Dissertation
Dissertation > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metallic materials > Non - ferrous metals and their alloys > Heavy non - ferrous metals and their alloys > Copper

Effects of Processing Technology and Stacking Fault Energies on the Mechanical Properties of Cu-Al Alloys

Author LongYan
Tutor ZhuXinKun
School Kunming University of Science and Technology
Course Materials Physical Chemistry,
Keywords copper alloy Ultra-fine crystal stacking fault energy MechanicalAnnealing hardening
CLC TG146.11
Type Master's thesis
Year 2013
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With the continuous development of human society, people are now paying more attention to the performance of materials. So, it is very necessary to propose some feasible methods to improve the properties of the materials and increase the practical applications of the materials. Cu and Cu-Al alloy make great contributions to the social development, the properties of the Cu-Al alloy could be improved in various ways, such as solution strengthening, grain refinement strengthening, dislocation strengthening, annealing strengthening, etc.All the materials that were selected in experiment of this article use weight percentage, Cu、Cu-2.2wt.%Al、Cu-4.5wt.%Al、Cu-6.9wt.%Al, respectively. This article obtained the Cu and Cu-Al alloy which have high strength and high plasticity simultaneously by using various test methods, these methods include rolling at room temperature, rolling in liquid nitrogen, High Pressure Torsion (HPT), rolling after the Split Hopkinson Pressure Bars, annealing strengthening and the best mechanical properties of the Cu-Al alloy was selected. In order to research the effects of the factors which include the stacking fault energy, processing method, rolling temperature, strain rate and annealing temperature on mechanical properties of materials, we precede stretch experiment on a series of samples, and to analyze the relation of the micro structure and mechanical properties, we precede XRD test on part of test samples.By testing the mechanical properties of samples which are prepared in various processes, we found:with the increasing of Al, the stacking fault energy of the materials decrease, the strength and plasticity of the materials increased simultaneously, the yield strength increased from377.3MPa in Cu to759.8MPa in Cu-6.9wt.%Al, the breaking strength increased from395.6MPa in Cu to882.6MPa in Cu-6.9wt.%Al, and the uniform elongation increased from1.2%in Cu to2.3%in Cu-6.9wt.%Al. By observing the XRD results of rolling samples, we found:with the increasing of Al, the grain size of materials reduced gradually, while the microscopic stress, dislocation density and the twin-crystal density greatly increased.Tensile tests were carried out after the rolling samples annealing at 150℃,200℃,250℃for1h, respectively. We found:the samples which have a high stacking fault energy, such as Cu and Cu-2.2wt.%Al, tend to soften slightly after annealing. However, the samples which have a low stacking fault energy, such as Cu-4.5wt.%Al, Cu-6.9wt.%Al, have a obvious hardening phenomenon after annealing. What’s more, the hardening phenomenon of Cu-6.9wt.%Al was more obvious, in order to research the reason of the hardening phenomenon, we proceed XRD test on Cu-6.9wt.%Al and it’s annealed samples.Tensile tests were carried out on samples that were rolled after Split Hopkinson Press Bars (SHPB)(strain rateε=104S-1) and rolled at room temperature(strain rate ε=5S-1), the result showed:compared to the rolled samples, Cu, Cu-2.2wt.%Al that was rolled after Split Hopkinson Press Bars (SHPB), the strength and plasticity of the materials increased simultaneously. However, compared to the rolled samples, the strength of Cu-4.5wt.%Al and Cu-6.9wt.%Al increased obviously and the plasticity reduced slightly. By observing the XRD results of samples, we found:the grain size of the samples that were rolled after Split Hopkinson Press Bars (SHPB) reduced gradually, while the dislocation density and the twin-crystal density greatly increased.Tensile tests were carried out on samples that were rolled in liquid nitrogen and rolled at room temperature, the result showed:compared to the samples rolled at room temperature, the strength and plasticity of the materials that were rolled in liquid nitrogen increased obviously. By observing the XRD results of samples, we found:the grain size of the samples that were rolled in liquid nitrogen is smaller, while the microscopic stress, dislocation density and the twin-crystal density greatly increased.

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