Influence of ageing on the high-temperature mechanical strength of the Al-4Mn-3Ni-2Cu-1Zr alloy produced by laser powder bed fusion
Résumé
The mechanical properties of additively manufactured aluminium alloys at room temperature are often optimized through post-fabrication heat treatment (peak ageing). However, at high temperatures, peak-ageing does not necessarily result in the best mechanical properties. This raises the question of whether there is an optimal microstructure depending on the operating temperature. Herein, we examine the influence of ageing in an Al-4Mn-3Ni-2Cu-1Zr (wt.%) alloy processed by laser powder bed fusion on the tensile yield strength from room temperature to 300 • C at 10 -2 and 10 -5 s -1 . In the stress-relieved conditions, the material shows a higher yield strength than in the peak-aged conditions at temperatures above 150 • C at 10 -2 s -1 and as low as 100 • C at 10 -5 s -1 . This evolution was not expected since nanoscale L1 2 -Al 3 Zr thermally stable precipitates form in the peakaged conditions. The microstructure evolutions upon ageing are characterized across all scales and provide insights to rationalize the evolution of the alloy strength with temperature. The role of different microstructural features such as grain size, intermetallic morphology, nanoscale precipitates and solid solution composition is discussed. While the nanoscale Zr-rich precipitates contribute greatly to the room-temperature yield strength, their effect at elevated temperatures, typically >150 • C, is minor. On the contrary, the supersaturation in Mn in the as-built material that is preserved after stress-relief is found to have a large impact on the tensile yield strength at elevated temperature. The globularisation of the elongated intermetallics observed in the stressrelieved microstructure is also identified to lower the elevated-temperature yield strength.
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