increase of the number of equiaxed grains contributed to the decrease of the average grain size and that there was a limit value of about 30 µm in the grain size after the thermal cycling of ∆T = 120 • C. The change of defects and the change of the orientation of grains that contributed to the dimensional instability may be caused by the formation of the equiaxed grains [15,19]. Thus, the formation of equiaxed grains may be the key factor in the dimensional instability of materials during thermal cycling.…”

“…The residual plastic strain along the axial direction of the extruded LY12 Al alloy after thermal cycling was about 13 times than that along the transverse direction [15]. The rolled alloy sheet investigated by several scholars demonstrates significant anisotropy in micro-yield, creep deformation and tensile properties due to the strong texture [16][17][18][19]. The strength degradation of commercially pure Al after annealing was the result of the evolution of texture and sub-grain growth during the recovery and recrystallization, which depended on the annealing temperature [20].…”

The Influence of Laser Surface Remelting on the Tribological Behavior of the ECAP-Processed AZ61 Mg Alloy and AZ61–Al2O3 Metal Matrix Composite

“…Moreover, there was a slight tendency towards smaller grain sizes in materials with 10 wt.% of Al 2 O 3 particles. It was also reported [25][26][27][28] that the hot deformation process of such materials leads to the creation of coherent Mg 17 Al 12 intermetallic precipitates.…”

Effect of Lattice Constants and Precipitates on the Dimensional Stability of Rolled 2024Al during Isothermal Aging

“…Many previous studies have shown that the precipitation of the second phase is one of the important factors affecting the dimensional stability of materials [ 24 , 25 , 26 , 27 , 28 , 29 ]. Song et al believed that when an external force is applied to the Al–Cu–Mg alloy during aging, the precipitated phase S’ in 2024 aluminum alloy will be uniformly distributed with the increase in the external stress, increasing the micro yield strength of the material, thereby improving the dimensional stability of 2024 aluminum alloy, which is related to the pinning effect of S’ relative dislocation [ 30 ].…”