بررسي رفتار مكانيكي و شكل پذيري ورق هاي نازك تركيبي جوشكاري شده به روش اغتشاشي

چكيده انگليسي :

Investigation of Mechanical Behavior and Formability of Friction Stir Welded Thin Sheet Tailor Blanks Farhad Teimouri f teimouri@me iut ac ir Date of Submission 2015 07 25 Department of Mechanical Engineering IsfahanUniversity of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Mahmoud Farzin Farzin@cc iut ac irAbstract Today need for using light weight components and decreasing cost of manufacturing processes isinevitable for various sections of industries So in sheet metal forming processes new concepts of fabricatingconsolidated sheets or in other words Tailor Welded Blanks emerged Friction Stir Welding is one themethods for manufacturing TWBs and has numerous advantages over fusion welding methods for joiningaluminum sheets In present study TWBs made by friction stir welding of 6061 T6 and 5754 O aluminumalloys were studied The effect of different tool rotational speeds and welding speeds on mechanicalproperties and microstructural characteristics of dissimilar joints were evaluated The results showed that inan appropriate range of speed combinations an optimum rotational speed exist at which maximum strength isachieved Regarding welding speed greater strength is attained at higher speeds The microstructuralanalyses confirm that above the optimum rotational speed the grain size of the nugget zone increases whichresults in decreasing tensile strength With regard to welding speed increasing speed will result in grain sizereduction and consequently higher tensile strength Positioning Al 6061 on advancing side of the dissimilarjoints lead to improved mechanical properties compared with positioning on retreating side It can be due toimprovement in mixing of the base materials as a wider nugget zone obtained at such situation It is notablethat the degree of such improvement in ductility is much more remarkable than strength which is valuableregarding formability concerns In the next section the formability of post rolled dissimilar sheets wasassessed by bulge test It was shown that the TWBs that are rolled perpendicular to the weld line theformability of Al 5754 side relatively reduced comparing with Al 6061 side It is in contradiction to the factthat Al 5754 base sheet has much more ductility comparing with Al 6061 base sheet It seems that the Al5754 is much more affected by the cold rolling process The TWBs that are rolled parallel to the weld line allof the rapture locations occur in the weld of Al 6061 side that are similar to the fracture locations in tensiletests Also it is shown that the formability decreases at higher rotational speeds and improves with increasingwelding speed At rotational speed of 1600 rpm and welding speed of 63 mm min comparing the results ofbulge test with tensile tests shows that although the ductility is highest in tensile test but the formabilityreduced in bulge test compared to lower rotational speeds Also the joint produced at speed combination of1000 rpm and160 mm min not only had greatest tensile strength in tensile test but also exhibited highestamount of formability in bulge test So it is concluded that both tensile strength and ductility are importantand should be simultaneously considered concerning formability of TWBs Keywords Tailor welded blank Dissimilar friction stir welding Aluminum Formability Bulgetest

تيموري، فرهاد

بررسي رفتار مكانيكي و شكل پذيري ورق هاي نازك تركيبي جوشكاري شده به روش اغتشاشي

جوشكاري ناهمجنس اصطكاكي اغتشاشي , آلومينيوم , تست بالج