EFFECT OF DOUBLE THERMOMECHANICAL TREATMENTS ON THE PROPERTIES OF 7075-AL-ALLOY

In this work, a 74.6 mm thick plate cast from 7075 Al alloy was subjec ted to two double-thermomechanical-treatment processes. The first of t hese processes includes FA-ITMT and a proposed new technique. In FA-IT MT homogenization, hot rolling, recrystallization, and finally hot rol ling again are carried out. The proposed new technique involves recrys tallization using a suitable time, temperature and cooling medium whic h gives good strength without decreasing the ductility, hot and cold r olling, then recrystalization under the same conditions. The second of these processes involves the FA-ITMT process associated with a newly developed FA-ITMT process. the latter containing four steps: (i) solid -solution heat-treatment; (ii) over-aging; (iii) hot- and cold-rolling and (iv) recrystalization. A detailed study of the microstructure and mechanical properties was carried out and their interrelations were a nalysed, the results revealing that both of the two double-thermomecha nical-treatment processes mentioned above led to improvement in streng th and ductility simultaneously. associated with a refinement of the g rain size. There was an increase in the ultimate tensile strength of u p to 84.3%. an increase in the yield strength of up to 116.7%, and als o an increase in ductility of up to 287.5%, associated with a decrease in the grain size from 45 to 16 mu m. The first technique gave a good combination of strength and ductility. Also, the cold deformation acc elerates the recrystallization rates, hence, fine grains can be obtain ed.