Effect Of Extrusion Technology On Microstructure And Mechanical Properties Of Mg-3Al-3Zn-3Ca Alloy

The density of pure Mg only is 1.74g/cm3.So magnesium alloy as the highest metal struchure material can reduce weight of the produce.In addition,magnesium alloys have great prospects in the aerospace,automotive and other fields,which have high specific strength,stiffness and good damping performance.Compared to as-cast,wrought magnesium alloy has relatively good mechanical properties.This paper mainly studied that the process of extrusion of Mg-3Al-3Zn-3Ca(AZC333)alloy was optimized,which prepared by using semi-continuous with water-cooled,and microstructure and mechanical properties of the detailed research.It is concluded that:The microstructure of as-cast Mg-3Al-3Zn-3Ca alloy was typical dendritic structure,which includes the coars of ?-Mg and second phase.The size of a-Mg is about 185?m.The second phases are continuous mesh structure Al2Ca and semi continuous mesh structure Ca2Mg6Zn3,which distribute on the grain boundary.After hot extrusion,the microstructure and mechaniucal properties of Mg-3Al-3Zn-3Ca alloy has obvious been improved.When extrusion ratio was 16,the volume of dynamic recrystallization decreased from 91.2%to 78.8%and the average size of grain reduced from 6.86?m to 3.14?m with the temperature dropping from 623K to 523K.At the same time,the size of Al2Ca and Ca2Mg6Zn3 of Mg-3Al-3Zn-3Ca alloy were about 3?m and 5?m.respectively.And the strength of the basical texture of(0002)enlarged,which along extrusion direction.The ultimate tensile strength and yield strength increased from 264MPa and 197MPa to 334MPa and 292MPa,respectively.The elongation reduced from 20%to 9%.When extrusion temperature was 623K,the microstructure and mechanical properties of AZC333 alloy wasn't obvious improved.During the hot extrusion process,Mg-3Al-3Zn-3Ca alloy occured dynamic recrystallization,which casued grain refinement and fine grain strengthening.It was explained by Hall-Petch relationship.According to Hall-Patch formula to calculate the yield strength of the as-extruded Mg-3Al-3Zn-3Ca alloy at 623K,573K and 523K,the resuilts were 186MPa,208MPa and 292MPa.And all results were lower than the actual values which were 197MPa,231 MPa and 292MPa.The results showed that Mg-3Zn-3Al-3Ca alloy produced the fine grain strengthening and second phase strengthening.When the extrusion temperature increased from 523K to 623K,the value of the fracture toughness of the alloys enlarged from 13.3521MPa·m1/2 to 21.6076MPa·m1/2.So the fracture toughness of the Mg alloy with same composition is closely relative to itself plastic.Under the conditions of the temperature between 523K to 673K and 1×10-3s-1 and 1×10-4s-1 of the strain rates,the tensile results show that the alloy has superplasticity with the temperature hiher 573K.When the temperature rised and the strain rate reduced,the elongation was incresed.The max elongation was 227.6%with the extrusion temperature 623K.The strain rate sensitivity(m)and superlastic deformation activation energy(Q)of the as-extruded alloys were calculated according to constitutive equation.When the extrusion temperature is 523K,573K and 623K,the averge m values of the as-extruded alloys were 0.0318,0.0253 and 0.02842,respectively,and the average Q values were 343kJ·mol-1,87.343kJ·mol-1 and 286.6343kJ·mol-1.Analysis shows that the superplastic deformaton mechanism of the as-extruded alloys is lattice diffusion coordination dislocation climbing controlled creep.Al2Ca and Ca2Mg6Zn3 were sheared and refined by the deformation disloction,and the min size were 0.2 and 1.1,respectively.Those fine particles promoted dynamic recrystallization as nucleation particles and inhibited the crystal grain growth and accommodated deformation by grain boundary,which unform distribution on grain boundary.