| Cu-0.4 wt.%Cr-0.02 wt.%Si alloys with different contents of Zr and Mg elements were prepared by casting, heat treating and cold drawing. The drawn microstructure of the alloys was investigated at different drawing ratios. The effects of Zr and Mg elements on the microstructure, mechanical and electrical properties during drawing deformation were discussed, and the alloy composition was suitably selected. Meanwhile, the effects of intermediate heat treatments on microstructure and properties were also studied in order to improve the heat treatment process. In these alloys, Cu-0.4 wt.% Cr-0.12 wt.% Zr-0.02 wt.% Si-0.05 wt.% Mg alloy showed a more excellent match between strength and conductivity. The cold drawing behaviour and the thermal stability of Cu-0.4 wt.% Cr-0.12 wt.% Zr-0.02 wt.% Si-0.05 wt.% Mg alloy were investigated. The relationship between the stored energy and flow stress which are connected by dislocation density has been discussed.The tensile strength of the four test alloys increases with extended plastic deformation and the tensile strength of adding Zr element alloy is always higher than that of non-Zr alloys. Mg element also shows some strengthening effect, but the effect of Mg element on the strengthening is lower than Zr element. As drawing deformation increases, the relative conductivity of the four alloys generally decreases. Zr addition shows a more significant negative effect on the electrical conductivity of the alloys at higher drawing ratios and the conductivity can drop by about 7.2% IACS withη=6.1. Mg addition maintains a basically constant effect on the electrical conductivity of the alloys at different drawing ratios and the conductivity fluctuations is about 2～3% IACS.With annealing time extending, the hardness of the four test alloys increases first and then decreases, reaching their peak values after annealing treatments at 500℃for 1 hour. The hardness of Zr containing element alloy is always higher than that of Zr free element alloy. The relative conductivity of the four test alloy increases sharply and then slowly with increasing annealing time and reaches their peak values after 1 hour annealing treatments.Cold drawing was conducted at room temperature to impose high strain into Cu-0.4 wt.%Cr-0.12 wt.%Zr-0.02 wt.%Si-0.05 wt.%Mg. An increasing cold drawing strain leads to a sharply decrease in filament size at first and then a saturation value of～490 nm. The crystal orientation is deviating from the as-cast specimens and<111> texture is gradually formed. The flow stress, microstrain, dislocation density and stored energy are gradually increasing beforeη= 6.7. The thermal analysis was carried out for the alloy at different draw ratios. The stored energy was calculated and utilized to estimate the dislocation density and the flow stress. It was found that the stored energy increases with the draw ratio rising until a peak is reached withη=6.7. The release of stored energy is primarily due to the decrease of dislocation density. The dynamic recovery has taken place as 6.7<η≤7.4, which is confirmed by the change of the crystal orientation, microstrain, stored energy, flow stress and dislocation density.The Cu-0.4 wt.% Cr-0.12 wt.% Zr-0.02 wt.% Si-0.05 wt.% Mg alloy was drawn toη=6.0 and annealed at different temperatures. With the annealing temperature increasing, the ribbonlike Cu crystals are gradually replaced by gross equiaxed grains, resulting in the reduction in hardness, flow stress and electrical resistivity. The crystal orientation of as-draw specimen is gradually approaching that of full annealed specimen and the hardness difference between longitudinal and transverse directions decreases as annealing temperature increasing. The release of stored energy and the reduction of resistivity are primarily due to the decrease of dislocation density. The main strengthening effect is attributed to dislocation mechanism in Cu-0.4 wt.%Cr-0.12 wt.%Zr-0.02 wt.%Si-0.05 wt.%Mg alloy.
|
PDF Full Text Request