Study on Ultra-Precision Cutting of Magnesium Alloys

首先研究了镁合金超精密切削的切削力、表面完整性和切屑形成等基本切削性能。发现工件材料中的夹杂物或缺陷会在成品表面产生划痕，影响镜面的完整性。在过去的一年里，主要研究了Al-Mn化合物在微观结构中对表面完整性的影响。结果表明：(1)Al-Mn化合物在az31和AZ6l（轧制薄板）的显微组织中析出。它们起到硬颗粒的作用，导致成品表面产生划痕。Al-Mg析出（Mg17Al12）在AZ91（铸轧薄板）的微观组织中不参与划痕的产生。(2)少量Mn （0.05 -0.1 wt. %）的az31在相同条件下加工后，成品表面产生的划痕大大减少。在材料的微观结构中未观察到Al-Mn化合物。(3)切屑形成和流动的方式影响划痕的产生。切削液使切屑积聚在刀具前刀面上，然后切屑附着在刀具上，产生划痕，但切削液可以防止由于微堆积边缘造成的划痕。(4) Mn为1.0 wt. %、0.1 wt. %和0.05 wt. %时az31的切削力大小无显著差异。而Mn用量越大，进给量越小，AZ31的推力分量越大。

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.