چكيده به لاتين
Abstract
The solid and semisolid deformation behavior of a 7075 aluminum alloy have been investigated through applying hot compression tests at different temperatures and strain rates (100, 200, 300, 450, 500, 520, 550, 580°C and 0.003, 0.03 and 0.3s-1. Dynamic recrystallization was proposed to justify the corresponding flow behavior at lower temperature range of 100-450°C. The deformed structure was also spheroidized in the semi-solid temperature range due to the liquid pressure. The valuable relationships were used as a calculation basis to simulate the materials flow responses. Accordingly, in the present study a hot working constitutive base analysis has been conducted on a 7075 aluminum alloy. A set of constitutive equations for 7075 Al alloy have been proposed employing an exponenttype equation. The related material constants (i.e., A, n and a) as well as the activation energy Q for each temperature regime have been determined. The correlation of flow stress to strain rate and temperature can be deduced from the proposed equations. Furthermore, a change in deformation mechanism has been realized in the semi-solid temperature range. This has been related to the onset of lubricated flow mechanism during processing. The strain rate sensitivies were calculated as 0.132 and 0.230 in the solid and semisolid regions, respectively. This was attrivuted to the dominant deformation mechanisms. The corresponding activation energies were fund to be 270 and 246 KJmole-1, respectively. The difference in activation energies in solid and semisolid state was justified considering the incipient melting of second phase precipitates at higher temperatures. The accuracy of the proposed models was investigated through comparing the experimented and numerical flow curves.
Keywords: Aluminum alloy; Plastic behavior; Semi-solid processing; Constitutive equations
