Fatigue strength analysis for friction stir lap welded joints of Mg/Al dissimilar alloys

This study investigated the fatigue performance of friction stir lap welds (FSLW) made of AZ31B/Al6061 dissimilar alloys. Specimens showed two fracture modes under different fatigue loading levels, which suggests the stress level significantly affects the weld failure mode. Fracture observation revealed unevenly distributed incomplete fusion defects in the weld seam, and the FSLW joints exhibited brittle-ductile mixed fatigue fracture. Finite element models for notch stress and local stress-strain methods were established accordingly to evaluate fatigue life, and then the prediction results were compared with experimental data. Both methods could effectively predict the fatigue life, with errors mostly falling within a factor of 3. Furthermore, the Manson-Coffin damage model of the local stress strain method was more suitable than Smith-Watson-Topper damage model for fatigue evaluation of the present experimental fatigue data.