The paper examines the tensile deformation behavior of the Al-Mg-Si alloy (6061 Al alloy) subjected to various aging conditions. 6061 Al alloy is commonly used in aerospace/aircraft industry due to its performance on corrosion resistance, formability, and weldability. Five different heat treatment procedures, including T4 natural aging and T6 peak-strength temper conditions, were designed to investigate the effect of artificial aging on the mechanical behavior of the alloy. Tensile tests were performed to determine the stress-strain behavior of the material both in uniform and non-uniform deformation regions. Mechanical material properties including yield, ultimate and fracture strengths, uniform and total strains, hardness, strength coefficient, and strain-hardening exponent were obtained experimentally. The relationship between equivalent strain, equivalent stress, and hardness is also examined. The fracture strength of specimens was determined to be less than the Holloman model predictions for the fracture strains of specimens. Void development, which is dependent on the amount of plastic strain development, is determined to be the main reason for this discrepancy between the Holloman model and fracture stress. To calculate the homogeneous stress in the metal matrix of the porous domain, Eshelby-based Mori-Tanaka method (MTM) was used. The calculated average stress in the metal matrix shows good agreement with the Holloman equation predictions. Thus, void development explains the interrupted strain hardening after necking.