The Cracking of Al-Mg Alloys Welded by MIG and FSW under Slow Strain Rating

Abstract

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.

Introduction of Coal Reinforcing Particles on the Dissimilar FSW AA608/AA5083 Joint via Friction Stir Processing

“…The flexing of the FSW face weld specimens toward the AA6082 side, which was the alloy with weaker strength, indicated that the FSW face weld joints possessed a higher joint strength than the base material, AA6082. This outcome aligned with prior research findings [36][37][38] and suggested that the welding process improved the overall mechanical properties of the joint, surpassing the inherent strength of AA6082. Remarkably, post-face specimens did not reveal any cracks except for the FSW E face weld specimen, which exhibited a minor defect crack at the edge of the TMAZ, coinciding with the bending end of AA6082 in the weld.…”

Exploring the Potential Application of an Innovative Post-Weld Finishing Method in Butt-Welded Joints of Stainless Steels and Aluminum Alloys

“…Reference [14] discusses diverse butt joints between 6061-T6 aluminum alloy and AISI 316 stainless steel fabricated through friction stir welding (FSW) with varying parameters. The studies cited as [15] examined aluminum-magnesium (Al-Mg) alloys, particularly alloy AW 5083 and its joints using both MIG arc welding and FSW methods. Paper [16] explored parameter optimization for welding aluminum alloy AW 5083 via the synchropulse welding process.…”

“…Finally, article [20] discusses the influence of semi-random and regular shot peening on selected surface layer properties of aluminum alloy. These materials find extensive applications across diverse industries, encompassing modern marine [15,21] and mechanical engineering [22,23], the military [24], chemical, aerospace, automotive [18], rail [25], and other [26]. Thus, it is imperative to explore the feasibility of an innovative post-weld finishing method for butt-welded joints involving the aforementioned materials.…”

Effect of Shielding Gas Arc Welding Process on Cavitation Resistance of Welded Joints of AlMg4.5Mn Alloy

“…It was shown that the fatigue strength of the welded joint was just 27% of the fatigue strength of the base metal, mostly due to increased sensitivity to cracking and the geometry of the welded joint. Sensitivity to cracking was also analyzed for Al–Mg alloys, used in the shipbuilding industry, welded by GMAW and friction stir welding (FSW) [ 17 ]. It was shown that cracking started mainly through decohesion at the matrix–precipitate interfaces and that the cracking mechanism was trans-crystalline ductile.…”