Pure Copper Sheets Research Articles

Evaluation on Microstructure and Mechanical Properties of Severely Deformed Pure Cu

The present study was carried out to evaluate the microstructural and mechanical properties of cross-roll rolled pure copper sheets, and the results were compared with those obtained for conventionally rolled sheets. For this work, pure copper (99.99 mass%) sheets with thickness of 5 mm were prepared as the starting material. The sheets were cold rolled to 90% thickness reduction and subsequently annealed at <TEX>$400^{\circ}C$</TEX> for 30 min. Also, to analyze the grain boundary character distributions (GBCDs) on the materials, the electron back-scattered diffraction (EBSD) technique was introduced. The resulting cold-rolled and annealed sheets had considerably finer grains than the initial sheets with an average size of 100 <TEX>${\mu}M$</TEX>. In particular, the average grain size became smaller by cross-roll rolling (6.5 <TEX>${\mu}M$</TEX>) than by conventional rolling (9.8 <TEX>${\mu}M$</TEX>). These grain refinements directly led to enhanced mechanical properties such as Vickers micro-hardness and tensile strength, and thus the values showed greater increases upon cross-roll rolling process than after conventional rolling. Furthermore, the texture development of <112>//ND in the cross-roll rolling processed material provided greater enhancement of mechanical properties relative to the case of the conventional rolling processed material. In the present study, we systematically discuss the enhancement of mechanical properties in terms of grain refinement and texture distribution developed by the different rolling processes.

Enhancement of Grain Refinement and Mechanical Properties of Cross-Roll Rolled Pure Copper

The aim of this work was to evaluate the effects of strain rate on the microstructural evolution of 5-mm-thick pure copper (99.99%) sheets subjected to conventional rolling (CR) and cross-roll rolling (CRR). The sheets were cold-rolled with a reduction ratio of 90% and then annealed at 400 � C for 30 min to obtain the fully recrystallized microstructures. The resulting cold-rolled and annealed sheets had considerably finer grains than the initial sheets. In particular, the average grain size became smaller by CRR (6.5 mm) than by CR (9.8 mm). The mechanical properties of the sheets, i.e., Vickers microhardness and tensile strength, were more enhanced by CRR than by CR. The microstructural development in these processes was systematically discussed. [doi:10.2320/matertrans.M2010406]

Characterisation of the mechanical behaviour and the forming limits of metal foils using a pneumatic bulge test

The characterisation of metals gains increasing importance due to advanced methods in numerical simulation and design of forming processes. With conventional methods being restricted in the case of characterisation of thin metal sheets, the bulge test is a promising approach with significant advantages compared e.g. to tensile testing. While the hydraulic bulge test is on the verge of being a standard characterisation method of metal sheets in conventional length scale, little knowledge exists about the bulge test using gas pressure. For thin metal foils, requiring relatively small pressure regimes, the pneumatic bulge test offers the possibility of a significant reduction in both experimental complexity and procedure. In this paper, the pneumatic bulge test is applied for the determination of true stress true strain curves and the forming limit diagram of pure aluminium and copper sheet with thicknesses ranging from 25 µm to 100 µm. With these investigations the principle applicability of the pneumatic bulge test for the mechanical characterisation of thin metal foils is verified.

On the evolution of flow stress during constrained groove pressing of pure copper sheet

Using a mechanical model and dislocation density based model, the evolutions of dislocation density and flow stress of pure copper during constrained groove pressing (CGP) process are investigated. In this regard, the strain and strain rate are achieved from the mechanical model and then input into the dislocation model. To verify the predicted flow stress, the process of constrained groove pressing is performed on the sheets of pure copper from one to three passes. The predicted flow stresses are compared with the experimental data and a good agreement is observed. Also, it is found that during the straining of the copper sheet in CGP process, the dislocation density and strength dropping occur in lower strain than that in other severe plastic deformation processes.

On the acting pressure in laser deep drawing

Through the continuing trend of miniaturization new cost efficient and fast methods for processing of small parts are required. In this paper a non-mechanical process for the forming process of micro deep drawing is presented. This new pulsed laser based deep drawing process utilizes an initiated plasma shock wave at the target, which forms the sheet. Several pulses can be applied at one point and therefore high forming degrees can be reached without increasing the energy density. In this article the pressure of the shock wave is measured and optimized. Furthermore laser deep drawing of samples made out of pure aluminum, copper and stainless steel sheet metal with thicknesses of 20 and 50 μm are shown. Finally the forming behavior after single pulses is presented.

Tensile Behavior of Commercially Pure Copper Sheet Fabricated by 2- and 3-Layered Accumulative Roll Bonding (ARB) Process

The tensile properties of two- and three-layered accumulative roll-bonding (ARB) processed copper sheets containing deoxidized low-phosphorous copper (DLP) and PMC90 are investigated with varying numbers of ARB process cycles. The tensile strength of the DLP is determined by the applied equivalent strain, showing that the tensile strength values for both 2-L and 3-L ARBed DLP specimens follow a single trend line. Unlike the DLP, the 3-L ARBed PMC90 follows a trend line that is completely different compared to that of its 2-L counterpart above an equivalent strain value of 7.6, suggesting that the amount of applied equivalent strain alone does not control the tensile strength of PMC90. The mechanism determining the tensile behavior of 2-L and 3-L ARB processed commercially pure copper sheets is discussed.

Corrosion-induced release of Cu and Zn into rainwater from brass, bronze and their pure metals. A 2-year field study

A 2-year field study has been conducted in an urban environment to provide annual release rates of copper and zinc from brass (20 wt% Zn) and copper and tin from bronze (6 wt% Sn) compared to sheets of their pure alloy constituents, copper and zinc. Despite relatively low nominal bulk alloy content, substantially more zinc was released from brass compared to copper. Both metals were released at a significantly slower rate from the brass alloy, compared to the pure metals. The proportion of release rates of copper and zinc from the alloy differed significantly from their proportions in the bulk alloy. Bronze showed relatively constant release rates of copper, being similar to that of pure copper sheet. The release of tin from bronze was negligible. The results clearly show that alloys and the pure metals behave very differently when exposed to rainwater. Accordingly, release rates from pure metals cannot be used to predict release rates of individual constituents from their alloys. Generated data are of importance within REACH, the new chemical policy of the European commission, where metal alloys erroneously are being treated as mixtures of chemical substances.

Electrical Conductibility of Copper Clad Steel Wire by Drawing at Room Temperature

By application of clad-bonding technique of pure copper sheet and plain low carbon steel rebar Q195, the cladding wires in different diameter by drawing at room temperature have been worked. The increasing ratio of the area of grain boundary is in direct proportion to deformation approximately. The resistivity of the cladding wires go up in direct proportion to deformation because the increment of the area of grain boundary results in increment of static disfigurement to electron dispersion. When deformation is less 9.6, the relative increment of resistivity is less 1.1%, i.e. the wire is provided with good electrical conductivity. And the resistance and resistivity of the wires can be estimeted based on copper ratio of transverse section of the cladding wire and the deformation by drawing at room temperature.

Change in Microstructure and Texture during Annealing of Pure Copper Heavily Deformed by Accumulative Roll Bonding

Pure copper sheets were heavily deformed up to equivalent strain of 4.8 by the accumulative roll-bonding (ARB) processed and then annealed. The ARB processed copper showed the ultra-fine grained microstructure which consisted of relatively equiaxed grains having grain thickness of about 0.2 mm. The DSC measurement of the ARB processed specimens revealed that the recrystallization temperature significantly decreased with increasing the number of the ARB cycles. The stored energy did not increase so much at later stage of ARB, which corresponded with the change in microstructure. The recystallization behavior of the ARB processed copper was governed by discontinuous recrystallization characterized by nucleation and growth process. Remarkable development of cube texture ({100}h001i) was found in the specimen deformed to the equivalent strain of 3.2 or larger and then annealed. The concentration of the cube recrystallization texture depended on the number of ARB cycles. [doi:10.2320/matertrans.MA200701]

Tribology of dry deep-drawing of various metal sheets with use of ceramics tools

Lubricant is essential in the conventional metal forming to reduce the friction between tool and workpiece and forming energy, to increase the forming limit, to shorten the forming process, and to prolong the tool life by prevention of galling and seizure. Huge amount of wasted lubricants has become a great nuisance of environmental issues. Dry deep-drawing is attractive toward zero emission of lubricants but it has great difficulty in application to metal sheets in general. As one of the most promising methods, use of ceramic die, are highlighted because of their high tribological properties. In the present paper, practical possibility of dry deep-drawing is studied using ceramic dies. Various ceramic die materials are prepared and actually applied to deep-drawing for various sheet materials without lubrication. The limiting draw ratio (LDR) as well as the drawing load, were used as a parameter to evaluate the friction between tool and blank. Each ceramic material has its own compatibility to sheet materials. Ceramic dies can be applied to deep-drawing of mild steel and pure copper sheets with success, while they failed to be utilized for titanium sheet. Deep-drawability of ceramic dies might be dependent on the covalency of ceramics: i.e. LDR(SiC)>LDR(Si 3N 4)>LDR(Al 2O 3)>LDR(ZrO 2). In case of deep-drawing for metal-alloy sheets, pretreatment to form the adhesive tribo-coating is effective to improve the workability when using alumina and zirconia dies. The adaptive design of ceramic die to each metallic sheet material is indispensable to realize the dry forming in practice.

Lap welding characteristics of thin sheet metals with combined laser beams of different wavelength

It is well known that arc welding of thin metallic sheets in difficult due to their easier distortion and deformation. On the other hand, in laser welding, such distortion and deformation is greatly reduced due to a smaller spot size and smaller heat input than in arc welding. Even in laser welding, thinner metallic sheets become more difficult to weld due to the loss of materials and the difficulty in supporting a shallow molten pool against evaporation and recoil pressure, leading to the formation of cut or drilled welds. In this study, therefore, lap welding characteristics of thin metallic sheets were investigated by utilizing combined beams or respective single beam of normal pulsed YAG laser and Q-switched SHG YAG laser. It was consequently found that the formation conditions for good lap welds in thin stainless steel sheets were broadened by using combined laser beams. Especially, lap welding of pure copper sheets was very difficult with single pulsed YAG laser; however, it was confirmed to be possible to weld them with combined laser beams of two different wavelengths in the air environment.

Effects of adherends recycling on the distribution of hardness in bonded region of adhesively bonded single lap joints

The phenomenon of work hardening in the bonded region of steel adherends has been studied, and the effect of adherends recycling on the shear strength of a single lap joint is analyzed in this paper. The values of hardness on the surfaces of failed joints were measured after being simply treated (removing the adhesive layer by solvent) before the specimen preparation next time. Mild steel or pure copper sheet and an epoxy adhesive were used to prepare the single lap joints and the same couple of adherend pieces underwent three or four times of strength and hardness tests. The results obtained show that the evident hardness change occurred after the adherends passed their first or second strength testing and most of the points tended to increase their values of hardness as the tests were performed. It may be due to the contribution of the stress concentration during loading, and the residual stress occurred after the adherends unloading. The results obtained also show that the increase of hardness occurring in the bonded zone is greater than that on the face opposite to the bonded region. The distribution of micro-hardness was verified by the strain gauges testing method.

異波長重畳レーザによる薄板重ね溶接特性

It is well known that arc welding of thin metallic sheets in difficult due to their easier distortion and deformation. On the other hand, in laser welding, such distortion and deformation is greatly reduced due to a smaller spot size and smaller heat input than in arc welding. Even in laser welding, thinner metallic sheets become more difficult to weld due to the loss of materials and the difficulty in supporting a shallow molten pool against evaporation and recoil pressure, leading to the formation of cut or drilled welds. In this study, therefore, lap welding characteristics of thin metallic sheets were investigated by utilizing combined beams or respective single beam of normal pulsed YAG laser and Q-switched SHG YAG laser. It was consequently found that the formation conditions for good lap welds in thin stainless steel sheets were broadened by using combined laser beams. Especially, lap welding of pure copper sheets was very difficult with single pulsed YAG laser; however, it was confirmed to be possible to weld them with combined laser beams of two different wavelengths in the air environment.

Deformation and Recrystallization Textures in Cross-Rolled Copper Sheet

A study has been made of the deformation and recrystallization textures of 99.99% pure copper sheets which were cross rolled by 82 and 96% reduction in thickness and recrystallized in a salt bath at 450°C for 1h. The deformation texture was approximated by the {011}〈755〉 orientation as the major component and {001}〈100〉 as a minor component. These deformation texture components were well simulated using the rate sensitive relaxed constraints model. The {001}〈100〉 orientation was calculated to be metastable while the {011}〈755〉 orientation was located in the middle of the rotation path between the stable orientations in two cross rolling directions. The recrystallization texture in the center layer of the 96% cross-rolled copper sheet was approximated by {86 50 9}〈10 34 94〉 for each rolling direction. The evolution of the recrystallization texture was discussed based on the strain energy release maximization model.

Solid state reactions in the CuZn system induced by plastic deformation at room temperature

CuZn alloys have been prepared by mechanical alloying of pure copper and zinc sheets and by co-sputtering on liquid N 2 cooled substrates. In the mechanically prepared samples the initial reaction is driven by the diffusion of copper into zinc which leads to the formation of the ε and γ phases. When the overall composition is sufficiently copper rich that the 7 phase is present together with unreacted copper further reactions proceed by the diffusion of zinc into the copper solid solution. The reaction rates appear to have roughly the same value whichever reaction is considered. No amorphous phases were found in alloys prepared both by mechanical alloying and by sputter evaporation.

Studies on Friction Spot Welding of Sheets by Using Vibrated Punching : 2nd Report, Influence of Various Factors on the Joining Process of Pure Copper Sheets

せん断圧接法の接合強度, 接合過程に及ぼす各種因子の影響を, 純銅薄板の接合実験を通して具体的に明らかにした. すなわち, ポンチ振動条件, 材料拘束条件, クリアランス, 表面処理, 予熱の影響を調べ, 板の拘束力とポンチの振動数, 振幅を高め, 予熱を与えることにより, 1秒以内の短時間で高い接合強度が安定して得られることを示した. さらに実験結果の考察の過程で, 前報にて提示した二つの接合過程モデルの検証を行った.

Studies on Friction Spot Welding of Sheets Using Vibrated Punching : 1st Report, Welding of Pure Copper Sheets and Welding Process

板を繰返しせん断する際に材料内部に生成する熱と圧力を利用し、薄板を接合しようとするせん断圧接法を新たに考案した。この方法によりスポット溶接の困難な純銅薄板の接合実験を行った結果、かなり高い接合強度が安定して得られることを確認した。またせん断圧接の接合形態と接合過程には、実験条件によって異なる典型的な二つのパターンが存在することを実験的に明らかにし、これに対応する二つの接合過程モデルを提示した。

アルミニウム合金および純銅の疲れ強さに及ぼす繰返速度の影響について

The effects of speed of cyclic stressing on the fatigue strength of pure Al, duralumin (D), super-duralumin (SD), extra-super-duralumin (ESD) and pure copper sheets were studied on Schenck's vibrating sheet bending machine. Tests carried out using completely reversed stress at 2, 60 and 3600 cycles per minute and the number of cycles to failure varied from 5×102 to over 105. The reduction of fatigue strength increased as speed of cyclic stressing decreased and those phenomenon markedly observed with repeated cycles. ESD showed the max. reduction of fatigue strength at the slowly speed of cyclic stressing and SD and D were next. The relations between the reduction of fatigue strength and the speed of cyclic stressing were shown in Fig. 8.