BS in Materials Engineering
Materials Engineering Department
The purpose of this project is to determine if over-aging of aluminum causes the yield or tensile strength to fall below the minimum strength values set by the aluminum industry. Extruded aluminum alloys, 6061-T6, 6063-T6, and two proprietary alloys, HS6X-T6 and RX82-T6, were exposed to reheating treatments at extended times and temperatures. The three temperatures were 350°F, 390°F, and 425°F. The times of reheat increased logarithmically from 30 minutes to 64 hours. The samples were tensile tested to determine the tensile strength and yield strength. Statistical methods helped model the behavior of yield and tensile strength as a function of alloy, time, and interaction of alloy and time for each temperature. This showed which alloy experienced a change in strength and at what time and temperature the strength fell below minimum acceptable values. The strongest to weakest untreated alloys respectively were HS6X, RX82, 6061, and 6063. As time progressed at each temperature, the strongest to weakest alloys changed to HS6X, 6061, RX82, and 6063 respectively. For the 6061 and 6063 alloys, the yield strength did not go below the lower bound value at 350°F, at 390°F it took 16 hours, and for 425°F it took 4 hours. For the HS6X alloy, the yield strength fell below the lower bound after 8 hours at 350°F, at 390°F it took 2 hours, and at 425°F it took 30 minutes. For the RX82 alloy, at 350°F, it took 32 hours for the yield strength to fall below the lower bound, at 390°F it took 8 hours, and at 425°F it took 30 minutes.