Keywords:Al-Zn-Mg-Cu alloy;Zn/Mg Ratio;Solution treatment;Second Phase dissolution
Abstract.The main alloying elements have a decisive influence on the type and quantity of thesecond phase of the Al-Zn-Mg-Cu alloy,and even on the dissolution of the second phase duringsolution treatment.The effect of Zn/Mg ratio on second phase dissolution during solution treatmentof Al-Zn-Mg-Cu alloys was investigated by means of differential scanning calorimetry (DSC)，scanning electron microscope (SEM)and electrical conductivity testing.The results showed thatMg(Zn,Cu,Al)2 phase and Fe-rich phase existed in the as-deformed alloys.In addition,a smallamount of Al2CuMg phase was found in the low and medium Zn/Mg ratio alloy.Mg(Zn,Cu,Al)2phase essentially dissolved into the matrix after solution treatment at 465C/2h.Increasing thesolution treatment temperature and time were both beneficial to the dissolution of the Al2CuMgphase.Conductivity is also a method of assessing the level of dissolution of the second phase.Afterthe second phase was fully dissolved in the alloy,the electrical conductivity gradually increasedwith the increase of the solution time.