Effect Of Grain Sizes On The N And R Value Of 3104 Aluminium Alloy Sheets

Currently,3104 aluminum alloy is a kind of thin sheet aluminum alloy with a highest single production.Due to its high toughness,strong corrosion resistance and better deep-draw performance,it is now being used to produce not only aluminum cans,but also the ductile containers,production and storage devices of chemical products,construction tools and parts of lamps.Both of strain hardening index n value and plastic strain ratio r value are important indexes which can be used to measure the deep drawability of sheet metal.Generally speaking,strain hardening index n value represents a deformation strengthening of material,and it shows different deformation mechanism in microcosmic.Other studies showed that n value could be affected by macro factors,such as the level of plastic deformation and the path of deformation,and micro factors,such as the microstructure of alloy and the dislocation configuration.From a researching about the deep-draw aluminum sheet 3104-H19,Mr.Ma Quancang from USTB found that the crystal orientation was the main reason which can determine the value of plastic strain ratio.However,researching about another main reason,grain size,which could also affect the value of strain hardening index n value and plastic strain ratio r value in microstructure are much less.In this paper,the author established a relationship between the grain size of aluminum in the 3104 aluminum alloy thin sheets by using an appropriate heat treatment which could control the micro structure,then made the configuration of second phase particles had the same orientation as recrystallized grain,followed with alloy sheets with different sizes of recrystallized grains,and finally studied the differences between n and r by unidirectional tensile test.(1)After a series of recrystallization annealing treatment(400?×1h,500?×1h,550?× 1h,550?×4h,550?×8h,550?×24 and 550?×96h),the second phase particles were mainly composed of granular and rod-like AlFeMn crystal phases whose sizes were 5-10 ?m in 3104 aluminum alloy cool-rolled sheets.The recrystallization treatment had no apparent impact on the species,distribution situation,numbers and sizes of crystal phases;3104 cold-rolled sheets all had occurred complete recrystallization after the recrystallization annealing treatment above.They had similar grain orientation,but different grain sizes which was 12.65?m?13.80?m?19.46?m?21.68?m?28.11?m?29.19?m and 31.63?m respectively.(2)After tensile deformation along the rolling direction respectively,to 0°,45° and 90°,granular and rod-like crystal phases had no apparent changes,but the grain shapes had been stretched along the stretching direction in 3104 aluminum sheets with different grain sizes;The rheological behavior of uniaxial tension were roughly the same:With an increase of strain,stress firstly increased rapidly,followed with a slowly decrease and then tend to stable;With an increase of the grain size,yield strength and strength of extension of aluminum sheets firstly reduced slowly followed with a rapid reduction.There was not a apparent change rue about the elongation.(3)The variation of continuous strain hardening index nc values and stage strain hardening index n,values with strain were roughly the same:With an increase of strain,nc values firstly increased rapidly,and then tend to unchanged.ns values firstly increased rapidly to the top,followed with a slowly decrease.The plastic strain ratio r values of 3104 aluminiun sheets with 3 directions were roughly the same.The variation of r values were not apparent with the growing of strain.(4)The variation of continuous strain hardening index nc values and stage strain hardening index ns values with grain size were roughly the same:Generally nc values had an increasing trend When grain size grew from 13.80 ?m to 19.46 ?m,nc values increased slowly.When grain size grew to 28.11 ?m,nc values had a small decrease.When nc values continued to grow to 31.63 ?m,nc values increased apparently;But stage strain hardening index nc values had no apparent variation with the growing of grain size.(5)r values of 3104 aluminum sheets with 3 directions had no apparent variation with the growing of grain size.The r value was not sensitive to the changes of grain size.