The Influence Of Stacking Fault Energy On The Propertype Mechians Of Nanocrystlline Cu-Al Alloy

From the beginning of human civilization to today, copper do great contribution on the continuous progress of human society. With the development of human civilization, copper and copper alloys are developed several new uses constantly. Thus copper and copper alloys have become modern engineering materials which are full of vigor and vitality. In the 21st century, as requirements on the properties of metal materials increasing, copper alloys which are widely used in civil and military industries also are required with high mechanical properties. So it has important value of theory and practice to raise an economic way which can get materials with high strength and good ductility simultaneously.This paper chooses different weight percents of Cu-Al alloy (Cu-2.2 wt%Al, Cu-4.5 wt% Al, Cu-6.9 wt% Al). The pure Cu is chosen as reference for the whole serials alloy. The relationship of material and their stacking fault energy are Cu=78 ergs/cm2, Cu-2.2 wt.%Al=35 ergs/cm2,Cu-4.5 wt.% Al=7 ergs/cm2,Cu-6.9 wt.%=5 ergs/cm2. We choose the way of cold-rolling at liquid nitrogen temperature and accumulating high plastic deformation value to get nanocrystalline. We choose A series to do tensile tests. For the purpose of investigating the influence of stacking fault energy on every stage of strain hardening, compression tests with hot-rolling serials are involved. For building the relationship between mechanical properties and microstructure, metallographic photos and XRD test are taken.By the analysis of XRD data of the cold-rolling sample, it is apparently that, with the Al content of alloy increasing, the grain size decreases. In another hand the micro-strain, the dislocation density and the twin density increases dramatically.By the comparison of metallographic photos in stage B and stage D, it is easily to find the phenomenon of primary twin and the second twin. The second twin is caused by twin intersection.The results of tensile tests tell us that with the Al content increasing, the strength of alloy increases. But the best ductility material is Cu-4.5 wt.% Al. The others follow the law of Cu>Cu-2.2 wt.% Al>Cu-4.5 wt.% Al. So it raises that the optimal stacking fault energy of Cu-Al alloy (Cu-4.5 wt.% Al) leads to high strength and good ductility simultaneously.The compression test results give us a good proof that work hardening rates of plastic deformation are different between low stacking fault energy materials and medium/high stacking fault energy materials. There are two platforms in normalized strain hardening rate and true strain curve. The first platform is the formation of primary twin. The second is the formation of the second twin which is caused by twin intersection.