The Study Of Interface And Solidified Microstructure Of Al-based Immiscible Alloys

Immiscible alloy is a class of material with good physical and mechanical properties.However, the components start to demix at critical temperature TC, and the initiallyhomogeneous liquid separates into two liquid phases that coexist in equilibrium down to themonotectic temperature TM. Macrosegregation and two layers separated by a distinct interfaceare easily occurred in their solidified structures at normal gravity conditions, which limitedtheir practical application. This paper selected the Al-based immiscible alloys as the studyobject. The main content includes the following aspects.The effect of electric current and holding time on the interface and the solidifiedmicrostructure of Al/Cd、Al/Pb and Al/Bi couple was investigated. The experimental resultsshowed that distinct interface formed in the solidified microstructures of Al/Cd、Al/Pb andAl/Bi couple holding at the temperature of700℃～750℃. Second phases precipitated in theAl matrix and some Al precipitated in other matrix at the vicinity of the interface. Appliedcurrent during holding and solidification process can promote the transition of Al/Cd、Al/Pband Al/Bi liquid/liquid couples toward the L1phase and L2phase, which resulted in theincrease of the amount of precipitated second phases in Al matrix and the amount ofprecipitated Al in other matrix near the interface. For Al/Cd couple, the size of precipitatedparticles in Al matrix and Cd marix in the solidified microstructure increase with the appliedcurrent. For Al/Pb and Al/Bi couples, the size of precipitated phases in solidifiedmicrostructure changes very small with the increase of applied current.The distribution of Al2O3particles in the solidified microstructure of Al-10%Pb andAl-10%Cd holding at the temperature of650℃～900℃was investigated. The experimentalresults showed thatAl2O3particles all distributed in the Pb phases in the Al-10%Pb alloysolidified microstructures, which indicated that Al2O3particles were perfectly wetted byPb-rich liquid phase in two immiscible liquid phases of Al-Pb alloy. In the solidifiedAl-10%Cd alloy, Al2O3particles were founded in the Cd phases and Al phases, whichindicated that Al2O3particles were partial wetted by Cd-rich liquid phase in two immiscible liquid phases of Al-Cd alloy. Combined with the wetting theory and the nucleation theory, areasonable analysis was conducted about above experience results and the possiblemechanisms of Al2O3particles in prepared the homogenous Al-Pb and Al-Cd immisciblealloys was analyzed.In addition, Al-Pb and Al-Bi thin film with fine and uniform distributed two phase wasprepared by Magnetron sputtering deposition method. The effect of vacuum heat treatment onthe stability of alloy film microstructure was studied. The experimental results showed that Pb(or Bi) grains in the alloy film have a small amplitude grew up after the heat treatment.