摘要
The microstructure and mechanical properties of rheo-diecasting Al-6Zn-2Mg-2Cu alloys microalloyed with Ti,Sc and Sc+Zr were studied by optical microscopy(OM),scanning electron microscopy(SEM),X-ray diffraction(XRD),hardness testing,and tensile testing.The swirled equilibrium enthalpy device(SEED)process was introduced to prepare the semisolid slurry.Results show that the addition of Ti,Sc,and Sc+Zr refines the grain size and improves the uniformity of the semisolid slurry and then suppresses the growth of theα-Al grain during solution heat treatment.The microstructure of the four alloys in as-cast state mainly consists of sphericalα-Al and the Mg(Al,Cu,Zn)_(2)(η)eutectic phase.Moreover,primary Al_(3)Sc,Al_(3)(Sc,Zr)and Al_(3)Zr are also found in the micro-alloying alloys.After solution and aging heat treatment,most of the Mg(Al,Cu,Zn)_(2) phases dissolve into theα-Al matrix,while part of Mg(Al,Cu,Zn)_(2) phases transform to Al_(2)CuMg(S)phases.However,the coarse primary Al_(3)Sc and Al_(3)(Sc,Zr)still remain in the matrix,and promote crack initiation and propagation.With the tensile strength of 553 MPa,yield strength of 463 MPa and elongation of 13.4%at T6 state,trace Ti addition generates more attractive mechanical properties than the other three alloys.
基金
financial support from the National Key R&D Program of China(No.2016YFB0301003).
