Research On The SCC And IGC Performance Of Welded Joints Of A7N01S Aluminum Alloy

These years, with the augment of railway passenger volume, the increase of the speed of the train, Al-alloy material is widely used in railway vehicle bodywork. Because Al-alloy has SCC susceptibility in moist atmosphere, it is necessary to study it's SCC resistance.This dissertation is about the design of welding procedure of A7N01S (correspond to homemade 7020 aluminum) and A6N01S Al-alloy which are used in aluminum express train, particular investigation is carried out about mechanical properties of the weld joint. A facility for the evaluation of stress corrosion of high strength aluminum alloys was designed and applied. The SCC mechanism and the factors influencing it of A7N01S is investigated by parcraked 4-point bend SCC experiment. In this dissertation, intergranular corrosion experiment is carried out about A7N01S Al-alloy.Acorroding to the experiment, the hardness distribution of A7N01S and A6N01S both are approximately symmetrical to the center line of welded joint. After compare the SCC crack growth velocity of base metal, weld metal and HAZ, it can be concluded that the area near the fusion line in HAZ is most sensitive to SCC. The SCC crack shape of A7N01S appears as branch, there are thin embranchment at crack tip and the trunk. There is IGC phenomenon around SCC crack, there are reticulate IGC grain boundary along the trunk and at the crack tip. At last, the influence of welding procedure on SCC is discussed, and measures to prevent SCC are put forward.