Research On The Influence Of Rare Earth And Ca Element On Microstructure And Properties Of Magnesium Alloy

RE and Ca are common adding elements in magnesium alloy.RE hassome advantages such as refining grains,improving the fire resistance of alloy, thermalstability, and the high-temperature creep properties. whereas the disadvantages of RE suchas low effective yield with high cost have limited the development and application of REmagnesium alloys, in spite that the effect of adding Ca to magnesium alloy is similar toadding RE and the cost is relatively low. There are many different opinions on the caexistence form in magnesium alloys, while few reports are about its influence on heattreatment technology and hot rolling process for magnesium alloys. Therefore, this topicrespectively smelt three different alloys containing Ca and RE(AZ80-2.0Ca，ZK60-Er，Mg-4Zn-0.5Er-1Y). This paper studies the influence of Ca on AZ80magnesium alloy inhomogenization, solid solution aging heat treatment, and microstructure and hardnessindex during hot rolling process, discusses the effect of Er on ZK60magnesium corrosionresistance, microstructure and mechanical properties, analyzes the effect of Er, Y elementon Mg-4Zn microstructure and mechanical properties after hot rolling under different heattreatment conditionsResearch shows that: as-cast AZ80magnesium alloy is for homogenization processing,heat preservation for4h at430℃, β-Mg17Al12phase dissolves in the grain boundary.After solid solution treatment under this condition, conducting aging treatment under150℃and300℃, a small piece of stratified alloy phase precipitates,the alloy hardnessvalue increases firstly, then decreases, the dynamic recrystallization appears after hotrolling, β-Mg17Al12phase is broken, the grains will be refined; Adding Ca elements toAZ80magnesium alloy, β-(Mg, Al)2Ca phase appears in alloy, which improves itsthermostability property,when the heat preservation is within0.5h, at515℃,β-Mg17Al12phase dissolves quickly.Then further extending the heat preservation time up to4h,(Mg,Al)2Ca phase begins to decompose, change into Al2Ca and Mg, the alloy eutecticphase decomposition process is over after Mg spread to matrix for4h, and the residualdecomposition is Al2Ca; With the extension of heat preservation, microhardnss value ofalloy gradually declines, there are no longer changes of the hardness value after thecomplete decomposition. Plasticity is poor in the process of hot rolling. Adding Er toZK60, MgZn2phase gradually reduces with the increasing of Er element. The increase ofrodlike quarternary phase leads to corrosion resistance property improving obviously andthe addition of Er capacity elevates the solidus line temperature and improves alloycasting performance. At the same time, tensile strength and the yield strength of ZK60magnesium alloy improve, but elongation declines, and rangeability is larger under hightemperature than room temperature; After more hot lane,the rolling deformation of Mg-4Zn-0.5Er-1Y alloy can be up to60%, and by different annealing treatment,comparing the size changes of grains, then determines the best annealing parameters(heatpreservation under250℃for1h), grain is equality and tiny at this time,there will be amarked static recrystalization, mechanical property is optimal. The yield strength σ0.2andd-1/2have linear relationship at different annealing temperature, conforming to theHall-Petch equation. The higher annealing temperature is, petch coefficient k is lower andthe smaller dependence of yield strength on the grain size will be.