Abnormal grain growth in the stir zone is one of the major challenges often occurs during post-weld heat treatment of friction-stir welded aluminum alloys. The aim of this research is to mitigate the abnormal grain growth during post-weld heat treatment of AA7075 aluminum alloy. To gain this goal, two methods including application of primary recovery annealing and dispersion of TiO 2 nanoparticles in the stir zone were used. The microstructure of experimental samples were characterized by means of optical microscope, scanning electron microscope, energy dispersive spectroscopy and X-ray diffraction. The mechanical properties of the samples were also evaluated by microhardness measurement and simple tensile test. Also, the digital image correlation technique was used to examine the local strain progression through the gage section of tensile specimens. The results of this research showed that increase in traveling speed from 24 to 86 mm/min caused increase in sensitivity of fine grained microstructure of the stir zone to abnormal grain growth and appearance of abnormally grown grains with the average size of 580 µm in more than 95% of the stir zone area during post-weld heat treatment. However, increment in rotation speed from 380 to 800 rpm had a reverse effect and caused increase in grain size. Therefore, after heat treatment only 45% of the stir zone surface was affected by abnormal grain growth. Applying 9 h primary recovery annealing at 375 °C on as-welded samples caused reduction in the size of abnormally grown grains to values lower than 300 µm. Also, the results of tensile tests showed that applying such a recovery annealing cycle before traditional T6 heat treatment caused 6% increase in tensile strength compared to the traditionally heat-treated samples. The elongation also increased from less than 2.4% to 6.8±0.5 %. In addition, in all samples the fracture occurred in the stir zone. On the other hand, addition of enough amount of nanometric TiO 2 particles in the stir zone caused effective suppression of abnormal grain growth during post-weld heat treatment. With addition of 0.9 wt.% of the particles, the abnormal grain growth suppressed to only 20% of the stir zone area. The tensile test results of these samples revealed that among the TiO 2 added samples, the maximum tensile strength and elongation occurred in the sample containing 0.9 wt.% powder with the values of 561±6 MPa and 11.7±1.9%, respectively. These values are about 96% and 83% of those in the base metal. However, addition of more than 0.9 wt.% of nanoparticles caused accumulation and agglomeration of the particles in some area of stir zone, causing decrement in tensile strength and elongation values to less than 94% and 60% of the related values in the base metal.