The recycling potential of solder affected scrap/waste copper is investigated in the current research under the influence of work hardening and thermal treatments. 35% turns out to be a critical deformation level where the hardness/strength of copper-tin alloy replaces pure copper and copper-tin-lead alloy replaces copper-tin alloy. The brazed copper has shown that its COF is between that of copper-lead alloy and copper-tin alloy with the maximum COF value of 0.533.
LIST OF TABLES
INTRODUCTION
Another issue is the operational lifetime of the workpiece, which is subject to thermal aging and recrystallization, which ultimately results in behavioral change of copper-based materials/alloys [22]. This thermal aging can again be done deliberately to comply with some of the product's properties during manufacture. Comparative assessment of the actual state of properties of the proposed alloy with respect to pure copper, conventional copper alloys as well as simulated alloys of copper with individual elements of solder.
MATERIALS AND METHODS
In this way, the bar thickness was reduced slowly and gradually with the increase of the number of passes of the cold rolling process. Samples of the first category were kept free from heat treatment to conduct the series of experiments to observe the individual effects of alloying elements and work hardening. Then, the volume loss values and densities of the sample materials were used to obtain the wear loss values in µg unit.
INVESTIGATION OF MICRO-HARDNESS
Measured microhardness values for four sample materials viz. material-I (pure Cu), material-II (Cu-Sn alloy), material-III (Cu-Pb alloy) and material-IV (SnPb solder affected Cu) are analyzed before and after work hardening. However, figures 3.6 and 3.7 show relatively smaller fluctuations in microhardness values than in fig. As a result, the inclusion of Pb with microhardness value of only 6.4 HV has lowered the hardness of material-III (Cu-Pb alloy).
INVESTIGATION OF TENSILE BEHAVIOR
The UTS values have been increased with the increase in work hardening levels for all four test materials. The UTS values of all four sample materials have been observed to increase initially with the increase in aging temperature as indicated by black, red, green and blue lines for material-I, -II, -III and -IV respectively. While the strain rate is varied from 10-4 s-1 to 10-3 s-1, all four sample materials have shown significant reduction in the ultimate elongation values.
After the samples were subjected to work hardening, the yield strength values increased with increasing work hardening levels for all four sample materials as shown in Fig. The yield strength values of material-I, -II, -III and -IV were observed after thermal aging at different temperatures from 25℃ to 450℃ for 75% cold roll work hardening conditions are shown in fig . The yield strength values of all four sample materials are observed to increase initially as shown by the black, red, green and blue lines for material-I, -II, -III and -IV, respectively.
The values of elastic modulus of material-I, -II, -III and -IV observed after thermal aging at different temperatures from 25℃ to 450℃ at 75% cold rolled work hardened conditions are shown in Figure. The values of tangent modulus of the material -I, -II, -III and -IV observed after thermal aging at different temperatures from 25 ℃ to 450 ℃ at 75% cold-rolled work hardened conditions are shown in Figure. However, the tangent modulus values of all four sample materials were found to increase slowly at a strain rate of 1.0 x 10-2 s-1 and higher.
The UTS and yield strength values were found to increase with increasing strain rate for all four sample materials. Increasing the strain rate decreased the ultimate elongation of all four sample materials. However, cold rolling work hardening has no effect on the elastic modulus of all four sample materials.
INVESTIGATION OF FRICTION AND WEAR BEHAVIOR
Taking this into account, the wear loss for Cu, Cu-Sn, Cu-Pb and Cu-Sn-Pb alloys was observed with respect to the sliding distance traveled at a speed of 0.513 ms-1 with a normal load of 20 N in dry sliding condition and shown in Fig. However, the sequence of wear loss after a sliding distance of 200 m or more is as follows: Cu-Sn alloy < Cu-Sn-Pb alloy < Cu-Pb alloy < pure Cu. 3.5, i.e. the hardest material (Cu-Sn alloy) showed the least wear loss (highest wear resistance), followed by Cu-Sn-Pb alloy as the second hardest alloy, then Cu-Pb alloy and pure Cu is found to be least wear resistant with maximum wear loss in dry sliding friction.
Specific wear rates of copper, high Cu-Sn alloys, high Cu-Pb alloys and SnPb solders are affected. Basically, the wear rate relative to the sliding distance is the highest for the Cu-Pb alloy. For initial sliding, it is followed by Cu-Sn-Pb alloy at wet sliding condition FW.
Here, pure Cu showed a higher wear rate than the Cu-Sn-Pb alloy in the initial sliding stage. The lowest COF was observed for the Cu-Sn alloy over the entire sliding distance with a maximum value of only 0.251 in the dry sliding condition. FE-SEM images of worn surfaces of pure Cu, high Cu-Sn alloy, high Cu-Pb alloy, and SnPb solder after wear for a sliding period of 90 minutes covering a sliding distance of 2772 m at an applied pressure of 1.02 MPa (load = 20 N) and a sliding speed of 0.513 ms-1 in the dry sliding condition are shown in Figure 1.
In addition, Cu-Sn alloys and Cu-Sn-Pb alloys showed the formation of some intermetallic spots after dry sliding.
INVESTIGATION OF CORROSION BEHAVIOR
In this study, the corrosion behavior of four model copper-based materials was investigated in freshwater and seawater environments. In order to investigate the corrosion behavior of four sample copper-based materials in a seawater environment, approximately 2000 liters of water were collected from each of three locations in the Bay of Bengal. Initially, all curves were found to be steeper, indicating greater weight loss per exposed surface due to the first attack of seawater constituents.
It is thus observed that the cumulative weight loss in seawater has been increased by 50.1%. Therefore, cold rolling reduces the weight loss for copper-based materials in a seawater corrosive environment. But the work hardening effects are found to be diminishing after immersion in seawater corrosion as observed in Figure 6.12(b) and (c).
6.13 (a) illustrates that the corrosion rates of the samples in seawater are highest on the first day of immersion, with values of 0.38 mmpy, 0.53 mmpy, 0.62 mmpy, and 0.54 mmpy, respectively. It indicates the immunity level of copper-based materials in plain water and moderate corrosion in seawater. The corrosion rates of the three sample materials in the same seawater environment with respect to the immersion period are shown in Fig.
SEM images of 75% cold-rolled four material samples after corrosion in seawater for 36 days are presented in Fig.
INVESTIGATION OF CONDUCTIVITY AND THERMAL STABILITY
As such, the electrical conductivity values of material-II, -III and -IV are found to be significantly reduced. Again, Sn has been found to have a prominent influence on the values of electrical conductivity compared to Pb in the copper alloys due to complex formation of CuxSny intermetallic compounds [34-35]. When the samples have undergone work hardening from zero to 75% strain levels, the electrical conductivity values of material-I, -II, -III and -IV are found to differ to different degrees as shown in Fig.
It indicates that the electrical conductivity of material-I, i.e. pure Cu, is found to vary insignificantly (black line in Figure 5.1) and is reduced by only 1.53% after 75% cold-rolled deformation from the conductivity value obtained before the hardening. It would be worth mentioning that the ~35% hardening deformation is realized as the optimal level of cold working for maximum recovery of electrical conduction loss due to incorporation of solder into copper. When the deformation further increases by more than 35%, the electrical conductivity of the alloys shows a decreasing trend, which, however, appears to contradict the hardness behavior (see Figure 3.3).
Therefore, it is generally found that the electrical conductivity of material-IV increases but not significantly with longer aging period along with aging temperature. In contrast, changes in electrical conductivity values with isothermal and isochronous aging were not significant. Therefore, electrical conductivity cannot be considered to be correlated with hardness with respect to thermal aging.
The electrical conductivity of copper is found to be significantly affected by the inclusion of trace amounts of lead and/or tin.
CONCLUSIONS AND RECOMMENDATIONS
It appears that alloying copper with tin or lead reduced its resistance to corrosion, especially in acidic environments. Influence of alloying elements on the physical-mechanical properties of copper and tin bronze, Russian Metallurgy (Metal. Hardening characteristics of copper from constant strain rate and stress relaxation testing, Materials Science and Engineering: A, 506, Issues.
Effect of degree of cold work and annealing temperature on the microstructure and properties of cold drawn copper wires and tubes. Investigation of Recrystallization and Grain Growth of Copper and Gold Bonding Wires, Metallurgical and Materials Transactions A, Vol. Effect of thermal aging on the tensile properties of hot- and cold-rolled commercial high-conducting metal and its alloy, AIP Conference Proceedings.
Investigation of mechanical properties of Cu/SiC composite fabricated by FSP: Effect of SiC particle size and volume fraction. Copper Development Association Inc., Web site data sheet on mechanical properties of copper and its alloy. Effect of strain rate on tensile mechanical properties of electron beam welded OFE copper and high purity niobium for SRF applications.
Mechanical and wear properties of copper-lead alloy produced by powder metallurgy processing technique, Journal of Chemical Technology and Metallurgy.
LIST OF PUBLICATIONS
![Fig. 4.3 True stress versus true strain curves of pure copper base metal (BM) and friction stir welded (R600T25, R600T75 and R900T75) samples [46]](https://thumb-ap.123doks.com/thumbv2/filepdfnet/10866039.0/71.918.214.737.111.481/stress-versus-strain-friction-r600t25-r600t75-r900t75-samples.webp)
![Fig. 4.5 The true stress–strain curve for pure aluminum and copper [48].](https://thumb-ap.123doks.com/thumbv2/filepdfnet/10866039.0/72.918.216.745.120.529/fig-true-stress-strain-curve-pure-aluminum-copper.webp)
![Fig. 4.6 Engineering stress–strain curves of the HT 50 µm copper wires with different gauge lengths: 10D, 50D and 100D (diameter of specimen) [49]](https://thumb-ap.123doks.com/thumbv2/filepdfnet/10866039.0/72.918.229.757.617.986/engineering-stress-strain-curves-different-lengths-diameter-specimen.webp)
