Synergistic Effects Of Nd And Y On Microstructure And Properties Of AZ31Magnesium Alloy

Magnesium alloys have received considerable attention as the lightest structuralmaterials due to their high specific stiffness and high specific strength, and wellcomprehensive mechanical properties. AZ31magnesium has been the mostcommonly commercial magnesium alloy because of low cost, excellent castabilityand moderate mechanical properties. However, the application of these alloys arerestricted in automotive and aerospace industries because of their poor formabilityand thermal instability at elevated temperatures. In this study, the influence of rareearth elements including Nd and Y on the microstructure and mechanical properties ofAZ31alloy has been investigated, as well as the flame retardation and corrosionresistance.Addition of Nd and Y refines the as-cast microstructure and restrain theprecipitation of β-Mg17Al12instead of forming the Al-RE phases. The Al-RE phasespin the grain boundaries during the heat treatment so that the addition of Nd and Ycan restrain the grain growth. During the heat–extrusion process, the grain size ofalloys decreases obviously because of the dynamic recrystallization (DRX).Meanwhile, the second phases are broken into small ones allocated in the matrixdispersively with the extrusion stress. As a result, the tensile strength and ductility canbe promoted synchronously. The AZ31-0.5Nd-0.5Y alloy has the optimum tensileproperties, the ultimate tensile strength, yield strength and elongation can reach to265MPa,193MPa and16.55%, respectively. In contrast, the UTS, YS and elongationof AZ31alloy are258MPa,167MPa and10.3%, respectively.Addition of Nd and Y can promote the ignition temperature of AZ31alloy.Because the affinity of rare earth elements and oxygen are bigger to form a denseoxide layer than magnesium oxide. As a result, the ignition temperature increasesdrastically. AZ31-1Nd-1Y alloy has the highest inflammation point of598oC, whilethe inflammation point of AZ31only is571oC.The electrochemical corrosion resistance of magnesium alloys in the3.5%NaClsolution has been investigated. Anode polarization curve has been changed whenaddition of RE rather than cathodic polarization curve. The AZ31-1Nd shows the bestcorrosion-resistance with the minimum corrosion current density.