Characterisation of different types of dispersoids present in homogenised Al–4·5Zn–1Mg alloy containing Zr,Cr and Mn

Abstract

In the present paper, various types of dispersoids possibly formed during homogenisation of AA7020 alloy containing Cr, Zr and Mn are described. It shows that, in addition to the Zr containing dispersoids, three other types of dispersoids may be present in the homogenised microstructure of AA7020 aluminium alloy. These dispersoids are Cr and Mn containing ones and the one with a mixture of different elements. The Zr and Cr containing dispersoids are formed in the grain interior at all of the homogenisation conditions. However, the Mn containing ones form only in the grain boundary regions in the vicinity of Al₁₇(Fe_3·2,Mn_0·8)Si₂ particles at temperatures ⩾510°C and holding times longer than 4 h.