On Improvement of Microhardness for Al-Zn-Mg-Cu Alloy via Cold ECAP

The commercial AA7050 alloys with T6 state were successfully processed by ECAP at room temperature. The microhardness evolutions were studied via the average values and color-code maps of microhardness. The effect of microstructure on the microhardness of AA7050 alloys was evaluated using TEM. After one pass ECAP, the microhardness dramatically increased from 179.0 HV to 208.1 HV. Following, the microhardness values are gradually increasing with the increases of ECAP passes number. Up to 6 passes, the maximum microhardness of 234.4 HV was achieved. Color-code maps of microhardness exhibited an obviously work-hardening processing of AA7050 alloys during the ECAP. The homogeneous hardness distribution was developed in this processing due to the saturation of the work-hardening in high strains applied in ECAP. The microstructure observation shows high density of dislocations were introduced to the grain interior of AA7050 alloy during the ECAP, accompanied by the strong grain refinement. The ultra-fine grains with an average size of 46 nm were obtained after six passes ECAP. The high-density dislocation and ultra-fine grains in the ECAPed alloy contribute to the continuously increased microhardness.