Effect Of Trace Sc And Zr Elements On Microstructure And Properties Of 5182 Aluminum Alloy

As a wrought Al-Mg alloy,5182 has many excellent properties.This metal is suitable for non-heat treatable alloys.Alloying and machining deformation are effective means to improve mechanical properties.Based on 5182 alloy,several alloy ingots were prepared by adding different amounts of Sc,Zr and composite（Sc+Zr）elements respectively.The homogenization heat treatment process of the alloy ingot with Sc+Zr element was optimized,and the hot extrusion test was carried out.Through optical metallographic microscope（OM）,scanning electron microscope（SEM）,transmission electron microscope（TEM）and X-ray diffraction（XRD）the microstructure observation and phase analysis of as cast,homogenized annealed and hot extruded alloys were carried out.The hardness and tensile properties of as cast,homogenized annealed and hot extruded alloys were tested by Brinell hardness tester and universal testing machine.The results show that:As cast 5182 alloy has typical dendrite morphology,serious Mg segregation and coarse grain size.The addition of trace Zr makes the grain slightly refined.When Sc element is added,the grain refinement degree is higher.When 0.4%Sc is added,the alloy grain basically turns into fine equiaxed dendrite,while the compound addition of 0.3%Sc+0.1%Zr makes the equiaxed grain further refined,with an average size less than 40μm.Grain refinement is more than 400%.The as-cast microstructure of 5182 alloy is mainly composed ofα-Al,network or skeleton Al₆（Fe,Mn）phase and massive Si-rich phase,among which Al₆（Fe,Mn）phase is larger in size and continuously distributed at grain boundaries.The size of the phase decreases with the addition of Sc and Zr.The existence of spherical Al₃Sc or Al₃（Sc,Zr）phase in the microstructure of single Sc element addition,compound Sc element addition and Zr element addition can promote grain refinement.The mechanical property analysis shows that the addition of 0.3%Sc+0.1%Zr increases the as-cast hardness by 50%and the tensile strength by 44.6%.When the homogenization annealing temperature reaches 465℃and holding time 20h,the dendrite segregation of the alloy is completely eliminated,and the eutectic phase with low melting point precipitates in the crystallization process basically melts back into the matrix.The secondary Al₆（Fe,Mn）phase precipitates in the alloy at this time.The morphology is short rod,the size is small and the edges are smooth,which is beneficial to the subsequent processing deformation.Nano-sized secondary Al₃（Sc,Zr）particles are precipitated at the homogenization temperature.The existence of the phase is beneficial to improve the hardness of the alloy and has a favorable effect on extrusion processing.The homogenization annealing process of465℃/20h was determined according to the actual situation.After the addition of Sc and Zr elements,the sub crystalline structure appears in the extruded 5182 alloy,there is a high-density dislocation network in local positions,and the grain structure is elongated into fibrous shape along the deformation direction,which proves that the alloy is in the dynamic recovery stage at room temperature without recrystallization;the rod Al₆（Fe,Mn）phase is crushed in the as cast state,and the existence of dispersed second phase hinders the dislocation movement,The mechanical properties of the alloy were improved by local dislocation entanglement.After adding 0.4%Sc element,the tensile strength of the alloy increased significantly and the elongation decreased;After adding0.3%Sc+0.1%Zr,the tensile strength of the alloy was further improved,22%higher than that of extruded 5182 alloy,and the elongation decreased slightly.