Fracture Strengths of Mg Alloy AZ31B-H24 Friction Stir Lap Welds

Abstract

The effects of selected friction stir lap welding parameters on fracture strength of Mg alloy AZ31B-H24 welds have been studied. Rotation speed has been found to affect significantly the flow related hook size formation. Furthermore, fracture strength decreased almost linearly with hook size. A small amount of softening was detected in fracture location that was outside the nugget zone and thus this softening may only adversely affect the fracture strength slightly. Finally, simulation results are presented to show the uneven stress distribution in a lap geometry which together with the relative brittleness of the stir material must be the cause to have significantly reduced the fracture strength.

Study of top sheet thinning during friction stir lap welding of AZ31 magnesium alloy

“…26 With the current welded material having an average grain size of ,8?6 mm, the fracture strength of the current welds is expected to be in the range of 200-275 MPa, since these are the lower and upper bounds of tensile strength corresponding to the easy activation or full suppression of the basal slip. Specimens tested under AS loading also exhibit a linear relationship with the EST by comparing current data with those (similar hooking geometry) of Chen et al 27 However, the fracture strength based on the best linear fit is significantly smaller than what can be inferred from previous defect free specimen tensile testing. 26 The stress concentration at the tip of the hooking feature is likely the reason for the lower computed fracture strength for AS loading.…”

“…Given that the loading condition is complex during lap shear testing as a result of specimen reorientation, which generally introduces bending to the shear test, a tensile dominated fracture mode is necessary for high fracture loads. Figure 10 is a plot of fracture load per unit width as a function of EST for tool B in both RS and AS loading 27 However, the fracture strength based on the best linear fit is significantly smaller than what can be inferred from previous defect free specimen tensile testing. 26 The stress concentration at the tip of the hooking feature is likely the reason for the lower computed fracture strength for AS loading.…”

“…Fracture load as function of EST for welds made using tool B: data from Yang et al 13 and Chen et al 27 are included…”

Friction Stir Lap Welding of Light Alloys

“…Our study on FSLW had earlier also extended to magnesium to magnesium alloy (Mg-to-Mg) [9]. The study has suggested that although these is a similarity in the general trend of rotation speed (ω) and forward speed (v) affecting h for both Al-to-Al and Mgto-Mg FSLW the effects of hooking on fracture strengths of the welds are significantly different.…”

“…Values of F m /w s for Al-to-Al and Mg-to-Mg FSL welds [8,9] are replotted as a function of h in Figure 7. For Al-to-Al welds, as a comparison, the range of F m /w s values of FS bead-on-plate samples, which should represent defect-free butt welds, is provided.…”