超细晶材料的制备过程中会产生大量的热，从而削弱材料的强度，为此，文中提 出了超低温挤出切削法( CT-EM) 制备超细晶材料的新工艺，以 7075 铝合金为工件材料， 与常温挤出切削( RT-EM) 作对比，研究两者切屑的形貌、微观组织与力学性能． 结果表 明: CT-EM 与 RT-EM 态的切屑分别呈连续和断续状，且前者表面缺陷少，完整性也更好; 切屑最大硬度分别可达 190( HV) 和 175( HV) ，远高于初始材料的硬度( 105) ; 经 CT-EM 工艺后，晶粒被极大程度地细化，直径可达200nm 以下;晶粒细化强化与位错强化是7075 铝合金主要的强化机制， CT-EM 态7075 铝合金的位错密度更高，位错强化对材料硬度的 贡献更为显著．

 Large amounts of heat generate during the preparation of ultrafine grained materials，which may decrease the strength of materials． In order to solve this problem，a new method named cryogenictemperature extrusion machining ( CT-EM) was put forward． In this method，Al 7075 alloy was chosen as the workpiece material and roomtemperature extrusion machining ( RT-EM) was also conducted for a comparison in terms of chip morphology，microstructure and mechanical properties． The results indicate that ( 1) the chips prepared by CT-EM and RT-EM are continuous and segmented，respectively; ( 2) the surface of the chip obtained by CT-EM possesses fewer defects with better integrity; ( 3) the maximum hardness of CT-EM and the RT-EM samples are 190 ( HV，the same as follows) and 175，respectively，which are far greater than that of the original material ( 105) ; ( 4) after the CT-EM process，the grains are highly refined to less than 200 nm in diameter; ( 5) the grain refinement and dislocation strengthening are two main strengthening mechanisms for Al 7075 alloy; and ( 6) as CT-EM Al 7075 alloy possesses higher dislocation density，the contribution of dislocation strengthening to hardness is greater．