5. Mechanical/tensile properties

Ductility and formability could be better indicated by average strain hardening exponent (nav), normal anisotropy value (rav), strain rate sensitivity (m) and navrav value, and these parameters increased as the annealing temperature increased (Figure 3).

As temperature increased, the navrav value increased, and formability also increased. The average strength coefficient (K) is comparatively less for the sheet

Figure 3. The variation of mechanical/tensile properties with respect to annealing temperatures [30, 32–35].

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

annealed at 200°C (i.e., low temperature) due to the presence of cold-worked microstructure. At annealing temperatures of 250, 300 and 350°C, the ultimate tensile strength and yield stress of metal sheets were found to be low. The percentage elongation, strain hardening index, anisotropy and k-value, however, increased with annealing temperature. At 350°C, the annealed sheet showed fully recrystallized microstructure, which may be due to relieving of internal strain energy formed during cold working and formation of new strain-free grains which increased the percentage elongation.

This may be due to the softening of metal at higher annealing temperatures. Similar behaviour was observed for all grades of aluminium sheets selected. In Al alloy sheet, the factor navrav formability index showed a direct relationship with formability of sheet metal. As the factor navrav increased, the formability also increased [2, 27, 28]. The percentage increase of navrav index in zone 3 was found to be highest due to fully recrystallized microstructure as shown in Figure 4. The next highest was observed in zone 1 (due to full recovery) followed by zone 2. Similar behaviour was observed in all commercially available Al sheets annealed at different temperatures.

Tables 2 and 3 show the different annealing temperatures of aluminium alloy sheet metals with different mechanical properties and formability properties, namely, strain hardening exponent, yield strength, tensile strength, r-value (plastic

Figure 4. The variation of formability properties with respect to annealing temperatures.


these alloys. An increase in the annealing temperature shows the presence of a larger amount of precipitated particles; the colour may be grey, which is due to the presence of silicon and white spots [25] is due to the presence of iron, which might ultimately increase the formability. The Fe and Si particles were capable of stabilizing a fine-grain/sub-grain structure, which could be used to develop interesting combinations of strength and ductility [2, 30–35]. Titanium increased the recrystallization temperature, induced grain refinement and remained mostly

Microstructure of aluminium alloy 1350 sheets annealing at four different temperatures [32, 33].

Ductility and formability could be better indicated by average strain hardening exponent (nav), normal anisotropy value (rav), strain rate sensitivity (m) and navrav value, and these parameters increased as the annealing temperature increased

As temperature increased, the navrav value increased, and formability also increased. The average strength coefficient (K) is comparatively less for the sheet

The variation of mechanical/tensile properties with respect to annealing temperatures [30, 32–35].

in solution [26].

Figure 2.

(Figure 3).

Figure 3.

36

5. Mechanical/tensile properties

Aluminium Alloys and Composites


Table 3.

Formability parameters of Al 1350 alloy sheets annealed at different temperatures.

strain ratio) and percentage elongation, were evaluated in this work. Since the sheet metals were anisotropic in nature, the normal anisotropy parameters such as rav, nrav and Δr were also evaluated.

The n-value and k-value were found to be maximum at 90°C to the rolling direction (RD) and minimum along the RD for the Al 1350 alloy sheet annealed at 200°C. Under similar conditions, the r-value was maximum along the RD and minimum at 90°C; the n-value showed similar observations, whereas the k-value and r-value were maximum at 45° to the RD and minimum at 90° to the RD.
