Studies On Microstructure And Mechanical Properties Of An Ultra-fine Grained Al-3.8wt.%Mg Alloy

The present study report an ultrafine-grained(UFG)structure in a Al-3.8 Mg alloy processed by conventional rolling(RT-rolling and cryo-rolling)and incomplete continuous recrystallisation induced by subsequent annealing,which consists mainly of recrystallized low-aspect-ratio or approximately equiaxed ultrafine grains mixed with retained ultrafine lamellae having a relatively high dislocation density.The microstructure evolution associated with the formation of UFG structure has been analyzed in detail with the assistance of X-ray diffraction(XRD)and transmission electron microscopy(TEM).The occurrence of continuous geometric recrystallisation is attributable to the extremely refined lamella spacing and the dominant fraction of HAGBs in the deformed Al-3.8 Mg.The present UFG Al-3.8 wt.%Mg alloy possesses both high yield strength(~392 MPa for the RT-rolled + 200 °C-annealed sample,~433 MPa for the cryo-rolled + 200 °C-annealed sample)and large uniform elongation(~9.3% for the RT-rolled + 200 °C-annealed sample,~11% for the cryo-rolled + 200 °C-annealed sample).The high yield strength in the UFG Al-3.8 Mg is due primarily to grain boundary strengthening by the ultrafine structures,and,to a lesser extent,to strengthening by the medium dislocation density,solute strengthening by the intermediate solute Mg content and precipitation strengthening of second-phase particles.The large uniform elongation is primarily attributed to the enhanced strain hardening resulting from the mixed UFG structure,the intermediate solute Mg content and the possible nanoscale precipitates.Most importantly,the present study revealed that the combination of conventional rolling technique and continuous recrystallisation induced by annealing can be utilized as a strategy to produce desirable UFG structure,obtaining high uniform ductility without sacrificing high strength.