| Alumina dispersion strengthened copper alloy which has high strength and high conductivity, and can retain high strength at elevated temperature, is one kind of advanced copper alloy with superior combination properties .And this alloy has been used in many high and new technology fields, such as, high power microwave tubes, aotomobive welding electrodes, lead wires, nuclear engineerings, aerospace,et al. Before study of this alloy are mainly focused on its preparation methods and processes, but the study of cold-working behavior and the change of properties and microstructure of dispersion strengthened alloy is few, and the system contrast studies of these properties in different alumina content dispersion strengthened copper alloy are much fewer. But these studies, either for the fabrication and application of dispersion strengthened copper alloy or for recovery and recrystalization theory, have important meaning.The different alumina content dispersion strengthened copper alloys are fabricated by simplified internal oxidation processs, and cold-working and annealing behaviors of low, middle and high alumina concentration dispersion strenghthened copper alloy have been investingated. The major results can be summarized as follows:1. Through studying the cold-working performance of oxygen-free copper and several different alumina concentration dispersion strengthened copper alloys, oxygen-free copper is found out not having work softening characteristics, but low, middle and high alumina concentration dispersion strengthened copper(alumina concentration is 0.23,0.54and 2.25vol% separately) have this characteristics, and with the alumina content increasing, work softening characteristics become weaker.2.By studying the cold rolled alumina dispersion strengthened copper alloy with TEM, it is found that nano alumina particles affect dislocation configuration of alloy, and dislocations produced in the process of deformation are homogeneously and radom distributed in the matrix, and are not easy to form dislocation cells. Especially for the high alumina concentration alloy, a large number of nano alumina particlesinhibite dislocation long-range moving and focusing, and result in dislocation cells being more difficult formed.3.When low alumina concentration dispersion strengthened copper alloy is rolled to a degree, unlike dislocations annihilate each other, and the smaller oritation difference neighbor dislocation cells merge into the larger subgrains. According to Hall-Petch theory, the increase of grain size results in the strength decreasing, therefore low alumina concentration dispersion strengthened copper alloy has work softening characteristics as cold rolled to a degree. With the increasing of alumina concentration, the drag force of alumina particle to dislocation is also increased, and the propability of unlike dislocations annihilating is decreased, therefore the higher alumina concentration, the weaker of work softening of alumina dispersion strengthened copper alloy.4.The grains of dispersion strengthened copper alloy are elongated and arranged into fibrous tissue through unidirection rolled,and rough alumina particles(0.2~0.5 u m) distributing on the original grain boundariy are inherited on the fibrous boundary during the rolled process, which results in the fibrous boundaries becoming weak bonding planes. And this change of structure leads to the strength of lateral direction is always lower than the strength of longitidunal direction either cold rolled state or 900°C lh annealing state for unidirectional rolled dispersion strengthened copper alloy, and the anisotropy of mechanical properties of alloy is serious.5.The anisotropy of mechanical properties of dispersion strengthened copper is weakened utilizing the tandem rolling technology. Recrystalization grains are smaller after annealing at 900 °C for one hour, and it is difficult to see the recrystalization grains under the metallographic microscope. The anisotropy of annealing state increasing a little, and which possibly resulted from the directional property of recrystalization grain growing along the rolling direction.6.Both the middle and high alumina concentration dispersion strengthened copper alloys , only the recovery is occurred even annealed at high temperature under 1020 °C therefore this two kinds of alloys have a higher ability to retain their strength at high temperatures than oxygen-free copper. During the high temperature annealingprocess, the rearrangement of dislocation is inhibited by high stable nano alumina particles, and with the increasing of alumina particle concentration, the subgrains formed during the same temperature annealing process are decreased, and subgrain size is much smaller. During the recovery process, the rearrangement of dislocation can produce a large number of dislocation cells uneasy formed during the cold working.7. The ability to retain strenghth at high temperature is worse for low alumina concentration dispersion strengthened copper alloy, the studies of mechanical properties, metallographic and TEM micrstructure all show that the recovery of low alumina concentration alloy cold rolled is main during annealing at 300-400°C for one hour, and the recrystalization is occurred after annealing at 500°C for one hour.8. The strength and hardness of low alumina concentration dispersion strengthened copper alloy annealing at the temperature above 700 °C are higher than that of annealing at 700 °C, and the elongation remains unchanged, the metallographic structure show that since the recrystallization grains formed after annealing at 900 °C are smaller than that of 700°C, fine grain strengthening is worked in the alloy, and the increment of theoretic fine grain strengthing is the same as the experimental measured. |
PDF Full Text Request