Microstructure and Mechanical Properties of an Al-Mg-Sc-Zr Alloy Subjected to Extensive Cold Rolling

Abstract

An Al-4.5%Mg-0.2%Sc-0.09%Zr alloy was subjected to cold rolling (CR) with reductions ranging from 20 to 90%. Extensive strain hardening upon the cold rolling resulted in the significant increase in strength. After cold rolling with a total reduction of 20 and 90% the yield stress (YS) increase is 30 and 62%, respectively. These increments are attributed to an increase in the density of lattice dislocations, the formation of numerous low-angle boundaries (LAB), deformation bands and microbands within interiors of initial grains. Introduction Al-Mg alloys are widely used for structural engineering applications due to a good combination of formability, ductility and excellent resistance to corrosion [1-4]. However, these alloys exhibit moderate strength. To increase strength of Al-Mg alloys, small additions of Sc are used [4]. These Sc additives provide the formation of nanosize coherent particles of Al 3 Sc phase, which are highly effective in dispersion strengthening. In general, Sc additions provide 50% increase in YS of wrought Al-Mg alloys [4]. Recently, second generation of aluminium alloys belonging to Al-Mg-Sc system was developed. The 0.2%Sc and 0.09%Zr modified Al-Mg alloys exhibit high strength and excellent workability, concurrently. Hence, these alloys could be processed by extensive rolling in strain hardened state. Among the alloys of the Al-Mg-Sc system, the alloy Al-4.7%Mg-0.2%Sc-0.09%Zr, designated in Russia as 1545 aluminum alloy [4] was aimed for the fabrication of plates and sheets for exploitation at cryogenic temperatures. The 1545Al exhibits excellent weldability in annealed conditions [4]. However, there were no attempts to process this alloy into hardened state. This alloy exhibits relatively high ductility that makes it possible to utilize extensive rolling at ambient temperature for production of work-hardened sheets which can be jointed by friction stir welding without strength loss. The aim of the present work is to evaluate the effect of CR on microstructure and mechanical properties of the 1545Al. The relationship between the deformation microstructures and mechanical behaviour will be considered in details.