| How to make magnesium alloys have high hardness and good plastic toughness has always been an important issue in the field of magnesium alloy research.Based on the idea of composition design of high entropy alloy and abandoned the tradition of using re as microelement to improve the properties of the alloy,the HCP rare earth element with obvious "solid solubility effect" with mg was selected as the main element to independently design and prepare a high strength and toughness cast Mg85Al6Zn3Y2Gd4 alloy.In this paper,the solidification microstructure,mechanical properties and corrosion resistance of the experimental alloys were studied by SEM and TEM.The effects of alloying elements on the microstructure of the experimental alloys were analyzed.The strengthening mechanism of high strength and ductile casting alloys was discussed.Research indicates:The microstructure of cast Mg85Al6Zn3Y2Gd4 alloy is mainly composed of fine equiaxed ?-Mg matrix(average size is 35 ?m),and ?-Mg grains are distributed in type 14 LPSO.The Mg12REZn phase of the 18R LPSO structure and the bulk Al2(Y,Gd)phase with a size of only 5-1 5 ?m(volume fraction of 27%)are distributed between the dendrites..The hardness of the experimental alloy is 110 HV,the compressive fracture resistance is up to 481 MPa,the compression strain failure is 16.89%,and the product of strength and plasticity is 8128.09 MPa-%.The corrosion resistance of Mg85Al6Zn3Y2Gd4 alloy is relatively poor.The self-corrosion potential Ecorr is-1.4755 V,the self-corrosion current density icorr is 0.0021272 A/cm2,and the corrosion rate is also relatively large(47.959 mm/a).The Al element in the Mg85Al6Zn3Y2Gd4 alloy preferentially combines with the Y and Gd elements to form Al2(Y,Gd),which produces a second phase strengthening.As the Al content decreases,the hard and brittle phase Al2(Y,Gd)decreases.Mg91Zn3Y2Gd4 alloy has the best strength and toughness blending ability,and its product of strength and plasticity is 0.86%higher than that of Mg85Al6Zn3Y2Gd4 alloy,but its hardness is 9.09%lower than that of Mg85Al6Zn3Y2Gd4 alloy.Zn element mainly affects the formation of LPSO phase in the alloy,whichl produces LPSO strengthening.With the decrease of Zn element,the tough phase LPSO is continuously reduced.The RE element originally combined with Zn is dissolved into the matrix,which will cause solid solution strengthening,and which makes the alloy hardness increase and the strong plastic product decrease.Among them,Mg88Al6Y2Gd4 alloy has the highest hardness(129 HV)and the product of strength and plasticity(5113.68 MPa·%),which is+17.27%and-37.06%higher than that of Mg85Al6Zn3Y2Gd4 alloy.The Y and Gd elements mainly affect the formation of Al2(Y,Gd)and LPSO phases in the alloy.As the RE element decreases,the hardness of the alloy decreases and the strong plastic product increases.Among them,the product of strength and plasticity of Mg85Al6Zn3Y1Gd2 alloy is the highest(8856.96 MPa·%),which is 9.02%higher than that of Mg85Al6Zn3Y2Gd4 alloy,but its hardness is decreased by 20.91%,In conclusion,the comprehensive mechanical properties of Mg85Al6Zn3Y2Gd4 alloy are the best,the ability to combine strength and plasticity of Mg85Al6Zn3Y1Gd2 alloy are the best,the hardness of Mg88Al6Y2Gd4 alloy is the highest,and the corrosion resistance of Mg91Zn3Y2Gd4 alloy is the best,all of which reflect the cocktail effect of high entropy alloy. |
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