Water cooling was applied during friction stir processing (FSP) of an Al-6061 alloy, and it was found that the strengthening efficiency induced by water cooling was varied, which was dependent on the initial base metal temper. As to the natural-aged Al-6061 alloy (6061-NA), the stir zone (SZ) was strengthened significantly by water cooling. Compared with the air-cooled FSP sample, the relatively high strength of the water-cooled FSP sample mainly arose from grain refinement, increased density of dislocations and large amounts of fine re-precipitated Guinier–Preston zones in the SZ. On the contrary, as to the annealed Al-6061 alloy (6061-O), the difference in the microstructural evolution between the FSP samples with and without water cooling was nonsignificant, where only finer grain morphology was observed in the water-cooled SZ, and thus the strengthening effects caused by water cooling became less.
Aluminum alloy Initial base metal temper Friction stir processing Water cooling Properties
This is a preview of subscription content, log in to check access.
The present study is financially supported by the Fundamental Research Funds for the Central Universities of China (No.N172410002-03). Besides, one of the authors, Zhaohui Ren gratefully acknowledges the financial support from the National Science Foundation of China (No.51475084) and National Support Program, National Key Research and Development (No.2017YFB1103700).