Effects of Process Variables on the Mechanical and Physical Properties of an Al-Cu-Mg Powder Metallurgy Alloy
Christensen, Bryce David
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The applications of aluminum powder metallurgy (PM) alloys require precise control of final mechanical properties. The final properties of an alloy are dictated by the processing steps performed during production. The goal of this research was to analyze the effects process variables have on the properties of Al-2.3Cu-1.5Mg-0.5Sn. Specifically, the impact of heat treatment and sizing on the tensile and fatigue properties was investigated. Three variations in heat treatment were explored, each in the sized and not-sized condition: naturally aged (T1/T2) , artificially aged (T6/T8), and solutionized-naturally aged (T4/T3). Uniaxial tensile testing was done to determine yield strength and ductility. 3-point bend fatigue using the staircase method was used to determine fatigue strength. For all heat treatments, sizing increased yield strength, but decreased ductility and fatigue strength. The T8 heat treatment resulted in the highest yield strength (325 MPa), but also the lowest fatigue strength (109 MPa). The T4 heat treatment resulted in the highest ductility (14%). Sizing decreased fatigue strength by up to 31% in the artificially aged samples. Delay time between sintering and sizing was investigated and no significant impact was seen in mechanical properties by increasing delay time. Differential scanning calorimetry (DSC) was used to determine if sizing impacted precipitate development. It was determined that the precipitation sequence of the S-type (Al2CuMg) was influenced by sizing. Through the DSC data it was inferred that there was a preferential tendency for S1-type precipitates to form in sized samples, supressing full aging to S2-type. This would have altered the mechanical performance of the alloy.