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Название Effect of post weld heat treatment on the properties and structure of friction stir welded joints of AV aluminium alloy
DOI 10.17580/tsm.2020.07.11
Автор Drits A. M., Ovchinnikov V. V.
Информация об авторе

ARKONIK – SMZ CJSC, Moscow, Russia:
A. M. Drits, Director for Business and New Technology Development, Сandidate of Technical Sciences, e-mail: Alexander.drits@arconic.com


Moscow Polytechnic University, Moscow, Russia:
V. V. Ovchinnikov, Professor at the Department of Metal Science, Doctor of Technical Sciences, e-mail: vikov1956@mail.ru


Comparative mechanical tests of the compounds of the Al – Mg – Si alloy sheets were performed by friction stir welding (FSW) and argon arc welding with A5 additive wire. Mechanical properties are defined immediately after welding, as well as after two thermal treatment of welded compounds after welding: artificial aging (170 oС, 14 hours) and hardening plus artificial aging (T1). It has been established that the temporary resistance of compounds welded by FSW in the T1 sheet state has a strength limit of 273 MPa. The use of artificial aging after welding increases the t strength limit to 309 MPa. Thus, with the strength of the main metal 332 MPa, the strength factor was 0.82 and 0.93 for these heat treatment modes. Artificial aging of the welded compounds of FSW sheets of alloy AV is accompanied by an increase in the temporary resistance of the seam metal to 319 MPa. It is important to note that the temporary resistance of the metal seam immediately after the FSW, as well as after artificial aging surpasses the temporary resistance of the welded compound. At sufficiently high levels of temporary resistance, welded compounds of adhesive sheets of AV alloy, made by FSW, are sufficiently plastic. Thus, the angle of the bend of the joints immediately after welding, as well as after artificial aging, is 175 and 170 degrees respectively, which is significantly higher than when welding melting. Artificial aging after welding friction with mixing samples of alloy AV in the temper of T1, visible change of macro and microstructure does not cause, both in the area of the main metal, and in the seam area. Metallographic studies of reheated compounds have shown significant grain growth. The growth of grain size is observed as in the welded compound, while in the main metal there are separate large grains in the surface layer of sheets. The estimated average grain size in the weld area was 0.7–0.8 mm. In the main, the metal in the share direction the size of the grains in the surface layer ranged in the range of 0.6–2.2 mm. And in the middle of the sheet remained at the level of 50–60 microns. Changes in the properties of different zones of the welded compound of the AV alloy correlate quite well with the values of micro-solidity measured in seam, thermomechanical affected zone (TMAZ), heat affected zone (HAZ) and mainly metal. The re-hardening of the welding and artificial aging is accompanied by a decrease in the size of micro-solidity for all structural areas of the FSW compound, which appears to be a consequence of the sharp increase in the size of the grain. The growth of grain size is caused by the presence of a critical deformation of the material during the FSW process and the development of recrystallization under the influence of heating during the thermal treatment of the compound. The use of artificial aging, or re-hardening and artificial aging of welded samples of the AV alloy, made by argon arc welding, leads to a significant reduction in the angle of the bend from 30 degrees to 12 degrees.

Ключевые слова Stir friction welding, alloys Al – Mg – Si, mechanical properties, heat treatment, grain size
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