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Stress corrosion tests have been performed by using slow-strain-rate testing method (SSRT) in compliance with PN-EN ISO 7539-7 standard. The tests were conducted in air and 3.5% NaCl water solution. The following parameters have been measured during the tests: time to failure -T [h], maximum failure load -F [N], fracture energy (area under stress-elongation curve) -E [MJ/m 3 ], relative elongation of specimen -A 10 [%], maximum tensile stress -R [MPa], as well as percentage reduction of area -Z [%]. On the basis of the obtained test results it was concluded that the joints welded by means of FSW methodshow good resistance to stress corrosion at satsifactory strength properties, which indicates that application of friction welding by using FSW method in shipbuilding industry is purposeful.

Al-Mg alloys used in the shipbuilding industry were tested. The most commonly used alloy AW 5083 and alloy AW 5059 with higher strength properties were selected. Both native materials and their joints welded by the traditional MIG arc welding method and the friction stir welding (FSW) method were tested. Both methods are approved by classification societies which allow them to be used in construction by the shipbuilding industry. The research was carried out in two stages. The first study was an “in-situ tensile test in SEM”. The surfaces of the deformed specimens’ changes were observed in the vacuum chamber of a Philips XL30 scanning electron microscope. During the tests, the force and elongation of the specimen were recorded. In addition, a chemical analysis of selected precipitates was performed by energy dispersive spectrometry (EDS) using the EDAX adapter. Slip lines were observed on the surface of the tested specimens, which are arranged in bands in the native material and in a disordered manner in the joints welded by MIG and FSW methods. Cracking starts mainly through decohesion at the matrix-precipitate interfaces. In the second stage of the research, slow strain rate testing (SSRT) was carried out in accordance with ISO 7539-7:2005. The tests were carried out on a specially designed test stand, where the FT-5307 strain gauge force sensor with a measuring range of 0–16 kN was used to measure the force value. The PSz 20 transducer with a measuring range of 0–20 mm was also used. The test consisted of subjecting the specimen to increasing deformation with the strain rate έ = 1.6 × 10−6 s−1 until destruction. The fracture surfaces of the SSRT specimens were subjected to fractographic analysis using a Philips XL-30 scanning electron microscope. The results of fractographic studies after the SSRT test of the native materials and their joints welded by the MIG and FSW methods indicate that the trans-crystalline cracking mechanism is dominant, characterized by ductile fracture, and cracks are initiated at the interfaces of the precipitates with the matrix. The research results show that the plastic deformation increases and micro-cracks develop and merge into a main crack, which, after reaching the critical dimension, rapidly develops, causing the destruction of the material. The fracture micrographs of the specimens of base metals and their joints welded by FSW and MIG after the SSRT test allow us to conclude that the cracking mechanism was trans-crystalline ductile.

Slow strain rate testing (SSRT) was used to test the stress corrosion cracking (SCC) of aluminium alloys AW 5083 and AW 5059 (Alustar) jointed by friction stir welding (FSW). The test was carried out in the air and 3.5% water solution NaCl. Cylindrical notch-free specimens and cylindrical notched specimens (R = 5 mm) were used. The following parameters were measured: time-to-failure-T [h], obtained max. load-F [N]; strain energy (the diagram surface under the stress-elongation curve)-E [MAJ/m 3 ]; relative elongation of the specimen-A 11.3 [%]; max. tensile stress-R [MPa] and narrowing-Z [%]. On the basis of obtained results, it was noted that FSW-welded joints show superior strength and resistance to stress corrosion, compared to MIG-welded joints. The fractions after SSRT testing were cleaved with some ductile areas. This article also gives the mechanical features of friction stir welded Al-Mg alloys. Tests have shown that the 5059 alloy, welded by FSW, has superior strength properties compared to the FSW 5083 alloy, along with comparable, good resistance to stress corrosion. FSW 5083 alloy joints have very good resistance to stress corrosion-better than those made using traditional welding methods (MUG). Original value are received results of the stress corrosion resistance of new method friction stir welded Al-Mg alloy compared with traditional MIG method.

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