This research experimentally determines the Gurson-Tvergaard-Needleman (GTN) model damage mechanics parameters for 6061 Al alloys. Five different heat treatment conditions including T4 (natural aging) and T6 (peak strength) conditions of 6061 Al alloy were investigated. The GTN parameters considering different heat treatment conditions of the alloy were obtained by tensile tests. Scanning electron microscope (SEM) micrographs were used as inputs to determine initial and nucleated volume fractions. SEM and energy dispersive X-ray spectrography (EDX) analyses also revealed that the second-phase precipitates are the origin of the incipient voids. SEM analyses enabled the fractographic investigations where the primary and secondary voids were exhibited and thus showing nucleation strain. Density measurements clarify the critical and final void volume fractions and the standard deviation of the nucleated void volume fraction distribution. The results show that the void volume fraction increases exponentially along with increasing effective tensile plastic strain. Hence, a total of six different GTN parameters have been identified experimentally. Finite element method simulations based on GTN damage model were performed to verify the GTN model parameters. The results show that the experimentally obtained GTN model parameters could be used when performing tensile deformation simulations of 6061 Al alloys fabricated with different heat treatment conditions. •Experimental methods to determine GTN damage model parameters were presented.•6061 Al alloy under different heat treatment conditions were subjected to the experiments.•A total of six different experimentally obtained GTN damage model parameters were used as the input parameters for the FEM.•The FEM results were compared and verified with the experimental tensile tests.