Influence of cold rolling and thermal treatment on microstructure and texture evolution, and tensile behaviour of high strength Al-Co-Sc-Zr alloys

Abstract

• The chilled suction casting of Al-0.1Co-0.15(Sc, Zr) at% alloy enabled substantial amounts of stable compounds of Al 9 Co 2 , primary Al 3 (Sc 1−x Zr x ) dispersoids, and Al 3 Sc precipitates. • Cold rolling and ageing at 375 °C, offer yield strength of 251 MPa and UTS of 276 MPa with good ductility (19%) was achieved. • Solid solution, precipitation and dispersion hardening, and formation of fine subgrained structure have enhanced the mechanical properties. The present work is an effort to develop a set of newer aluminum alloys with a minor amount of alloying additions such as Co, Sc and Zr to pure Al in order to achieve higher strength along with a reasonable tensile ductility and improved microstructural stability at elevated temperatures. The alloys were melted using vacuum arc melting and were produced in rectangular slabs by suction casting. The slabs were cold rolled at room temperature up to ~80% reduction followed by direct aging at two different temperatures of 375 °C and 450 °C for 24 h. The effects of alloying additions, cold rolling and subsequent thermal aging were investigated by detailed microstructural examination and tensile testing at room temperature. Microstructural analysis revealed that the alloy contained significant volume fraction of second phase particles such as Al 9 Co 2, Al 3 Sc and Al 3 (Sc 1−x Zr x ) and were preferentially distributed in supersaturated equiaxed cells of Al matrix. The existence of Al 3 (Sc 1−x Zr x ) precipitates together with large fraction of Al 9 Co 2 phase led to higher yield strengths of ~180–250 MPa and 17–20% tensile elongation. Electron backscattered diffraction observations showed equiaxed cells extensively deformed columnar grains and subgrain formation within the elongated grains in the rolling direction. The cold rolled plus aged samples exhibited a major fraction of rotated cube texture along with improved microstructural stability after high-temperature aging. This could be related to the existence of fine and stable Al 9 Co 2 phase and Al 3 (Sc 1−x Zr x ) precipitates, which control grain growth and thereby these alloys thermally stable at high temperatures.