11490

10553

كارشناسي ارشد

شناسايي و انتخاب مواد

اصفهان: دانشگاه صنعتي اصفهان، دانشكده مهندسي مواد

1395

چهارده، 85ص.: مصور

فتح اله كريم زاده، عبدالمجيد اسلامي

محمدحسين عنايتي، محمود منيرواقفي

1395/07/13

مهندسي مواد

ID10553

86 Evaluation of bimodal microstructure properties in Al 6061 alloy weldment during resistance spot welding process Vahid Zohoori v zohoori52@gmail com Date of submission Junne 18 2016 Department of Materials Engineering Isfahan University of Thechnology Isfahan Iran Degree M Sc Language FarsiSupervisores Fathallah Karimzadeh karimzadeh f@cc iut ac irAbdolmajid Eslami m eslami@cc iut ac irAbstractDespite studies regarding mechanical and corrosion properties of Al 6061 alloy weldment there is not sufficient information about fusion welding of nanostructured and bimodal nano micro grained aluminum The nonostructured material have attracted great interestdue to their excellent physical and mechanical properties Therefore it is important toevaluate the mechanical and corrosion properties of their joints Although nanocrystallinematerials exhibit high strength they display low ductility One efficientapproach to compensate this defect is to develop bimodal microstructures For thispurpose in this resurch samples were solution treated at 530 C for 3 hours andsubsequently cryorolled up to 90 reduction in thickness For obtaining simultaneousstrength and ductility the cryorolled alloy was then subjected to aging treatment at 130 Cfor 25 hours A bimodal microstructure consist of nano sized and micron sized grainsalong with nano sized 50 150 nm stregthening precipittes was obtained after cryorollingand aging treatment Transmission electron microscopy TEM was used formicrostructural characterization of cryorolled samples The average size of fine grains inaged sample was estimated about 60 nm Improved ultimate tensile strength of 365 MPa hardness of 140 HV and ductility of 12 was obtained for the produced aluminum sheets The samples in as rolled AR and peak aged PA condition and also the 6061 T6 Al alloysheets witness samples were then resistance spot welded with welding current of 40 100kA electrode force of 3 kN and welding time of 0 1 s Mechanial tests reaveld that thehighest peak load of weld spot of nanostructured samples was about 5700 N obtainedthrough weldig current of 95 kA All welded specimens failed in an interfacial fracturemode At constant welding parameters microhardness of weld metal was similar fornanostructured samples and conventional grained samples owing to similar microstructureand grain size According to the results of phase analysis of weld nugget dissolution ofMg2Si precipitates in fusion zone occured during welding process which led to decrease ofmicrohardness in this region Similar corrosion behaviour of weld zone was observed fornanostructured and conventional grained samples in tafel polarization tests For allspecimens corrosion potential of weld metal was lower than base metal due to dendriticmicrostructure of the weld metal Keywords Bimodal microstructure Cryorolling Resistance Spot Welding Mechanicalproperties Corrosion

فتح اله كريم زاده، عبدالمجيد اسلامي

محمدحسين عنايتي، محمود منيرواقفي