Influence of kinematic factors of friction stir welding on the characteristics of welded joints of forged plates made of EN AW 7049 A aluminium alloy

Abstract

M. Perović i dr.Utjecaj kinematičkih faktora zavarivanja trenjem miješanjem na karakteristike zavarenog spoja kovanih ploča od legure aluminija EN AW 7049 A Original scientific paper In this paper, the influence of rotation speed and welding speed on the impact strength, microstructure and cross section micro hardness of FSW welded joints of Al-Zn-Mg-Cu high strength aluminium alloy is studied. Rotation speed was varied from 750 min −1 to 850 min −1 and welding speed from 60 mm/min to 80 mm/min. It was found that the energy of crack propagation is up to three times higher than the energy of crack initiation. This ratio was found by testing the Charpy notched specimens taken from left and right from the weld centre, 4 mm from the notch in a direction opposite to a direction of welding. Micro hardness distribution in the nugget does not show large dissipation of value regardless if the measuring point is in the upper or lower section of the nugget. Weld microstructure characteristics and zones are clearly defined at the basis of grain size and material flow. Keywords: dynamic recrystallization; friction stir welding; impact strength; micro hardness distributionUtjecaj kinematičkih faktora zavarivanja trenjem miješanjem na karakteristike zavarenog spoja kovanih ploča od legure aluminija EN AW 7049 A Izvorni znanstveni članak U radu se analiziraju utjecaji broja okretaja i brzine zavarivanja na udarnu žilavost, metalografska obilježja i raspodjelu mikrotvrdoće po površini poprečnog presjeka FSW zavarenog spoja kovanih ploča od visokočvrste legure aluminija faznog sastava Al-Zn-Mg-Cu. Broj okretaja je mijenjan u rasponu od 750 min −1 do 850 min −1 , a brzina zavarivanja od 60 mm/min do 80 mm/min. Razdvajanjem energije inicijacije pukotine od energije potrebne za njezinu propagaciju, uočava se da je čak i do tri puta veća vrijednost energije koja je potrebna za njezinu propagaciju. Odnos energije inicijacije i energije propagacije je dobiven ispitivanjem Charpy epruvete sa zarezom u središtu, lijevo i desno od središta metala šava 4 mm u smjeru suprotnom od smjera zavarivanja. Distribucija mikrotvrdoće metala šava ne pokazuje veliko rasipanje vrijednosti bez obzira da li je mjerno mjesto u gornjoj ili donjoj razini površine zavarivanih komada. Na mikrograficima jasno se uočavaju zone strukturnih sadržaja zavarenog spoja na osnovi veličine zrna i linija tečenja materijala.

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“…In current study, single influencing factor is commonly studied at a time by fatigue test, there is still a lack of comprehensive analysis on the influencing factors of fatigue life of welded joints. For example, influence of dimension factors on welding residual stress and deformation in SUS304 butt-welded joint whose thickness of plate is 4 mm is investigated by means of both numerical simulation and experiment [8]; the influence of rotation speed and welding speed on the impact strength, microstructure and cross section micro hardness of FSW welded joints of Al-Zn-Mg-Cu high strength aluminum alloy is studied [9]. In these researches, there is still lack of comprehensive and quantitative evaluation of the fatigue life influencing factors.…”