Micro/Meso-Scale Equal Channel Angular Pressing of Al 1070 Alloy: Microstructure and Mechanical Properties

In the present study, Al 1070 alloy pins were processed via micro/meso-scale equal channel angular pressing (channel diameter 1.5 mm, the smallest channel diameter has ever been achieved in mesoscale), up to four passes at room temperature. The microstructure characteristics, i.e., grain size, and misorientation angle distributions were analyzed by high-resolution electron backscatter diffraction on the transverse plane for the ECAPed samples. Tensile properties for such small processed pins were measured by constructed micro/meso-scale tensile machine. The gauge length and the gauge diameter were 2 mm and 1.5 mm, respectively. After the fourth ECAP pass, the results revealed that the microstructure was refined remarkably from 15.5 mu m (the initial undeformed sample) to nearly 1.9 mu m due to the gradual transformation of the low-angle grain boundaries into high-angle grain boundaries as a result of the occurrence of grain subdivision. Micro/meso-scale ECAP does a significant enhancement in the ultimate tensile strength by 63%, whereas the ductility decreased after the fourth ECAP pass by 47.3% and this is supposed to be ascribed to the continuous decrease in subgrain size. The above results prove that the ECAP process has the potential for obtaining fine grains and improving material tensile properties even in micro/meso-scale.