Abstract: The influences of tool rotational speed and dwell time on the mechanical properties of AZ31 friction stir spot welds were investigated.Along with the increase in tool rotational speed,the mechanical properties of AZ31 friction stir spot welds which were made by different tool designs increased first and then decreased.Along with the increase of dwell time,the mechanical properties of AZ31 friction stir spot welds increased first and then kept relatively constant.Bonded width affected the properties of friction stir spot welds significantly.The bigger the bonded widths,the better the properties of the friction stir spot welds were.In addition,the feature of the interface between the upper and the lower sheet also had an important influence on the properties of AZ31 friction stir spot welds.