During the heat treatment of aluminum alloys, there is usually a delay time between quenching and the final artificial aging. This delay is called natural aging or preaging at room temperature This research was conducted in order to study the effect of various natural aging times (0, 6, 12 and 20 hours) on the properties of unmodified and strontium modified A356 aluminum alloys solution heat-treated 4 hours at 540 deg C, water quenched and artificially aged 6 hours at 155 deg C and 170 deg C. The samples were tested for electrical conductivity, microhardness, and tensile properties. In the case of the samples artificially aged at 155 deg C from the results it can be seen a decrease in the microhardness and yield strength with natural aging. Regarding the samples aged at 170 deg C it is noticed that natural aging at 12 hours will result in the lowest electrical conductivity, yield strength and microhardness. However, there is evidence of recovery of those properties at 20 hours of natural aging. Regarding the elongation, natural aging seems to have a positive effect when artificial aging is carried out at 155 deg C, but at 170 deg C an optimum elongation is obtained only at 12 hours.
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