Effect Of Al Content And Heat Treatment On Fatigue Properties Of Mg-4Y-3Nd Alloy

As the lightest metal structural material,magnesium rare earth alloy has shown outstanding advantages in the field of lightweight.Magnesium rare earth alloys are usually prepared by casting lightweight structural parts,which are often subjected to alternating loads during use,resulting in fatigue failure,resulting in immeasurable consequences.Therefore,it is extremely important to study the fatigue of magnesium rare earth alloys.The research group has developed a new Al-refined Mg-4Y-3Nd alloy.The mechanical properties are comparable to those of commercial WE43 alloy,but the cost is lower.In this paper,the fatigue properties of Al-refined Mg-4Y-3Nd alloy were studied.Firstly,the effects of Al content on the tensile properties,fatigue properties and failure fracture mechanism of Mg-4Y-3Nd-x Al(x = 0,0.5 wt.%,1.0 wt.%,1.5 wt.%,2.0 wt.%)alloys were studied.The results indicate that when the Al content is less than 0.5 wt.%,the grain size of the alloy is coarse,and a large number of network eutectic phases distribute at the grain boundaries,and the performance of the alloy is poor.When fatigue failure occurs,cracks initiate at twins,and more cracks are generated at eutectic phases during propagation.When the Al content is higher than0.5 wt.%,the grain is clearly refined,the size of the network eutectic phase at the grain boundary is reduced,the distribution is uniform,and the mechanical performance of the alloy is improved.When the failure fracture occurs,the crack initiates at the slip band,and more cracks are generated at the eutectic phase during the propagation process.When Al is not added,the mechanical properties of the alloy show the lowest.The tensile strength,yield strength,elongation and fatigue strength are 121 MPa,95 MPa,2.8 % and 18 MPa.When the Al content is 1.5 wt.%,the mechanical properties of the alloy show the highest.The tensile strength,yield strength,elongation and fatigue strength are 191 MPa,135 MPa,6.2 % and 66 MPa.On this basis,the effects of solution and aging treatment on the tensile properties,fatigue properties and failure fracture mechanism of Mg-4Y-3Nd-1.5Al alloy were studied.The results indicate that heat treatment can significantly improve the tensile properties and fatigue properties of Mg-4Y-3Nd-1.5Al alloy,and change the fatigue failure fracture mechanism.After solution treatment,the network phase at the grain boundary is completely dissolved,improving the plasticity of the alloy significantly.The tensile strength,yield strength elongation and fatigue strength are 193 MPa,125 MPa,13.7 % and 77 MPa,respectively(17 % higher than that of as-cast).When fatigue failure occurs,cracks initiate at the twins inside the alloy,and more cracks are generated at other twins during propagation.After aging treatment,abundant nanoscale precipitated phases are precipitated in the matrix,improving the strength of the matrix and the fatigue performance significantly the peak-aged alloy has the best performance.The tensile strength,yield strength elongation and fatigue strength are283 MPa,195 MPa,5.7 % and 95 MPa,respectively(44 % higher than that of the ascast state).During fatigue failure,cracks initiate at the slip band,and more cracks are generated in the Al2 RE particles during the expansion process.