Effects Of Al Addition And Heat Treatment On The Microstructure,mechanical Properties And Corrosion Resistance Of Mg-4Y Alloys

Recently,the government calls for the energy saving and emission reduction,magnesium alloys are known as the"green engineering materials"in twenty-first Century due to their advantages such as light weight,high specific strength and specific stiffness,and recyclable green and pollution-free advantages.The Mg-4Y system alloys have become the research hotspot because of their widely used in industry.The research on high strength and anticorrosive RE magnesium alloy and its heat treatment process have become an important research direction in the magnesium alloys field.The effect of Al element and heat treatment on the microstructure and properties of Mg-Y magnesium alloys is useful and valuable.The methods of Optical microscope?OM?,X ray diffraction?XRD?,scanning electron microscopy?SEM?and its accompanying energy spectrum?EDS?,tensile test,hardness test,polarization curves and electrochemical impedance spectroscopy and other modern analytical methods were used to reveal the effect of Al addition and heat treatment on the microstructure and properties of Mg-4Y magnesium alloy.The conclusions are as follow:The microstructure of the as-cast Mg-4Y-xAl alloy is composed of Al₂Y and Mg₂₄Y₅ phase.The Al element will react with the Y element to generate the Al₂Y phase preferentially.The solidification process of Mg-4Y-xAl alloy are as follows:firstly,the Al₂Y phase formed directly from the melt at high temperature,then the peritectic reaction occurred at 630°C:L+Al₂Y??-Mg,The addition of Al also affected the eutectic reactions;the intergranular residual liquid phase transformed into?-Mg and Mg₂₄Y₅ phases for Al contents?2%;in contrast,the pseudo-binary eutectic reaction occurred,forming?-Mg and Al₂Y phases,for Al contents?2%.With the increase of Al content,the mechanical properties of the alloy gradually increased.When the Al content is 4%,the maximum yield strength and tensile strength of the alloy are 81 MPa and 208MPa.With the increase of Al content,the polarization curve shifted negatively,the corrosion current density of alloy decreased,the high frequency capacitance arc radius increased,so that the corrosion resistance of the alloy increased significantly.The optimal solid solution process of Mg-4Y-4Al alloy is 525°C/8h.The microstructure of Mg-4Y-xAl alloy consists of?-Mg and Al₂Y phase.After the solid solution treatment,the hardness and tensile strength of the alloy decreased,and the yield strength and elongation increased significantly.With the increase of Al content,the mechanical properties of the as-solution alloy increased,and the elongation decreased gradually.Compared with the as-cast alloy,the self corrosion current density of the as-solution alloy decreased,and the corrosion resistance of the alloy increased significantly.When the Al content increased from 1%to 2%,the corrosion potential were decreased and the corrosion trend of the alloy increased,when the Al content increased to 3%,the corrosion potential were improved,the alloy got the highest corrosion potential-1.416V/SCE and the maximum linear polarization resistance 724?·cm²,the as-solution alloy with 3%Al has the best corrosion resistance.The optimal heat treatment process for Mg-4Y-4Al alloy is 525°C/8h+225°C/20h.The mechanical properties of the alloy improved significantly and the corrosion resistance decreased after the solid solution and aging treatment.The microstructure of Mg-4Y-xAl alloy consists of?-Mg,Mg₂₄Y₅ and Al₂Y phase.With the increase of Al content,the tensile strength and yield strength increased gradually,but the elongation decreased.When the Al content increased from 1%to 4%,the tensile strength of the alloy increased from 183.6MPa to 245.3MPa,which increased by 33.6%,the yield strength increased from 88.7MPa to 121.8MPa,which increased by 37.3%.The self corrosion current density of the alloy increased and the corrosion resistance of the alloy declined after the aging treatment.With the increase of Al content,the corrosion potential were improved,so that the corrosion tendency of the alloy decreased.The linear polarization resistance increases with the increase of Al content,it reached to 583?·cm² when the Al content reached to 2%,the corrosion current density reached to the value of 4.407×10^-5 A·cm^-2.The linear polarization resistance decreased to 391?·cm² and the corrosion current density decreased to 7.509×10^-5 A·cm^-22 when the Al content is4%,the corrosion resistance decreased.