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Design Of Extrusion Mode And Extrusion Processing Of Wrought Magnesium Alloys With Complex Cross-Section

Posted on:2007-05-01Degree:MasterType:Thesis
Country:ChinaCandidate:X H YinFull Text:PDF
GTID:2132360212460068Subject:Materials Processing Engineering
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Wrought Mg alloys have found wide application in transportation,aerospace, aerospace vehicle, 3C products, etc., due to its excellent mechanicalproperties and physical properties, including low density, high specific strength,high specific modulus, electromagnetic radiation absorption, etc. But fewerreports on the extrusion modes of Mg alloys products with complexcross-section.In this thesis, plain divergent extrusion modulus for Mg alloys weredesigned; wrought AZ31, AZ91 and ZK60 sectional bars were extruded. Thesolid solution processing and its influences combined with extrusion processingvariables on the formability, the microstructures and mechanical properties ofthe as-extruded alloy. The main content and experimental results are drawn asfollows;1.The Mg alloy hollow sections for automotive was selected as studyobject. According to the deformation properties of the Mg alloys duringextrusion, the designing elements, including diversion ratio, diversion bridge,seaming room, modulus core and its working band, and the shape, size anddistribution of the divergent orifices, etc. were systematically analyzed. Theresets of plain divergent extrusion dies with"日","目"and"田"cross-section weredesigned. The main structural parameters of the dies include 4 fanning divergentorifices symmetrically distributed, teardrop bridge, the working band of the diecore of 10.3mm, the height of the seaming room of 16mm, the diversion ratiosof 8.06, 9.55 and 8.11 respectively. The experimental results that the as-designeddies are proper for production of thin wall wrought Mg alloy sections.2.The solid solution treatment processing of AZ31, AZ91 and Zk60 alloyingots were investigated. The influences of solid solution temperature andholding time on the microstructures of the ingots were examined. Theexperimental results show that high temperature and long holding time canobviously reduce dendrite segregation and coarse precipitates. The shape of theprecipitates change from network to dispersoid which can improve theworkability of Mg alloy ingots. The optimized temperature and time for AZ91and ZK60 alloy ingots in this study are 460℃, 10~15h and 480℃, 15h,respectively.3.The effects of extrusion temperature, extrusion speed, extrusion ratio, etc. on the formability of the ingot and the microstructures of the as-extrudedsections were investigated. The seaming features in the sections were examined.The experimental results show that the extrusion temperature and extrusionspeed are the two key variables for Mg alloys. The two optimized parameters forAZ91 and ZK60 alloy are 380℃, 3~5mm/s and 340℃, 3~5mm/s, respectively.Higher or lower temperature easily leads to cracking during extruding. Higherextrusion speed can also lead to coarse grains in the sections. On the other hand,larger extrusion ratios can lead to higher room temperature mechanicalproperties. The tensile strength and fracture elongation of AZ31 and ZK60 alloysections of with"田"cross-section extruded at extrusion ratio of 36.7 are239MPa, 14.3% and 297MPa, 17.1% respectively. The fracture mechanisms ofthe two alloy samples during tensile are quasi-cleavage cracking.
Keywords/Search Tags:Mg alloy, divergent extrusion modulus, solid solution treatment, extrusion
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