Mg-3%Al-1%Zn (AZ31) alloy was subjected to ECAE (Equal Channel Angular Extrusion) processing under various processing conditions. Then tensile tests were carried out at room temperature to investigate the relationship between tensile properties and microstructural parameters that include grain size and the texture generated by ECAE processing. In 4-pass ECAE specimens processed at 523 K, tensile ductility is improved as a result of easy basal slip during tensile test along the extrusion direction, because such specimens have textures in which the basal plane is inclined at 45 to the extrusion direction. On the other hand, in the specimens processed at 573 K, 0.2% proof stress is higher than those of specimens processed at lower temperatures, but elongation is smaller. This is because of difficult basal slip caused by the textures in which the basal plane is oriented parallel to the extrusion direction. However, 8-pass specimens processed at 473 K and subsequently annealed, which have similar textures but different grain sizes (d), exhibit clear grain size dependencies of 0.2% proof stress ( 0:2 ) according to Hall-Petch relationship; 0:2 ¼ 30 þ 0:17d À1=2 . Therefore, crystallographic orientation has a profound effect on the tensile properties of AZ31 alloy, and grain size has a little effect.

In order to achieve low temperature superplasticity at relatively high strain rate in magnesium alloys, Mg-10 mass%Li-1 mass%Zn (LZ101) α + β two phase alloy was subjected to ECAE (Equal Channel Angular Extrusion) processing and tensile tests of the obtained specimens of the alloy were carried out to investigate the superplastic properties. In a specimen of the LZ101 alloy, which has improved microstructure through repetitive ECAE processing at 323 K, superplasticity occurs at 423 K, which is below T m /2 (T m : melting point of the alloy), under a relatively high strain rate of 1 × 10 −3 s −1 with fracture elongation of 391%. Such a specimen after tensile test contains fine grains due to dynamic recrystallization and the precipitation of β phase along the grain boundaries and at triple points in recrystallized α phase. This microstructural change enhances grain boundary sliding, resulting in the occurrence of low temperature superplasticity at relatively high strain rate.

In order to achieve same level of high strength and high ductility as 6061 aluminum forging alloy that is currently used for automobile applications, AZ31 magnesium alloy rod with a large diameter of 40 mm was subjected to ECAE-processing, and the microstructures and mechanical properties of the ECAE-processed specimens were investigated. Furthermore, automobile knuckle arm was produced by forging using the ECAE-processed material, and the mechanical properties of the forged product and their strain rate dependencies were investigated under impact tensile load conditions. 4pass-ECAE-processed specimen has fine and uniform microstructure and a texture whose basal planes are mainly parallel to the extrusion direction with some inclined at angles up to 45 to the extrusion direction. Therefore, they show high ductility even if the tensile direction is parallel to the extrusion direction. The knuckle arm forged using the ECAE-processed material exhibits high elongation even in the high strain rate region. Furthermore, the tensile strength, fracture elongation and absorption energy of the forged product increase with increasing strain rate and their values are higher than those of T6-treated 6061 aluminum forging alloy specified by JIS.

Shigeharu KAMADO  and Yo KOJIMA   Mg 3Al 1Zn (AZ31) alloy was subjected to ECAE (Equal Channel Angular Extrusion) processing under various processing conditions in order to reveal the eŠect of the microstructural parameters on tensile properties of magnesium alloy. Then tensile tests were carried out at room temperature to investigate the relationship between tensile properties and microstructural parameters including the texture generated by ECAE processing and grain size. As a result, in 4 pass ECAE specimens processed at 250°C, tensile ductility is improved as a result of basal slip that occurs easily when tensile test was performed along the extrusion direction, because such specimens have textures in which the basal plane is inclined at 45°to the extrusion direction. On the other hand, in the specimens processed at 300°C, which have textures in which the basal plane is oriented parallel to the extrusion direction, 0.2 proof stress is higher than those of specimens processed at lower temperatures, but elongation is smaller because basal slip is di‹cult to occur. However, 8 pass specimens processed at 200°C and annealed, which have similar texture but diŠerent grain sizes (d) exhibit clear grain size dependencies of 0.2 proof stress (s 0.2 ) according to HallPetch relationship; s 0.2 ＝30＋0.17d -1/2 . Therefore, crystallographic orientation has a profound eŠect on the tensile properties of AZ31 alloy, and grain size also has a little eŠect.

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