This work aims to develop a reliable method to predict mechanical properties of friction-stir-welded 6xxx-series alloys with experimentally measured welding heat input.A calorimetrical method was utilized to experimentally measure the welding heat input in the friction stir welded of aluminum alloy 6063-T5.Good correlations between the input variables,i.e.,welding parameters and physical properties of the materials,and the welding heat inputs obtained with experimental measurements were discovered.The welding heat input can be predicted using the empirical equation derived based on these correlations.Moreover,the results suggested that the thermal conductivities of the welded alloys affected the welding heat input significantly.Mechanical properties,including hardness and tensile properties,of friction-stir-welded aluminum alloy 6063 were in good correlation to the heat input obtained with experimental measurement.These correlations were explained by the evolution of the strengthening precipitates during welding.This work proposed a reliable new route to predict these mechanical responses through the estimation of heat input.