On the problem of tool destruction when obtaining fixed joints of thick-walled aluminum alloy blanks by friction welding with mixing

OBRABOTKAMETALLOV MATERIAL SCIENCE Том 23 № 3 2021 EQUIPMEN . INSTRUM TS Vol. No. 3 2021 Fig. 2. Panoramic images of the stir zone of welded joints produced by modes 1 ( a ), 2 ( b ), 3 (c) and 4 (d) in cross-section: 1 – tool shoulder affected zone; 2 – stir zones formed by tool grooves; 3 – defects of the welded joint; 4 – weld cores formed by local material flows а b c d samples 2 and 4, the tool was destroyed, and in sample 2 – at an early stage of the process. In this regard, Figure 2b shows the cross-section in the area after the tool destruction. As can be seen from the figure, sample 1, obtained at high welding speeds, has the narrowest mixing zone, while in samples 3 and 4 the mixing zone is wider, with a clearly different zone of influence of the tool shoulders and concentric rings, also known as “onion rings”, forming the core of the welded joint [21]. It is worth noting that, unlike welded joints with a thickness of up to 10 mm, a large number of small cores are formed, not a single seam core. This character of the mixing zone formation is due to the uneven heating of the weld material in height [14], which leads to inhomogeneity of the adhesive interaction of the material with the tool being welded. As a result, the transfer layer is divided into smaller ones, mainly carried by the grooves of the tool, which is clearly seen in Figure 2, b , d : in the lower part of the weld, strips of separately transferred material are allocated, which, nevertheless, have a periodic nature. Figure 2a shows that in Sample 1, a structure with tunnel-type defects and voids was formed in the zone of influence of the tool shoulders. High welding speeds with a relatively low loading force led to the fact that the thermal conditions for the formation of transfer layers were violated in the upper part of the sample. In turn, this led to a deterioration of the adhesive interaction during the welding process. However, in this case, the destruction of the tool did not occur, whereas when welding sample 2, obtained at a higher loading