ABSTRACT
In the middle ofthe 1990's Matsuda & al discovered that at temperatures above 200°C 13' is not the only phase to form in Si-rich alloys as previously thought, but it nucleates in combination with three other precipitates called A, B and C [1]. The names U1, U2 and B' respectively are instead used by our group. X-ray (EDS) analysis show that, unlike 13" and 13', the U-phases contain aluminium in addition to Mg and Si in their composition [1]. In light of the new discoveries the precipitation sequence during heating becomes: ssss -> atomic clusters -> GP zones -> 13" -> 13'/U1/U2/B' -> 13, where ssss refers to the initial super saturated solid solution and GP to Guinier-Preston zones.
