Effects of heat input on tensile properties and fracture behavior of friction stir welded Mg–3Al–1Zn alloy

6.3 mm thick Mg–3Al–1Zn plates were friction stir welded with different shoulder dimensions at a traverse speed of 100 mm/min and a rotation rate of 800 rpm. With increasing the heat input by enlarging the shoulder diameter from 18 to 24 mm, the tensile strength of the welds tended to increase and the elongation was significantly improved, and the facture location shifted from the thermomechanically affected zone (TMAZ) in the advancing side to the stir zone. The highest ultimate tensile strength of the welds was obtained by using the shoulder 24 mm in diameter and reached up to 86% of the base material. The variation in the mechanical properties and fracture location was mainly attributed to the texture change in the TMAZ. However, the hardness profiles of the welds were hardly influenced by the shoulder size.