Study Of The Effects Of Grain Size And Temperature On The Mechanical Properties Of Cu-zn Alloy

Cu-Zn alloys deserve a special attention in their applications in transport, electronic, electric, national defense, building and so on due to their good combination of strength and toughness and excellent corrosion resistances. H62 brass, also called commercial brass, is a typical type of Cu-Zn alloys. To enhance the strength of the Cu-Zn alloy without losing its good plasticity is the key to enlarge its application. In addition, since the service environment is complex, the mechanical properties of the Cu-Zn alloy under different temperatures need to be testified.In this study H62 brass was used. After cold rolling to 80% thickness reduction, the material was annealed at a series of temperatures for various holding times. Optical microscopy, transmission electron microscope(TEM), microhardness testing and tensile testing were employed to study the microstructures and mechanical properties of the processed materials. Samples with different grain sizes were tested by tension at various temperatures and different strain rates. By utilizing electron backscatter diffraction(EBSD) technique and TEM, temperature dependence of work hardening, and strengthening and toughening mechanisms of deformed twinning were studied. The main results are as follows:① A nanostructured brass was achieved by 80% cold rolling. The structure was mainly composed of nano-spaced deformation twins. By annealing at different temperatures, a series of brass samples with different grain sizes was produced. By annealing at a low temperature(250℃), an ultra-fine grained(UFG) material was obtained; there were still many nano-spaced deformation twins preserved in the ɑ phase. By annealing at a high temperature(550℃), an coarse grained(CG) materials was obtained.② The microhardness of deformed alloy increased when the alloy was annealed in the low temperature range from 150℃ to 280℃. The strength of the cold rolled sample was increased and the ductility decreased after annealing at 150℃. The 300℃ annealed sample has a good combination of strength and toughness.③ The strength and elongation of the CG sample decreased with increasing testing temperature. The elongation of the sample decreased significantly when tested at 290℃. However, the strength of UFG sample decreased and elongation increased with increasing testing temperature.④ The strength and elongation of both the UFG and CG samples increased when tested at low temperatures. The working hardening rate of both the UFG and CG samples increased with decreasing temperature. The UFG sample showed higher work hardening rates in the early stage of plastic deformation than the CG sample at all testing temperatures. Low temperature facilitated nano-twinning in the ɑ phase of the Cu-Zn alloy investigated.