Abstract: To study the fatigue properties of magnesium alloy weld structures, the fatigue strength of butt joint and non-load-carrying longitudinal cruciform joint of AZ31B magnesium alloy with 10 mm thickness are evaluated by hot spot stress approach. The test data is statistically treated with the method recommended by International Institute of Welding(IIW). The hot spot stress S-N curves are obtained and compared with the nominal stress S-N curves. The test analysis shows that the fatigue data of two kinds of joints is dispersed greatly when it is evaluated by nominal stress approach, and its correlation coefficient is 0.916, the test fatigue level are respectively FAT35 and FAT25. In comparison with nominal stress approach, the dispersibility evaluated by hot spot stress is reduced obviously. Correlation coefficient is 0.948, which improves about 4.48 %, thus the fatigue strength can be expressed a single one S-N curve, and fatigue level is FAT33. The test fatigue level of these two evaluation methods is higher than the fatigue level obtained by using 3 recommended by IIW, which indicates there is a higher safety factor in weld structure design if 3 is applied.

Key words: AZ31B magnesium alloy, Fatigue evaluation, Hot spot stress approach, Nominal stress approach