MICROSTRUCTURE AND MECHANICAL PROPERTY OF ALPHA-AL-ZN-CU ALLOYS AGED AT ROOM-TEMPERATURE

Al-Zn-Cu alloys with five different compositions in the alpha-phase re gion have been prepared and their microstructures have been characteri sed employing X-ray diffraction, optical and scanning electron microsc opy. The mechanical property of the alloys has also been characterized from the measure of hardness. A close correlation between the microst ructure and hardness of the alloys has been observed. X-ray studies of ageing at room temperature of the materials in the deformed state rev ealed faster stress-induced precipitation of Zn and Cu whereas the tra nsformation is slow in the homogenized materials. The rate of G.P. zon e formation is either very slow or not detectable. The results of phas e-transformation study have been supplemented by DSC study along with subsequent measurement of hardness values which are reduced on complet ion of Zn and Cu-rich precipitations.