Abstract: Effects of multiple strengthening treatments (i.e. aging either at three or four consecutive temperatures) on mechanical properties and stability of nanoscale precipitated phases in an AA2090 alloy have been evaluated in this research. Various tests such as hardness, tensile, electrical resistance, differential scanning calorimetric (DSC), and transmission electron microscopy (TEM) have been performed. The results show that the ultimate tensile strength (UTS) and the yield strength of the samples aged at four consecutive temperatures (i.e. natural aging+190°C+150°C+100°C) can be increased approximately to 660 and 610 MPa, respectively. It is also found that precipitation of T1 phase occurs during multiple aging process of the alloy and the higher amounts of enthalpies shown in DSC charts are linked to higher volume fraction of this precipitate. Furthermore, TEM observations reveal that T1 phase has plate shape morphology and its crystal structure is in the form of hcp with lattice parameters of a=0.467 nm and c=0.878 nm.

Key words: Multiple strengthening, Thermo mechanical treatment (TMT), Selected area electron diffraction (SAED) pattern, Inter planar spacing (d)