This thesis investigates the connections between friction stir welding (FSW) parameters, simple energy/heat input metrics, and the resultant residual stresses on AA5052-H32 plates. A range of weldments were produced with different tool rotational and traverse speeds to produce the same values of the pseudo heat index (PHI). Average residual stresses inside the stir zone and peak residual stress in the thermo-mechanically affected zone were systematically recorded using laboratory x-ray diffraction. In addition, thermal cycles on the advancing side of the welds were collected and analyzed for comparison with the predictions of heat input based upon FSW parameters. Based upon these results, the PHI is not a good predictor of the peak residual stress for welding conditions which produced sound welds. Increasing traverse speed, V, with fixed rotational speed does increase the residual stresses inside the stir zone. The data in this thesis suggests that there is a complex relationship between frictional heating and mechanical stirring of the material. As a result, there is a rotational speed, which requires minimum torque during welding.