Influence of Mechanical and Thermo Mechanical Treatment on Micro Structure and Hardness of Al-Zn-Mg Alloy

Abstract

The present work is aimed at studying the effect of mechanical and thermomechanical treatment on microstructure and hardness of Al5Zn1.8Mg alloy. The alloy samples prepared by casting. Mechanical treatment included casting with the effect of mechanical mold vibration of 0.5mm amplitude and a frequency of 25Hz, warm forming at 200oC using a forming pressure of 200,300, and 400MPa. Thermomechanical treatment includedwarm forming after precipitation and age hardening.
The results of X-ray diffraction analysis showed that the second phase particles (AlMg4Zn11 and Mg32(Al, Zn)49) were distributed within the ?-aluminum phase. The microstructure analysis of samples cast with mechanical mold vibration showed a grain size of 35µm,a Brinellhardness of 86kg/mm2, and a porosity of 0.073%, while that of samples cast without mechanical mold vibrationwere 63µm, 78kg/mm2, and 0.172% respectively. Warm forming of samples cast with mechanical mold vibration reduces the grain size to 27µm, increases the Brinellhardness to102kg/mm2and reduces the porosity to 0.0093%. Heat treatment then warm forming for samplescast without mechanical mold vibration gave a grain size of 26µm, a Brinell hardness of 141kg/mm2, and a porosity of 0.002%.