Quenched-in vacancy defects in commercial Al-Mn alloys

Abstract

helices and voids. Westmacott and Peck [3] have attempted a rationalization of the secondary defect structure based on the minimum concentration of the alloying elements necessary for the replacement of faulted loops by rhombus-shaped (R) perfect loops. The misfit between the solute and aluminium atoms is expected to provide the stress necessary for converting the faulted loops to perfect loops. Most of the studies of quenched-in defects in aluminium alloys are carried out on materials prepared from super-pure elements. A number of solutes are present in cormnercial alloys in the dissolved condition and as insoluble particles. The effects of the dissolved elements and the insoluble particles on the formation of secondary defects are studied in this investigation using a super-pure A1-Mn, commercial 3003 and 3008 aluminium alloys. The high temperature stability of these defects is examined in samples bulk-annealed at temperatures of 473,723, 773 and 823 K. An Al-1%Mn* alloy based on super-pure aluminium, a commercial 3003 alloy (1.14% Mn, 0.22% St, 0.58% Fe, 0:01% each of Cu, Ti and Mg, balance AI) and a commercial 3008 alloy * All compositions are expressed in weight per cent. (1.38% Mn, 0.46% Fe, 0.12% St, 0.29%Zr, 0.09% Cu, 0.01% Ti, balance A1) were used in the present investigation. The as-received materials were coldrolled with intermediate annealing treatments at 773 K to a final thickness of ~ 0.7 mm. They were solution treated at 913 K for 24h and then quenched in water. All the samples were chemically thinned in a mixture of orthophosphoric acid, sulphuric acid and nitric acid (70:20:10 by volume) at 343K to a thickness of 0.1 ram followed by electrochemical thinning in a mixture of ethanol and perchloric acid (80! 20) at 273 K using the window technique. The thin foils have been examined in a Philips EM 301 transmission electron microscope operated at 100kV.