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The phase relations of arc-melted alloys in the ternary system Ce-Al-Cu （Cu-poorportion） in the as-cast state formed by conventional arc-melting were investigated byX-ray diffraction（XRD）,differential thermal analysis （DTA） and scanning electron mi-croscopy （SEM） techniques. The structure and lattice parameters of some compoundswere refined by the Rietveld refinement program Fullprof.2k （Version 2.40）. In addi-tion to this,the constructed phase relations of the Ce-Al-Cu ternary alloys is used tofurther explain the mechanism of amorphous metallic plastic（AMP）. In the end of thepaper,element substituting and different heat treatments were used to improve theelectrochemical properties of the compound Ce(Cu1-xAlx)5.It is well known that ternary Ce-Al-Cu alloys show good glass forming ability（GFA） and can be easily formed in a wide composition range by the conventional cop-per mold cast technique. Considering that the Ce-Al-Cu AMPs were fabricated viathe copper mold cast technique in a conventional arc-melting furnace. After arc melt-ing,the AMP is suck-cast into a copper mold. We investigated the phase compositionof as-cast alloys formed by conventional arc-melting. Based on the constructed phasecomposition regions of the Ce-Al-Cu ternary system,it reveals that the compositionregion of the bulk glass alloys in the Ce-Al-Cu system falls in the Ce-rich phase regionswithα-Ce3Al as the common phase. It also indicates that the good glass-forming abil-ity of the Ce-based AMPs benefits from the low eutectic temperatures in the Ce-richphase regions and the special crystal structure of Ce3Al. On this basis,we propose themechanism Cluster Stacking Frustration（CSF） in the Ce-based AMPs forming process.In comparison with its isothermal equilibrium phase diagram,a study on phase com-position of the alloys in the ternary system Ce-Al-Cu in the as-cast state formed byconventional arc-melting can provide useful information for better understanding theformation and performance of the AMPs.The study on phase relations of Ce-Al-Cu ternary system（Cu-poor portion） indi-cates that the investigated composition region consists of 16 single-phase,32 two-phaseand 17 three-phase regions. The 16 single-phase regions are:θ（Al2Cu）,η2（AlCu）,*τ1(CeAl12-xCux),*τ2(Ce2Al17-xCux),*τ3(CeAl13-xCux),*τ4(CeAl4-xCux),*τ5（Ce2AlCu2）,α（CeCu5）,β(α-Ce3Al11),γ（CeAl3）,δ（CeAl2）,ε（CeAl）,ζ（α-Ce3Al）,ι（CeCu）,κ（Al） andλ（γ-Ce）. The 32 two-phase regions are:κ+θ,κ+ *τ1,κ+ *τ4,κ+β,θ+ *τ1,*τ1+ *τ2,*τ2 + *τ4,*τ1 + *τ4,*τ4+β,*τ4+γ,β+γ,γ+δ,*τ4+δ,α+δ,*τ4+α,α+*τ2,*τ3 +α,*τ2 + *τ3,*τ1 + *τ3,θ+ *τ3,η2 + *τ3,θ+η2,α+ *τ5,δ+ *τ5,δ+ε,ε+ *τ5,ε+ζ,ζ+ *τ5,ι+ *τ5,ζ+ι,λ+ζ,λ+ι. The 17 three-phase regions are:κ+θ+ *τ1,κ+ *τ1 + *τ4,κ+ *τ4 +β,θ+η2 + *τ3,θ+ *τ3+ *τ1,*τ3+ *τ1+ *τ2,*τ1+*τ2+ *τ4,*τ4+β+γ,*τ4 +γ+δ,*τ3+ *τ2 +α,*τ2 +α+ *τ4,α+ *τ4 +δ,δ+α + *τ5 ,*τ5 +ε+δ,*τ5+ε+ζ,*τ5 +ζ+ι,ζ+ι+λ.In the as-cast state,the maximum solid solubilities of Cu in Al,α-Ce3Al11,CeAl3and CeAl2 are about 2.48 at.%,1.6 at.%,3.7 at.% and 5.3 at.%,respectively,andAl in CeCu5 is about 44.1 at.%. The homogeneity ranges of Al2Cu and AlCu extendsfrom about 32.1 to 32.7 at.% and 53.5 to 57.3 at.% Cu,respectively. Five ternarycompounds and their solid solutions have been observed in this work: CeAl12-xCux（4.0≤x≤4.53）,Ce2Al17-xCux （6.49≤x≤7.87）,CeAl4-xCux （0.73≤x≤1.10）,CeAl13-xCux（6.62≤x≤6.92） and Ce2AlCu2.The compound Ce2AlCu2was reported in former papers .However,its crystal struc-ture is not studied . In this work,by the TREOR program we have indexed its crystalstructure.Results are listed as follows: the space group Immm,and lattice parametera= 4.273（3） A,b= 5.523 （7） A,c= 8.527 （8） A.The electrochemical properties of the alloy Ce(Cu1-xAlx)5 were also studied in thispaper. Element substituting and different heat treatments were used to improve itselectrochemical properties. Results show that the alloy Ce(Cu1-xAlx)5（x=0,0.5,1.0,1.5,2.0,2.5） almost cannot discharge. The experiment on the element substituted al-loysCe1-xLaxNi3.6Al0.65Cu0.75（x=0,0.2,0.4,0.6,0.8,1） indicated that the maximumdischarge capacity increased when the La content increased,and the right amountof Ce is good for improving its cycling stability. In our experiment ,three kinds ofalloys with the same compound,samples arch-melted,anealed at 500℃,and remeltedafer anealed at 500℃,were used to test their electrochemical properties. By compar-ison,samples remelted afer anealed at 500℃have exhibited the best electrochemicalproperties.
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