Design of High-Strength Wrought Al-Cu Based Alloys for High Temperatures by Concurrent Hot Working and Precipitation

Abstract

The paper reports the design and development of wrought Al-Cu alloys that retain high strength until 250 °C. It is achieved by minor alloying of Zr (<0.15 at%) and Nb (<0.1 at%) and inducing precipitation of stable nanometric dispersion of L1 2 ordered precipitates during controlled thermomechanical treatment (rolling) of cast alloys before conventional heat treatment (solutionizing and ageing). The rolling temperature was optimized to 450 °C by quantitatively evaluating the size distribution of the dispersions at different rolling temperatures. The dispersions influence the microstructure and the nature of the precipitation of the strengthening θ′ plates during subsequent conventional heat treatment. The microstructure of the processed alloy show stability at high temperatures. The atom probe tomography reveals Zr enrichment at the broad faces of θ′ plates. The presence of Zr plays a critical role in the high-temperature strength by promoting the stability of θ′ precipitates and resisting its coarsening. The composite microstructure of Al-Cu-Nb-Zr alloy displayed 0.2% yield strength (YS) of 415 MPa and 220 MPa at room temperature and at 250 °C, which are higher by 26% and 45% respectively as compared to a commercial Al-Cu based alloy (2219-T851). The present results are promising for developing wrought Al alloys for high-temperature applications.

Keywords: Al-Cu based alloys, Thermo-mechanical treatment, L12 precipitates, High-temperature strength, Electron microscopy, Atom probe tomography