孔口倒角工艺及刀具研究

孔、轴加工必然带有轴头、孔口的倒角工序,由其所起的功能和作用不同而具有不同的要求.倒角工序在工艺设计中常常被认为是辅助工序而被工艺设计人员所忽视.这种认识上的偏差,导致对倒角工序的研究长期以来处于停滞状态.由于缺乏对刀具和工艺方法的研究而出现加工效率下降或难以完成整个工序加工内容的现象.现通过对倒角型式的分类、作用的归纳与总结,针对不同的倒角型式采用不同的工艺方法和刀具进行研究,并对常见的结构提出建议与解决方法.     

Improvements of elevated temperature strength and creep resistance of Mg-12Zn-4Al based alloy with calcium addition

A series of Mg-12Zn-4Al-0.3Mn (ZA124) based alloys with additions of calcium have been prepared and their microstructure and properties have been investigated. The results show that Mg-12Zn-4Al-0.3Mn alloy consists of the ??-Mg matrix and block quasicrystal and exhibits excellent creep resistance compared to commonly used AZ91 alloy. A small amount of calcium addition to the ZA124 based alloys increased the yield strenghth at both ambient and elevated temperatures as well as creep resistance, although the ductility decreased slightly. Microanalysis indicated that the addition of calcium decreased the quasicrystalline phase and caused the formation of some lamellar precipitates of Al₂Mg₅Zn₂ with orthorhombic crystal structure. This Ca-containing Al₂Mg₅Zn₂ phase with high stability straddled the grain boundaries and strengthened grain boundaries by inhibiting crack propagation during creep tests at elevated temperature.     

南通市可再生能源利用现状与前景

文章介绍了可再生能源资源状况,分析了南通市可再生能源的利用现状,指出了南通市可再生能源发展的前景,并对南通市的能源政策提出了建议.