A Study on micro and macro structures on directionally solidified aluminum

A fixed mold-stationary furnace combination apparatus was designedfor directional solidification. 99,3% purity aluminum was directionallysolidified for 900 oC, 950 oC, 1000 oC ve 1050 oC furnace temperatures.A single crystal macro structures was aimed to obtain temperaturegradients and solid-liquid interface velocities. Macro and microstructural analyses were carried out.During the experiments, single crystal structure could not be producedachieved. Columnar grains were observed opposite to the heat flowdirection. Fixed furnace and chill temperatures were obtained. However,average temperature gradients vary between 20,03 ile 26,70 oC/cm andaverage growth velocities vary between 0,0191 ile 0,0208 mm/sec.Results showed that, lower gradients for lower furnace temperaturesand higher gradients for higher furnace temperatures were obtained.Increasing furnace temperatures from 900 to 1050 oC caused averagegrowth velocities to decrease while average temperature gradientsincrease. Completely cellular solidificaton occurred inside the columnargrain structures. These cells oriented through the opposite direction ofthe heat flow. Bigger cells existed in the bottom parts of the specimenswhile smaller cells existed through the top parts of the specimens. Thenumber of cells per unit area decreased as the furnace temperatureincreased.