Formation mechanism of giant intermetallic compounds in 7N01 aluminum alloys

The formation mechanism of brittle and coarse giant intermetallic compounds in Al-Zn-Mg alloys corresponding to the 7N01 alloy containing Cr, Mn, Zr and Ti has been investigated. Two kinds of giant intermetallic compounds are observed. The first one is found to be a CrAl7 phase into which Mn and Fe dissolve. The second one is a ZrAl3 phase into which Ti dissolves. They crystallize as primary crystals prior to the crystallization of α-Al. The primary crystallization fields of these compounds are given as follows: CrAl7 phase: [%Mn]+3.25[%Cr]=0.905 at 648.8°C ZrAl3 phase: [%Zr]+0.909[%Ti]=0.127 at 648.8°C Applying these equations, it is possible to predict and prevent the precipitation of the compounds during solidification.