MATERIALS ENGINEERING SEMINAR "Mechanical Testing of Semi-Solid AL-MG Binary and 7050 Aluminum Alloys Using the Reheating Cooling Method" By Christopher J. McCleary Purdue MSE MS Final Advisors: Professor David R. Johnson and Matthew J. M. Krane ABSTRACT Elevated temperature tensile testing beyond the non-equilibrium solidus demonstrates the advantage of a new method called the Reheating Cooling Method(RCM) for determining mechanical properties of Al-Mg binary alloys and cast alloy 7050 aluminum in the solid-liquid two phase mushy zone. Using the RCM, it is possible to achieve semi-solid tensile behavior with standard testing equipment and to retain a non-equilibrium casting microstructure, which is necessary to gain insight into hot tearing. Hot tearing, a virtually impossible to repair defect, is known to worsen with increasing Direct Chilled (DC) cast ingot size. Further data gathered from mechanical testing of alloys within the semi-solid mushy zone is necessary to better understand hot tearing and improve ingot production. First, RCM 0.9 fs modulus of toughness results show Al-10%Mg absorbed an average of 240 KJ/m3 while Al-1%Mg an average of 58 KJ/m3. The modulus of toughness at 0.9 fs matches the expected trend seen in hot tearing susceptibility between the two Al-Mg binary alloys. Longer dwell at elevated temperature during heat up is found to decrease an Al-Mg alloy's semi-solid modulus of toughness. Secondly, when above 90% of the non-equilibrium melting point, a basic model of diffusion shows a need for diffusion mitigation. Finally, using 7050 at 0.9 fs, a comparison between the traditional ramp method to the RCM demonstrates an average reduction from 389 KJ/m3 to 10.6 KJ/m3 in modulus of toughness. When compared to the ramp method, the RCM fracture surface contains more evidence of liquid grain boundaries and no sign of plastic deformation, indicating less back diffusion during testing. Increasing strain rate was found to increase specimen modulus of toughness at and above 0.9 fs but lower the modulus of toughness at 0.8 fs. RCM testing shows similarities between the ramp method at 0.9 fs and the mechanical response of the same alloy at 0.95 fs. Date: Tuesday, November 21, 2017 Time: 1:00 P.M. Place: HAMP 2107