PSI - Issue 36

Robert Kosturek et al. / Procedia Structural Integrity 36 (2022) 153–158 Robert Kosturek, Janusz Mierzyński, Marcin Wachowski et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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( Çam et al. (2014), Kosturek et al (2020), Vuherer et al (2019)). It is used predominantly to joint aluminum alloys but it gives also very good results when it comes to magnesium and some titanium alloys ( Myśliwiec et al. (2018), Kosturek et al. (2018)). One of the most popular magnesium alloys is AZ31, which due to its low density and good mechanical properties offers potential for aircraft manufacturing. It is used to produce some parts such as gearboxes and housing for antennas and air-conditioning systems in helicopters (Dziubińska et al. (2015)) . Also, in the recent years AZ31 finds its application as a component in multilayer composites used as ballistic panels (Wachowski et al. (2020), Wachowski et al. (2019)). Poor weldability of magnesium by conventional means (mostly due to its high vapor pressure and oxidation) makes FSW a good pick for producing joints ( Myśliwiec et al. (2018)). For FSW is a solid-state welding process it eliminates a majority of problems in joining AZ31. FSW process parameters (tool rotation speed, tool traverse speed [which is also welding velocity], the shape of a tool, etc.) influence joint structure and mechanical properties and their optimization is important in terms of achieving welds of the highest possible quality (Janeczek et al. (2021). Industrial applications often require to maximize welding velocity to accomplish a welding process faster and to limit an affection of heat on welded components (Kosturek et al. (2020), Kallee et al. (2010)). In the recent years, some works concerned with friction stir welding of AZ31 have been conducted. Aydin and Bulut performed a study on the weldability of AZ31 magnesium alloy by friction stir welding and achieved the highest joint efficiency of 93% (Aydin et al. (2010)). Venkateswarlu et al. investigated the influence of process parameters on the microstructure of friction stir processed AZ31 and found that the rotational speed has greatly influenced the homogenization of the material (Venkateswarlu et al. (2017)). Liu et al. focused on effects of welding speed and post-weld got rolling (PWHR) on microstructure and mechanical properties of friction stir welded AZ31 and stated that the mechanical properties of the FSW joints and the joint coefficient can be effectively improved by PWHR (Liu et al. (2018)). Yang et al. researched effects of heat input on tensile properties and fracture behavior of friction stir welded AZ31 and concluded that with increasing the shoulder diameter, the tensile strength of the joints tended to increase and the elongation was significantly improved, with the failure location of the joints shifting from the TMAZ to the SZ (Yang et al. (2010)). In this investigation, the aim was to check the influence of welding velocity on the properties of AZ31 FSW in the low cycle regime to evaluate their behavior in a condition of high strain-rate loading. 2. Materials and methods The material to be welded was annealed AZ31 in the form of 5 mm-thick sheets having the size of 80x250 mm. The chemical composition and mechanical properties of the material are presented in the table below (Tab. 1). Table 1. Chemical composition and mechanical properties of used AZ31 Chemical composition, wt% Al Zn Mn Si Cu Ca Fe Mg 2.50< 0.60< 0.20 0.10 0.050 0.040 0.0050 rest Mechanical properties ‹‡Ž† •–”‡‰–Š ‡•‹Ž‡ •–”‡‰–Š Elongation (failure) 80 MPa 240 MPa 11.5% Before the welding process, the surfaces of the sheets were grounded and washed by isopropanol to reduce oxide layers. The workpieces have been welded by ESAB Legio 4U machine, dedicated for FSW process, with the following parameters: 1600 rpm tool rotation speed, 4.8 mm plunge depth, 2  angle of MX Triflute type tool. The welding velocity was different for each sample and it is presented in the table below (Tab. 2). Table 2. Welding velocities and sample designations. Sample designation Welding velocity M1 150 mm/min M2 300 mm/min M3 600 mm/min M4 900 mm/min