Effect of homogenizing annealing on the burning temperature for alloy 1973

A study was done on the effect of temperature and time of homogenization and the hot rolling temperature on overheating temperature of 110 mm diameter ingots of 1973 Al alloy (6.5 Zn, 2.5 magnesium, 1.9 Cu, 0.034 Cr, 0.08 Mn, 0.11 Zr, 0.14 Fe, 0.08 Si, 0.025% Ti, Al remainder) produced by semicontinuous casting. Raising teh single step homogenization temperature > 490 deg C resulted in a drop in the overheating temperature from the maximum of 493 deg C at a homogenization temperature of 480 deg C (15 h homogenization time). Homogenization for 24 h at 470 plus/minus 10 deg C resulted in optimum effect, with an overheating temperature of 498 deg C. Microstructural analysis showed how the nonequilibrium inclusions at the grain boundaries became redistributed upon homogenization. Increasing single step homogenization time to 60 h raised the overheating temperature to 523 deg C. Two step homogenization with heating > 500 deg C (nonequilibrium solidus) in the second step was not advantageous. Hot rolling of homogenized billet also raised the overheating temperature.