عنوان مقاله [English]
The effect of artificial ageing on tensile properties and fracture behavior of 2024 Al alloy in the presence and absence of notch was investigated. The tensile samples having two V notches, as well as, common tensile specimens were prepared according to ASTM E8. T8 heat treatment consisting of solutionizing, cold rolling, and aging was selected to establish precipitation hardening in Al2024 alloy. Considering T8 condition, following solutionizing of Al sheet at 500° C, samples were cold rolled with 30% reduction, and finally artificial aging was applied at 200° C via different times. The results of Brinell test shows that, the maximum values of hardness achieved at 1 hr, which indicated the peak aging condition. Moreover, soaking samples in aging condition at 200° C for 15 minutes and 4 hours considered as under-aging and over-aging states, respectively. Similar to hardness results, the superior amount of yield strength and ultimate tensile strength of common tension specimens observed at peak aging time, while in notched samples, the role of aging time was not prominent due to the presence of V shaped flaws. By applying notches on specimens, the yield and ultimate stress was found to increase with simultaneously decrease in elongation at fracture. It was found that the presence of notches increases the strength of 2024 Al alloy, due to localizing plastic deformation around flaws, while elastic behavior controls deformability far from notches. The energy absorbed till fracture, which was indicated as toughness, was found to be absolutely dominated by the elongation at fracture and significantly decrease in these specimens. The peak-ageing condition of notched tensile specimens had the lowest toughness compare to under-ageing and over-ageing conditions. Although three fracture mechanisms, such as matrix deformation, particle cracking and matrix/particle debonding observed in all samples, the distribution of these mechanisms were further homogeneous in un-notched specimens. In the other words, one may claim that, the presence of flaws enhanced the cracked particles, which accompanied with lowering matrix deformability lessened the elongation and toughness.