Microstructural and fatigue crack growth behavior inhomogeneity of trace
Sc added 7085 alloy friction stir welded joint
The inhomogeneity of friction stir weld (FSW) joint of a 7085 Al-based
alloy containing trace Sc was investigated by comparing the hardening
phase morphology, grain structure, mechanical properties and fatigue
crack growth (FCG) behavior in based metal (BM), heat-affected zone
(HAZ) and weld nugget zone (WNZ). The results showed that
microstructural evolution during FSW was remarkably affected by Sc
addition. The recrystallization and growth of grains in BM and HAZ were
restrained by coherent Al3(Sc,Zr) particles. In HAZ, partially
dissolution and slight growth of precipitates resulted in softening but
contributed to enhance the FCG resistance according to shear mechanism.
In WNZ, high frictional heating and intense plastic deformation induced
recrystallization and supersaturated solid solution which decomposed to
form new reprecipitates, including many new GPII zones, ′ phases and
some coarse equilibrium phases attached to grown incoherent Al3(Sc,Zr).
Owing to combined influences of fine random orientated grain structure
and reprecipitates, WNZ possessed the best fatigue endurance.