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In this paper, an attempt was made to study the effects of various types of tunneling defects in friction stir welding (FSW). Two types of welding tool were used, one with a threaded and the other with a polygonal pin. To enable the formation of tunneling defects, the shoulder-to-pin-volume ratio was larger than 1 for both tools, while the ratio of rotation speed to welding speed was optimized as well. Tunneling defects were tested on EN-AW 5052 H32 and H38 alloys, having the thicknesses of 3 mm and 8 mm. It was found that the threaded tool produced a single or double triangular, as well as crack-shaped tunnel. The polygonal tool produced a multiple triangular tunnel (the material flows toward the weld face) with a complex shape or a crack-type tunnel with a complex shape. The most unfavorable tunnel obtained with the polygonal tool was the crack-shaped one, resulting in the 62 % and 46 % joint yield and ultimate tensile-strength efficiency. The corresponding values for the threaded tool were 40 % and 36 %. The hardness efficiencies did not follow the trends of the proof and ultimate tensile strengths due to the prevention of the tunneling during indentation. Another effect on the hardness is the presence of microcracks that may influence the apparent decrease in the hardness in spite of the detected grain-refinement effect in the nugget. These effects influence the hardness distribution in the weld, shifting the maximum hardness value into the thermo-mechanical zone. Članek predstavlja študij vpliva različnih vrst tunelskih napak pri drsno mešalnem varjenju (FSW). Uporabljeni sta bili dve vrsti varilnega orodja, eno z navoji in drugo s poligonalnim nastavkom. Da bi preprečili nastanek tunelske napake, je bilo razmerje med nosilcem in nastavkom večje od 1 pri obeh orodjih, medtem ko je bila optimirana tudi rotacija glede na hitrost varjenja. Tunelska napaka je bila preizkušena po EN-AW 5052 na zlitinah H32 in H38, debelih 3 mm in 8 mm. Ugotovljeno je bilo, da orodje z navoji povzroči enojni, dvojni trikotni tunel, kot tudi tunel v obliki razpoke. Poligonalno orodje povzroči več kompleksnih tunelov s trikotnim prerezom (material steče proti čelu zvara) ali kompleksnih vrst tunelov v obliki razpok. Najbolj nezaželen tunel, dobljen s poligonalnim orodjem, je bil v obliki razpoke, kar je povzročilo 62-odstotni in 46-odstotni izkoristek spoja oziroma učinkovitost natezne trdnosti. Ustrezne vrednosti pri orodju z navoji so bile 40 % in 36 %. Učinkovitost trdote ni sledila tem usmeritvam in končni natezni trdnosti zaradi izogibanja tunelom med merjenjem trdote. Nadaljnji vpliv na trdoto imajo mikrorazpoke, ki lahko povzročijo navidezno zmanjšanje trdote, kljub odkritemu zmanjšanju zrn v jedru zvara. Ti pojavi vplivajo na razporeditev trdote v zvaru in potiskajo vrednosti največje trdote v termomehansko območje. |
