Influence of joining method for hardness distribution in joints of AlZnSMg1 alloy

The article presents the research results of hardness values distribution of friction s tir welded joint (FSW) alloy AW 7020 (AlZn5Mg1). The joints welded by traditional MIG method of the same aluminium alloy were chosen as reference points. Friction stir welding (FSW) - a new technology can be successfully used for butt welding of sheet metal with different types of aluminium alloys. The parameters of friction stir welding (FSW) and MIG welding used to join metal alloy AlZn5Mg1 (7020) were presented. Metallographic analysis showed the correct structured both MIG welded joints and FSW welded aluminum alloy 7020. The study was carried out using Vickers hardness HV5 accordance with the requirements of the Polish Standard PN-EN 1043-1:2000. The study was conducted in three rows, and the indenter load was 50 N. In order to determine the structural changes in the bonded joints, the samples were polished and then micro-etched KELLER reagent. Metallographic examination was carried out using optical microscope Axiovert ZAISS 25. Metallographic examination revealed the existence of an explicit heat affected zone of HAZ in case of MIG welded joints and virtually lack there of, in case of FSW welded joints. In case of FSW welded joint, maximum hardness was observed in the middle of joint, but at a distance of approximately 25 mm from the middle of the weld there is a hardness decrease of about 10% relative to the base material. In the MIG weldedjoint lowest hardness of the weld occurred in the middle of the joint.