PSI - Issue 2_B

Donka Angelova et al. / Procedia Structural Integrity 2 (2016) 2315–2322 Author name / Structural Integrity Procedia 00 (2016) 000–000

2317

3

Table 3. Parameters of cold rolling for obtaining copper strips in soft, half hard and hard temper.

Cold rolling parameters Soft temper

Number of passes

Half hard temper Thickness (mm)

Hard temper

Thickness (mm)

Reduction (%)

Reduction (%)

Thickness (mm)

Reduction (%)

16,3 12,8

29,13 21,47 25,00 29,17 30,88 44,68 52,69 41,46

1 2 3 4 5 6 7 8

15,3 10,7

30,07 18,69 33,33 18,97 55,32 58,10 20,45 30,07

18,3

25,68 23,77 31,18 29,17 30,88 44,68 42,31 50,00

13,95

9,6 6,8 4,7 2,6

8,7 5,8 4,7 2,1

9,6 6,8 4,7 2,6 1,5

1,23 0,72

0,88

0,7

0,75

For producing ETP-copper strips in half hard temper, the copper slabs are subjected to: (a) hot rolling (their parameters at different passes are shown in Table 2); and (b) cold rolling (their parameters at different passes are shown in Table 3). After the cold rolling a process of annealing is performed in Continuous annealing and cleaning machine “Junker” at a temperature of 650 o C for a proper homogenization of the copper microstructure. In order to produce half hard temper the strip is subjected to additional plastic deformation (a skin pass) and to flattening done on Tension leveling machine. The needed additional deformation is 12% which leads to the final thickness of the strip of 0,70 mm. The final process of strip produce is that of strip cutting up to a given width; in this case an additional tension is applied during the coiling process in order to obtain a necessary strip flattening. For producing ETP-copper strips in hard temper, after the hot rolling (all parameters at different passes are shown in Table 2) the copper is subjected to cold rolling (its parameters at different passes are shown in Table 3) reaching an intermediate thickness. Then for microstructural homogenization the strip is annealed in Continuous annealing and cleaning machine “Junker” at a temperature of 650 o C. The final thickness is reached by cold rolling on Cold rolling mill “Senzimir” at a deformation of 18 %. The final process of strip produce is that of strip cutting up to a given width; an additional tension is applied during the coiling process in order to obtain a necessary strip flattening. Mechanical tensile test characteristics – tensile strength, yield strength and elongation after fracture – are obtained by using Standard mechanical testing machine “Zwick/Roell”. Vickers hardness is obtained by Hardness testing device “Instron” on the same specimens (those used for the tensile tests). The electrical conductivity is measured by using Electrical conductivity testing device “Sigma”. All tests are performed at room temperature with standard flat specimens for tensile testing (accordingly to the Standard BDS EN ISO 6892-1:2009) shown in Fig. 1. The shape of specimens ensures homogeneous uni-axial stress state in the working part of each specimen during the testing. The obtained values of all mechanical characteristics – tensile and yield strength, and Vickers hardness – depend on a given copper-strip temper, Table 4. The Vickers hardness is measured accordingly to the Standard BDS EN ISO 6507-1:2006. In order to find the influence of the copper microstructure on electrical conductivity of the rolled strips and their mechanical properties, a metallographic examination is done on specimens made of the three different tempers; the grain size of each temper is determined accordingly to the Standard BDS 11174:1982.

Fig. 1. Geometry of specimens for mechanical testing, all dimensions are in mm