Abstract
Overall fatigue strengths and hardness distributions of the aluminum alloy similar and dissimilar friction stir welding (FSW) joints were determined. The local fatigue strengths as well as local tensile strengths were also obtained by using small round bar specimens extracted from specific locations, such as the stir zone, heat affected zone, and base metal. It was found from the results that fatigue fracture of the FSW joint plate specimen occurred at the location of the lowest local fatigue strength as well as the lowest hardness, regardless of microstructural evolution. To estimate the fatigue strengths of aluminum alloy FSW joints from the hardness measurements, the relationship between fatigue strength and hardness for aluminum alloys was investigated based on the present experimental results and the available wide range of data from the references. It was found as: σa (R = −1) = 1.68 HV (σa is in MPa and HV has no unit). It was also confirmed that the estimated fatigue strengths were in good agreement with the experimental results for aluminum alloy FSW joints.
Highlights
From both environmental and energy considerations, the demand for light weight structures and machines are increasing
The fatigue strengths of friction stir welding (FSW) joints, where fatigue failure often nucleates at the heat affected zone (HAZ)/thermo-mechanically affected zone (TMAZ), tend to be lower than those of corresponding base materials but much higher than those of traditional fusion welded joints [2,3,4,7,8,9]
As the step of this series of studies, tensile strength and fatigue strength tests of the 6N01-7N01 dissimilar FSW joint and the 7N01 similar FSW joint were carried out. Fatigue characteristics of these FSW joints were investigated in detail by combining the local tensile strength and local fatigue strength obtained by using small round bar specimens extracted from the respective locations of the joint
Summary
From both environmental and energy considerations, the demand for light weight structures and machines are increasing. In the previous work [12], as the first step towards the study of fatigue behavior and a fatigue strength estimation method of aluminum alloy FSW joints, the tensile strength and fatigue strength characteristics of the 6N01 similar FSW joints were investigated in detail. As the step of this series of studies, tensile strength and fatigue strength tests of the 6N01-7N01 dissimilar FSW joint and the 7N01 similar FSW joint were carried out. Fatigue characteristics of these FSW joints were investigated in detail by combining the local tensile strength and local fatigue strength obtained by using small round bar specimens extracted from the respective locations of the joint. A convenient cost-performance fatigue strength estimation method based on local mechanical properties for the aluminum alloy FSW joints has been proposed
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