اصلاح ريز ساختار مقاطع جوش آلياژ آلومينيومT6-7075 ايجاد شده به روش جوشكاري قوسي تنگستن-گاز توسط فرايند اصطكاكي اغتشاشي

چكيده انگليسي :

84 Influence of friction stir processing on mechanical and microstructural properties of AA7075 T6 aluminum alloy jointed by gas tungsten arc welding Hamed Fotoohi H fotoohi@ma iut ac ir Data of submission 2013 10 12 Department of Materials Engineering Isfahan University of Technology Isfahan 84156 8311 IranAbstractThe welding of aluminum and its alloys has always represented a great challenge for designers andtechnologists The preferred welding processes for aluminum alloy are gas metal arc welding andgas tungsten arc welding due to their comparatively easier applicability and better economy butpast research on structural aluminum alloys demonstrated lower mechanical and microstructuralproperties in gas tungsten arc welds when compared to base metal BM that mainly related to thepresence of a tenacious oxide layer high thermal conductivity high coefficient of thermalexpansion solidification shrinkage high solubility of hydrogen and other gases in molten state However there is a continual emphasis on decreasing the cost or weight of a givenstructure Friction stir processing FSP is a technique that produces local microstructuralmodification and when applied to gas tungsten arc welds improves the microstructure andcorresponding mechanical properties at the weld toe and crown locations Aluminum alloyAA7075 Al Zn Mg Cu is one of the high strength aluminum alloys Its high strength to weightratio together with its natural aging characteristics makes it attractive for a number of aircraftstructural applications The alloy derives its strength from precipitation of Mg2Zn and Al2CuMgphases The aim of the present work is to investigate Influence of friction stir processing onmicrostructure and mechanical properties of AA7075 T6 aluminum alloy jointed by gas tungstenarc welding The bare and friction stir processed welds were comparatively evaluated for theirmicrostructural characteristics and mechanical properties Friction stir processing was found toresult in substantial microstructural refinement with fine and uniformly distributed particles Theuse of friction stir processing has been found to improve the mechanical and microstructuralproperties of the welds compared to those of jointed by gas tungsten arc welding of this alloy dueto grain refinement occurring in the fusion zone The friction stir processing at 1600 rpm 80 mmmin 1 improved the tensile strength hardness and percentage of elongation of 7075 T6 aluminumalloy jointed by gas tungsten arc welding by 14 pct 66 pct and 300 pct respectively The hardnessof base metal unwelded parent metal in its initial T6 condition is approximately 120 VHN Butthe hardness of the gas tungsten arc welding joint in the weld metal region center is 60 VHN In thecase of friction stir processed joints the weld metal hardness has been found to increase comparedto unprocessed welds and arrive 90 VHN in friction stir processed weld at welding speed of 80 mmmin 1 and rotational speed of 1600 rpm This work demonstrates that friction stir processing is aneffective strategy for improving mechanical and microstructural properties in aluminum zinc alloyfusion welds Keywords Gas tungsten arc welding Friction stir Processing 7075 T6 aluminum alloy Microstructure

فتوحي، حامد

اصلاح ريز ساختار مقاطع جوش آلياژ آلومينيومT6-7075 ايجاد شده به روش جوشكاري قوسي تنگستن-گاز توسط فرايند اصطكاكي اغتشاشي