Study on Ultra-Precision Cutting of Magnesium Alloys

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In the first year, the basic machinability such as the cutting force, the surface integrity and the chip formation in an ultra-precision cutting of magnesium alloys was investigated. It was found that the inclusions or the defects in the work material caused to generate the scratches on the finished surface and influenced the integrity of the mirror surface. In the last year, the influence of Al-Mn compounds in the micro structure on the surface integrity was mainly investigated. The results are summarized as follows:(1)Al-Mn compounds separate out in the micro structure of AZ31and AZ6l (rolled sheet). They play a role as the hard particles and cause to generate the scratches on the finished surface. Al-Mg precipitation (Mg17Al12) in the micro structure of AZ91 (cast sheet) does not get involved with the generation of scratches.(2)The scratches generated on the finished surface are drastically reduced when AZ31with a small quantity of Mn (0.05 -0.1 wt. %) is finished under the same conditions. Al-Mn compounds are not observed in the micro structure of the materials.(3)The manner of the chip formation and flow affect the generation of scratches. The cutting fluids cause the chip accumulation on the tool rake face and then the chips attached on the tool, generate the scratches, though the cutting fluids prevent the scratches due to the micro built-up edge.(4)There is no significant difference in the magnitude of cutting force among AZ31s which include Mn of 1.0,0.1 and 0.05 wt. %. However, the thrust force component of AZ31 with larger quantity of Mn increases under the condition of smaller feed rate.