Three kinds of magnesium based titanium particles-dispersed functionally graded materials (FGMs) were fabricated by a centrifugal solid-particle method. Materials were pure magnesium, AZ91D (9.23Al–0.7Zn–0.028Si–0.23Mn–0.0019Fe–0.0014Cu–0.001Ni–0.0009Be–bal.Mg) and Mg–6 mass%Zn alloys. The specimen shape was cylinder with 15–20 mm in length. Microstructures of FGM specimens were observed using an optical microscopy (OM) or a scanning electron microscopy (SEM). 2 vol%Ti was added into Mg–6 mass%Zn by a vortex addition technique in order to fabricate Mg–6 mass%Zn–2 vol%Ti master alloy. It was found that a large number of titanium particles were observed in the outer region of the cylinder, since the titanium particles migrate to outer region during the centrifugal solid-particle method. In this way, the magnesium based titanium particles dispersed FGM can be successfully fabricated by the centrifugal solid-particle method. Moreover, Vickers hardness increases with increasing the amount of titanium particles.

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Grain refinement in a magnesium alloy AZ31 was studied in multi-directional forging (MDF) with decreasing temperature from 623 K to 423 K and at a strain rate of 3×10⁻³ s⁻¹. The MDF was carried out up to large cumulative strains with changing the loading direction during decreasing temperature from pass to pass. The structural changes are characterized by the generation of many mutually crossing kink bands at low strain, followed by the development of very fine grains at large strains. The dynamic change in grain size can be expressed by two different power law functions of flow stress for the region of flow stress above or below 100 MPa. The MDF with decreasing temperature can accelerate the uniform development of much finer grains and the improvement in plastic workability, leading to the minimal grain size of 0.23 μm at 423 K. The mechanism of grain refinement is discussed in detail.

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Experiments have been conducted on AZ31B magnesium alloy cutting chips in order to investigate the feasibility of producing a compaction with homogeneous mechanical properties at room temperature using equal–channel angular (ECA) pressing. Repetitive pressings, consisting of a total of 4 passages through a die at 573 K with and without MoS₂ as a lubricant, were conducted on each sample. After the initial pressing of each sample was completed the samples were rotated 90 degrees and pressed again. This pressing procedure was repeated two more times for all four samples. It was shown that ECA pressing without lubricant was capable of obtaining the compaction with crack–free smooth surfaces after a single pressing. This was most likely because after pressing, a thin, continuous surface layer is created by the heavy shear strain caused by the resulting friction constraint from the die surface. The FEM analysis confirmed the heavy shear strain distribution in the surface layer of the compaction after the single pressing without lubricant. Grain refining after the pressing was observed via the TEM. However, the mechanical properties at room temperature were not homogeneous even after repetitive pressings up to a total of 4 passages through a die. Contrary to the non–lubricated samples, samples that were ECA pressed using lubricant did not display the thin shear strained surface layer. The lack of the distributed shear strain surface layer was most likely caused by a lower coefficient of friction created by the MoS₂ lubricated die. Experimental procedures also concluded that the pressing force required for the lubricated samples was remarkably low in comparison with that for the non–lubricated pressings. However, surface crack formation could not be avoided during the pressings that utilized the lubricated ECA pressing process. It was shown that a combined ECA pressing process consisting of an initial pressing without lubricant followed by repetitive pressings up to a total of 3 passages with lubricant was an effective method for producing a compaction with homogeneous mechanical properties at room temperature under low pressing force.

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Magnesium and magnesium alloys are increasingly being applied for various products and the application to precise machine parts is expected. This paper deals with an experimental study of ultra-precision diamond cutting of magnesium and magnesium alloys. In order to investigate the micro cutting performance and clarify the problem in the generation of good mirror surface, the ultra-precision cutting tests of magnesium and magnesium alloys with single crystal diamond tool are carried out. The cutting force, the chip formation and the surface integrity of finished surface in the micro cutting are mainly examined and discussed. Consequently, it is observed that the specific cutting force and the ratio of thrust force to principle force significantly increase under the condition of smaller depth of cut. The mirror surface with roughness (R_y) of 100 nm or less is obtained in this experiment. However, Al–Mn compounds cause the scratches on the finished surface and deteriorate the surface integrity. The continuous type of chip is formed in micro cutting, while the saw-tooth type of chip is formed in the conventional cutting.

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Structure and passivity of the films formed on magnesium in alkaline solutions containing aluminate ions were evaluated by using various methods including electrochemical measurements and a field emission scanning electron microscope. When concentration of sodium ions was kept constant, increase in aluminate ions effectively depressed the peak current at around 5 V and increased the breakdown voltage. This is caused by the improvement of surface passivity of magnesium and oxide protectively. Aluminum content incorporated in the film lineally increased with log of increasing concentration of aluminate ions added in the solution. However, besides the concentration of aluminate ions in the solution, the corrosion resistance evaluated by salts spray test was highest in the thick films formed at around 5 V with extremely high current density. Further, it is clarified that all films formed at 5 V exhibit vertical cylindrical cellular structure similar to the Keller model of porous anodic alumina.

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