Study On The Mechanism Of The Strength And Tensile Behavior Of Cu-Zn And Cu-Al Alloys

At present, the work hardening theory is the main aspect for the study of the strength and ductility of the metal. Work hardening is concerned with evolution of microstructure in materials(for example, the dislocation motion). The main goal of the work hardening theory is to explain the stress-strain curve and learn the evolution of microstructure over the process of strain. Therefore, it is necessary to deepen the research on working hardening. UFG/NC materials which have been fabricated by severe plastic deformation (SPD) techniques usually have high strength but disappointingly low ductility, and subsequently these materials are not used extensively. Therefore, the influence mechanism of the strength and ductility is becoming the one of the hot focuses for these materials which were fabricated by the SPD techniques.Based on the compression tests we analyze the true stress and true strain curve of the different stacking-fault energy (SFE) of Cu-Zn alloys (Cu Cu-10wt.%Zn Cu-20wt.%Zn and Cu-30wt.%Zn with SFE-80,36,18and14mJ/m2respectively). Through the true stress and true strain curve we have proposed that the work hardening behavior of Cu and Cu-Zn alloys should be divided two distinct stages by defining a true train of0.1as the dividing point. The mechanism of materials is very complicated before a true strain of0.1, the strength of Cu Cu-10wt.%Zn Cu-20wt.%Zn and Cu-30wt.%Zn decreased with increasing strain, which is especially effected by twinning solid-solution strengthening ordering strengthening and dislocation cell, etc. After a true strain of0.1, the mechanism of materials mainly included fine grain strengthening and the strengthening of deformation twins. Therefore, through the analysis of the different stages in the compression tests we have demonstrated the behavior of the materials'work hardening and the microstructure evolution mechanism of the material during the strain.Through the stress-relaxation experiments were performed on Cu alloys (including Cu-Al Alloys Cu-Zn Alloys) which were fabricated by the multiple passed cold rollding for five times, each time lasted for50s. These experiments characterized the influence of physical activation volume(Ⅴ*) mobile dislocations density(ρm/ρm0) and strain rate sensitivity(m) on the strength and ductility of different composition of alloys. In the tensile tests, the value of Ⅴ*is between Ib3-100b3which indicates that the deformation process of the material includes the accumulation nucleation and delivery of the dislocation and the slip of the grain boundaries. The value of m is between0.02-0.03which indicates that the materials fabricated by the SPD techniques do not have the superplasticity. The value of ρm/ρm0decreases indistinctly with the increase of the Zn and Al in the metal Cu, which indicates that large numbers of deformation twinning exist in the materials fabricated by the SPD techniques. At the same time, the deformation twinning could promote the work hardening efficiently and maintain the mobile dislocation.