8.3 Void size

For the blanks subjected to tension-compression strain condition, the SEM images showed many bigger micro-voids and dimples, and their surface was rough

Figure 7. Forming limit diagram of Al sheet of various grades [34, 35].

and irregular. This showed shear type of fracture with deep dimples [1]. The surface of the metal sample was smooth with shallow dimples and less voids in plain strain condition, whereas in TC condition, the SEM images showed larger voids and deep dimples, and hence the surface was irregular. This indicated the presence of shear type fracture with deep dimples [2]. For the blanks subjected to plane strain condition (blank width of 120 mm), the surface was smooth compared to the tension-compression condition with less number of voids, shallow dimples and less fracture area.

#### 8.4 Void area fraction

The number of voids as well as their type were affected by the forming conditions [1]. The sheets annealed at 350°C showed a larger number of voids and deformation than sheets annealed at 200, 250 and 300°C. This could be due to the presence of fully recrystallized grains. The microstructure also clearly indicated a favourable interaction between precipitation and recrystallization [26] at 350°C. If the strain hardening index (n) value was more, the strain required for the plastic deformation was also more. During annealing at 350°C, the strain hardening index value was high.

#### 8.5 L/W ratio

Length-to-width ratio in the void. The L/W ratio of void for the sheet annealed at 200°C was found to be the highest.

The slope value obtained for void size was high for TC region because they showed

L/W ratio of voids vs. minor strain at fracture (ε2) at various annealing temperatures and thickness.

Variation of void properties in Al 1350 alloy with respect to annealing temperatures in different regions.

This might be due to the fact that one stress was tension and the other was compression which increased the maximum shear stress of the Mohr's circle. The intercept value for void area fraction plot was high for TC region compared with

The slope value and the ligament thickness of annealed sheet were found to decrease in the TC region than that in TT region. This might be due to plastic

TT region because in TC region the plastic deformation was higher.

more plastic deformation.

Figure 9.

43

Figure 8.

Aluminium and Its Interlinking Properties DOI: http://dx.doi.org/10.5772/intechopen.86553

deformation of the metal sheet.

#### 9. Interlinking effects of void parameters

#### 9.1 Effect of void properties with annealing temperatures

Figures 8 and 9 showed the variation of void properties with respect to annealing temperatures in different regions such as (a) TC, (b) PS and (c) TT.

Figure 8. Variation of void properties in Al 1350 alloy with respect to annealing temperatures in different regions.

#### Figure 9.

and irregular. This showed shear type of fracture with deep dimples [1]. The surface of the metal sample was smooth with shallow dimples and less voids in plain strain condition, whereas in TC condition, the SEM images showed larger voids and deep dimples, and hence the surface was irregular. This indicated the presence of shear type fracture with deep dimples [2]. For the blanks subjected to plane strain condition (blank width of 120 mm), the surface was smooth compared to the tension-compression condition with less number of voids, shallow dimples and less

Forming limit diagram of Al sheet of various grades [34, 35].

Aluminium Alloys and Composites

The number of voids as well as their type were affected by the forming condi-

Length-to-width ratio in the void. The L/W ratio of void for the sheet annealed

Figures 8 and 9 showed the variation of void properties with respect to annealing temperatures in different regions such as (a) TC, (b) PS and (c) TT.

tions [1]. The sheets annealed at 350°C showed a larger number of voids and deformation than sheets annealed at 200, 250 and 300°C. This could be due to the presence of fully recrystallized grains. The microstructure also clearly indicated a favourable interaction between precipitation and recrystallization [26] at 350°C. If the strain hardening index (n) value was more, the strain required for the plastic deformation was also more. During annealing at 350°C, the strain hardening index

fracture area.

Figure 7.

value was high.

8.5 L/W ratio

42

at 200°C was found to be the highest.

9. Interlinking effects of void parameters

9.1 Effect of void properties with annealing temperatures

8.4 Void area fraction

L/W ratio of voids vs. minor strain at fracture (ε2) at various annealing temperatures and thickness.

The slope value obtained for void size was high for TC region because they showed more plastic deformation.

This might be due to the fact that one stress was tension and the other was compression which increased the maximum shear stress of the Mohr's circle. The intercept value for void area fraction plot was high for TC region compared with TT region because in TC region the plastic deformation was higher.

The slope value and the ligament thickness of annealed sheet were found to decrease in the TC region than that in TT region. This might be due to plastic deformation of the metal sheet.

### 9.2 Effect of L/W with minor strain

#### 9.3 Effect of void area with minor strain

Figure 10 shows a plot between void area fraction and the mean strain for all sheets which have been tested. As observed from the figure, the void area fraction for the sheet annealed at 200°C has been found to be the lowest of all sheets tested. 9.4 Effect of d-factor with strain triaxiality ratio

Aluminium and Its Interlinking Properties DOI: http://dx.doi.org/10.5772/intechopen.86553

d-factor vs. mean strain (εm) at various annealing temperatures.

Void area fraction (Va) vs. strain triaxiality factor (To) at various annealing temperatures.

temperatures.

Figure 12.

Figure 13.

45

Figure 11 shows a plot between d-factor and strain triaxiality ratio for all sheets tested. As the strain triaxiality ratio increase, the d-factor also increased. As the d-factor increased, the formability of the sheet decreased and vice versa.

The d-factor was found to be lowest for the metal sheet annealed at 350°C indicating formability property compared to the sheets annealed at different

Figure 11. d-factor vs. strain triaxiality factor (To) at various annealing temperatures.

9.2 Effect of L/W with minor strain

Aluminium Alloys and Composites

Figure 10.

Figure 11.

44

9.3 Effect of void area with minor strain

Void area fraction (Va) vs. mean strain (εm) at various annealing temperatures.

d-factor vs. strain triaxiality factor (To) at various annealing temperatures.

Figure 10 shows a plot between void area fraction and the mean strain for all sheets which have been tested. As observed from the figure, the void area fraction for the sheet annealed at 200°C has been found to be the lowest of all sheets tested.
