Principles of equal-channel angular pressing as a processing tool for grain refinement

The process of grain refinement in equal-channel angular pressing

Texture analysis in hexagonal materials

Twenty-five years of ultrafine-grained materials: achieving exceptional properties through grain refinement

Pure Mg and Mg alloys generally exhibit only limited ductilities at ambient temperatures. Experiments were conducted to evaluate the potential for improving the mechanical properties of pure Mg and an Mg–0.9% Al alloy at room temperature by subjecting these materials to severe plastic deformation through the procedure of equal-channel angular pressing (ECAP). It is shown that ECAP may be applied successfully to these materials at elevated temperatures and this leads to grain refinement due to the occurrence of recrystallization during the pressing process and to significant improvements in the strength and ductility of these materials. Since these improvements are apparent after only a single pass through the ECAP die, it is concluded that the introduction of ECAP provides a simple and effective procedure for improving the ambient temperature mechanical properties of materials, such as hcp metals, where the measured ductilities are generally limited.

Improving the mechanical properties of magnesium and a magnesium alloy through severe plastic deformation

Low temperature superplasticity in an AZ91 magnesium alloy processed by ECAE

Microstructural evolution and superplasticity of a Mg-9Al-1Zn alloy rolled at 673 K were investigated at 573 K and 1.5×10−3 s−1. The grain size of the as-rolled Mg alloy was 39.5 μm. However, the grain size of the specimen deformed to a true strain of 0.6 was 9.1 μm. The grain refinement was attributed to dynamically continuous recrystallization during an initial stage of tensile test. Stabilization of subgrain boundaries by fine particles and stimulation of continuous recrystallization by prior warm-deformation were not needed to attain dynamically continuous recrystallization in the Mg alloy. As a result of the grain refinement, the rolled Mg alloy exhibited superplastic behavior.

Microstructural evolution and superplasticity of rolled Mg-9Al-1Zn

Novel equilibrium two phase Mg alloy with the long-period ordered structure

Stretch formability of AZ31 Mg alloy sheets was investigated by Erichsen tests at room temperature and stretch forming tests at 523 K. The as-received specimens with lower Lankford value (r-value) and higher strain hardening exponent coefficient (n-value) showed excellent stretch formability at room temperature. On the other hand, the as-received specimens with smaller grain size (higher ductility) exhibited excellent stretch formability at elevated temperature. It is suggested that reduction of strain and plastic anisotropies related to texture intensity and texture distribution should be dominant factor for excellent stretch formability at room temperature, and ductility related to fine grain size becomes important factor for stretch formability at elevated temperature, at which effects of strain and plastic anisotropies are negligibly small.

Stretch formability of AZ31 Mg alloy sheets at different testing temperatures

BlowformingcharacteristicsofAZ31Mgalloyrecycledbysolid-staterecyclingwereinvestigated.Cylindricalscrapsandmachinedchipswere recycled by hot extrusion and hot rolling in air. Oxide layers were observed in the recycled specimens by oxygen mapping with EPMA(Electron Probe Micro Analyser). The interval of the oxygen layers for the specimen from machined chips was much shorter than that for thespecimenfromcylindrical scraps.Asaresultoftensiletests,themechanicalpropertiesofthespecimenfromcylindrical scrapswerefoundtobealmost the same as those of a rolled specimen from a virgin ingot. On the other hand, at elevated temperatures, the elongation of the specimensfrom machined chips was low, compared with those of the rolled specimens from a virgin ingot. The large amount of oxide contamination islikely to be responsible for the lower elongation of the specimens from machined chips. In blow-forming tests, the specimen from cylindricalscraps exhibited excellent formability similar to the rolled specimen from a virgin ingot. However, the specimen from machined chips showedpoor formability. Thus, oxide contamination adversely aﬀected the formability of recycled Mg alloy.(Received November 5, 2003; Accepted January 6, 2004)Keywords: magnesium alloy, solid-state recycling, tensile tests, superplasticity, blow forming

Hajime Iwasaki

Papers

Low temperature superplasticity in an AZ91 magnesium alloy processed by ECAE

Microstructural evolution and superplasticity of rolled Mg-9Al-1Zn

Novel equilibrium two phase Mg alloy with the long-period ordered structure

Stretch formability of AZ31 Mg alloy sheets at different testing temperatures

Blow Forming of Mg Alloy Recycled by Solid-State Recycling